Terms andPhrases i#8S ; i§i ■ § §§§ jl i:.::\-^I IMP LIBRARY OF CONGRESS. D STATES OF OIVKU \. DICTIONARY ELECTRICAL WORDS, TERMS AND PHRASES. J^Y / W EDWIN J. HOUSTON, A. M. Professor of Natural Philosophy and Physical Geography in the Central High School of Philadelphia ; Professor of Physics in the Franklin Institute of Pennsylvania ; Electrician of the International Electrical Exhibition, etc. r ^o o F p 19188%/ THE W. J. JOHNSTON CO., Ld., Times Building , NEW YORK. CopruiGHT, 1889, BY The W. J. Johnston Co., Ld. s* «$ ^W* PREFACE. The rapid growth of electrical science, and the almost daily addition to it of new words, terms and phrases, coined, as they too frequently are, in ignorance of those already existing, have led to the production of an electrical vocabulary that is already bewildering in its extent. This multiplicity of words is extremely dis- couraging to the student, and acts as a serious obstacle to a general dissemination of electrical knowledge, for the following reasons : 1. Because, in general, these new terms are not to be found even in the unabridged editions of dictionaries. 2. The books or magazines, in which they were first proposed, are either inaccessible to the ordinary reader, or, if accessible, are often written in phraseology unin- telligible except to the expert. 3. The same terms are used by different writers in conflicting senses. 4. The same terms are used with entirely different meanings. 5. Nearly all the explanations in the technical dic- tionaries are extremely brief as regards the words, terms and phrases of the rapidly growing and comparatively new science of electricity. In this era of extended newspaper and periodical pub- lication, new words are often coined, although others, II PREFACE. already in existence, are far better suited to express the same ideas. The new terms are used for a while and then abandoned; or, if retained, having been imperfectly- defined, their exact meaning is capable of no little ambiguity ; and, subsequently, they are often unfortun- ately adopted by different writers with such varying shades of meaning, that it is difficult to understand their true and exact significance. Then again, old terms buried away many decades ago< and long since forgotten, are dug up and presented in such new garb that their creators would most certainly fail to recognize them. It has been with a hope of removing these difficulties to some extent that the author has ventured to present this Dictionary of Electrical Words, Terms and Phrases to his brother electricians and the public generally. He trusts that this dictionary will be of use to electricians, not only by showing the wonderful extent. and richness of the vocabulary of the science, but also by giving the general consensus of opinion as to the sig- nificance of its different words, terms or phrases. It is, however, to the general public, to whom it is not only a matter of interest but also one of necessity to fully understand the exact meaning of electrical literature, that the author believes the book will be of greatest value. In order to leave no doubt concerning the precise meaning of the words, terms and phrases thus defined^ the following plan has been adopted of giving, (1) A concise definition of the word, term or phrase* PREFACE. Ill (2) A brief statement of the principles of the science involved in the definition. (3) Where possible and advisable, a cut of the appar- atus described or employed in connection with the word, term or phrase defined. It will be noticed that the second item of the plan makes the Dictionary approach to some extent the nature of an Encyclopedia. It differs, however, from an encyclopedia in its scope, as well as in the fact that its definitions in all cases are concise. Considerable labor has been expended in the collection of the vocabulary, for which purpose electrical literature generally has been explored. In the alphabetical ar- rangement of the terms and phrases defined, much per- plexity has arisen as to the proper catch-word under which to place them. It is believed that part of the difficulty in this respect has been avoided by the free use of cross-references. In elucidating the exact meaning of terms by a brief statement of the principles of the science involved there- in, the author has freely referred to standard text books on electricity, and to periodical literature generally. He is especially indebted to works or treatises by the fol- lowing authors, viz.: S. P. Thompson, Larden, Cum- ming, Hering, Prescott, Ayrton, Ayrton and Perry, Pope, Lockwood, Sir Wm. Thomson, Fleming, Martin and Wetzler, Preece, Preece and Sivewright, Forbes, Max- well, De Watteville, J. T. Sprague, Oulley, Mascart and Joubert, Schwendler, Fontaine, Noad, Smee, Depretz, De la Rive, Harris, Franklin, Cavallo, Grove, Hare, Daniell, Faraday and very many others. IV PREFACE. The author offers his Dictionary to his fellow elec- tricians as a starting point only. He does not doubt that his book will be found to contain many inaccuracies, ambiguous statements, and possibly doubtful definitions. Pioneer work of this character must, almost of neces- sity, be marked by incompleteness. He, therefore, in- vites the friendly criticisms of electricians generally, as to errors of omission and commission, hoping in this way to be able finally to crystallize a complete vocabulary of electrical words, terms and phrases. The author desires in conclusion to acknowledge his indebtedness to his friends, Mr. Carl Hering, Mr. Joseph Wetzler and Mr. T. C. Martin for critical ex- amination of his proof sheets ; to Dr. GL Gr. Faught for examination of the proofs of the parts relating to the medical applications of electricity, and to Mr. C. E. Stump for valuable aid in the illustration of the book ; also to Mr. Geo. D. Fowle, Engineer of Signals of the Pennsylvania Railroad Company, for information con- cerning their System of Block Signaling, and to many others. Central High School, Edwin J. Houston. Philadelphia, Pa. September, 1889. A DICTIONARY OF TD IK Abscissas, Axis of- — Ouc of the axes of co-ordi- nates used for determining the position of points in a curved line. Thus the position of the point D, Fig. B 1, in the curved line O D R, is deter- mined by the vertical distances D 1, and D 2, of such point from two straight lines AB, and AC, called the axes of co- ordinates. AC, is called the axis of ab- scissas, and AB, the axis of ordinates. A, the point where the lines may be considered as starting or originating, is called thepoint of origin. (See Co-ordinates, Axes of.) Absolute.— Complete in itself. The terms absolute and relative are used in electricity in the same sense as ordinarily. Thus, a galvanometer is said to be calibrated absolutely when the exact current strengths required to produce given deflections are known ; or, in other words, when the absolute current, strengths are known ; it is said to be calibrated rela- tively when only the relative current strengths required to produce given deflections are known. 2 A DICTIONARY OF ELECTRICAL The word absolute, as applied to the units employed in elec- trical measurements, was introduced by Gauss to indicate the fact that the values of such units are independent both of the size of the instrument employed and of the value of gravity at the particular place whore the instrument is used. The absolute units of length, mass, and time are more prop- erly called the C. G. S. units, or the eenti metre-gramme- second units. An absolute system of units based on the milligramme, millimetre, and second, was proposed by Weber, and was called the millimetre-milligramme-second units. It has been replaced by the C. G. S. units. Absolute Calibration. — (See Calibration, Absolute., Absolute Galvanometer. — (See Galvanometer, Abso- lute.) Absolute Units. — A term sometimes used to indicate the C. G. S. units, but now generally replaced by the term centi- met re-gramme-second units, or, more briefly, the C. G. S. units. Absolute Unit of Current. — A current of ten amperes. (See Ampere. Units, Practical.) Absolute Unit of Electromotive Force.— The one hundred millionth of a volt. (See Volt. Units, Practical.) Absolute Unit of Resistance.— The one thousand millionth of an ohm. (See Ohm. Units, Practical.) Absolute Vacuum. — (See Vacuum, Absolute). Absorption, Electric The apparent soaking of an electric charge into the glass or other solid dielectric of a Leyden Jar or Condenser. (See Charge. Condenser.) The capacity of a condenser, or its ability to hold an elec- tric charge, varies with the time the condenser remains charged. Some of the charge acts as if it soaked into the solid dielectric, and this is the cause of the residual charge. (See Charge, Residual.) Therefore, when the condenser is WORDS, TERMS AND PHRASES. 3 discharged, loss electricity appears than was passed in; hence the term electric absorption. Absorptive Power. — The property possessed by many solid bodies of taking in and condensing gases within their pores. Carbon possesses marked absorptive powers. The absorp- tion of gases in this manner by solid bodies is known techni- cally as the occlusion of gases. (See Occlusion of Gases.) One volume of charcoal, at ordinary temperatures and pres- sures, absorbs of Ammonia 90 volumes Hydrochloric Acid .85 Sulphur Dioxide .65 " Hydrogen Sulphide 55 " Nitrogen Monoxide 40 " Carbonic Acid Cas 35 " Ethylene 35 Carbon Monoxide 9.42 " Oxygen 9.25 " Nitrogen 6.50 " Hydrogen 1.25 " (Saussure.) Acceleration. — The rate of change of velocity. Acceleration is thus distinguished from velocity : velocity expresses in tune the rate-of-change of position, as a velocity of three metres per second ; acceleration expresses in time the rate-of-change of velocity, as an acceleration of one centi- metre per second. Since all matter is inert, and cannot change its condition of rest or motion without the application of some force, ac- celeration is necessarily due to some force outside of matter itself. A force may therefore be measured by the accelera- tion it causes in a given mass of matter. Acceleration is termed positive when the velocity is in- creasing, and negative when it is decreasing. Acceleration, Unit of That acceleration which 4 A DICTIONARY OF ELECTRICAL will give to a body unit -velocity in unit-time ; as, for ex- ample, one centimetre per second. Bodies falling' freely in a vacuum, and approximately so in air, acquire an acceleration which in Paris or London, at the end of a second, amounts to about 9S1 centimetres per second, or nearly 32.2 ft. per second, v a — — , or in other words, the acceleration equals the ve- T locity divided by the time. But, since the velocity equals the Distance, or the Length L traversed in a unit of time, v = — . T L V T L Therefore, a = — = = — , or, the acceleration equals the T T T~ 1 length, or the distance passed through, divided by the square of the time in seconds. These formulae represent the Dimensions of Acceleration. Accumulator, or Condenser.— A term often applied to an apparatus called a Leyden Jar or Condenser, which per- mits the collection from an electric source of a greater charge than it would otherwise be capable of giving. The ability of the source to give an increased charge is due to the increased capacity of a plate or other conductor when placed near another plate or conductor. (See Condenser. Jar, Leyden.) Accumulator, Storage or Secondary Cell. — Two inert plates dipping into a liquid incapable of acting chemicalty on either of them until after the passage of an electric current, when they become capable of furnishing an independent electric current. F F hPc B \ X "m F A F' WORDS. TERMS AND PHRASES. 5 This use of the term accumulator is the one most commonly employed. (See Storage Cells or Accumulators.) Accumulator.— A term sometimes applied to Sir Win. Thomson's Electric Current Accumulator. The copper disc D, Fig-. 2, has freedom of rotation, on a horizon- tal axis at O, in a magnetic field, the lines of force of which, repre- sented by the dotted lines in the drawing, pass down perpendicu- larly into the plane of the paper. Fig. 2. If, now, a current from any source be passed in the direc- tion A, O, B, C, A, through the circuit A, O, B, C, A, which is provided with spring- contacts at O, and A, the disc will rotate in the direction of the curved arrow. This motion is due to the current acting on that part of the disc which lies between the two contacts — A and O. This apparatus is known as Barlow's Wheel. If, when no current is passing through the circuit, the disc be turned in the direction of the arrow, a current is set up in such a direction as would oppose the rotation of the disc. (See Lenzs Laic.) If, however, the disc be turned in the opposite direction to that of the arrow, induction currents will as before be pro- duced in the circuit. xVs this rotation of the disc tends to move the circuit O A, towards the parallel but oppositely directed circuit B 0, these two circuits, being parallel and in opposite directions tend to repel one another, and there will thus beset up induced currents that tend to oppose the motion of rotation, and the current of the circuit will therefore increase in strength. (Sec Electro-Dynamics). Should then a current be started in the circuit, and the original field be removed, the induction will be continued, and a current which, up to a cer- tain extent, increases or accumulates, is maintained in the circuit during rotation of the disc. (Larden.) 6 A DICTIONARY OF ELECTRICAL Barlow's Wheel, when used in this manner, is known as Thomson's Electric Current Accumulator. Accumulator, Water-Dropping An appa- ratus devised by Sir W. Thomson lor increasing- the difference of potential of an electric charge. The tube X Y, Fig-. 3, connects with a reservoir of water which is maintained at the zero potential of the earth. The water b eseapes from the openings at G and D in small drops and falls on funnels provided, as shown, to receive the separate drops nd again discharge them. The vessels A, A', and B, B', which are electrically connected as shown, are main- tained at a certain small difference of potential, as indicated by the respective -f and — signs. Under these circumstances, therefore, C and D, will be charged inductively with charges opposite to those of A and B, or with — and -f electricities respectively. As the drops of water fall on the funnels, the charges which the funnels thus constantly receive, are given up to B' and A', before the water escapes. Since, therefore, B, B', and A, A', are receiving- constant charges, the difference of potential between them must continually increase. This apparatus operates on the same principle as the replenisher. The drops of water act as the carriers, and A, A', and B, B', as the hollow vessels. (See Replenisher.) Accumulators or Condensers ; L. C. — An abbreviation used in medical electricity for Anodic Duration Contraction. Adhesion. — The attraction that exists between unlike molecules. (See Attraction, Molecular.) 12 A DICTIONARY OF ELECTRICAL Ad iat h erm an cy.— Opacity to heat. A substance is said to be diathermanous when it is trans- parent to heat. Clear, colorless crystals of rock salt are very transparent both to light and to heat. Rock salt, covered with a layer or deposit of lamp-black or soot, is quite transparent to heat. An adiathermanous body is one which is opaque to heat. Heat transparency varies not only with different sub- stances, but also with the nature of the source from which the heat is derived. Thus, a substance may be opaque to the heat from a non-luminous source, such as a vessel filled with boiling- water, while it is comparatively transparent to that from a luminous source, such as an incandescent solid, or the voltaic arc. A similar difference exists as regards transparency to light. A colorless glass will allow light of any color to pass through it. A blue glass will allow blue light to pass freely through it, but will completely prevent the passage of any red light ; and so with other colors. T]|»iiiu*' Condenser. — (See Condenser.) Affinity, < iieinieal Atomic attractions. The force that causes atoms to unite and form chemical molecules. Atomic, or chemical attraction generally results in a loss of the characteristic qualities, or properties, that dis- tinguish one kind of matter from another. In this respect it differs from adhesion, or the force which holds unlike molecules together. (See Adhesion.) If, for example, sulphur is mixed with lamp-black, no matter how intimate the mix- ture, the separate particles, Avhen examined by a glass, ex- hibit their peculiar color, lustre, etc. If, howerer, the sul- phur is chemically united with the carbon, a colorless, trans- parent, mobile liquid, called carbon bisulphide, results, that possesses a disagreeable, penetrating odor. Chemical affinity, or atomic combination, is influenced by a variety of causes, viz. ; WORDS, TERMS AND PHRASES. 13 (1) Cohesion. Cohesion, by binding- the molecules more firmly tog-ether, opposes their mutual atomic attractions. A solid rod of iron will not readily burn in the flame of an ordinary lamp, but if the cohesion be overcome by reducing the iron rod to filings, it burns with brilliant scintillations when dropped into the same flame. (2) Solution. Solution, by imparting to the molecules greater freedom of motion, favors their chemical com- bination. (3) Heat. Heat favors atomic combination by decreasing the cohesion, and possibly, by altering the electrical rela- tions of the atoms. If too great, heat may produce decom- position. (See Dissociation.) (4) Light. Decomposition, or the lessening of chemical affinity through the agency of light, is called Actinism. Light also causes the direct combination of substances. A mix- ture of equal volumes of hydrogen and chlorine unites ex- plosively when exposed to the action of full sunlight. (See Actinism.) (5) Electricity. An electric spark will cause an explosive combination of a mixture of oxygen and hydrogen. Electric- ity also produces chemical decomposition. (See Electrolysis.) AgOlie. — A line connecting places on the earth's surface where the magnetic needle points to the true geographical north. The line of no declination or variat ion of a magnetic needle. (See Declination or Variation of Magnetic Needle.) As all the places on the earth where the magnetic needle points to the true north may be arranged on a few lines, it will be understood that the pointing of the magnetic needle to the true geographical north is the exception and not the rule. In many places, however, the deviation from the true geographical north is so small that thue direction of the needle may be regarded as approximately due north. Agonic*. — Pertaining to the Agone. 14 A DICTIONARY OF ELECTRICAL Air-Bla§t.— An invention of Prof. Elihu Thomson to pre- vent the injurious action of destructive sparking at the com- mutator of a dynamo-electric machine. A thin, forcible blast of air is delivered through suitable tubes at points on the three-part commutator cylinder of the Thomson Houston dynamo, where the collecting- brushes bear on its surface. The effect is to blow out the arc and thus pre- vent lis destructive action on the commutator segments. The use of the air-blast also permits the free application of oil. thus further avoid- ing wear. The blast-nozzles are shown at B 3 , B 3 , Fig. 8, near the collecting brushes. The air-supply is ob- tained from a centri- fugal blower attached directly to the shaft of the machine. Its con- struction and operation will be readily under- stood from an inspec- tion of Fig. 9, in which the top is removed for a ready examination of the interior parts. Fig, 0. Alarms, Electric Various automatic devices by which attention is called to the occurrence of certain events, such as the opening of a door or window; the stepping of a person on a mat or staircase ; the rise or fall of temperature bej^ond a given predetermined point ; or to call a person to a telegraphic or telephonic instrument. WORDS, TERMS AND PHRASES. 15 Electric alarms arc operated by either the closing or the opening of an electric circuit, generally the former, by means of which an electro-magnetic or Electric alarms may be di- vided into two classes, viz. : 1. Mechanically operated alarms, or those operated by clock-work, that is started by means of an electric current. 2. Those in which the alarm is both set into operation and operated by the action of an electric current. In Fig. 10, is shown the general construction of an electrically started mechani- cal alarm. The attraction of the armature B, by the electro- magnet A, moves the arma- ture lever pivoted at C, and thus releases the catch e, and permits the spring or weight connected with the strike the bell. Electrically actuated alarm-bells automatic make-and-break form, operated by the attraction of the mechanical bell is rum itlF 1 Fig. 10. clock movement to set it in motion and are generally of the The striking lever is armature of an electro- magnet, and is provided with a contact-point, so placed that when the hammer is drawn away from the bell, on the electro-magnet losing its magnetism, the contact-point is closed, but when it is drawn towards the bell the contact is opened. When, therefore, the hammer strikes the bell, the circuit is opened, and the electro-magnet releases its armature, permitting a spring to again close the contact by moving the striking lever away from the bell. Once set into 16 A DICTIONARY OF ELECTRICAL action, these movements are repeated while there is battery power sufficient to energize the magnet. T In Fig. 11, the battery terminals are connected with the right and left hand binding- posts, P and M. The hammer K, is connected with a striking lever, which forms part of the circuit, and which is attached to the armature o f the electro- Fig. n. magnet e. A me- tallic spring g, bears against the armature when the latter is away from the magnet, but does not touch the armature when it is moved towards the magnet. The movements of the armature thus automatically open and close the circuit of the electro-magnet. This form of make-and-break is called an automatic make- and-break. Alarms, Electric Burglar An electric device to automatically announce the opening of a door, window, closet, drawer, or safe, or the passage of a person through a hallway, or on a stairway. Electric burglar alarm devices generally consist in mechan- ism for the operation of an automatic make-and-break bell on the closing of an electric circuit. The bell may either continue ringing only while the contact remains closed, or, may, by the throwing on of a local circuit or battery, con- tinue ringing until stopped by some non-automatic device, such as a hand-switch. WORDS, TERMS AND PHRASES. 17 The alarm-bell is stationed either in the house when occu- pied, or on the outside when the house is temporarily vacated, or may connect directly with the nearest police station. Burglar-alarm apparatus is of a variety of forms. Generally, devices are provided by moans of which, in case of house pro- tection, an annunciator shows the exact part where an entrance has been at- tempted. (See Annunciator.) Switches are provided for disconnecting all or parts of the house from the alarm when so de- sired, as well as to permit windows to be partly raised for purposes of ventilation without sounding the alarm. A clock' is frequently connected with the alarm for the purpose of automatically disconnecting any portion of the house at or for certain intervals of time. Fig. 12, shows a burglar alarm with annunciator, switches, switch-key, cut-oil, and clock. Fig. 12. A I sir ins, Electric Burglnr- -Yalc Lock Switch lor. — An alarm whereby the opening of a door by an authorized party provided with the regular key will not sound an alarm, but any other opening will sound such alarm. Alarm§, Electric Fire or Temperature In- struments for automatically sounding an alarm on an increase of temperature beyond a certain predetermined point. Fire-alarms are operated by thermostats, or by means of mercurial contacts; i. e., a contact closed by the expansion of a column of mercury. (See T 'her most 'at.) In systems of fire-alarm telegraphs, the alarm is automati- cally sounded in a central police station and in the district fire-engine house. (See Telegraphy, Fire-alarm.) The action of mercurial contacts is dependent on the fact that, as the mercury expands hy the action of the heat, it reaches a contact-point placed in the tube and thus completes 18 A DICTIONARY OF ELECTRICAL the circuit through its own mass, which forms the other or movable contact. Sometimes both contacts are placed on opposite sides of a tube and are closed when the mercury reaches them. Mercurial-temperature or thermostat alarms are employed in hot-houses, incubators, tanks, and buildings, for the purpose of maintaining a uniform temperature. Alarms, Electric Water or Liquid Level Devices for sounding an alarm electrically when a water sur- face varies materially from a given level. An electric bell is placed in a circuit that is automatically closed or broken by the movement of contact-points operated by a change of liquid level. Alarms, Telegraphic Alarm bells for calling the attention of an operator to a telegraphic instrument when the latter is of the non-acoustic or needle type. In acoustic systems of telegraphy, the sounds themselves are generally sufficient for this purpose. Alarms, Telephonic An alarm-bell for calling a correspondent to the telephone. These alarms generally consist of magneto-electric bells. (See Magneto-Electric Call-Bell) Alcohol, Electrical Rectification of. A process whereby the bad taste and odor of alcohol, due to the presence of aldehydes, are removed by the electrical con- version of the aldehydes into true alcohols through the ad- dition of Ivydrogen atoms. An electric current sent through the liquid, between zinc electrodes, liberates oxygen and hydrogen from the decom- position of the water. The hydrogen converts the aldehydes into alcohol, and deprives the products of their fusel oil, while the ox}'gen forms insoluble zinc oxide. Algebraic dotation.— (See Notation, Algebraic.) Alphabet, Telegraphic —An arbitrary code consisting of dots and dashes, sounds, deflections of a mag- WORDS, TERMS AND PHRASES. 19 netic needle, flashes of light, or movements of levers, follow- ing- one another in a given predetermined order, to represent the letters of the alphabet and the numerals. Alphabet, Morse's Telegraphic Various groupings of dots and dashes, or deflections of a magnetic needle to the right and left, that represent the letters of t lie alphabet or other signs. In the Morse alphabet dots and dashes are employed in recording systems, and sounds of varying- lengths, correspond- ing to the dots and dashes in the sounder system. American Morse Code, alphabet. a n b o - - c - - - p d --- q e - r - - • f s --- g t - h u i - - v k x 1 y m z — - & - --- NUMERALS. 1 9. 7 3 8 — - 4 9 — - 5 PUNCTUATION marks. Period Interrogation Comma Exclamation 20 A DICTIONARY OF ELECTRICAL Iii the needle telegraph, the code is similar to that used in the Morse Alphabet. (.See Telegraphy, Single-needle.) Alphabet, Telegraphic: Continental Code. Single Single Printing Needle Printing Needle a s/ n A b A* o /// c AA p . nAs d A q /A/ e . \ r sA f vsA s ... W\ g /A t / h .... WW U .. ss/ i w V ... wn/ j ■,/// w sA k A/ X __ .. /sv/ 1 nAn y A A m : A Z ANS Similar symhols are emploj r ed for the numerals and the punctuation marks. It will be observed that it is mainly in the characters of the American Morse, in which spaces are used, that the Conti- nental characters differ from the American. This is due to the use of the needle instrument. A movement or deflection of the needle to the left signifies a dot; a movement to the right, a dash. For methods of receiving the alphabet, see Sounder, Morse WORDS, TERMS AND PHRASES. 21 Telegraphic. Recorder, Morse's. Recorder, Chemical. Re- corder, Siphon. Relay or Receiving Magnet. All-night Arc Lump. — (See Double-Carbon Arc Lamp.) Alloy. — A combination, or mixture, of two or more metallic substances. Alloys in most cases appear to be true chemical compounds. In a few instances, however, they may form simple mixtures. The composition of a few important alloys is here given : Solder, plumber's ; Tin GO parts, Lead 31 parts. Pewter, hard ; Tin 92 parts, Lead 8 parts. Britannia metal ; Tin 100 parts, Antimony 8 parts, Copper 4 parts, Bismuth 1 part. German silver ; Copper 50, Zinc 25, Nickel 25 parts. Type metal ; Lead 80, Antimony 20 parts. Brass, white ; Copper 65, Zinc 35 parts. Brass, red ; Copper 00, Zinc 10 parts. Speculum metal ; Copper 07, Tin 33 parts. Bell metal ; Copper 78, Tin 22 parts. Aluminium bronze; Copper 90, Aluminium 10 parts. Alloys, Palladium (See Palladium Alloys.) Allotropy, Allotropic Stale.— A modification of a substance, in which, without changing its chemical compo- sition, it assumes a condition in which its physical and chem- ical properties are distinct from those it ordinarily possesses. Thus the element carbon occurs in three widely different allotropic states, viz.: (1) As charcoal, or ordinary carbon ; (2) As graphite, or plumbago ; and (3) As the diamond, Alternating Current. — An electric current that alter- nately tlows in opposite directions. (.See Current, Alterna- ting.) Alternating Motor. — (See Motor, Alternating Cur- rent.) 22 A DICTIONARY OF ELECTRICAL Alternating Dynamo-Electric Machine.— A dy- namo-electric machine that furnishes alternating- currents, (See Dynamo-Electric Machine. ) Alternating System of Distribution.— A system of electric distribution in which lamps, motors, or other electro- receptive devices are operated by means of alternating- cur- rents that are sent over the line, but which, before passing through said devices, are modified by apparatus called con- verters or transformers. (See Converter or Transformer.) For details of the alternating system of distribution, see Systems of Distribution by Alternating Currents. Alternatives, Voltaic A term used in medical electricity to indicate sudden reversals of polarity of the elec- trodes of a voltaic battery. An alternating current from a voltaic battery, obtained by tin 1 use of i suitable commutator. Sudden reversals of polarity produce more energetic effects of muscular contraction than do simple closures or comple- tions of the circuit. Since all electricity is one and the same thing or force, what- ever its source, the necessity for the term voltaic alternative in place of alternating current is by no means clear. The only consideration that would appear to warrant its con- tinued use is that the alternating currents obtained from the voltaic batteries generally employed in electro thera- peutics, by the action of a pole-changer, possess a much smaller electro-motive force than do faradic currents, which are also alternating. Amalgam. — The combination or mixture of a metal with mercury. Amalgam, Electric A substance with which the rubbers of the ordinary frictional electric machines are covered. Electric amalgams are of various compositions. The fol- lowing is excellent : WORDS, TERMS AND PHRASES. 23 Melt together five parts of zinc and three of tin, and gradu- ally pour the niolten metal into nine parts of mercury. Shake the mixture until cold, and reduce to a powder in a warm mortar. Apply to the cushion by means of a thin layer of stiff grease. Mosaic gold, or bisulphide of tin, and powdered graphite, both act as good electric amalgams. An electric amalgam not only acts as a conductor to carry off the negative electricity, but being highly negative to the glass, produces a far higher electrification than would leather or chamois. Amalgamation. — The act of forming an amalgam, or effecting the combination of a metal with mercury. Amalgamation of* Zinc Battery Plates. — Cover- ing the surface of the zinc plate of a voltaic cell with a thin layer of amalgam in order to avoid local action. (See Action, Local. ) For details of process, see Zinc, Amalgamation of. Amber. — A resinous substance, generally of a transparent, yellow color. Amber is interesting electrically as being believed to be the substance in which the properties of electric attractions and repulsions imparted by friction or rubbing were first noticed. It was called by the Greeks rfXeicTpov from which the word electricity is derived. This property was mentioned by the Greek, Thales of Miletus, 600 B. c, as well as by Theophrastus. Amorphous. — Having no definite crystalline form. Mineral substances have certain crystalline forms, that are as characteristic of them as are the forms of animals or plants. Under certain circumstances, however, they occur without definite crystalline form, and are then said to be amor- phous solids. Ampere. — The practical unit of electric current. Such a current (or rate of flow or transmission of electricity) 24 A DICTIONARY OF ELECTRICAL as would pass with an E. M. F. of one volt through a circuit whose resistance is equal to one ohm. That is to say, a cur- rent of the definite strength that would How through a circuit of a certain resistance and with a certain electro-motive force. (See Electro-Motive Force. Volt. Resistance. Ohm.) Since the ohm is the practical unit of resistance, and the volt the practical unit of electro-motive force, the ampere, or the practical unit of current, is the current that would flow against unit resistance, under unit pressure or electro-motive force. To make this clearer, take the analogy of water flowing through a pipe under the pressure of a column of water. That which causes the flow is the pressure or head ; that which resists the flow is the friction of the pipe, winch will vary with a number of circumstances. The rate of flow may he represented by so many cubic inches of water per second. As the pressure or head increases, the flow increases pro- portionally ; as the resistance increases, the flow diminishes. Electrically, electro-motive force corresponds to the pres- sure or head of the water, and resistance to the friction of the water and the pipe. The ampere, which is the unit rate of flow per second, may therefore be represented as follows, E viz.: c = — , as was announced by Ohm in his law. (See R Ohm's Laic.) This expression signifies that C, the current in amperes, is equal to E, the electro-motive force in volts, divided by R, the resistance in ohms. We measure the rate of flow of liquids as so many cubic inches or cubic feet per second — that is, in units of quantity. We measure the rate of How of electricity as so much elec- tricity per second. The electrical unit of quantity is called the Coidomb. (See Coidomb.) The coulomb is such a quantity as would pass in one second through a circuit in which the rate of flow is one ampere. WORDS, TERMS AND PHRASES. 25 An ampere per second is therefore equal to one coulomb. The electro-magnetic unit of current is such a current that, passed through a conducting wire bent into a circle of the radius of one centimetre, would attract a unit magnetic pole held at its centre, and sufficiently long to practically remove the other pole from the influence, with unit force, i.e., the force of one dyne. (See Dyne.) The ampere, or practical electro-magnetic unit, is one-tenth of such a current ; or, in other words, the absolute unit of current is ten amperes. An ampere may also be defined by the chemical decom- position the current can effect as measured by the quantity of hydrogen liberated, or metal deposited. Delined in this way, an ampere is such a current as will deposit .00032959 grammes, or .005084 grains, of copper per second on the plate of a copper voltameter (See Voltameter), or winch will decompose .00009336 grammes, or .001439 grains, of dilute sulphuric acid per second, or pine sulphuric acid at 50' F. diluted with about Qfteen percent, of water, that is, dilute sulphuric acid of Sp. Gr. of about 1.1. Impc i < -iloin . Ampere-Minute, Ampere-See- ond. — One ampere flowing for one hour, one minute, or one second respectively. The ampere-hour is in reality a unit of quantity like the coulomb. It is used in the service of electric currents, and is equal to the product of the current delivered, by the time during which it is delivered. The ampere-hour is not a meas- ure of energy, but when combined with the volt, and ex- pressed in watt-hours, it is a measure of energy. The storing capacity of accumulators is generally given in ampere-hours. The same is true of primary batteries. One coulomb = .0002778 ampere-hours. One ampere-hour = 3,600 coidombs. (See Watt-Hour, Watt- Minute, Watt-Second.) Ampere-Meter; Am-meter. — A form of galvanometer originally designed by Ayrton and Perry to indicate directly, 26 A DICTIONARY OF ELECTRICAL the strength of current passing in amperes. (See Galvano- meter.) Like all galvanometers, the strength of current passing, i. e., the number of amperes, is indicated by the deflection of a magnetic needle placed inside or over a coil of insulated wire through which the current to be measured is passed. In the form originally devised by Ayrton and Perry, the needle came to rest almost immediately, or was dead beat in action. (See Dead Beat.) It moved through the field of a permanent magnet. The instrument was furnished with a number of coils of insulated wire, which could be connected either in series or in multiple-arc by means of a commutator, thus permitting the scale reading to be verified or calibrated by the use of a single voltaic cell. (See Circuits, Varieties of. Commutator. Calibration, Absolute or Relative, of Instru- ment.) In this case the coils were turned to series, and the plug to the left pulled out, thus introducing a resistance of one ohm. Q Fig. 13, represents a form of Ayrton and Perry's Am- meter. A device called a commutator for connect- ing the coils either in series or parallel is shown at C. Binding-posts are provided at P, PS, and S. The dy- namo terminals are con- nected at the posts P, P, and the current will pass only when the coils are in multiple, thus avoiding accidental burning of the coils. In this case the entire current to be measured passes through the coils so coupled. The posts S, and PS are for connect- ing the single battery cell current. A great variety of ampere-meters, or am-meters, have been Fig. 13. WORDS, TERMS AND PHRASES. 27 devised. They are nearly all, however, constructed on es- sentially the same general principles. Ampere-Feet. — The product of the current in amperes by the distance in feet through which that current passes. It has been suggested that the term ampere-feet should be employed in expressing- the strength of electro-magnetism, in the field magnets of dynamo-electric machines or other similar apparatus. Ampere-Turns, or Ampere- Win dings. — A single turn or winding through which one ampere passes. The number of amperes multiplied by the number of wind- ings or turns of wire in a eoil give the total number of am- pere-turns in the coil. The magnetism developed by a given number of ampere-turns is independent of the current or of the number of turns of wire, as Jong as the product of the amperes and the turns remains the same. That is to say, the same amount of magnetism can be obtained by the use of many windings and a small current, as in shunt dynamos, or by a few turns and a proportionally large current, as in series dynamos. (See Dynamo-Electric Machines.) Amperc-Voll. — A watt, or -.},, of a horse-power. This term is generally written volt-ampere. (See Volt-Am- pere.) Amperian Currents.— The electric currents that are assumed in the Ampenan theory of magnetism to How around the molecules of a magnet. (See Magnetism, Amperian Theory or Hypothesis of.) The Ampenan currents are to be distinguished from the Eddy, Foucault, or Parasitical Currents, since, unlike them, they are directed so as to produce useful effects. (Sec Cur- rents, Eddy, Foucault, Parasitical.) Amplitude of Vibration or Wave.— The ratio that exists in any sound-wave between the degree of condensation and rarefaction of the air or other medium in which the wave is propagated. 28 A DICTIONARY OF ELECTRICAL The amplitude of a wave is dependent on the amount of energy charged on the medium in which the vibration or wave is produced. A vibration or wave is a to-and-fro motion produced in an elastic material or medium by the action thereon of energy. Sound, light and heat are effects produced by the action of vibrations or waves, which, in the case of sound, are set up in the air, and, in that of light and heat, in a highly tenuous medium called the luminiferous ether. As the amplitude of a sound wave increases, the loudness or intensity of the sound increases. As the amplitude of the ether-wave increases, the brilliancy of the light or the inten- sity of the heat increases. Let AC, Fig. 14, represent an elastic cord or string tightly stretched between A and C. It' the string be plucked by the finger, it will move to and fro, as shown by the dotted fines. Each to-and-fro motion is called a vibration. The vertical *<: B ^^C E Fig. Ik. distance B D, or B E, represents the amplitude of the vibration, and the sound produced is louder, the greater the amount of energy with which the string has been plucked, or, in other words, the greater the value of B D, or B E. Vibrations assume various forms in solid or fluid media, but in all cases the amplitude will be proportional to the amount of energy that causes the vibration. Analogous Pole.— (See Pole, Analogous.) Analysis.— The determination of the composition of a compound substance by separating it into the simple sub- stances of which it is composed. Chemical analysis is qualitative when it simply ascertains WORDS, TERMS AND PHRASES. 29 the kinds of elementary substances present. It is quanti- tative when it ascertains the relative proportions in which the different components enter into the compound. Analysis, Electric Ascertaining the composi- tion of a substance by electrical means. Various processes have been proposed for electric analysis ; they consist essentially in decomposing the substance by means of electric currents, and are either qualitative or quantitative. (See Electrolysis, or Electrolytic Decomposi- tion,) An elect rot on us. — In electro therapeutics, the decreased functional activity that occurs in a nerve in the neighbor- hood of the anode, or positive electrode. (See Electro- tonus.) Angle. — The deviation in direction between two lines. Angles are measured by arcs of cir- cles. The angle at B A C, Fig. 15, is the deviation of the straight line A B from A C. In reading the lettering of an angle the letter placed in the middle indicates the angle referred to. Tims B A C, means the angle between AB ^ . and AC; BAD, the angle between B A and A D. Angles are valued in degrees, there being 360 degrees in an entire circumference or circle. Degrees are indicated thus : 90°, or ninety degrees. The complement of an angle is what the angle needs to make its value 90°, or a right angle. Thus B A E, is the complement of the angle E A D, since BAE + EADr= 90°. The supplement of an angle is what the angle needs to make its value 180°, or two right angles. Thus E AC is the supple- ment of E A D, because EA D|EAC= 180°, or two right angles. Angle of Declination or Variation.— The angle 30 A DICTIONARY OF ELECTRICAL Fig. 16. which measures the deviation of the magnetic needle from the east or west of the true geographical north. Thus, in Fig. 16, if N S represents the true north and south line, the angle of declination is N O A, and the sign of the variation is east, because the deviation of the needle is toward the east. For f u ether details see Declination or Variation of Magnetic Needle. Angle of I>ip or Inclination.— The angle which a magnetic needle, free to move in a vertical and horizontal plane, makes with a horizontal line passing through its point of support. A magnetic needle supported at its centre of gravity, and capable of moving freely in a vertical as well as in a horizontal plane, does not retain a horizontal position at all parts of the earth's surface. The angle which marks its deviation from the horizontal position is called the angle of dip or inclination. For further details see Dip, Magnetic. Angle of Lag. — The angle through which the axis of magnetism of the armature of a dynamo-electric machine is shifted by reason of the resistance its core offers to sudden reversals of magnetization. A bi-polar armature of a dynamo-electric machine, has its magnetism reversed twice in every rotation. The iron of the core resists this magnetic reversal. The result of this resist- ance is to shift the axis of magnetization in the direction of rotation. The angle through which the axis has thereby been shifted is called the angle of lag. This term, angle of lag, is sometimes incorrectly applied so as to include a similar result produced by the magnetization due to the armature current itself. It is this latter action which, in armatures with soft WORDS, TERMS AND PHRASES. 31 non cores, is the main cause of the angle of lead. (See Angle of Lead. Lead of Brushes.) Angle of Lead. — The angular deviation from the normal position which must be given to the collecting brushes on the commutator cylinder of a dynamo-electric machine, in order to avoid destructive binning. (See Burning at Commutator.) The necessity for giving the collecting* brushes a lead, arises both from the magnetic lag, and the distortion of the field of the machine by the magnetization of the armature current. The angle of lead is, therefore, equal to the sum of the angle of lag and the angular distortion due to the magnetization produced by the armature current. Angular Velocity. — The velocity of a body moving in a circular path, measured, not, as usual, by the length of its path divided by the time, but by the angle that path subtends times the length of the radius, divided by the time. If f* is the radius, a the angle, and t the time, then ra Angular Velocity = — . t Unit Angle is that angle subtended by a part of the circum- ference equal to the length of the radius, or 57° 17' 44". 8 nearly (Daniell). Unix Angular Velocity is the velocity under which a particle moving in a circular path whose radius equals unity would traverse unit angle in unit time. Animal Electricity. — Electricity produced during life in the bodies of certain animals, such as the Torpedo, the Gym- notus, and the Silurus. Some of these animals, when of full size, are able to give very severe shocks, and use this curious power as a means of defence against their enemies. All animals probably produce electricity. If the spinal cord of a recently killed frog be brought into contact with the muscles of the thigh, a contraction will ensue (Matteucci). 32 A DICTIONARY OF ELECTRICAL The nerve and muscle of a frog, connected by a water con- tact with a sufficiently delicate galvanometer, show the presence of a current that may last several hours. Du Bois- Reymond showed that the ends of a section of muscular fibres are negative, and their sides positive, and has obtained a current by suitably connecting them. All muscular contractions apparently produce electric cur- rents. Anion. — The electro-negative radical of a molecule. Literally, the term ion signifies a group of wandering atoms. An anion is that group of atoms of an electrically decomposed or electrolysed molecule which appears at the anode. (See Electrolysis. Anode ) As the anode is connected with the electro-positive termi- nal of a battery or source, the anion is the electro-negative radical or group of atoms, and therefore appears at the electro- positive terminal. A kathion, or electro-positive radical, ap- pears at the kathode, which is connected with the electro- negative terminal of the battery. Oxygen and chlorine are anions. Hydrogen and the metals are kathions. Anisotropic Conductor.— A conductor which, though homogeneous in structure like crystalline bodies, has different physical properties in different directions, just as crystals have different properties in the direction of the different crystalline axes. Anisotropic conductors possess different powers of electric conduction in different directions. They differ in this respect from isotrojric conductors. (See Isotropic Conductor.) Anisotropic Medium. — A medium, homogeneous in structure like crystalline bodies, possessing different powers of specific inductive capacity in different directions. The term is used to distinguish it from an isotropic medium. (See Isotropic Medium.) Anode — The conductor or plate of a decomposition cell WORDS, TERMS AND PHRASES. 33 connected with the positive terminal of a batteiy, or other electric source. That terminal of an electric source out of which the current flows into the liquid of a decomposition cell or voltameter is called the anode. That terminal of an electric source into which the current flows from a decomposition cell or volta- meter is called the kathode, The anode is connected with the carbon or positive ter- minal of a voltaic battery, and the kathode with the zinc, or negative terminal. Therefore the word anode has been used to signify the positive terminal of an electric source, and kathode, the negative terminal, and in this sense is employed generally in electro therapeutics. It is preferable, however, to restrict the Avords anode and kathode to those terminals of a source at which electrolysis is taking place. The terms anode and kathode in reality refer to the electro- receptive devices through which the current flows. Since it is assumed that the current flows out of a source from its positive pole or terminal, and back to the source at its nega- tive pole or terminal, that pole of any device connected with the positive pole of a source is the part by or at which the current enters, and that connected with the negative pole, the part at which it leaves. Hence, probably, the change in the use of the words already referred to. Since the anion, or the electro-negative radical, appears at the anode, it is the anode of an electro-plating bath, or the plate connected with the positive terminal of the source that is dissolved. When the term anode was first proposed by Faraday, vol- taic batteries were the only available electric source, and the term referred only to the positive terminal of a voltaic battery when placed in an electrolyte. Anodic Opening Contraction.— The muscular con- traction observed on the opening of a voltaic circuit, the anode of which is placed over a nerve, and the kathode at some other part of the body. 34 A DICTIONARY OF ELECTRICAL This term is generally written A. O. C. When the anode is placed over a nerve and a weak current is employed, if the circuit be kept closed for a few minutes, it will be noticed that, on opening, the contraction will be much greater than if it had been opened after being closed for only a few seconds. The effect of the A. O. C. therefore depends not only on the rent has passed through the nerve. Annunciator, Electro-Magnetic An electric device for automatically indicating the places at which one or more electric contacts have been closed. Annunciators are employed for a variety of purposes. In hotels they are used for indicating the number of a room the occupant of which desires some service which he signifies by pushing a button, thus closing an electric circuit. This is in- dicated or announced on the annunciator by the falling of a drop on which is printed a number corresponding with the room, and the ringing of a bell to notify the attendant. The number is released by the action of the armature of an electro- magnet. The drops are replaced in their former position by some mechanical device operated by the hand. In the place of a drop a needle is sometimes used, which points to the number sig- nalling, by the attraction of the armature of an electro-magnet. Annunciators for houses, bur- glar-alarms, fire-alarms, eleva- tors, etc., are of the same general construction. Fig. 17, shows an annunciator suitable for use in hotels. WORDS, TERMS AND PHRASES. 35 The numbers 28 and 85 are represented as having been dropped by the closing of the circuit connected with them. Anomalous Magnet. — A magnet possessing more than two free poles. There is no such thing as a unipolar magnet. All magnets have two poles. Sometimes, however, several magnets are so grouped that there appear to be more than two poles in the same magnet. Fig. 18. Thus, in Fig. 18, the magnet ABC appears to possess three poles, two positive poles at A and C, and a central negative pole at B. It is clear, however, that the central pole is in reality formed of two juxtaposed negative poles, and that ABC actually consists of two magnets with two poles to each. A B Fig. 19. The magnet A B C D, Fig. 19, which in like manner ap- pears to possess four separate poles, in reality is formed of three magnets with two poles to each. Since unlike magnetic poles neutralize each other, it is clear that only similar poles can thus be placed together in order to produce additional magnet poles. 36 A DICTIONARY OF ELECTRICAL The six-pointed star shown in Fig. 20, is an anomalous magnet with apparently seven poles. The formation of the central N-pole, as is evident 5 from an inspection of the drawing, is due to the six separate north poles, n, n, n, n, n, n, of the six separate magnets Sn, Sn, etc. Such a magnet would be formed by touching the star at the point N with the S-pole of a sufficiently powerful magnet. These extra poles are sometimes called consequent poles. Their presence may be shown by means of a compass needle, or by rolling the magnet in iron filings, which collect on the poles. Anti-Induction Conductor. — A conductor so con- structed as to avoid injurious inductive effects from neighbor- ing telegraphic or electric light and power circuits. Such anti-induction conductors generally consist of a con- ductor and a metallic shield surrounding the conductor, which is supposed to prevent induction taking place in the wire itself. The anti-induction conductor sometimes consists of a con- ductor enclosed by some form of metallic shield, which is supposed to prevent the action of electrostatic induction. Antilogous Pole— (See Pole, Antilogous.) Anvil. — The front contact of a telegraphic key that limits its motion in one direction. (See Telegraphic Key.) A. O. C— A contraction used in medical electricity for Anodic Opening Contraction. (See Anodic Opening Con- traction.) Apparatus, I utcrlockin? (See Interlocking Apparatus Block System for Railroads.) WORDS, TERMS AND PHRASES. 37 Arago'§ Disc. — (See Disc, Arago's.) Arc Lamp, Electric (See Lamp, Arc, Electric.) Arc, Metallic A voltaic arc formed between me- tallic electrodes. When the voltaic arc is formed between metallic electrodes instead of carbon electrodes, a flaming arc is obtained, the color of which is characteristic of the burning metal ; thus copper forms a brilliant green arc. The metallic arc, as a rule, is much longer than an arc with the same current taken between carbon electrodes. Arc Micrometer. — (See Micrometer, Arc.) Arc, Voltaic The brilliant arc or bow of light that appears between the carbon electrodes or terminals of a sufficiently powerful source of electricity. The source of light in the electric arc lamp. It is called the voltaic arc because it was first obtained by the use of the battery invented by Volta. The term arc was given to it from the shape of the luminous bow or arc formed between the carbons. To form the voltaic arc the carbon electrodes are first placed in contact and then gradually separated. A brilliant arc of flame is fonned between them, which consists mainly of vola- tilized carbon. The electrodes are therefore consumed, first, by actual combination with the oxygen of the air, and, second, by volatilization under the combined influence of the electric current and the intense heat. As a result of the formation of the arc, a tiny crater is formed in the end of the positive carbon, and appears to mark the point out of which the greater part of the current flows. The crater is due to the greater volatilization of the elect- rode at this point than elsewhere. It marks the position of greatest temperature of the electrodes, and is the main source of the light of the arc. When, therefore, the voltaic arc is employed for the purposes of illumination with vertically op- 38 A DICTIONARY OF FXECTRICAL posed carbons, the positive carbon should be made the upper carbon, so that the focus of greatest intensity of the light may be favorably situated for illumination of the space below the lamp. The crater in the end of the positive carbon is seen in Fig-. 21. On the opposed end of the negative carbon a projection or nipple is formed by the deposit of the electrically volatil- ized carbon. The rounded masses or globules that appear on the surface of the electrodes are due to deposits of molten foreign matters in the car- bon. The carbon, both of the crater and its opposed nipple, is converted into pure, soft graphite. Arc, Voltaic Resistance of. — The resistance offered by the voltaic arc to the passage of the current. Like all conductors, the ohmic resistance of the arc increases with its length, and decreases with its area of cross-section. An increase of temperature decreases the resistance of the voltaic arc. The total apparent resistance of the voltaic arc is composed of two parts, viz. : (1.) The true ohmic resistance. (See Ohmic or True Resist- ance.) (2.) The counter electro-motive force, or spurious resistance. (See Spurious Resistance.) Areometer or Hydrometer— An instrument for de- terming the specific gravity of a liquid. A common form of hydrometer consists, as shown in Fig. 22, of a closed glass tube, provided with a bulb, and filled at the lower end with mercury or shot. When placed in different WORDS, TERMS AND PHRASES. 39 so liquids, it floats with part of the tube out of the liquid. The lighter the liquid the smaller is the portion that ': 50 remains out of the liquid when the instrument floats. The specific gravity is determined by observing the iQ depth to which it sinks when placed in different liquids, as compared with the depth it sinks when placed in 30 water. Argaiul Lighter, Electric An electric 20 device for lighting the gas by pulling a pendant B, Fig. 23, after it is turned on by hand. The gas is ignited by means of an electric spark obtained from the extra current of a spark coil. (See Current, Extra). 9 Argaml Valve Burner, Electric A burner in which the pulling of the ball B, Fig. 24, turns on and lights the FtgTss. gas, while the motion of the slide extinguishes it. In some forms of argand burner, a| second pulling of the ball B, turns off the gas. ^ Armature. — A mass of iron or other magnetizable materi- al placed on or near the pole or poles of a p ig% ^ Fig. 23. magnet. In the case of a permanent magnet the armature, when used as a keeper, is of soft iron and is placed directly on the magnet poles. In this case it preserves or keeps the magnetism by closing the lines of magnetic force of the 40 A DICTIONARY OF ELECTRICAL magnet through the soft iron of the armature, and is then called a keeper. In the case of an electro-magnet, the arma- ture is placed near the poles, and is moved toward them whenever the magnet is energized by the passage of the cur- rent. This movement is made against the action of a spring or weights, so that on the loss of magnetism by the magnet, the armature moves in the opposite direction. (See Magnet, Permanent. Keeper of Magnet.) When the armature is of soft iron it moves towards the magnet on the completion of the circuit through the coils, no matter in what direction the current flows, and is then called a non-polarized armature. When made of steel, or of another electro-magnet, it moves towards or from the poles, according to whether its poles are of the same or of different polarity. Such an armature is called a. polarized armature. (See Arm- ature, Polarized.) Armature, Dynamo The part of a dynamo- electric machine in which the useful currents are gene- rated. The armature usually consists of a series of coils of insu- lated wire or conductors, that are wrapped around or grouped on a central core of iron. The movement of these wires or conductors through the magnetic field of the machine pro- duces an electric current by means of the electro-motive forces so generated. Sometimes the field is rotated ; sometimes both armature and field rotate. The armatures of dynamo-electric machines are of a great variety of forms. They may for convenience be arranged under the following heads, viz.: Cylindrical or drum armatures, disc armatures, pole or radial armatures, ring armatures, and spherical armatures. For further particulars see above terms. Armatures are also divided into classes according to the character of the magnetic field through which they move— into uni-polar, b>.- WORDS, TERMS AND PHRASES. 41 polar, and multi-polar armatures. (See Dynamo-Electric Ma- chines.) The term armature as applied to a dynamo-electric machine was derived from the fact that the iron core acts to magnet- ically connect the two poles of the field magnets as an ordi- nary armature does the poles of a magnet. Armatures of Holt z Machine.— A badly chosen term for the pieces of paper on the stationary plate of the Holtz and other similar machines. Armature, Polarized An armature that pos- sesses a polarity independent of that imparted by the mag- net pole near which it is placed. In permanent magnets the ai matures are made of soft iron, and therefore, by induction, become of a polarity opposite to that of the magnet poles that lie nearest them. They have, therefore, only a motion of attraction towards such poles. (See Induction, Magnetic.) In electro-magnets the armatures may either be made of soft iron, in which case they are attracted only on the passage of the current ; or they may be formed of permanent steel magnets, or may be electro-magnets themselves, in which case the passage of the current through the coils of the elec- tro-magnet or electro-magnets may cause either attraction or repulsion according as the adjacent poles are of opposite polarity or are of the same polarity. Armature Coils, Dynamo The coils of wire or conductors on the armature of a dynamo-electric machine. (See Dynamo-Electric Machine, Armature Coils.) Armature Core, Dynamo The core of iron around or on which the armature coils are wound or disposed. (See Dynamo-Electric Machine, Armature Cores.) Armor of Cable. — The protecting sheathing or metallic covering" on the outside of a submarine or other electric cable. 42 A DICTIONARY OF ELECTRICAL Arms of Bridge or of Elec- tric Balance.— The electric re- sistances in an apparatus for the p measurement of resistance, known as Wheatstone's Balance or Bridge. An unknown resistance, such for example, as that at D, Fig. 25, is measured by so proportioning- the known resistances A, C, and B, that no current Hows through the Fig. 25. galvanometer G, across the circuit or bridge M G N. (See Balance, Wheatstone's Electric.) A nil* or Brackets, Telegraphic Arms or brackets placed on telegraph poles for the support of the in- sulators. (See Brackets or Arms, Telegraphic.) Arrester, Lightning A device for protecting instruments on any line from disturbance by lightning. (See Lightning Arrester.) Artificial Carbons. — (See Carbons, Artificial.) Artificial Illumination.— (See Illumination, Artificial.) Artificial Magnets. — Any magnet not formed naturally. All magnets other than magnetic iron ore, or lodestone, or meteoric iron. (See Magnets, Artificial.) Articulate Speech. — The successive tones of the human voice that are necessary to produce intelligible words. The phrase articulate speech refers to the joining or arti- culation of the successive sounds involved in speech. The receiving diaphragm of a telephone is caused to reproduce the articulate speech uttered near the transmitting diaphragm. Asphyxia. — Suspended respiration, resulting eventually in death, from the non-aeration of the blood. In cases of insensibility by an electric shock a species of asphyxia is sometimes brought about. This is due, probably, to the failure of the nerves and muscles that carry on respira- WORDS, TERMS AND PHRASES. 43 tion. The exact manner in which death by electrical shock results is not known. (See Death, Electrical.) Astatic Circuits.— (See Circuits, Astatic.) Astatic Needle. — A magnetic needle consisting of two magnets rigidly connected together and placed parallel and directly over each other, with opposite poles opposed. An astatic needle is shown in Fig. 26. The two mag- nets N S, and S' N', are di- rectly opposed in their po- larities, and are rigidly con- nected together by means of the axis a a. So disposed, the two magnets act as a very weak single needle when placed in a magnetic [Jot field. Fig. 26. Were the two magnets N S, and S' N', of exactly equal strength, with their poles placed in exactly the same ver- tical plane, they would completely neutralize each other, and the needle would have no -directive tendency. Such a system would form an Astatic Pair or Couple. In practice it is impossible to do this, so that the needle has a directive tendency, which is often east and west. The cause of the east and west directive tendency of an unequally balanced astatic system will be understood from an inspection of Fig. 27, a. Unless the two needles, n s, and s'n', are exactly opposed, they will form - w ra 1 ; isc Electrometer.— (See Electrometer, Attracted Disc.) Attraction. — Literally the act of drawing together. In science, a name for a series of unknown causes that effect, o." are assumed to effect, the drawing together of atoms, molecules or masses. The phenomena of attraction and repulsion underlie nearly all natural phenomena. While their effects are well known, it is doubtful if anything is definitely known of their true causes. Attraction, Atomic. (See Affinity, Chemical.) Attraction, Electro-Dynamic —The mutual WORDS, TERMS AND PHRASES. 49 attraction of electric currents, or of conductors through which electric currents are passing. (See Electro- Dynamics.) Attraction, Electro -Magnetic The mutual attraction of the unlike poles of electro-magnets. (See Elec- tro-Magnet.) Attraction, Electrostatic The mutual attrac- tion exerted between unlike electric charges, or bodies pos- sessing unlike electric charges. Fig. 29. Fig. 29a. For example, the pith ball supported on an insulated string is attracted, as shown at A, Fig. 29, hy a bit of sulphur which has been briskly rubbed by a piece of silk. As soon, however, as it touches the sulphur and receives a charge, it is repelled, as shown at B, Fig. 29a. These attractions and repulsions are due to the effects of electrostatic induction. (See Induction, Electrostatic.) Attraction, Ulasriietic- -The mutual attraction exerted between unlike magnet poles. Magnetic attractions and repulsions are best shown by means of the magnetic needle N S, shown in Fig. 30. The N. pole of an approached magnet attracts the S. pole of the needle but repels the X. pole. 50 A DICTIONARY OF ELECTRICAL The laws of magnetic attraction stated as follows, viz. : N and repulsion may be (1) Magnet poles of the same polarity repel each other. (2) Magnet poles cf unlike names at- tract each other. A small bar mag- laid on the top of a light vessel floating on the surface of a liquid, may be readily employed to illus- trate the laws of magnetic attraction and repulsion. Attraction, Mass or Molar Gravitation. — The mutual attraction exerted between masses of matter. (See Gravitation.) Attraction, Molecular =, The mutual attraction exerted between molecules. |pii=~ The attraction of like molecules, or Fig. 31. those of the same kind of matter, is called Cohesion ; that of unlike molecules, Adhesion. The strength of iron or steel is due to the cohesion of its molecules. Paint adheres to wood, or ink to paper, by the attraction between unlike molecules. Audiphone. — A thin plate of hard rubber placed in the human mouth in contact with the teeth, and maintained at a certain tension by strings attached to one of its edges, for the purpose of aiding the hearing. The plate is so held that the sound-waves from a speaker's voice impinge directly against its flat surface. It operates by means of some of the waves being transmitted to the ear directly through the bones of the head, WORDS, TERMS AND PHRASES. 51 Aurora Korea I is. — Literally, the Northern Light. Lu- minous sheets, columns, arches, or pillars of a pale flashing light, generally of a red color, seen in the northern heavens. The auroral light assumes a great variety of appearances, to which the terms auroral arch, bands, coronce, curtains and streamers are applied. The exact cause of the aurora is not as yet known. It would appear, however, beyond any reasonable doubt, that the auroral flashes are due to the passage of electrical cur- rents or discharges through the upper, and therefore rarer, regions of the atmosphere. The intermittent flashes of light are probably due to the discharges being influenced by the earth's magnetism. Auroras are frequently accompanied by magnetic storms. (See Magnetic Storms.) The occurrence of auroras is often simultaneous with that of an unusual number of sun spots. Auroras are there- fore probably connected with outbursts of the solar en- ergy. (See Sun Spots.) The auroral light examined by the spectroscope gives a spectrum characteristic of luminous gaseous matter, i. e., contains a few bright lines ; but, according to S. P. Thomp- son, this spectrum is produced by matter that is not refer- able with certainty to that of any known substance on the earth. Whatever may be the exact cause of auroras, their ap- pearance is almost exactly reproduced by the passage of elec- tric discharges through vacuous spaces. (See Geissler Tubes.) Aurora Australis. — The Southern Light. A name given to an appearance in the southern heavens similar to that of the Aurora Borealis, Austral Pole. — A name sometimes employed in France for the north-seeking pole of a magnet. That pole of a magnet which points to the earth's geo- graphical north. 52 A DICTIONARY OF ELECTRICAL It will be observed that the French regard the magnetism of the earth's Northern Hemisphere as north, and so name the north-seeking pole of the needle, the austral or south pole. battery The south-seeking pole of the magnet is some- times called the boreal or north pole. (See Boreal Pole.) Automatic Burner. — (See Burner, Auto- matic, Electric.) Automatic Contact Breaker, or Auto- matic lake-and- Break.— A device for causing an electric cur- rent to rapidly make and break its own circuit. The spring c, Fig. 32, carries an armature of soft iron, B, and is placed in a circuit in such a manner that the circuit is closed when platinum contacts placed on the ends of D and B touch each other. In this case the arm- ature B is attracted to the core A, of the electro-magnet, thus breaking the circuit and causing the magnet to lose its magnetism. The elasticity of the spring C, causes it to fly back and again close the contacts, thus again energizing the electro-magnet and again attracting B, and breaking the circuit. The makes and breaks usually follow each other so rapidly as to produce a musical note. (See Alarm, Electric.) Automatic Cut-Out, Electric A device by means of which an electric circuit is either opened or short circuited, whenever the current passing might injure the electro receptive devices, (See Short Circuit.) BA1TERV Fig, 32. WORDS, TERMS AND PHRASES. 53 The safety devices for arc lights, or series circuits, differ in their construction and operation from those for incandescent lights, or multiple circuits. (See Circuits, Varieties of. Safety Device for Arc Light Circuits. Safety Catch. Cut- out, Automatic. Safety-Fuse. Safety-Strip. Fusible Plug.) Automatic Regulation.— Such a regulation of a dy- namo-electric machine as will preserve constant either the current or the electro-motive force generated by it. The automatic regulation of dynamo-electric machines may be accomplished in the following ways, viz. : (1) By a Compound Winding of the machine. This method is particularly applicable to constant-potential machines. By this winding the magnetic strength of the shunt- coils is constant, while that of the series-coils varies proportion- ally to the load on the machine. The series-coils are prefer- ably wound close to the poles of the machine, and the shunt- coils nearer the yoke of the magnets. Custom, however, varies in this respect, and very generally the shunt-coils are placed nearer the poles than the series-coils. (See Compound-Wind- ing, Dynamo-Electric Machines.) (2) By Shifting the Position of the Collecting Brushes. In the Thomson-Houston system the current is kept prac- tically constant by the following devices : The collecting brushes are fixed to levers moved by the regulator magnet R, as shown in Fig. 33, the armature of which is provided with an opening for the entrance of the paraboloidal pole piece A. A dash-pot is provided to prevent too sudden movement. When the current is normal, the coil of the regulator mag- net is short-circuited by contact points at S T which act as a shunt of very low resistance. These contact-points are operated by the solenoid coils of the Controller traversed by the main current. The cores of this solenoid are suspended by a spring. When the current becomes too strong the con- tact-point is opened, and the current, traversing the coil of the regulator magnet A attracts its armature, which shifts 54 A DICTIONARY OF ELECTRICAL the collecting brushes into a position at which a smaller cur- rent is taken off. A carbon shunt, r, of high resistance, is provided to lessen the spark at the contact-points S T, which occurs on opening the circuit. SMlflOr Fig. 33. In operation the contact-points are continually opening and closing, thus maintaining a practically constant current in the external circuit. (3) By the Automatic Variation of a Resistance shunting the field magnets of the machine, as in the Brush System. In Fig. 34, the variable resistance C forms a part of the shunt circuit around the field magnets F M. This resistance is formed of a pile of carbon plates. On an increase of the cur- rent, such, for example, as would result from turning out some of the lamps, the electro-magnet B, placed in the main circuit, attracts its armature A, and, compressing the pile of carbon plates C, lowers their resistance, thus diverting a pro- portionally larger portion of the current from the field magnet coils F M, and maintaining the current practically constant. In some machines the same thing is done by hand, but this is objectionable, since it requires the presence of an attendant. WORDS, TERMS AND PHRASES. 55 Fig. 3h. 4. By the Introduction of a Variable Resistance into the shunt circuit of the machine, as in the Edison and other systems. This resistance may b e adjusted either automatical] y by an electro- mag net whose coils are in an independent shunt across the mams, or may be operated by hand. In Fig. 35, the vari- able resistance is shown at R, the lever switch being in this case operated by hand whenever the potential rises or falls below the proper value. The machine shown is thus en- abled to maintain a constant potential on the leads to which the lamps, L L L, etc., are connected in multiple-arc. 5. Dynamometric Governing, in which a series dynamo is made to yield a con- stant current by gov- erning the steam engine that drives it, by means of a dynamo- metric governor that maintains a constant torque or turning moment, instead of the usual contrifugal governor which maintains a constant speed. 6. Electric Governing of the Driving Engine, in which the 1 r < < ' < i . > i > c , — ■' 1 .» U Fig. 35. 56 A DICTIONARY OF ELECTRICAL governor is regulated by the current itself instead of by the speed of rotation as usual. (See Addendum Automatic Regulation.) Automatic Telegraphy.— (See Telegraphy, Automatic.) Automatic Telephone Switch.— (See Switch, Tele- phone, Automatic.) Average Electro-UIotive Force.— The mean value of a number of separate electro-motive forces of different values. When a wire in the armature of a dynamo-electric machine cuts the lines of magnetic force in the field of the machine, the electro-motive forces produced depend on the number of lines of force cut per second. This will vary for different positions of the coil. The mean of the varying E. M. F.'s is the average E. M. F. Axe§ of Co-Ordinates.— (See Co-Ordinates, Axes of.) Axis of Abscissas. — (See Abscissas, Axis of.) Axis of Ordinate*.— (See Abscissas, Axis of.) Axis, of a Magnetic — Straight Needle. — A straight line drawn through the magnet, joining its poles. The magnetic axis of a straight needle may be regarded as a straight line passing through the poles of the needle and its point of support. The magnetic axis may not corre- spond with the geometric axis of the needle. This leads to an error in read- ing the true direction in which the needle is pointing, which must be cor- rected. Thus, the needle N S, Fig. 36, points to 31° on the scale. In reality, if the magnetic axis of the needle lies in the line N' S', the true deflection of the needle is only 28°. WORDS, TERMS AND PHRASES. 57 Azimuth.— In astronomy, the angular distance between an azimuth circle and the meridian. The azimuth of a heavenly body in the Northern Hemisphere is measured on the arc of the horizon intercepted between the north point of the horizon, and the point where the great circle that passes through the heavenly body cuts the horizon. Azimuth Circle. — The arc of a great circle passing through the point of the heavens directly overhead, called the Zenith, and the point directly beneath, called the Nadir. Azimuth Compass. — A compass employed by navigators for measuring the horizontal distance of the sun or a star from the magnetic meridian. (See Compass, Azimuth.) Azimuth, Magnetic The arc intercepted on the horizon between the magnetic meridian and a great circle passing through the observed body. B. A. Ohm. — The British Association Unit of Resistance, adopted prior to 1884. The value of the Unit of Electric Resistance, or the ohm, was determined by a Committee of the British Association as being equal to the resistance of a column of mercury at 0° C, one square millimetre in area of cross-section and 104.9 centimetres in length. This length was taken as com- ing nearest the value of the true ohm deduced experimentally from certain theoretical considerations. Subsequent re-deter- minations showed the value so obtained to be erroneous. The value of the ohm is now taken internationally, as adopted by the International Electric Congress in 1884, as the resistance of a column of mercury 106 centimetres in length, and one square millimetre in area of cross-section. This last value is called the legal ohm, to distinguish it from the B. A. ohm which, as above stated, is equal to a mercury column 104.9 centimetres in length. Usage now sanctions the use of the word ohm to mean the legal ohm. This value of the legal ohm is provisional until the exact length of the mercury column can be finally determined. 58 A DICTIONARY OF ELECTRICAL The following are the relative values of these units, viz. : 1 Legal Ohm = 1.0112 B. A. Ohm. " = 1.0600 Siemens Unit. 1 B. A. Ohm = .9889 Legal Ohm. 1 B. A. Ohm = 1.0483 Siemens Unit. 1 Siemens Unit = .9540 B. A. Ohm. " = .9434 Legal Ohm. Back Electro-Molive Force. — A term sometimes used for Counter Electro-Motive Force. The term counter electro- motive force is the preferable term. (See Counter Electro- Motive Force.) Back or Return Stroke of Lightning.— An elec- tric shock, caused by an induced charge, produced after the discharge of a lightning flash. The shock is not caused by the lightning flash itself, but by a charge which is induced in neighboring conductors by the discharge. A similar effect may be noticed by standing near the conductor of a powerful electric machine, when shocks are felt at every discharge. The effects of the return shock are sometimes quite severe. They are often experienced by sensitive people on the occur- rence of a lightning discharge at a considerable distance. In some instances the return stroke has been sufficiently intense to cause death. In general, however, the effects are much less severe than those of the direct lightning discharge. Balance, Arms of (See Arms of Bridge or Elec- tric Balance.) Balance, Bi-filar Suspension An instrument similar in its construction to Coulomb's torsion balance, but in which the needle is hung by two fibres instead of a single one. Any deflection of the needle shortens the vertical distance between the points of support and the needle, and so tends to lift the needle. The motions are therefore balanced against the force of gravity instead of against the torsion of the fibre. WORDS, TERMS AND PHRASES. m Fig. 37. between the A bi-filar suspension is shown in Fig-. 37. The two threads, a b and a' b', are connected to the needle M N, so as to permit it to hang in a true horizontal c position. Any twisting- around the im- «',oHo tf O w oi 2 6 D s i a a 6 io io 20 so o^~o ft o ft o ft o ft~o ft o ft o ft ^ww aow looo low mo m ioo ioo , / ((>)o^ o j(o{(oj)o}|o)(cj|o \( r § induction, among- Fig. U2. ance C, of Fig. 40, is composed of separate resistances of 1, 2, 2, 5, 10, 10, 20, 50, 100, 100, 200 500, 1,000, 1,000, 2,000, and 5,000 ohms. In some forms of box bridges, additional decimal resistances are added. The resistance coils are wound, as shown in Fig. 43, after the wire has been bent on itself in the middle, in order to avoid the effects of which are a disturbing action on a gaivano- u A DICTIONARY OF ELECTRICAL meter used near them, and the introduction of a spurious resistance in the coils themselves. (See Spurious Resistance.) To avoid the effects of changes of resistance occasioned by changes of temperature, the coils are made of German silver, or preferably of alloys called Platinoid, or Platinum silver. (See Platinoid. Platinum Silver.) Even when these alloys are used, care should be taken not to allow the currents used to pass through the resistance coils but for a few moments. The coils, C C, are connected with one another in series by connecting their ends to the short, thick pieces of brass, E E E, Fig. 43. On the insertion of the plug keys, at S S, the coils are cut out by short-circuiting. Care should be taken to see that the plug keys are firmly inserted and free from grease or dirt, otherwise the coil will not be completely cut out. The following are the connec- tions, viz. : The galvanometer is inserted between q and r, Fig. 44; the unknown resistance be- tween z and r ; the battery is connected to x and z. A con- venient proportion being taken for the value of the proportional coils, resistances are inserted in C, until no deflection is shown by the galvanometer G. The simi- larity between these connections and those shown in Fig. 42. will be seen from an inspection of Fig. 44. (See Balance, Wheatstone's Electric.) The arms, A and B, correspond to q x and q z, of Fig. 42 ; C, to the arm x r, Fig. 42 ; and D, to the unknown resistance. We then have as before A : B : : C : D., or AXD = BXC, .-. D= ( — ) C. The advantage of the simplicity of the ratios, A and B, or 10, 100, and 1,000 ? of the Bridge Box, will therefore be mani- WORDS, TERMS AND PHRASES. 65 fest. The battery terminals may also be connected to q and r, and the galvanometer terminals to x and z, without disturb- ing' the proportions. Fig. U5. Balance, Wheatstone's, Slide Form of- 66 A DICTIONARY OF ELECTRICAL balance in which the proportionate arms of the bridge are formed of a single thin wire, of uniform diameter, generally of German silver, of comparatively high resistance. A Spring Key slides over the wire ; one terminal of the key is connected with the galvanometer and the other with the gfllo n>t«i> tnira) ~ "nU B Eld, ( 00 I 860 I Fig. IS. wire when the spring key is depressed. As the wire is of uniform diameter, the resistances of the arms, A and B, Fig. 46, will then be directly proportional to the lengths. A scale placed near the wire serves to measure these lengths. A thick metal strip connected to the slide wire has four gaps at P, Q, R and S. When in ordinary use, the gaps at P and S are either con- nected by stout strips of conducting material or by known resistances, in which case they act simply as un graduated extensions of the slide wire, and, like lengthening the slide wire, increase the sensibility of the instrument. The unknown resistance is then inserted in the gap at Q, and a known resistance, generally the resistance box, in that at E. The galvanometer has one of its terminals connected to the metal strip between Q and R, and its other terminal to the sliding key. The battery terminals are connected to the metal strips between P and Q, and R and S, respectively. These connections are more clearly seen in the form of bridge shown in Fig. 45. The slide wire w w, consists of three separate wires each a metre in length, so arranged that only one wire, or two in series, or all three in series, can be used. Matters being now arranged as shown, the sliding key is moved until no current passes through the galvanometer. WORDS, TERMS AND PHRASES. i;t The sliding bridge is not entirely satisfactory, since the uncertainty of the spring-contact causes a lack of correspond- ence between the point of contact and the point of the scale on which the index rests. The loss of uniformity of the wire, due to constant use, causes a lack of correspondence between the resistance of the wire and ils length. With care, however, very accurate re- sults can be obtained. Ballistic Curve. — The curve actually described by a pro- jectile thrown in any other than a vertical direction through the air. Theoretically, the path of a pro- jectile in a vacuum is a parabola —that is, the path A E B, Fig. 47. Actually, the effects of fluid resist- ances cause it to take the path A C D, called a ballistic curve. The ballistic curve has a smaller verti- cal height than the parabola. The projectile also has a smaller vertical range. Instead of reach- ing the point B, it continually approaches the perpendicular EF. Ballistic Galvanometer.— A form of galvanometer suitable for measuring* momentary currents, such as those produced by the discharge of a condenser, winch rise rapidly from zero to a maximum, and then as rapidly fall to zero. (See Galvanometer, Ballistic.) Barart— A unit of pressure recently proposed by the Brit- ish Association. One barad equals one dyne per square centimetre. Barometer. — An apparatus for measuring the pressure of the atmosphere. Barometric Column. — A column, usually of mercury, approximately thirty inches in vertical height, sustained in a barometer or other tube by the pressure of the atmosphere. Fig. >,. OS A DICTIONARY OF ELECTRICAL The space above the barometric column contains a vacuum known as the Torricellian vacuum. Bars, Krizlk'* Gores of various shapes, provided for solenoids, in which the distribution of the metal in the bar is so proportioned as to obtain as nearly as possible a uniform attraction or pull while in different positions in the solenoid. Various Krizik's bars are shown in Fig. 48. As will be observed, in a 1 I cases the mass of metal is greater towards the middle of the bar or core than near the ends. When a core of uniform diameter is drawn into a sole- Fiq. IS. noid, the attraction or pull is not uniform in strength for dif- ferent positions of 1 ho bar. When the bar is just entering the solenoid, the pull is the strongest; as soon as the end passes the middle of the core the attraction grows less, until, when the centres of the bar and core coincide, the motion ceases, since both ends of the solenoid attract equally in opposite directions. By proportioning the bars, asshown in the figure, a fairly uniform pull for a considerable length may be ob- tained. Batli, Electro-Therapeutic A bath furnished with suitable electrodes and used in the application of elec- tricity to curative purposes. Such baths should be used only under the advice of an intelligent physician. Bath, Electro-Plating — Tanks containing me- tallic solutions in which articles are placed that are to be electro-plated. (See Electro-Plating :) Bathometer— An instrument invented by Siemens for WORDS, TERMS AND PHRASES. 69 obtaining deep-sea soundings without the use of a sounding 'ine. The bathometer depends for its operation on the decreased attraction of the earth for a suspended weight, that takes place in parts of the ocean differing in depth. As the vessel passes over deep portions of the ocean, the solid land of the bottom, being further from the ship, exerts a smaller attraction than it would in shallow parts, where it is nearer ; for, although in the deep pails of the ocean the water lies between the ship and the bottom, the smaller density of the water as compared with the land causes it to exert a smaller attraction than in the shallower parts, where the bottom is nearer the ship. The varying attraction is caused to act on a mercury column, the reading of which is effected by means of an electric contact. Batlis, Copper, Gold, Silver, INiekel, etc., Tanks containing solutions of metals suitable for electric deposition by the process of electro-plating. (See Electro- Plating.) Batteries, Varieties of Voltaic (See Cell, Vallate. Varieties of.) Battery, Dynamo The combination or coup- ling together of several separate dynamo-electric machines so as to act as a single electric source. The dynamos may be connected to the leads either in series, in multiple-arc, in multiple-series, or in series-multiple. Battery, Electric A general term applied to the combination, as a single source, of a number of separate electric sources. The separate sources may be coupled either in series, in multiple-are, in multiple-series, or in series-multiple. (See Cir- cuits, Varietiesof.) The term battery is sometimes incorrectly applied to a single voltaic couple or cell. Battery.* L.ey A Fig. 68. by the circumference in feet of the circle of which the bar is a radius, and tin's product by the number of turns of the driving shaft per minute. The product will be the number of foot- pounds per minute, and, when divided by 33,000, will give the Fig. 69. Horse-Power. (See Horse-Poiver.) Some modified forms of the Prony Brake are shown in Figs. 68, and 69. Branch -Block. — A device employed in electric wiring for taking off a branch from a main circuit. Breaking Weight of Telegraph Wires.— The weight which when hung at the end of a wire will break it. WORDS, TERMS AND PHRASES. 91 Ordinary copper wire will break at about 17 tons to the square inch of cross-section. Common wrought iron breaks at 25 tons to the square inch. When drawn, the breaking weight is often as great as 40 or 50 tons to the square inch. These figures are to be regarded as approximate only, since differ- ences in the physical conditions of metals, as well as slight variations in their chemical composition, often produce marked differences in their breaking weights. Breath Figures, Electric (See Figures, Elec- tric or Breath.) Bridge, Electric (See Balance, Wkeatstone's Electric) Bridge, magnetic An apparatus invented by Edison for measuring magnetic resistance, similar in principle to Wheatstone's Electric Bridge. Fig. 70. The magnetic bridge is based on the fact that two points at the same magnetic potential fail, when connected, to produce any action on a magnetic needle. The magnetic bridge may be arranged as shown in Fig. 70, of four sides made of pure, soft iron. The poles of an electro-magnet are connected, as shown, to projections at the middle of the short side of the rectangle. By this means a difference of magnetic potential is 92 A DICTIONARY OF ELECTRICAL maintained at these points. The two long sides are formed of two halves each, which form the four arms of the balance. Two of these only are movable. Two curved bars of soft iron, of the same area of cross-sec- tion as the arms of the bridge, rest on the middle of the long- arms, in the arched shape shown. Then- ends approach near the top of the arch within about a half inch. A space is hol- lowed out between these ends, for the reception of a short needle of well-magnetized hardened steel, suspended by a wire from a torsion head. The movements of the needle are measured on a scale by a spot of light reflected from a mirror. The electro-magnet maintains a constant difference of mag- netic potential at the two shorter ends of the rectangle. If, therefore, the four bars, or arms of the bridge, are magneti- cally identical, there will be no deflection, since no difference of potential will exist at the ends of the bars between which the needle is suspended. If one of the bars or arms, how- ever, be moved even a trifle, the needle is at once deflected, I he motion becoming a maximum when the bar is entirely re- moved. If replaced by another bar, differing in cross-section, constitution, or molecular structure, the balance is likewise disturbed. The magnetic bridge is very sensitive. It was designed by its inventor for testing the magnetic qualities of the iron used in the construction of dynamo-electric machines. Bridge, Whcatstoiic's Electric (See Wheat- stone's Balance, Electric.) Broken Circuit. — An open circuit. A circuit, the electrical continuity of which has been broken, and through which the current has therefore ceased to pass. Broken Circuit. — (See Circuit, Broken.) Brush Discharge The faintly luminous dis- charge that occurs from a pointed positive conductor. (See Discharge, Convective.) WORDS, TERMS AND PHRASES. 98 ■An electrode in the form of a Brush, Faradic brush employed in the medical application of electricit} 7 . The bristles are generally made of nickelized copper wire. Brusli Holders for Dynamo-Electric Machines. — Devices for supporting the collecting brushes of dynamo- electric machines. As the brushes require to be set or placed on the commu- tator in a position which often varies with the speed of the machine, and with changes in the external circuit, all brush holders are provided with some device for moving them con- centrically with the commutator cylinder. Brushes, Adjust in cut of tlie of Dynamo- Electric Machines. — Shifting the brushes into the required position on the commutator cylinder, either non-automatically by hand, or automatically by the current itself. (See Auto- matic Regulation of Dynamo-Electric Machines.) Brushes for Dynamo-Electric Machines.— Strips of metal, bundles of wire, or slit plates of metal, or carbon, that bear on the commutator cylinder and carry off the current generated. Rotating brushes consisting of metal discs are sometimes employed. Copper is almost universally used for the brushes of dynamo-electric machines. The brush shown at B, Fig. 71, is formed of copper wires, soldered to- gether at the non-bearing end. A cop- per plate, slit at the bearing end, is shown at C, and bundles of copper plates, soldered together at the non- healing end, are shown at D. The brushes should bear against the commutator cylinder with sufficient force to prevent jumping, and conse- Fir/. 71. quent burning, and yet not so hard as to cause excessive wear. 94 A DICTIONARY OF ELECTRICAL Brushes, Lead of The angle through which the brashes of a dynamo-electric machine must be moved for- wards, or in the direction of rotation, in order to diminish sparking and to get the best output from ihe dynamo. The necessity for the lead arises from the counter magnetism of the armature, and the magnetic lag of its iron core. (See Angle of Lead.) Brushes, Scratch Brushes made of wire or stiff cleaning the surfaces of metallic bristles, etc., suitable for objects before placing them in the plating bath. These brushes are of various shapes and are provided with wires or bristles of varying coarseness. Buoy, Electric A buoy, on which luminous electric signals are displayed. Bunseii's Voltaic Cell.— (See Cell, Voltaic.) Burner, Electric A gas- burner whose gas-jet is electrically ignited. On pulling the pendant C, Fig. 72, a spark from a spark coil ignites the gas. On pull- ing the slide the gas is turned off. (See Argand Burner.) Burner, Automatic Electric — An electric device for either turning on the gas and lighting it, or for turning it off. One push-button, usually a white one, turns the gas on and lights it by means of a succession of sparks from a spark coil. Another push-button, usually a black one, turns the gas off. Automatic burners are Fig. 72. also made with a single button. Burglar Alarm.— (See Alarm, Electric, Burglar.) Burnetizing. — A method adopted for the preservation of wooden telegraph poles by injecting a solution of zinc chlor- ide into the pores of the wood. (See Poles, Telegraphic.) WORDS, TERMS AND PHRASES. 95 Burning at Commutator of Dynamo.— An arcing at the brushes of a dynamo-electric machine, due to their im- perfect contact, or improper position, which results in loss of energy and destruction of the commutator segments. Butt Joint.— (See Joint, Butt.) Button, Pu§li A device for closing an electric circuit by the movement of a button. A button, when pushed by the hand, closes a contact, and thus completes a circuit in which some electro-receptive device is placed. This circuit is opened by a spring, on the removal of the pressure. Some forms of push-buttons are shown in Figs. 73 and 73a. Fig. 73, Fig. lh. A floor-push for dining-rooms and offices is shown in Fig. 74. B. W. O. — A contraction for Birmingham Wire Gauge. (See Wire Gauge.) Buzzer, Eleetrie A call, not as loud as that of a bell, produced by an automatic make and break. (See Alarms. Electric.) Cable Armor— (See Armor of Cable.) Cable Clip.— (See Cable Hanger.) 96 A DICTIONARY OF ELECTRICAL Cable Core.— (See Core of Cable.) Cable, Aerial —A cable for telegraphic or tele- the from suitable phonic communication, suspended poles. Cable, Electric A conductor containing either a single conductor, or two or more separately insulated electric conductors. Strictly speaking, the word cable should be limited to the case of more than a single conductor. Usage, however, sanctions the employment of the word to indicate a single insulated conductor. The conducting wire may consist of a single wire, of a number of separate wires electrically connected, or of a num- ber of separate wires insulated from one another. An electric cable con- sists of the following parts, viz. : (1) The conducting wire or core. (2) The insulating material for separating the several wires, and (3) An armor or pro- tecting covering, con- sisting of strands of iron wire, or of a metallic coating or covering of lead. As to their position, cables are, aerial, sub- marine, or under- ground. As to their purpose, they are tele- graphic, telephonic, or electric light and power cables. Fig. 75 shows a form of submarine cable in which the armor is formed of strands of iron wire. WORDS, TERMS AND PHRASES. 97 Cablegram.— A message received by means of a sub- marine telegraphic cable. Cable Hanger.— A hanger or hook, suitably secured to the cable, and designed to sustain its weight by intermediately supporting it on iron or steel wires. A cable hanger, or cable clip, is shown in Fig. 76. The weight per foot of an aerial cable is generally so great that the poles or supports would require to be very near together, unless the device of inter- mediate supports, by means of cable ,* clips, were adopted ff Cable Serving. — Strands of tarred hemp or jute, wrapped around the in- Fig. 76. sulated core of a cable, to protect it from the pressure of the metallic armor. Cables, Submarine Cables designed for use under water. These are either shallow -water, or deep-sea, cables. Gutta- percha answers admirably for the insulating material of the core. Various other insulators are also used. Strands of tarred hemp or jute, known as the cable-serving, are wrapped around the insulated core, to protect it from the pressure of the galvanized iron wire armor afterwards put on. To prevent corrosion of the iron wire, it is covered with tarred hemp, galvanized, or otherwise coated. Cables, Underground Cables designed for use underground. These are either placed directly in the ground, or in coiu ditits, or subways, especially prepared to receive them. (See Conduit, Electric Underground. Subway, Electric.) Calibration, Absolute and Relative of In- strument. — The determination of the absolute or the rela- 98 A DICTIONARY OF ELECTRICAL tive values of the reading of an electrometer, galvanometer, voltmeter, amperemeter, or other similar instrument. The calibration of a galvanometer, for example, consists in the determination of the law that governs its different de- flections, and by which is obtained in amperes, either the ab- solute or the relative current required to produce such deflections. For various methods of calibration, see standard works on Electrical Testing, or on Electricity. Calibration, Invariable of Galvan- ometer. — In galvanometers with absolute calibration, a method for preventing the occurrence of variations in the in- tensity of the field of the galvanometer, due to the neighbor- hood of masses of iron, etc. Callaud Voltaic Cell.— (See Cell, Voltaic.) Call-Bell, Electric (See Alarm, Electric. Belt- Call, Electric.) Caloric. — A term formerly applied to the fluid that was believed to be the cause or essence of heat. The use of the word caloric at the present time is very unscientific, since heat is now known to be an effect and not a material thing. (See Heat.) Calorie, or Calory. — A heat unit. There are two calories, the small and the large calorie. The amount of heat required to raise the temperature of one gramme of water, 1° C. is called the small calorie. Sometimes the term is used to mean the amount of heat required to raise 1,000 grammes of water 1° C. This is called the large calorie. The first usage of the word is the com- monest. Calorescence. — The transformation of invisible heat-rays into luminous rays, when received by certain solid substances. The term was proposed by Tyndall. The light and heat from a voltaic arc are passed through a hollow glass lens filled with a solution of iodine in bisulphide of carbon. WORDS, TERMS AND PHRASES. 99 This solution is opaque to light but quite transparent to heat. If a piece of charred paper, or thin platinum foil, is placed in the focus of these invisible rays, it will be heated to brilliant incandescence. (See Focus.) Calorimeter. — An instrument for measuring- the quan- tity of heat possessed by a given weight or volume of a body at a given temperature. Thermometers measure temperature only. A thermometer plunged in a cup full of boiling water shows the same temper- ature that it would in a tub full of boiling water. The quantity of heat present in the two cases is of course greatly different and can be measured by calorimeters only. Various forms of Calorimeters are employed. In order to determine the quantity of heat in a given weight of any body, this weight may be heated to a definite temperature, such as the boiling point of water, and placed in a vessel containing ice, and the quantity of ice melted by the body in cooling to the temperature of the ice, is determined by measuring the amount of water derived from the melting of the ice. Care must be observed to avoid the melting of the ice by external heat. In this way the amount of heat required to raise the tem- perature of a given weight of a body a certain number of de- grees, or the capacity of the body for heat, may be compared with the capacity of an equal weight of water. This ratio is called the Specific Heat. (See Heat, Specific.) The heat energy, present in a given weight of any substance at a given temperature, can be determined by means of a calorimeter ; for, since a pound of water heated 1° F. absorbs an amount of energy equal to 772 foot-pounds, the energy can be readily calculated if the number of pounds of water and the number of degrees of temperature are known. (See Me- chanical Equivalent of Heat.) 100 A DICTIONARY OF ELECTRICAL Calorimeter, Electric uring the heat developed in a conductor an electric current. An instrument for meas- in a given time, by A vessel containing water, is provided with a thermometer T, Fig. 77. The electric current passes for a measured time through a wire N M, immersed in the liquid. The quantity of heat is deter- mined from the increase of temperature, and the weight of the water. According to Joule, the num- ber of heat units (See Heat Un- Fi &- 77 - its, English) developed in a con- ductor by an electric current is proportional, 1. To the Resistance of the Conductor. 2. To the Square of the Current passing. 3. To the Time the current is passing. The heating power of a current is as the square of the cur- rent only when the resistance remains the same. (See Heat, Electric.) Calorimetric Photometer.— (See Photometer, Calori- metric. ) Candle, Elcctric- -A term applied to the Jab- lochkoff candle, and other similar devices. The Jabiochkoff electric candle consists of two parallel carbons, separated by a layer of kaolin or other heat-resisting' insulating material, as shown in Fig. 78. The current is passed into and out of the carbons at one end of the candle, and forms a voltaic arc at the other end. In order to start the arc, a thin strip called the igniter, consisting of a mixture of some readily ignitable substance, connects the upper ends of the carbons. WORDS, TERMS AND PHRASES. 101 An alternating current is generally employed with these candles, thus avoiding the difficulty which would otherwise occur from the more rapid consumption of the positive than the negative carbon. (See Current, Alternating.) Candle, Foot A unit of illumination equal to the illumination produced b}* a standard candle at the distance of one foot. Proposed by Hering. According to this unit, the illumination produced by a stand- ard candle at the distance of two feet would be but the one- fourth of a foot-candle ; at three feet, the one-ninth of a foot- candle, etc. The advantage of the proposed standard lies in the fact that knowing the illumination in foot-candles required for the particular work to be done, it is easy to calculate the position and intensity of the lights required to produce the illumina- tion. Candie, Metre — The illumination produced by a standard candle at the distance of one metre. Candle, Standard A candle of definite compo- sition which, with a given consumption in a given time, will produce a light of a fixed and definite brightness. A candie which burns 120 grains of spermacetti wax per hour, or 2 grains per minute, will give an illumination equal to one standard candle. Candle. A , or, Unit of Photometric Meas- nremciit. — The unit of photometric intensity. Such a light as would be produced by the consumption of two grains of a standard candle per minute. An electric lamp of 16 candle-power, or one of 2,000 candle- power, is a light that gives respectively 16 or 2,000 times as bright a light as that of one standard candle. Capacity, Dielectric (See Dielectric Capacity.) Capacity, Electro§tatic The ability of a con- 102 A DICTIONARY OF ELECTRICAL ductor or condenser to hold a certain quantity of electricity at a certain potential. The electrostatic capacity of a conductor, or of a condenser, is measured by the quantity of electricity which must be given it as a charge, in order to raise its potential a certain amount. (See Condenser. Potential.) In this respect the electrostatic capacity of a conductor is not unlike the capacity of a vessel filled with a liquid or gas. A certain quantity of liquid will fill a vessel to a level dependent on the size or capacity of the vessel. In the same manner a given quantity of electricity will produce, in a conductor or condenser, a certain difference of electric level dependent on the electrical capacity of the con- ductor or condenser. Or, the quantity of gas that can be forced into a vessel de- pends on the size of the vessel and the pressure with which it is forced in. A tension or pressure is thus produced by the gas on the walls of the vessel that is greater, the smaller the size of the vessel, and the greater the quantity forced in. In the same manner, the smaller the capacity of a conduc- tor, the smaller is the charge required to raise it to a given potential, or the higher the potential a given charge will raise it. The capacity K, of a conductor or condenser, is therefore directly proportional to the charge Q, and inversely propor- tional to the potential V, or Q K =- . V From which we obtain Q = KV; or, The quantity of electricity, required to charge a conductor or condenser to a given potential, is equal to the capacity of the conductor or condenser multiplied by the potential through which it is raised. Capacity, Electrostatic Unit of ; The Farad. — A conductor or condenser of such a capacity that WORDS, TERMS AND RHRASES. 103 an electro-motive force of one volt will charge it with a quan- tity of electricity equal to one coulomb. (See Farad.) Capacity of Polarization of a Voltaic Cell.— The quantity of electricity required to be discharged by a voltaic cell in order to produce a given polarization. (See Cell, Vol- taic. Polarization of Negative Plate.) During the discharge of a voltaic battery, an electro-motive force is gradually set up that is opposed to that of the battery. The quantity of electricity required to produce a given polariza- tion, depends, of course, on the condition and size of the plates. Such a quantity is called the Capacity of Polarization. Capacity of a Telegraph Line or Cable.— The ability of a wire or cable to permit a certain quantity of elec- tricity to be passed into it before acquiring a given difference of potential. Before a telegraph line or cable can transmit a signal to its further end, its difference of potential must be raised to a definite amount dependent on the character of the instru- ments and the nature of the system. The first effect of a given quantity of electricity being passed into a line, is to produce an accumulation of electricity on the line, similar to the charge in a condenser. Cables especially act as condensers, and from the high specific induc- tive capacity of the insulating materials employed, permit considerable induction to take place between the core, and the metallic armor or sheathing, or the ground. The capacity of a cable depends on the capacity of the wire ; i.e., on its length and surface, on the specific inductive capacity of its insulation, and its neighborhood to the earth, or to other conducting wires, casings, armors, or metallic coatings. Submarine or underground cables therefore have a greater capacity than air lines. This accumulation of electricity produces a retardation in the speed of signaling, because the wire must be charged be- fore the signal is received at the distant end, and discharged 104 A DICTIONARY OF ELECTRICAL or neutralized before a current can be sent in the reverse direction. This latter may be done by connecting- each end to earth, or by the action of the reverse current itself. The smaller the electrostatic capacity of a cable, therefore, the greater the speed of signaling. (See Retardation.) Capacity, Specific Inductive ; Dielectric Capacity, or Dieletric Constant.— The ability of a dielec, trie to permit induction to take place through its mass, as compared with the ability possessed by a mass of air of the same dimensions and thickness, under pre- cisely similar conditions. The inductive capacity of a dielectric is compared with that of air. According- to Gordon and others, the specific inductive capacities of a few sub- stances compared with air, are as follows : Air. ...1.00 Glass 3.013 to 3.258 Ebonite 2.284 Gutta-percha 2.462 India rubber 2.220 to 2.497 Paraffin (solid) 1.994 Shellac 2.740 Sulphur 2.580 Turpentine 2.160 Petroleum 2.030 to 2.070 Carbon bisulphide 1.810 Vacuum 0.99941 Hydrogen 0.99967 Carbonic acid... 1.00036 Fig. 70. Faraday, who proposed the term specific inductive capac- ity, employed in his experiments a condenser consisting- of a metallic sphere A, Fig. 79, placed inside a large hollow sphere B. WORDS, TERMS AND PHRASES. 105 The concentric space between A and B was filled with the substance whose specific inductive capacity was to be de- termined. Capillarity. — The elevation or depression of liquids in tubes of small internal diameter. The liquid is elevated when it wets the walls, and depressed when it does not wet the walls of the tube. The phenomena of capillarity are due to the molecular at- tractions existing- between the molecules of the liquid for one another, and the mutual attraction between the molecules of the liquid and those of the walls of the tube. Capillarity, Effects of, on Battery Cells.— Disturb- ing- effects of the proper action of a voltaic battery caused by capillary action. These effects are as follows, viz. : (1) Creeping, or Efflorescence of salts. (See Creeping. Efflorescence.) (2) Oxidation of Contacts and consequent introduction of increased resistance into the battery circuit. The liquid enters the capillary spaces between the contact surfaces and oxidizes them. Capillary Eleetrometer. — An electrometer in which Fig difference of potential is measured by the movements of a drop of sulphuric acid in a horizontal tube filled with mercury. The horizontal glass tube with a drop of acid at B, is shown in 106 a Dictionary oe electrical Fig. 80. The ends of the tube are connected with two vessels, M and N, filled with mercury. If a current be passed through the tube, a movement of the drop toivards the negative pole will be observed. Where the electro-motive force does not exceed one volt, the amount of the movement is proportional to the electro-motive force. Carbon. — An elementary substance which occurs naturally in three distinct alio tropic forms, viz. : charcoal, graphite and the diamond. (See Allotropy.) Carbon, Artificial Carbon obtained by the car- bonization of a mixture of pulverized carbon with different carbonizable liquids. Powdered coke, or gas-retort carbon, sometimes mixed with lamp-black or charcoal, is made into a stiff dough with molasses, tar, or any other hydro-carbon liquid. The mixture is moulded into rods, pencils, plates, bars or other desired shapes by the pressure of a powerful hydraulic press. After drying, the carbons are placed in crucibles and covered with lamp-black, or powdered plumbago, and raised to an intense heat at which they are maintained for several hours. By the carbonization of the hydro-carbon liquid the carbon paste be- comes strongly coherent, and by the action of the heat its conducting power increases. To give increased density after baking, the carbons are sometimes soaked in a hydro-carbon liquid, and subjected to a re-baking. Carbon Electrodes for Arc Lamps. — Rods of artifi- cial carbon employed in arc lamps. Carbons for arc lamps are generally copper-coated, so as to somewhat decrease their resistance, and to ensure a more uniform consumption. They are sometimes provided with a central core of soft carbon, which fixes the position of the arc and thus ensures a steadier light. (See Carbons, Cored.) WORDS, TERMS AND PHRASES. 107 Carbon Holders for Arc Lamps.— Various clamping- devices for holding the carbon electrodes of an arc lamp in the lamp rods. Carbon Telephone Transmitter.— A telephone transmitter consisting of a button of compressible carbon. The sound-waves impart their to-and-fro-movements to the transmitting diapraghm, and this to the carbon button thus varying its resistance by pressure. This button is placed in circuit with the battery and induction coil. (See Telephone.) Carbonic Acid Gas. — A gaseous substance formed by the union of one atom of carbon with two atoms of oxygen. Carbonic acid gas is formed by the combustion of carbon in a full supply of air. Carbonization, Processes of Means for suit- ably carbonizing carbonizable material. Carbonizable material is placed in suitably shaped boxes, covered with powdered plumbago or lamp-black, and subjected to the prolonged action of intense heat while out of contact with air. The electrical conducting power of the carbon which results from this process is increased by the action of the heat, and, probably, also by the deposit in the mass of the carbon, of carbon resulting from the subsequent decomposition of the hydro-carbon gases produced during carbonization. When the carbonization is for the purpose of producing' con- ductors for incandescent lamps, in order to obtain the uniformity of conducting power, electrical homogeneity, purity and high refractory power requisite, selected fibrous material, cut or shaped in at least one dimension prior to car- bonization, must be taken, and subjected to as nearly uniform carbonization as possible. Carbonized Cloth for High Resistances.— Discs of cloth carbonized by heating them to an exceedingly high tem- perature in a vacuum, or out of contact with air. 108 A DICTIONARY OF ELECTRICAL After carbonization the discs retain their flexibility and elasticity and serve admirably for high resistances. When piled together and placed in glass tubes, they form excellent variable resistances when subjected to varying pressure. Carbons, Cored for Arc Lamps.-A cylindri- cal carbon electrode that is moulded around a central core of charcoal, or other softer carbon. These carbons, it is claimed, render the arc light steadier, by maintaining the arc always at the softer carbon, and hence at the central point of the electrode. A core of harder carbon, or other refractory material, is sometimes provided for the negative carbon. Carbons, Concentric*, Cylindrical A cylin- drical rod of carbon placed inside a hollow cylinder of carbon but separated from it by an air space, or by some other insulating, refractory material. Someti nes Jablochkoff candles are made with a solid cylindrical electrode, concentri- cally placed in a. hollow cylindrical carbon. Carcel. — The light emitted by a lamp burn- ing 42 grammes of pure colza oil per hour, with a flame 40 millimetres in height. One carcel = 9.5 to 9.6 standard candles. Carcel Lamp. — An oil lamp employed in France as a photometric standard. Fig. 81 shows a form of carcel lamp. Carcel Standard Gas Jet.— A lighted gas jet employed for determining the candle power of gas by measuring the height of a jet of g»as burning under a given pressure, and used in connection with the light of a larger gas burner, burning under similar conditions, for the photo- metric measurement of electric lights. WORDS, TERMS AND PHRASES. 109 In Fig-. 82, is shown a section of a seven-carcel standard gas jet, and, in Fig. 83, a section of a " candle burner,"' connected with the same service pipe. The gas for both burners is re- ceived in a chamber from whence it passes v~_\ by an opening to the burner under the con- stant pressure obtained by the weight of the bell C, and the tube A. The burner shown in Fig. 83, which is used as the standard of compar- ison, will give a candle power determined from the height of the jet of the burning gas. This height is measured in millimetres by a mov- able circular screen. The determination of the candle power of gas by means of a jet photometer is only approximately cor- rect, unless many precautions are taken. Card, Compass A card used in a mariner's com- pass, on which are marked the points of the compass. (See Compass Card. Azimuth Compass.) Cascade, Charging Leyden Jars by — A device for charging jars or condensers by means of the free electricity liberated by induction in one coating, when a charge is passed into the other coating. The jars are placed as shown in Fig. 84, with the inside coat- ing of one jar connected with the outside coating of the one next it. There is in reality no increase in the entire charge obtained by the use of charging by cascade since the sum of the Fig. 82. Fig. SS. 110 A DICTIONARY OF ELECTRICAL charges given to the separate jars is equal to the same charge given to a single jar separately charged. The energy of the discharge in cascade can be shown to be less than that of the same charge when confined to a single jar. Fig. Sh. i at liion. — A term sometimes used instead of Kation. More correctly written Kathion. (See Kathion.) Cathode. — A term sometimes used instead of Kathode. More correctly written Kathode. (See Kathode.) Caoutchouc, or India-rubber. — A resinous sub- stance obtained from the milky juices of certain tropical trees. Caoutchouc possesses high powers of electric insulation. Cautery, Electric or Galvano-Cautery. —In elec- tro therapeutics, the application of platinum wires of various shapes, heated to incandescence by the electric current, and used, in place of a knife, for removing diseased growths, or for stopping hemorrhages. The operation, though painful during application, is after- wards less painful than that with a knife, since secondary hemorrhage seldom occurs, and the wound rapidly heals. Galvano-cautery is applicable in cases where the knife would be inadmissible owing to the situation of the parts or their surroundings. Cell, Voltaic The combination of two metals, or of a metal and a metalloid, which when dipped into a liquid or liquids called electrolytes, and connected outside the liquid by a conductor, will produce a current of electricity. WORDS, TERMS AND PHRASES. Ill Different liquids or gases may take the place of the two metals, or of the metal and metalloid. (See Gas Battery.) Plates of zinc and copper dipped into a solution of sulphuric acid and water, and connected outside the liquid by a conduc- tor form a simple voltaic cell. If the zinc be of ordinary commercial purity, and is not con- nected outside the liquid by a conductor, the following- pheno- mena occur : (1) The sulphuric acid or hydrogen sulphate, H 2 S0 4 , is de- composed, zinc sulphate, ZnS0 4 , being formed, and hydro- gen, H 2 , liberated. (2) The hydrogen is liberated mainly at the surface of the zinc plate. (3) The entire mass of the liquid becomes heated. If, however, the plates are connected outside the liquid by a conductor of electricity, then the phenomena change and are as follows, viz. : (1) The sulphuric acid is decomposed as before, but (2) The hydrogen is liberated at the surface of the copper plate only. (3) The heat no longer appears in the liquid only, but also in all parts of the circuit, and (4) An electric current now flows through the entire cir- cuit, and will continue so to flow as long as there is any sul- phuric acid to be decomposed, or zinc with which to form zinc sulphate. The energy which previously appeared as heat only, noiv appears as electric energy. Therefore, although the mere contact of the two metals with the liquid will produce a difference of potential, it is the chemical potential energy, which become kinetic during the chemical combination, that supplies the energy required to maintain the electric current. (See Energy. Kinetic Po- tential. Simple Voltaic Cell. — A simple voltaic cell consists of two 112 A DICTIONARY OF ELECTRICAL plates of different metals, or of a metal and a metalloid (or of two gases, or two liquids, ot* of a liquid and a gas), each of which is called a voltaic element, and which, taken tog-ether, form what is called a voltaic couple. The voltaic couple dips into a liquid called an electrolyte, which, as it transmits the electric current, is decomposed by it. The elements are connected outside the electrolyte by any conducting- material. Direction of the Current. — In any voltaic cell the current is assumed to flow through the liquid, from the metal most acted on to the metal least acted on, and outside the liquid, through the outside circuit, from the metal least acted on to the metal most acted on. In Fig. 85, a zinc-copper voltaic couple is shown, immersed in dilute sulphuric acid. Here, since the zinc is dissolved by the sulphuric acid, the zinc is oosi- tive, and the copper negative in the li- quid. The zinc and copper are of oppo- site polarities out of the liquid. It will of course be understood that in the above sketch the current flows only on the completion of the circuit outside the cell, that is, when the conductors at- tached to the zinc and copper plates are electrically con- nected. Amalgamation of the Zinc Plate. — When zinc is used for the positive element, it will, unless chemically pure, be dis- solved by the electrolyte when the circuit is open, or will be irregularly dissolved while the circuit is closed, producing currents in little closed circuits from minute voltaic couples formed by the zinc and such impurities as carbon, lead, or iron, etc., always found in commercial zinc. (See, Action, Local.) As it is practically impossible to obtain chemically pure zinc, it is necessary to amalgamate the zinc plate, that is, to cover Fig. 85. WORDS, TERMS AND PHRASES. 113 it with a thin layer of zinc amalgam. (See Zinc, Amalgama- tion of.) Polarization of the Negative Plate. — Since the evolved hy- drogen appears at the surface of the negative plate, after a while the surface of this plate, unless means are adopted to avoid it, will become coated with a film of hydrogen gas, or as it is technically called, will become polarized. (See Polari- zation of Voltaic Cell.) The effect of this polarization is to cause a falling off or weakening of the current produced by the battery, due to the formation of a counter-electro-motive force produced by the hydrogen-covered plate ; that is to say, the negative plate, now being covered with hydrogen, a very highly electro-posi- tive element, tends to produce a current in a direction opposed to that of the cell proper. (See Counter-Electro-Motive Force.) In the case of storage cells, this counter-electro-motive force is employed as the source of secondary currents. (See Storage of Electricity. Storage Cells.) In order to avoid the effects of polarization in voltaic cells, and thus ensure constancy of current, the bubbles of gas at the negative plate are mechanically carried off either by roughen- ing its surface, by forcing the electrolyte against the plate as by shaking, or by a stream of air ; or else the negative plate is surrounded by some liquid which will remove the hydrogen, by entering into combination with it. (See Polarization of Voltaic Cell.) Voltaic cells are therefore divided into cells with one or with two fluids, or electrolytes, or, into (1) Single-fluid cells, and (2) Double-fluid cells. Very many forms of voltaic cells have been devised. The following are among the more important, viz. : Single-Fluid Cells. The Grenet, Poggendorff, or Bichromate Cell. — A zinc-car- bon couple used with an electrolyte known as electropoion, a 114 A DICTIONARY OF ELECTRICAL solution of bichromate of potash and sulphuric acid in water. (See Electropoion Liquid.) The zinc, Fig. 86, is amalgamated and placed between two carbon plates. The terminals connected with the zinc and carbon are respect- ively negative and positive. In the form shown in the figure, the zinc plate can be lifted out of the liquid when the cell is not in action. The bichromate cell is excellent for pur- poses requiring strong currents, where long action is not necessary. As this cell readily polarizes, it cannot be advan- tageously employed for any considerable period of time. It becomes depolarized, however, when left for some time on open circuit. The following chemical reaction takes place when the cell is furnishing cur- Fig.86. rent, viz.: K 2 Cr 2 7 -f7H 3 S0 4 +3Zn=K 2 S0 4 +3ZnS0 4 +Cr 2 3(S0 4 )+7H 2 0. This cell gives an electro-motive force of about 1.987 volts. The Smee Cell— A zinc-silver couple used with an electro- lyte of dilute sulphuric acid, H 2 S0 4 . The silver plate is covered with a rough coating of metallic platinum, in the condition known as jjlatinum black. (See Platinum Black.) This cell was formerly extensively em- ployed in electro-metallurgy but it is now replaced by dyna- mo-electric machines. (See Electro-Metallurgy. Dynamo- Electric Machine.) A zinc-carbon couple is sometimes used to replace the zinc- silver couple. A couple of zinc-lead is also used, though not very advantageously. The Zinc-Copper Cell— A zinc-copper couple used with dilute sulphuric acid. WORDS, TERMS AND PHRASES. 115 This was one of the earliest forms of voltaic cells. In the zinc-silver, or the zinc-copper couple, the chemical reaction that takes place when the cell is furnishing' current is as follows, viz. : Zn + Ho S0 4 = Zn S0 4 + H 2 . The Smee cell gives an electro-motive force of about .65 volts. Double-Fluid Cells. Grove's Cell. — A zinc-platinum couple the elements of which are used with electrolytes of sulphuric and nitric acids respectively. The zinc, Z, Fig. 87, is amalgamated and placed into dilute sulphuric acid, and the platinum, P, into strong nitric acid (H N0 3 ), placed in a porous cell to separate it from the sul- phuric acid. (See Porous Cells.) In this cell the cur- rent is moderately constant, since the polarization of the platinum plate is prevented by the nitric acid that oxy- dizes and thus removes the hydrogen that tends to be liberated at its surface. The constancy of the current is not maintained for any considerable time, since the two liquids are rapidly decom- posed, or consumed, zinc sulphate forming- in the sulphuric acid, and water in the nitric acid. The chemical reactions are as follows, viz. : Zn + H 8 S0 4 =ZnS0 4 + H.; 6H + 2H NO a = 4H + 2NO; 2NO + 2 =N 2 4 . Fig. 87. 116 A DICTIONARY OF ELECTRICAL Fig. 88. This cell gives an electro-motive force of 1.93 volts. BunserCs Cell.— A. zinc-carbon couple, the elements of which are immersed respectively in electrolytes of dilute sulphuric and strong nitric acids. Bunsen's cell is the same as Grove's except that the platinum is replaced by carbon. The zinc surrounds the porous cell contain- ing the carbon. The polarity is as indicated in Fig. 88. The Bunsen cell gives an electro- motive force of about 1.96 volts. DanielVs Cell. — A zinc-copper couple, the elements of which are used with electrolytes of dilute sulphuric acid, and saturated so- lution of copper sulphate respectively. The copper element is made in the form of a cylinder c, Fig. 89, and is placed in a porous cell. The copper cyl- inder is provided with a wire basket near the top, filled with crystals of blue vitriol, so as to maintain the strength of the solution while the cell is in use. The zinc is in the shape of a cylinder and is placed so as to surround the porous cell. This cell gives a nearly constant electro-mo- tive force. The constancy of its action depends on the fact that for every molecule of sulphuric acid decomposed in the outer cell, an additional molecule WORDS, TERMS AND PHRASES. 117 of sulphuric acid is supplied by the decomposition of a mole- cule of copper sulphate in the inner cell. This will be better understood from the following- reactions which take place, viz. : Zn + H 2 S0 4 = Zn S0 4 + H 2 Ho + Cu S0 4 — Ho S0 4 -f Cu. The H 3 S0 4 , thus formed in the inner cell, passes through the porous cell, and the copper is deposited on the surface of the copper plate. The Daniell's cell gives an electro-motive force of about 1.072 volts. A serious objection to this form of cell arises from the fact that the copper is gradually deposited over the surface and in the pores of the porous cell, thus greatly varying its resistance. Callaud's Gravity Cell. — A zinc-copper couple, the ele- ments of which are em- ployed with electrolytes of dilute sulphuric acid, or di- lute zinc sulphate, and a con- centrated solution of cop- per sulphate respectively. This cell was devised in order to avoid the use of a porous cell. As its name in- dicates, the two fluids are separated from each other by gravity. The copper plate is the lower plate, and is surround- ed by crystals of copper sul- ig ' phate. The zinc, generally in the form of an open wheel, or crowfoot, is suspended near the top of the liquid, as shown in Fig. 90. The reactions are the same as in the Daniell cell. A dilute solution of zinc sulphate is generally used to replace the dilute sulphuric acid. It gives a somewhat lower electro- motive force, but ensures a greater constancy for the cell. 118 A DICTIONARY OF ELECTRICAL The Leclanche Cell. — A zinc-carbon couple the elements of which are used with a solution of sal-ammoniac, and a finely divided layer of black-oxide of manganese respectively. The zinc is in the form of a slender rod and dips into a sat- urated solution of sal-ammoniac, NH 4 CI. The negative element consists of a plate of carbon, C, Fig. 91, placed in a r porous cell, in which is a mix- ture of black ox- ide of manganese and broken gas- retort c a r b o n , tightly packed around the c a r- b o n plate. By this means a greatly extended surface of carbon surrounded by black oxide of manganese, Mn 2 , is secured. The entire outer jar, and the spaces inside the porous cell are filled with the solution of sal-ammoniac. This cell, though containing but a single fluid, belongs, in reality, to the class of double- fluid cells, being one in which the negative element is sur- rounded by an oxidizable substance, the black oxide of man- ganese, which replaces the nitric acid, or copper sulphate in the preceding cell. The reactions are as follows, viz. : Zn+2(NH 4 Cl) = ZnCl 2 + 2NH 3 +H 2 . The Zn Cl 2 and NH 3 react as follows : Zn C1 2 + 2(NH 3 ) = (2NH 2 ) Zn Cl 2 +H 2 . 2H + 2(Mn 2 2 ) = H 2 + Mn 2 3 , or, possibly, 4H + 3Mn 2 = Mn 3 4 -f- 2H 2 O. The Leclanche cell gives an electro-motive force of about 1.47 volts. It rapidly polarizes, and cannot, therefore, give a steady current for any prolonged time. When left on open circuit, however, it rapidly depolarizes. WORDS, TERMS AND PHRASES. 119 Of all the voltaic cells that have been devised two only, viz., the Gravity and the Leclanche, have continued until now in very general use. The gravity cell being used on closed-circuit lines and the Leclanche on open-circuit lines ; the former being the best suited of all cells to furnish con- tinuous constant currents employed in most systems of tele- graphy, and the latter for furnishing the intermittent cur- rents required for ringing bells, operating annunciators, or for similar work. The Siemens- Halske Cell. — A zinc-copper couple the ele- ments of which are employed with dilute sulphuric acid and saturated solution of copper sul- phate respectively. This cell is a modification of Daniell's. A ring of zinc, Z Z, Fig. 92, surrounds the glass cylinder c, c. The porous celJ is replaced by a diaphragm, / /, of porous paper, formed by the action of sulphuric acid on a mass of paper pulp. Crystals of copper-sulphate are placed in the glass jar, c c, ___ and rest on the copper plate A:, ~~ formed of a close copper spiral. Terminals are attached at b and h. The entire cell is charged with The resistance of the cell is high. The Meidinger Cell. — A zinc-copper couple the elements of which are employed with dilute sulphuric acid, or solution of sulphate of magnesia, and strong nitric acid, respectively. This is another modification of the Daniell cell. The zinc- copper couple is thus arranged : Z Z, Fig. 93, is an amalga- mated zinc ring placed near the walls of the vessel, A A. The Fig. 92. dilute sulphuric acid. 120 A DICTIONARY OF ELECTRICAL copper element c is similarly placed with respect to the ves- ,4- sel b b. The glass cylinder h filled with crystals of copper sul- phate, has a small hole in its bot- tom, and keeps the vessel, b b, supplied with saturated solution of copper sulphate. The cell is charged with dilute sulphuric acid, or a dilute solution of Epsom salts, or magnesium sulphate. Cell, Standard Voltaic (See Standard Voltaic Cell) Cements, Insulating — Various mixtures of gums, resins and other substances, possessing the ability to bind two or more Fig. 93. substances together and yet to electrically insulate one from the other. Centi (as a prefix). — The one hundredth of. Centigrade Thermometer Scale. — A thermometer scale on which the freezing point of water is marked 0°, and the boiling point at 30 inches of the barometer 100°. Centigrade degrees are indicated by a C, thus 0° C. or 100° C, to distinguish them from Fahrenheit degrees that are marked F. — (See Thermometer.) Centigramme. — The hundredth of a gramme, or 1544 grains. (See Metric System of Weights and Measures.) Centimetre. — A length equal to the one hundreth of a metre or .3937 inch. (See Metric System of Weights and Measures.) Centimetre-Gramme-Second System, or the C. O. S. System. — A system of units of measurement in which the centimetre is adopted for the unit of the length, the WORDS, TERMS AND PHRASES. 121 gramme for the unit of mass, and the second for the unit of time. This is the same as the Absolute System of Units. (See Absolute Units.) Central Station Lighting.— (See Lighting, Central Station. Centre of Oravity.— (See Gravity, Centre of.) Centre of Oscillation.— (See Oscillation, Centre of.) Centre of Peren§§ion.— (See Percussion, Centre of.) Centrifugal Force (so called).— The force that is sup- posed to urge a rotating body directly away from the centre of rotation. If a stone be tied to a string and whirled around, and the string break, the stone will not fly off directly away from the centre, but will move along the tangent to the point where it was when the string broke. The centrifugal force in reality is the force which is repre- sented by the tension to which the string is subjected during rotation. Centrifugal Governor A device for maintain- ing constant the speed of a steam engine or other prime mover, despite sudden changes in the load, or work. In a ball governor any increase in speed causes the balls to fly out from the centre of rotation by centrifugal force, which is utilized to control a valve or other regulating device. If the speed falls the balls move towards the centre, shifting the valve or regulating device in the opposite direction. Chain, Molecular (See Molecular Chain.) Chamber of Lamp.— The glass bulb or chamber of an incandescing electric lamp in which the incandescing con- ductor is placed, and which is generally maintained at a high vacuum. Characteristic Curves.— Diagrams in which curves are employed to represent the ratio of certain varying values. 122 A DICTIONARY OF ELECTRICAL The electro-motive force generated in the armature coils of a dynamo-electric machine, when the magnetic field is of a constant intensity, is theoretically proportional to the speed of rotation. (In practice this is prevented by a number of cir- cumstances). The relation existing between the speed and electro-motive force may be graphically represented by refer- ring the values to two straight lines, one horizontal and the other vertical, called respectively the axes of abscissas and ordinates. (See Abscissas, Axis of.) If, in a given case, the number of revolutions are marked off along the horizontal line from the point 0, Fig. 94, in dis- 600 vm lances from 0, proportional to the Fig. 9h. number of revolutions, and the cor- responding electro-motive forces are marked off along the vertical line in distances from 0, proportional to the electro- motive forces, the points where these lines intersect, will form the characteristic curve as shown for the particular case. Charge, Bound and Free Free Charge.) — (See Bound and Charge, Density of or Electrical Density. The quantity of electricity at any point on a charged surface. Coulomb used the phrase Surface Density to mean the quantity of electricity per unit of area at any point on a surface. Charge, Electric -The quantity of electricity that exists on the surface of an insulated electrified conductor. When such a conductor is touched by a good conductor con- nected with the earth, it is discharged. Charge, Dissipation of - Charge.) Charge, Distribution of -(See Dissipation of — The variations that WORDS, TERMS AND PHRASES. 1*23 exist in the density of an electrical charge at different portions of the surface of all insulated conductors except spheres. The density of charge varies at different points of the sur- face of conductors of various shapes. It is uniform at all points on the surface of a sphere. It is greatest at the extremities of the longer axis of an egg shaped body, and greater at the sharper end. It is five times greater at the corners of a cube than at the middle of a side. It is greatest round the edge of a circular disc. It is greatest at the apex of a cone. Charge, Residual The charge possessed by a charged Leyden jar a few moments after it has been dis- l-uptively discharged by the connection of its opposite coatings. The residual charge is probably due to a species of dielectric strain, or a strained position of the molecules of the glass caused by the charge. Such residual charge is not present in air condensers. Charge, Return (See Back Stroke or Return.) Charging' Aeeuuiulators. — Sending an electric current into a storage battery for the purpose of rendering it an elec- tric source. There is, strictly speaking, no accumulation of electricity in a storage battery, such for example as takes place in a condenser. (See Storage Batteries). Charaeteristies of Sound.— The peculiarities that enable different musical sounds to be distinguished from one another. The characteristics of musical sounds are : (1) The Tone or Pitch, according t which a sound is either grave or shrill. (2) The Intensity or Loudness, according to which a sound is either loud or feeble. (3) The Quality or Timbre, the peculiarity which enables us 124 A DICTIONARY OF ELECTRICAL to distinguish between two sounds of the same pitch and intensity, but sounded on different instruments, as for example on a flute and on a piano. Chemical Effect or Change. — Such a change, occa- sioned by chemical combination, as results in a loss of thoce properties or peculiarities by which the substances entering into combination are ordinarily recognized. Black carbon, and yellow sulphur, for example, both solids, unite chemi . ; Ay to form a transparent colorless liquid. Chemical changes differ from physical changes, which latter can occur in a substance without the loss by it of the proper- ties it ordinarily possesses. Thus a sheet of vulcanite, electrified by friction, still retains its characteristic density, shape, color, etc. Chemical Equivalent. — (See Equivalent, Chemical.) Chemical Photometer. — (See Photometers.) Chemical Potential Energy. — (See Energy Atomic, or Energy Potential.) Chemical Recorder. — (See Recorder, Chemical, Bain's.) Chimes, Electric -Bells, repul- Fig. 95. rung by the attractions and sions of electrostatic charges. B and B, Fig. 95, are directly con- nected to the prime or positive conductor -f-j of a frictional machine. C is insulated from this conductor by means of a silk thread, but is con- nected with the ground by the me- tallic chain C. Under these circum- stances the clappers, I I, insulated by silk threads, t t, are attracted to B, B, by an induced charge and repelled to C, where they lose their charge only to be again WORDS, TERMS AND PHRASES. 125 attracted to B, B. In this way the bells will continue ringing as long as the electric machine is in operation. Chronograph, Electric — An apparatus for electrically measuring and registering small intervals of time. Chronographs, though of a variety of forms, generally regis- ter minute intervals of time by causing a tuning fork or vibrat- ing bar of steel, whose rate of motion is accurately known, to trace a sinuous line on a smoke blackened sheet of paper, placed on a cylinder driven by clockwork, at a uniform rate of motion. If a fork that is known to produce, say, 256 vibra- tions per second be used, each sinuous line will represent ? |g part of a second. An electro-magnet is used to make marks on the line at the beginning and the end of the observation, and thus permit its duration to be measured. An apparatus for elec- Chrono§cope, Electric trically indicating, but not necessarily recording, small inter- vals of time. The small interval of time required for a rifle ball to pass between two points may be determined by causing the ball to pierce two wire screens placed a known distance apart. As the screens are successively pierced, an electric circuit is thus made or broken, and marks are registered electrically on any apparatus moving with a known velocity. Circle, Azimuth —(See ^ Azimuth Circle.) ^ Circle, Voltaic or Galvanic A name formerly employed t for a voltaic cell or circuit. Circuit, Astatic A cir- | + s cuit consisting of two closed curves "' |b enclosing equal surfaces. Fig. 96. Such a circuit is not under the action of the earth's field. The circuit disposed ? as shown in Fig. 96, is astatic and pro- 126 A DICTIONARY OF ELECTRICAL duces two equal and opposite fields at S and S'. (See Mag- netism, Ampere's Theory of.) Circuit, Broken or Opened, Made, Closed, or Completed A circuit is broken or opened, when its conducting continuity is disturbed, or when the current can- not pass. Circuit, Closed, Completed or Made A circuit is closed, completed, or made when its conducting continuity is such that the current can pass. Circuit, Compound A circuit containing more than a single source, or more than a single electro-receptive device, or both, connected by conducting wires. The term compound circuit is sometimes applied to a series circuit. (See Circuit, Series.) The term, however, is a bad one, and is not generally adopted. Circuit, Earth' A circuit in which the ground or earth forms part of the conducting path. (See Circuit, Varieties of.) Circuit, Electric Literally to go around. The path in which electricity circidates or passes from a given point, around or through a conducting path, back again to its starting point. All simple circuits consist of the following parts, viz. : (1) Of an electric Source, which may be a voltaic battery a thermo-pile, a dynamo-electric machine, or any other means for producing electricity. (2) Of Leads or Conductors for carrying the electricity out from the source, through whatever apparatus is placed in the line, and back again to the source. (3) Various Electro-Receptive Devices, such as electro-mag- nets, electrolytic baths, electric motors, electric heaters, etc., through which the current passes and by which they are ac- tuated or operated, WORDS, TERMS AND PHRASES. 127 Circuit, External external, or outside the electric Circuit, Grounded -That part of a circuit which is source. A circuit in which the through which the current good conductor, the terminals gas or water pipes, or with plates. Such connection, or is usually termed the ground ground forms part of the path passes. As the ground is not always a should be connected with the metallic plates, called ground any similar ground connection or earth. Circuit Indicator.— (See Indicator.) Circuit, Internal ■ — That part of a circuit which is included within the electric source. Circuit, Line The wire or other conductors in the main line of any telegraphic or other electric circuit. (See Circuits, Varieties of.) Circuit, Local ■ —The circuit in a telegraphic system in which is placed a local battery as distinguished from a main battery. (See Telegraph, Morse System.) Circuit, Main Battery -A term sometimes used for Line Circuit. (See Circuit, Line.) Circuit, Magnetic —The path through which the lines of magnetic force pass. All lines of force form closed circuits. In the bar magnet, shown in Fig. 97, part of this path is through the air. In order to reduce or lower the resistance Fig. 97 of a magnetic circuit, iron is often placed around the mag- net. The magnet is then said to be iron-clad. The armature of a magnet lowers the masrnetic resistance 128 A DICTIONARY OF ELECTRICAL oy affording a better path for the lines of magnetic force than the air between the poles. Circuit, Metallic A circuit in which the ground is not employed as any part of the path of the current. Circuit, multiple-Series ——(See Circuits, Varie- ties of.) Circuit, Parallel or Multiple-Arc (See Cir- cuits, Varieties of.) Circuit, Simple A circuit containing a single electric source, and a single electro-receptive device, connected by a single conductor. The term simple circuit is sometimes applied to a multiple arc circuit. The term is not, however, a good one, and is not in general use. Circuit, Series (See Circuits, Varieties of.) Circuit, Series-Multiple (See Circuits, Varie- ties of.) Circuit, Shunt or Derived A circuit which forms an additional path for an electric current. (See Shunt, or Derived Circuit.) Circuits, Varieties of Conducting paths pro- vided for the passage of an electric current. Electric circuits may be divided according to their complex- ity into (1) Simple. (2) Compound. According to the peculiarities of their connections into (1) Shunt or Derived. (2) Series. (3) Parallel or Multiple- Arc, (4) Multiple-Series. (5) Series-Multiple. WORDS, TERMS AND PHRASES, 129 According to their resistance into (1) High Resistance. (2) Low Resistance. According to their relation to the electric source into (1) Internal circuits. (2) External circuits. According to their position in the circuit, or the work done, circuits are divided into very numerous classes; thus in telegraphy we have the following, viz. : (1) The Line circuit. (2) The Earth or Ground circuit. (3) The Local Battery circuit. (4) The Main Battery circuit, etc. A simple circuit is one which contains but a single electric source and a single electro-receptive device, connected by a single conducting wire. A compound circuit is one which contains more than a single electric source, or more than a single electro-receptive device, or both, connected by conducting wires. Either the circuits, the sources, or the electro-receptive de- vices ma} r be connected in series, in multiple, in multiple-series, or in series-multiple. The most important of these are as follows : (1) Series circuits or connections. Compound circuits, in which the separate circuits, or sources, are connected in one line by joining their opposite poles so that the current pro- duced in each passes successively through the circuit. Fig. 98. The six cells, shown in Fig. 98, are connected in series by joining the positive pole of each cell with the negative 130 A DICTIONARY OF ELECTRICAL pole of the succeeding cell, the negative and positive poles at the extreme ends being connected by any conductor. The connection of three Leclan- cle cells in series is clearly shown in Fig. 99. The carbons, C C, of the first and sec- ond cells are con- Fig.99. nected to the zincs, Zn Zn, of the second and third cells, thus leaving the zinc, Zn, of the first cell, and the carbon, C, of the third cell, as the terminals of the battery. The direction of the current is shown by the arrows. The resistance of such a connection is equal to the sum of the resistances of each of the separate sources. The electro-motive force is equal to the sum of the separate electro-motive forces. If the electro-motive force of a single cell is equal to E, its internal resistance to r, and the resistance of the leads and electro-receptive devices to r', then the current in the circuit, E C = r -\-r' If six of such cells are coupled in series, the current becomes 6E C= . 6r -j-r If, however, the internal resistance of each cell be so small as to be neglected, the formula becomes 6E a •* — ; or the current is six times as great as with one cell. WORDS, TERMS AND RHRASES. 181 The series connection of battery cells is used on telegraph linen, or in all cases where a high electro-motive force is re- quired in order to overcome a considerable resistance in the circuit. The instruments are also generally connected to the line in series. This series connection was formerly called Connection for Intensity. The term is now abandoned. C ^ A C Fig. 100. (2) Parallel Circuit, or Multiple-Arc. — A compound circuit in which the separate sources, or the separate electro-receptive devices, or both, are connected by one set of terminals, such as the positive, to one lead, or main positive conductor ; and all the negative terminals are similarly connected to another lead, or main negative conductor, as shown in Fig. 100. Fig. 101. The connection of three Bunsen cells, in multiple-arc, is shown in Fig. 101, where the three carbons, C C C, are con- 132 A DICTIONARY OF ELECTRICAL nected together to form the positive, or -f- terminal of the battery, aud the three zincs, Zn Zn Zn, are similarly connected together to form the negative, or — terminal. The electro-motive force is the same as that of a single cell, or source. The internal resistance of the source is as much less than the resistance of any single source as the area of the combined negative or positive plates is greater than that of any single negative or positive plate ; or, in other words, is less in proportion to the number of cells, or other separate sources so coupled. In the case of the six cells above referred to, the current would be, E C = r -+r> 6 where E, is the electro-motive force, r, the internal and r\ the external resistance. The effect of multiple connection on the internal resistance of the source is to increase the area ol cross section of the liquid in the direct proportion of the number of cells added. C 1 Fig. 102. "When strong or large currents of low electro-motive force are required, connections in multiple-arc are generally employed. The multiple-arc connection was formerly called the Con- nection for Quantity. This term is now abandoned. WORDS, TERMS AND PHRASES. 133 (3) Multiple-Series Circuit.— A compound circuit in which the separate sources, or electro-receptive devices, are con- nected in groups in multiple- arc, and the members of each group subsequently connected in series. In Figs. 102 and 103, multiple-series circuits of six sources are shown. The "— current takes the paths indicated ^f. by the arrows. The electro-mo- tive force of the source will be in- creased in pro- portion to the Fig. 103. number of cells in series, and the internal resistance decreased in proportion to the number in parallel. Supposing the circuit closed by a resistance equal to r', the current would be, in Fig. 102, 2E and that in the Fig. 103, J 1 2r + r' 3 3E c = = 3r +*' (4) In Series- Multiple; the method adopted in the use of dis- tribution boxes, a number of multiple groups or circuits are =* 1 * } * =^^~ — — r~ — =t * 4= * * *_ * Fig. 10k. connected with each other, in series, as shown in Fig. 104. (See Box, Distribution, for Arc Light Circuits.) 134 A DICTIONARY OF ELECTRICAL In this connection the resistance of each multiple group is equal to the resistance of a single branch divided by the num- ber of branches. The total resistance of the circuit is equal to the sum of the resistances of the multiple groups. The resistances of the separate compound circuits is as fol- lows : Calling E', R", and R'", the resistance of each of the separate parts and the joint resistance R. (1) For the series circuit, R = R' _|_ R" _j_ R'". (2) For the parallel circuit, R= R'XR"XR"' R' R" -f R" R'" -f R' R'" ; or, what is the same thing, the conductivity of a multiple cir- cuit is the sum of the reciprocals of the separate resistances; 1 1 1 or, Conductivity = 1 1 . R' R" R'" (3) For the multiple-series circuit, if the resistance of each circuit is r, then the total resistance 2r R= - , 3 when three are in parallel and two in series ; and dr R= - , 2 when two are in parallel and three in series. (4) For the series-multiple circuit, calling r the resistance of each separate circuit in the five parallel circuits, then the resistance of each of the parallel groups is r R= -; 5 and the total resistance of the three groups is r r r 3r R=-+- + - = -. 5 5 5 5 WORDS, TERMS AND PHRASES. -$5 Circular Units. — Units based upon the value of the area of a circle whose diameter is unity. Circular Units (Cross-Sections), Table of. 1 circular mil. _ = .78540 square mil. " = .00064514 circular millimetre. = .00050669 square millimetre. 1 square mil = 1.2732 circular mils. _ = .00082141 circular millimetre. 1 circular millimetre = 1550.1 circular mils. " = 1217.4 square mils. " = . 78540 square millimetre. 1 square millimetre = 1973.6 circular mils. " -. = 1.2732 circular millimetres. If d is the diameter of a circle, the area in other units is ■ If d is in mils., area in sq. millimetres _ . . = d 2 x .00050669. d in millimetres, area in sq. mils = d 2 x 1217.4. d in centimetres, area in sq. inches = d 2 x 12174. d in inches, area in sq. centi- metres = d 2 x 5.0669. (Hering.) Clamp or Clutch for Arc Uamps.— A clamp for gripping the lamp-rod, i. e., the rod that supports the carbon electrodes of arc lamps. (See Lamp, Electric Arc.) Cleats. — Insulating supports for attaching wires to the walls or ceilings of buildings. Clepsydra, Electric An instrument for measur- ing time by the escape of water or other liquid under electrical control. Clocks, Electric Clocks, the works of which are moved either entirely or partially by the electric current, are controlled or regulated by the electric current, or «,re wound thereby. 136 A DICTIONARY OF ELECTRICAL Electric clocks may therefore be divided into three classes, (1) Those in which the works are moved entirely or partially by the electric current. (2) Those which are controlled or regulated by the electric current. (3) Those which are merely wound by the current. A clock moving- independently of electric power, is given a slight retardation or acceleration electrically and is thus pre- vented from gaining or losing time. The entire motion of the balance wheel is sometimes imparted by electricity. An example of one of many forms of electric clock is shown in Fig. 105, where the split battery (See Battery, S})lit), P N, is connected, as shown, to the spring contacts S and S'. Fig. 105. By these means currents are sent into the circuit in alter- nately opposite directions. The pendulum bob, Fig. 106, of the controlled clock is formed of a hollow coil of insulated wire, which encircles one or both of two permanent magnets, WORDS, TERMS AND PHRASES. 137 A and A', placed with their opposite poles feicing each other. In this manner a slight motion forwards or backwards is im- parted to the pendulum which is thus kept in time with the controlling- clock. The controlling clock is shown in Fig. 105, and the controlled clock in Fig. 106. Mercury contacts are sometimes employed in place of the springs S and S'. Induction currents may also be employed. Clocks of non-electric action may be electrically controlled, or correctly set at certain intervals, either automatically by a central clock, or by the depression of a key operated by hand from an astronomical observatory. In a system of Time Telegraphy, the controlling clock is called the Master Clock, and the controlled clocks the Second- ary Clocks. Secondary clocks are generally mere dials, containing step- by-stcp movements, for moving the hour, minute and second hands. (See Telegraphy, Stcp-by-Step.) Fig. 107. In Spellier\s clock, a series of armatures H, Fig. 107, mounted on the circumference of a wheel, connected with the 138 A DICTIONARY OF ELECTRICAL escapement wheel, pass successively, with a step-by-step move- ment, over the poles of electro-magnets. On the completion of the circuit, they are attracted towards the magnet, and on the breaking of the circuit they are drawn away by the fall of the weight F, placed on the lever D, pivoted at E. A pulley at E, runs over the surface of a peculiarly shaped cog on the escapement wheel. Clock, Electric Annunciator A clock, the hands or works of which, at certain predetermined times, make electric contacts and thus ring bells, release drops, trace records, etc. Clock, Master The controlling clock used in a s3 T stem of time telegraphy. (See Clocks, Electric.) Clock-work Feed for Arc Lamps- Arrangements of clock-work for obtaining a uniform feed motion of one or both electrodes of an arc lamp. The clock-work is automatically thrown into or out of action by an electro-magnet, usually placed in a shunt circuit around the carbons. Clocks, Secondary The clocks in a system of time telegraphy that are controlled by the master clock. (See Clocks, Electric.) Clocks, Self- Winding Clocks that at regular intervals are automatically wound by the action of a small electro-magnetic motor contained in the clock. Closed Circuit,— (See Circuit, Closed, Completed or Made.) Closure. — The completion of an electric circuit. Coatings, Condenser The sheets of tin foil on opposite sides of a Leyden Jar or condenser, which receive the opposite charges. Coatings, Metallic Coverings or coatings of metals, deposited from solutions of metallic salts by the action of an electric current. (See Electro-Plating.) WORDS, TERMS AND PHRASES. 139 Code, Cipher A code in which a number of words or phrases are represented by single words. The message thus received requires the possession of the key to render it intelligible. Code, Telegraphic The pre-arranged signals of any system of telegraphy. (See Alphabet, Telegraphic ; Morse, Continental.) Coefficient, Algebraic A number prefixed to any quantity to indicate how many times that quantity is to be taken. The number 3, in the expression 3a, is a coefficient and in- dicates that the a, is to be taken three times, as a -f- a -\- a = 3a. Coefficient, Economic of a Dynamo Electric Machine. — The ratio between the electrical en- ergy or the electrical horse power developed by the current produced by a dynamo, and the mechanical horse power ex- pended in driving the dynamo. The Efficiency may be the Commercial Efficiency, which is the useful or available energy in the external circuit divided by the total mechanical energy ; or it may be the Electrical Efficiency, which is the available electrical energy divided by the total electrical energy. The, Efficiency of Conversion in the total electrical energy developed, divided by the total mechanical energy applied. If M, equals the mechanical energy, \V, the useful or available electrical energy, and w, the electrical energy absorbed by the machine, and m, the Stray Power, or the power lost in friction, eddy currents, air friction, etc. Then, since M = W-|-!P-(- m, W W Commercial Efficiency . . Electrical Efficiency Efficiency of Conversion M W+w + ib W W-fw _ W-fw M W-fw-fm 140 A DICTIONARY OF ELECTRICAL Coefficient, Economic (See Economic Coeffi- cient.) Coefficient of magnetization, or Coefficient of Magnetic Induction. — A number representing- the inten- sity of magnetization produced in a magnetizable body as compared with the intensity of magnetization of the induc- ing body. A magnetizable body, when placed in a magnetic field, con- centrates the lines of magnetic force on it, or causes them to run through it. The intensity of the magnetization so pro- duced depends, therefore, (1) On the intensity of the magnetizing field. (2) On the ability of the metal to concentrate the lines of force on it, that is, on the nature of the metal, or, on its mag- netic permeability. (See Magnetic Permeability.) The intensity of magnetization will therefore be equal to the product of the coefficient of magnetization, and the in- tensity of the magnetizing field. The coefficient of magnetization of paramagnetic bodies is said to be positive ; that of diamagnetic bodies to be negative because the former concentrate the lines of magnetic force on them, and the latter appear to repel them. (See Paramag- netic. Diamagnetic.) Coefficient of Mutual Induction.— A quantity rep- resenting the relative number of lines of magnetic force which each of two neighboring electric circuits induce in the other. Coefficients of Expansion. — The fractional increase in its dimensions of a bar or rod when heated from 32° to 33° F., or from 0° to 1° C. The fractional increase in its length is called the Coefficient of Linear Expansion. The fractional increase in its surface is called the Coefficient of Surface Expansion, WORDS, TERMS AND PHRASES. 141 The fractional increase in its volume is called the Coeffi- cient of Cubic Expansion. Coefficients of Linear Expansion. — Gold 0.000015153 Steel 0.000010972 Silver 0.000019086 Copper 0.000017173 Brass 0.000018782 Tin 0.000019376 Iron 0.000012350 Flint glass 0.000008116 Platinum 0.000009918 Lead 0.000088483 Zinc 0.000029416 {Laplace and Lavoisier). Coercive, or Coercitivc Force. — The power of resist- ing magnetization or demagnetization. Coercive Force is sometimes called Magnetic Retentivity. Hardened steel possesses great coercive force ; that is, it is magnetized or demagnetized with difficulty. Soft iron possesses very feeble coercive force. It is on account of the feeble coercive force of the soft iron core of an electro-magnet that its main value depends, since it is thereby enabled to rapidly acquire its magnetization, on the completion of a battery circuit through its coils, and to rapidly lose its magnetization, on the opening of the circuit. Coils, Armature (See Dynamo-Electric Ma- chines, Armature Coils.) Coils, Electric Convolutions of insulated wire through which an electric current may be passed. (See Elec- tro-Magnet. Coils, Henry's A number of separate induction coils so connected that the currents induced in the secondary wire of the first coil are caused to induce currents in the 142 A DICTIONARY OF ELECTRICAL secondary wire of the second coil, with whose primary it is connected in series. A series of three of Henry's coils is shown in Fig. 108. An intermittent battery current is sent into a, the secondary of which, b, is connected with the primary c, of the second coil. The secondary d, of the second coil, is connected with the primary e, of the third coil, and the currents finally in- duced in /, are employed for any useful purpose, such as the magnetization of a bar of iron at g. Fig. 108. Fig. 109. The current in b is sometimes called a Secondary Current; that induced by this secondary current in d is called a Ter- tiary Current, or a Current of the Third Order; that in/, a Current of the Fourth Order. Henry carried these successive inductions up to currents of the Seventh Order. Henry's coils in reality consist of separate induction coils, connected, as above explained, in series. In Fig. 109, the tertiary current induced in IV., may be employed to give shocks to a person grasping the handles, e and/. WORDS, TERMS AND PHRASES. 143 Coils, Induction (See Induction Coils.) Coils, Magnet (See Magnet Coils.) Coils, Resistance Coils of wire, the electrical resistance of which is known, employed for measuring- the re- sistance of any circuit. In order to avoid the mag- netizing effects of the coils on the needles of the galvanome- ters used in electric measure- ments, the wire of the re- sistance coil is doubled on itself before being wound, and its ends electrically con- nected with the brass bars, . E, E, Fig. 110. The insertion of the plug-key cuts the coil out of the circuit by short- Fig. 110. circuiting. (See Box, Resistance. Balance, W heat stone' s> Electric. Standard Resistance Coil.) The coils are made of German silver, or platinoid, whose resistance is not much affected by heat. Coil*, Shu ill Coils placed in a derived or shunt circuit. (See Circuit, Shunt.) Collectors of Dynamo Electric Machines.— The metallic brushes that rest on the commutator cylinder, and carry off the current generated on the rotation of the arma- ture. Collectors are familiarly called commutators. Collectors, Electric. — Devices employed to collect or take off electricity from a moving electric source. Collectors of Frictional Electric Machines.— The metallic points that collect the charge from the glass plate or cylinder of a frictional electric machine. Column, Electric A term formerly applied to a voltaic pile. (See Pile, Voltaic.) 144 A DICTIONARY OF ELECTRICAL Completed Circuit.— (See Circuit, Closed, Completed or Made.) Commercial Efficiency of Dynamo.— The useful or available electrical energy in the external circuit, divided by the total mechanical energy required to drive the dynamo that produced it. (See Coefficient, Economic, of Dynamo.) Commutator. — Generally, a device for changing the di- rection of an electric current. That part of a dynamo-electric machine that causes the cur- rents that alternate or change their direction twice in every revolution of the armature, between a pair of magnet poles, to flow in one and the same direction in the external circuit. One end of an armature coil is connected with A', Fig. Ill, and the other with A. The brushes are so set that A and A' are in contact with B' and B, respectively, as long as the current flows in the same direction, in the armature coil connected therewith, but enter into contact with. B and B', when the current changes its di- rection, and continue in such conjtact as as it flow T s in this direction. The current will therefore flow through any circuit connected with the brushes in one and the same constant direction. The number of metallic pieces A and A', in the commutator cylinder depends on the number, arrangement and con- nection of the armature coils, and on the disposition of the magnetic field of the machine. For details of various commutators of this description, see Dynamo-Electric Machines. The Reverscr used by Kuhmkorff in his induction coil, for cutting off, or for reversing the direction of the primary current is shown in Fig. 112, and was called by him the commutator. (See Ruhmkorff Coil.) Two metallic strips, V V, supported on a cylinder of insu- WORDS, TERMS AND PHRASES. 145 lating material are in contact with the battery terminals P and N through two vertical springs that bear on them. On a half rotation of the cylinder by the thumb screw L, the strips V, V, change places as regards the vertical springs, and thus reverse the direction of the battery current. Fig. 112. Compass, Azimuth, or Mariner's- -A compass used by mariners for measuring the horizontal distance of the sun or stars from the magnetic meridian. (See Azimuth, Magnetic.) A single magnetic needle, or several magnetic needles, are placed side by side on the lower surface of a card, called the compass card. This card is divided into the four cardinal points, N, S, E and W, and these again sub-divided in thirty- two points called Rhumbs. In the azimuth compass these divisions are supplemented by a further division into degrees. 146 A DICTIONARY OF ELECTRICAL A form of azimuth compass is shown in Fig. 113. In order to maintain the compass box in a horizontal position, despite the rolling of the ship, the box, A B, is suspended in the larger box, P Q, on two concentric metallic circles, C D, and E F, pivoted on two horizontal axes at right angles to each other ; or, as it is technically term- ed, in Gimbals. Sights, G H, are provided for meas- uring the magnetic azimuth of any ob- ject. Compass Card. — (See Compass, Az- imuth.) Compensating Magnet.— (See Magnet, Compensating.) Component, Horizontal and Ver- tical, of Earth's Magnetism.— That portion of the earth's directive force which acts in a horizontal direction. Let A B, Fig. 114,. represent the direction and magnitude of the earth's magnetic field on a magnetic needle. The magnetic force will lie in the plane of the magnetic meridian, which will be assumed to be the plane of the paper CAD. The earth's field, A B, can be resolved into two components, A D, the hori- zontal component, and A C, the vertical component. In the case of a magnetic needle, which, like the ordinary compass needle, is free to move in a horizontal plane only, the. Fig. Ilk. WORDS, TERMS AND PHRASES. 147 horizontal component alone directs the needle. When the needle is free to move in a vertical plane, and the plane cor responds with that of the magnetic meridian, this entire mag- netic force, A B, acts to place the needle, supposed to be properly balanced, in the direction of the lines of force of the earth's magnetic field at that point. In the vertical plane at right angles to the plane of the magnetic meridian, the ver- tical component alone acts, and the needle points vertical ly downwards. Components. — The two or more separate forces into which any single force may be resolved ; or, conversely, the separate forces which together produce any single resulting force. When two or more forces simultaneously act to produce motion in a bod}*, the bod}* will move with a given force in a single direction called the resultant. The separate forces, or directions of motion, are called the componods. Two forces acting simultaneously on a body at A, Fig. 115, tending to move it in the direction of the arrows, along A B and A C, with intensi- ties proportioned to the lengths of the lines A B and A C, respectively, will move it in the direc- tion A D, obtained by drawing B D and D C, parallel to A C and A B, respectively, and draw- ing A D through the point of intersection, D. This is called the Composition of Forces. A D is the resultant force and A B and A C are its components. Conversely, a single force, acting in the direction of D B, Fig. 116, against a surface, B C, may be regarded as the resultant of the two separate forces, D E and D C, one parallel to C B, and one perpendicular to it. D E, being parallel to Fig. in 148 A DICTIONARY OF ELECTRICAL C B, produces no pressure, and the absolute effect of the force B E will De represented by - CD. This is called the reso- lution of forces, the force, D B, being- resolved into the components D E and DC. That component of the Fig. 116. earth's magnetic force which acts in a horizontal,or in a vertical direction respectively. Compound, Binary Compound, Chatter- ton's. — A compound for cementing together the alternate coatings of gutta-percha employed on a cable conductor, or for filling up the spaces between the strand conductors. (See Binary Compound.) The composition is as follows : Stockholm tar 1 part by weight. Resin 1 " Gutta-percha 3 " (Clark & Sabine.) Compound, Clark's. — A compound for the outer casing of the sheath of submarine cables. Its composition is as follows : Mineral pitch 65 parts by weight. Silica 30 " Tar 5 (Clark & Sabine.) Compound Magnet.— (See Magnet, Compound.) Compound Winding of Dynamo-Electric Ma- chines. — A method of winding in which shunt and series coils are placed on the field magnets. (See Dynamo-Electric Machines.) WORDS, TERMS AND PHRASES. 149 Concentric Carbon Electrodes,— (See Carbons, Cored.) Condenser, or Accumulator.— A device for increasing- the capacity of an insulated conductor by bringing it near another insulated earth-connected conductor, but separated from it by a medium that will readily permit induction to take place through its mass. If the conductor A, Fig. 117, standing alone and separated from other conductors, be connected with an electric machine, it will receive only a very small charge. Fig. W. If, however, it be placed near C, but separated from it by a dielectric, such as a plate of glass B, and C be connected with the ground, A will receive a much greater charge. (See Die- lectric.) Suppose, for example, that A be connected with the posi- tive conductor of a frictional electric machine ; it will by induction produce a negative charge to the surface of C, nearest it, and repel a positive charge to the earth. The presence of these two opposite charges on the opposed surfaces of A and C produces a neutralization that permits A to receive a fresh charge from the machine. (See Induction, Electrostatic.) The charge in a condenser in reality resides on the opposite 150 A DICTIONARY OF ELECTRICAL b ; a A b a b S a \ surfaces of the glass, or other dielectric separating the metallic coatings, as can be shown by removing the coatings after charging. The condenser resulted from the discovery of the Leyden jar. (See Jar, Leyden.) The capacity of a condenser is meas- ured in microfarads (See Farad.) In practice condensers are made of sheets of tin foil, a, a, a, b, b, 6, connected at A and B, respectively, and separated from one another by sheets of oiled silk, or thin plates of mica. Conducting Power, Order of.— The ability of a given length and area of cross section of a substance to conduct electricity, as compared with an equal length and area of cross section of some other substance, such as pure silver or copper. No substance is known that does not offer some resistance to the passage of an electric current. The following table is taken from Sylvanus P. Thompson's " Elementary Lessons in Electricity and Magnetism :" Silver. _ 1 SEmet^ Charcoal. J Water. "1 The human body | Cotton Dry wood Marble Paper Oils.... Porcelain.. Wood Silk Eesins Gutta-percha Shellac Ebonite Paraffin... Glass Dry air V Partial conductors. M on- conductors. WORDS, TERMS AND PHRASES. 151 Conductive Discharge.— (See Discharge, Conductive.) Conductor, Anisotropic —(See Anisotropic Conductor.) Conductor, Am i-Induction (See Anti-Induc- tion Conductor. Conductor, Conjugate "In a system of linear conductors, any pair of conductors are said to be con- jugate to one another when a variation of the resistance or the E. M. F. in the one causes no variation in the current of the other." {Brough.) Conductors, Isotropic (See Isotropic Con- ductor.) Conductors. — Substances which will permit the passage of an electric current through them. This term is opposed to non-conductors, or those which will not permit the passage of an electric current through them. Conduit, Electric, Underground A space or place for the reception of electric wires or cables. (See Sub- way, Electric.) Conservation of Energy. — The indestructibility of en- ergy. The total cmantity of energy in the universe is unalterable. The total energy of the universe is not, however, available for the production of useful work for man. When energy disappears in one form it reappears in some other form. This is called the correlation or conservation of energy. The commonest form in which energy reappears is as heat, and in this case some of the heat is lost to the earth by radiation. This degradation, or dissipation of energy causes some of the energy of the earth to become non-available to man. Energy is therefore available and non-available. (See En- tropy.) 152 A DICTIONARY OF ELECTRICAL Consequent Magnet Poles.— The name given to the magnetic poles formed by two free N. poles or two free S. poles placed together. (See Anomalous Magnets.) Contact Electricity. — Electricity produced by the mere contact of dissimilar metals. The mere contact of two dissimilar metals results in the pro- duction of opposite electrical charges on their opposed sur- faces, or in a difference of electric potential between these surfaces. The mere contact of dissimilar metals cannot produce a constant electric current. An electric current possesses kinetic energy. To produce a constant electric cur- rent, therefore, energy must be expended. In the voltaic pile though the contact of dissimilar metals produces a difference of potential, yet the cause of the current is to be found in chemical action. (See Cell, Voltaic.) Contact-Series. — A series of metals arranged in such an order that each becomes positively electrified by contact with the one that follows it. The contact values of some metals, according to Ayrton and Perry, are as follows : Contact-Series. Difference of Potential in Volts. Zinc ) Lead f Lead _ / Tin J Tin I Iron j Iron ) ..210 069 Iron..... f 313 Copper f" --"- - 140 H°aE m -:::::::::::l- *» Platinum - ) 1 1 Q Carbon............ ' WORDS, TERMS AND PHRASES. 153 The difference of potential between zinc and carbon is equal to 1.089, and is obtained by adding the successive differences between them. This fact is known technically as V olio's Law, which may be formulated as follows : The difference of potential produced bytlie contact of any two metals is equal to the sum of the differences of potentials between the intervening metals in the contact series. Contact Theory of Voltaic Cell.— (See Cell, Vol- taic.) Contacts. — A variety of faults occasioned by the accidental contact of a circuit with any conducting body. Contacts of this character are of the following varieties, viz. : (1) Full, or Metallic, as when the circuit is accidentally placed in firm connection with another metallic circuit. (2) Partial, as by imperfect conductors being placed across wires, or bad earths, or defective insulation. (3) Intermittent, as by occasional contacts of swinging wires, etc. Contractures.— In electro-therapeutics, a prolonged mus- cular spasm, or tetanus, caused by the passage of an electric current. Controlling Clocks, Electric In a system of time telegraphy, the master clock, whose impulses move or regulate the secondary clocks. (See Clocks, Electric.) Controlled Clocks, Electrically In a system of time telegraphy, the secondary clocks, that are either driven or controlled by the master clock. (See Clocks, Electric.) Convection. Electric ; Convection Streams. —The air particles, or air streams, that are thrown off from the pointed ends of a charged, insulated conductor. Convection streams, like currents flowing through conduct- ors, act magnetically, and are acted on themselves by mag- 154 A DICTIONARY OF ELECTRICAL nets. The same thing 1 is true of the brush discharge of the voltaic arc, and of convective discharges in vacuum tubes. Convection, Electrolytic A term proposed by Hehnholtz to explain the apparent conduction of electricity by an electrolyte, without consequent decomposition. Hehnholtz assumes that molecules of oxygen or hydrogen, adhering to the electrodes during electrolysis, are mechan- ically dislodged and diffused through the liquid, thus car- rying off the electricity by the charges received by them while in contact with the electrodes. Convection of Heat, Electric A distribution of heat during the passage of a current through an unequally heated conductor. If the central portions of a metallic bar are heated, the curve of heat distribution is symmetrical. On sending an electric current through the wire it is heated according to Joule's law, and the curve of heat distribution is still symmetrical. But the current in passing from the colder to the hotter parts of the wire produces an additional heating effect at this point, and in passing from the warmer to the colder parts of the wire, produces a cooling effect. (See Effect, Peltier. Effect, Thomson.) The curve of heat distribution is then no longer symmetrical. The term the Electrical Convection of Heat has been given to the dissymmetrical distribution of heat so effected. Sir Wm. Thomson, who studied these effects, found that the electrical convection of heat in copper takes place in the opposite direction to that in iron ; that is to say, the electrical convection of heat is negative in iron, (i. e. , the direction is opposite to that of the current) and positive in copper. Convective Discharge. — (See Discharge, Convective.) Converter, or Transformer. — The inverted induction coil employed in systems of distribution by means of alternat- ing currents. WORDS, TERMS AXD PHRASES. 155 A converter, or transformer, consists essentially of an induc- tion coil in which the primary wire, P P, Fig. 119, is long- and thin, and consequently of high electric resistance as compared with the secondary wire, S S, which is short, thick, and of low resistance. a ! ! A ! P i 1 — £) Fig. 110. To prevent heating and loss of energy in conversion, the core is thoroughly laminated. To lower the magnetic resistance, the converter is iron-clad. In a system of electrical distribution by means of trans- formers, alternating currents, of small volume and compara- tively considerable difference of potential, are sent over a line from a distant station, and passing into the primary wire of a number of converters, generally connected to the line in mul- tiple-arc produce, by induction, currents of comparatively large volume and small difference of potential in the secondary wires. Various electro-receptive devices are connected in multiple-arc with the secondary wires. 156 A DICTIONARY OF ELECTRICAL This method of distribution greatly reduces the cost of the main conducting wires or leads in certain cases, since consider- able energy may be conveniently sent over a comparatively thin wire, if the difference of potential is sufficiently great. The general arrangement of the converters on the main Fig. 120. line, and the connection of the secondary circuits with the electro-receptive device in such a system, is shown in Fig. 120. The converters are supported on the line poles, as more clearly shown in Fig. 121, in which the termi- nals of the primary and secondary of the converter are readily seen. When the converter is properly constructed the loss of conversion is but small at full load ; that is to say, the watts in the secondary are very nearly equal to those in the primary. A current of 10 amperes, at 2000 volts, when passed into a converter, the number of whose turns in the primary is twenty times the number in its secondary, will produce in its sec- ondary, a current of 200 amperes at about 100 volts. Here, the number of watts in the two cases is exactly the same, or theoretically 20,000 watts. In reality, it is somewhat WORDS, TERMS AND RhRASES. 157 smaller. In gen- eral, the shorter the wire on the sec- ondary, and the smaller its number of turns, the great- er is the reduction in the difference of potential, and the greater is the cur- rent produced. Co-Ordinales, Axes of — The axes of ab- scissas and o r d i- nates. The two straight lines, perpendicu- lar to each other, to which distances representing v a 1- Fi $' 121 - ues are referred for the graphic representation of such values. (See Abscissas, Axis of.) Copper Bath.— (See Baths, Copper, etc.) Cords, Eleetric Flexible, insulated electric con- ductors, generally containing at least two parallel wires. They are named from the purposes for which they are em- ployed, battery cords, dental cords, lamp cords, motor cords, switch cords, etc. Core of Cable. — The conducting wires of an electric cable. (See Cable, Electric.) Core Ratio of Cable.— The ratio between the diameter of the insulator of a cable and the mean diameter of the strand. 158 A DICTIONARY OF ELECTRICAL The core ratio is represented by -r ; where D, is the diam- eter of the insulator, and d, the mean diameter of the strand. Should the extreme diameter of the strand of a cable be used in calculations for insulation resistance, inductive capacity, etc., erroneous values would be obtained. The measured diameter of the copper conductor is consequently decreased some five per cent, by means of which the correct values are approximately given. (Clark & Sabine.) Cored Carbons.— (See Carbons, Cored.) Cores, Armature (See Armature Cores.) Cores, Armature, Ventilation of Means for the passage of fluids, such as air through the armature cores of dynamo-electric machines so as to prevent the undue ac- cumulation of heat. A properly proportioned dynamo-armature should need no ventilation, since in such the amount of heat generated is small as compared with the extent of the radiating surface. Cores, Lamination of Structural subdivisions of the cores of magnets, armatures, and pole pieces of dynamo- electric machines, electric motors, or similar apparatus, in order to prevent heating and subsequent loss of energy from the production of loecd, eddy or FoueauH currents. These laminations are obtained by forming the cores of sheets, rods, plates, or wires of iron insulated from one another. The cores of armatures should be divided in planes at right angles to the armature coils ; or in planes parallel to the di- rection of the lines of force and to the motion of the arma- ture ; or in general, in planes perpendicular to the currents that would otherwise be generated in them. Pole pieces should be divided in planes perpendicular to the direction of the currents in the armature wires. WORDS, TERMS AND PHRASES. 159 Magnet cores should be divided in planes at right angles to the magnetizing current. Cosine. — One of the trigonometrical functions. (See Trigonometry.) Cotangent. — One of the trigonometrical functions. (See Trigonometry.) Coulomb. — The unit of electrical quantity. A definite quantity or amount of the thing or effect called electricity. Such a quantity of electricity as would pass in one second in a circuit whose resistance is one ohm, under an electro-mo- tive force of one volt. The quantity of electricity contained in a condenser of one farad capacity, when subjected to an electro-motive force of one volt. Coulomb- Volt. — A Joule, or .7373 foot pound. The term is generally written volt-coulomb. (See Volt- Coulomb.) Couiiter-Electro-UIotivc Force.— An opposed or re- verse electro-motive force produced in an electric source, which tends to produce a current in the opposite direction to that regularty produced by the source. In an electric motor, an electro-motive force contrary to that produced by the current which drives the motor, and which is proportional to the velocity attained by the motor. Counter-electro-motive force acts to diminish the current in the same manner as a resistance would, and is therefore sometimes called the spurious resistance in order to distin- guish it form the ohmic or true resistance. Counter-elect ro-mot ire force is sometimes expressed in ohms, though it is not true ohmic resistance. (See Spurious Resistance.) The counter-electro-motive force of a voltaic battery is due to the polarization of the cells. Since this force is due to the 160 A DICTIONARY OF ELECTRICAL current in the cell, it can never exceed such current or reverse its direction. It may, however, equal it and thus stop its flow. (See Polarization of Voltaic Cell.) In a storage cell, the charging current produces an electro- motive force counter to itself, which, as in a motor, is a true measure of the energy stored in the cell. Economy requires that the electro-motive force of the charging current should be as little greater as possible than that of the counter-electro- motive force of the cell it is charging. In a voltaic arc a counter-elect'-'O-motive force is set up by polarization. Counters, Electric Various devices for count- ing and registering such quantities as the number of fares collected, gallons of water pumped, sheets of paper printed, revolutions of an engine per second, votes polled, etc. Various electric devices are employed for this purpose. They are, generally, electro-magnetic in character. Couple. — In mechanics, two equal parallel forces acting in opposite direc- tions and tending to cause rotation. The moment, or effective power of a s couple, is equal to the intensity of one of Fig. n%. the forces multiplied by the perpendicular distance between the directions of the two forces. Couple, magnetic The couple which tends to tarn a magnetic needle, placed in the earth's field, into the plane of the magnetic meridian. If a magnetic needle is in any other position than in the magnetic meridian, there will be two parallel and equal forces acting at A and B, Fig. 122, in the directions shown by the arrows. Their effect will be to rotate the needle until it comes to rest in the magnetic meridian N S. The total force acting on either pole of a needle free to move in any direction is equal to the strength of that pole WORDS, TERMS AND PHRASES. 161 multiplied by the total intensity of the earth's field at that place, or, if free to move in a horizontal direction only, is equal to the intensity of the earth's horizontal component of magnetism at the place at which the needle is situated, multi- plied by the strength of that pole. The effective power or moment of the magnetic couple is equal to the force exerted on one of the poles multiplied by the perpendicular distance, P Q, between their directions. Couple, Tlienno-E lee trie Any two dissimi- lar metals which, when connected at their ends only, will produce an electric current when one set of ends is heated more than the other. Couple, Voltaic The two plates of dissimilar metals, or other substances in a voltaic battery which are immersed in the liquid of the cell, as for example, the zinc and copper plates of the simple voltaic cell. All voltaic cells have two metals, or a metal and a metal- loid, or two gaseous or liquid substances which are of such a character that, when dipped into the battery solution, one only is chemically acted on. Each of these substances is called an element of the cell, and the two taken collectively form a voltaic couple. The elements of a voltaic couple may consist of two gases or two liquids. (See Gas Battery. ) Coupling of Yoltaie Cells or Other Electric Sources. — A term indicating the manner in which a num- ber of separate electric sources are connected so as to form a single source. (See Circuits, Varieties of.) C. P. — A contraction frequently used for candle power. (See Candle, Standard.) Crater in Positive Carbon,— The depression at the end of the positive carbon which appeal's when a voltaic arc is formed. (See Arc, Voltaic.) 162 A DICTIONARY OF ELECTRICAL Creo§oting. — A process employed for the preservation of wooden telegraph poles by injecting creosote into the pores of the wood. (See Pole, Telegraphic.) Creeping. — The formation of salts by efflorescence on the sides of the porous cup of a voltaic cell, on the walls of the vessel containing the electrolyte, or on the walls of any vessel containing a saline solution. Paraffining the portions of the walls out of the liquid, or covering the surface of the liquid with a neutral oil, obviates much of this difficulty. (See Efflorescence.) Critll. — A term proposed by A. W. Hoffman, as a unit of volume, or the volume of one litre, or cubic decimetre, of hydrogen at 0° C. and 760 mm. barometric pressure. Critical Current. — The current at which a certain result is reached. Critical Current of a Dynamo.— That value of the current at which the characteristic curve begins to depart from a nearly straight line. (Sylvanus P. Thompson.) As a rule the critical current of a dynamo occurs when the speed is such that the electro- motive force is nearly two-thirds the maximum value. In Fig. 123 the critical current is shown in three different cases, as occuring where the dotted vertical line cuts the characteristic curves. The speed at which a series dynamo excites itself is often called the critical speed. A connection, generally metallic, accidentally established between two conducting lines. A defect in a telegraph or telephone circuit caused by two wires coming into contact by crossing one another. A swinging or intermittent cross is caused by wires which are too slack, being occasionally blown into contact by the wind, WORDS, TERMS AND PHRASES. 163 A weather cross arises from defective action of the insulators in wet weather. Crossing Wire§. — A device employed in telegraphic circuits whereby a faulty conductor of a telegraph line is cut out of the circuit by crossing over to a neighboring, less used, line. To cut out a faultv A B C D E section of wire in any circuit, such as C D, in the circuit ABC D E, Fig. 124, a cross Fig. 12k. connection is made to a line X Y, running near it, and which may be temporarily thrown out of use. By this means the interruption of an important circuit may be avoided. Crucible, Electric — — A crucible in which the heat of the voltaic arc, or of electric incandescence, is employed either to perform difficult fusions, or for the purpose of effecting the reduction of metals from their ores, or the forma- tion of alloys. (See Furnace, Electric.) Crystal. — A solid body bounded by symmetrically disposed plane surfaces. A definite form or shape is as characteristic of an organic substance, as it is of the animal or plant. Each substance has a form in which it generally occurs. There are, however, certain modifications of the typical form which cause plane surfaces to appear curved, and the symmetrical arrangement of the faces to disappear. These modifications often render it extremely difficult to recognize the true typical form. For the different fundamental crystalline forms, or systems of crystals, see any standard work on chemistry. Crystallization. — Solidification from a state of solution or fusion, with the assumption of definite crystalline forms. The crystallization of a dissolved solid is favored by any cause that gives increased freedom of movement to the par- 164 A DICTIONARY OF ELECTRICAL tides of the solid, such for example as, solution, fusion, sublimation, or precipitation. Crystallization by Electrical Decomposition.— The crystalline deposition of various metals by the passage of an electric current through solutions of their salts under certain conditions. A strip of zinc immersed in a solution of sugar of lead, (acetate of lead) soon becomes covered with bright metallic plates of lead, that are electrically deposited by the weak currents due to minute voltaic couples (See Couple, Voltaic), formed with the zinc by particles of iron, carbon, or other impurities in the zinc. The deposit assumes at times a tree- like growth, and is therefore called a lead tree. Cube, Faraday's (See Net, Faraday's.) Current, Alternating or Reversed A cur- rent which flows alternately in opposite directions. A current whose direction is rapidly reversed. The non-commuted current generated by the differences of B potential in the armature of a /fljiiK dynamo-electric machine is an / | ! j j | | \ alternating current. /I | j ;\ In a characteristic curve of the A C \ j J j j IE electro-motive forces of alternat- \1 | j j { ! j / m g currents, positive electro- \J! j | \y motive forces, or those that would q produce currents in a certain Fig. 125. direction, are indicated by values above a horizontal line, and negative electro-motive forces, by values below the line. The curves ABC and C D E, Fig. 125, are often called phases, and represent the alternate phases of the current. Current, Alternative or Voltaic Alterna- tives. — A term sometimes used in electro-therapeutics for a sudden alternating current. (See Alternatives, Voltaic.) WORDS, TERMS AND PHRASES. 165 Current, Commuted The current of any elec- tric source which produces alternating currents, that have been caused to flow in one and the same direction by the aid of a commutator*. (See Commutator.) Current, Continuous An electric current which flows in one and the same direction. This term is used in the opposite sense to alternating cur- rent. Current, Critieal (See Critical Current.) Current Density The quantity of current which passes in any part of a circuit as compared with the area of cross section of that part of the circuit. In a dynamo-electric machine the current density in the ar- mature wire should not, according to Sylvanus P. Thompson, exceed 2,500 amperes per square inch of area of transverse section of conductor. In electro-plating, for every definite current strength that passes through the bath, a definite weight of metal is depos- ited, the character of which depends on the current density. The character of an electrolytic deposit will therefore depend on the current density at that part of the circuit where the deposit occurs. Current, Diaeritieal (See Diacritical Cur- rent.) Current, Direct A current constant in direction, as distinguished from an alternating current. Current, Electrie The quantity of electricity which passes per second through any conductor or circuit, or the rate at which a definite quantity of electricity passes or flows through a conductor or circuit. An electric current represents the ratio existing between tho. electro-motive force, causing the current, and the re- sistance which may be regarded as opposing it. This ratio is then expressed in terms of quantity of electricity per second. 166 A DICTIONARY OF ELECTRICAL The unit of current or the ampere is equal to one coulomb per second. (See Ampere. Coulomb.) The word current must not be confounded with the mere act of flowing-; electric current signifies rate of flow, and always supposes an electro-motive force to produce the cur- rent and a resistance to oppose it. The electric current is assumed to flow out from the positive terminal or of a source, through the circuit and back into the source at the negative terminal, and is assumed to flow into the positive terminal of an electro-receptive device such as a lamp, motor, or storage battery, and out of its nega- tive terminal; or, in other words, the positive pole of the source is always connected to the positive terminal of the electro-re- ceptive device. Current, Element of A term employed in mathematical discussions, to indicate a very small part of a current in considering its action on a magnetic needle or other similar body. Current, Faradic (See Faradic Current.) Current Induction.— (See Voltaic Induction. Electro- Dynamics.) Current, Intensity of. — (See Intensity of Current.) Current meter. — (See Galvanometer.) Current, Reversed A current whose direction is changed at intervals. (See Current, Alternating.) Current Re vers er. — A switch, or other apparatus, to re- verse the direction of a current. Currents, Amperian -(See Amperian Currents. Magnetism, Ampere's Theory of.) Currents, Diaphragm — (See Diaphragm Cur- rents.) Currents, Earth ■ -(See Earth Currents.) WORDS, TERMS AND PHRASES. 167 Currents, Eddy, Local, Foucault, or Parasit- ical Useless currents produced in the metallic masses of the pole pieces, armatures, or field magnet cores of dynamo-electric machines or motors, either by the motion of these parts through magnetic fields, or by the variations in the strength of electric currents flowing near them. Eddy currents may even be produced in the mass of the conducting wire on the armature, when this is compara- tively heavy. These currents are called eddy currents, local currents, Foucault currents, or parasitical currents. They form closed circuits of comparatively low resistance, and tend to cause undue heating of armatures or pole pieces. They not only cause a useless expenditure of energy, but interfere with the proper operation of the device. To reduce them as much as practicable, the pole pieces and armature cores are laminated. (See Cores, Lamination of.) Since eddy currents in dy- n a m o - electric machines are due to v a na- tions in the mag- net i c strength of the field mag- Fig. 126. nets, or of the armature, they will be of greatest intensity when the changes in the magnetic biiength are the greatest and most sudden. These changes are most marked, and consequently the eddy currents are particularly strong, at those corners of the pole pieces of a dynamo from which the armature is moved in its rotation, as will be seen from an inspection of Fig. 126. Fig. 127, shows eddy currents generated in pole pieces. 168 A DICTIONARY OF ELECTRICAL Currents, Extra.— In a coil of wire through which a cur- rent is passing, the current produced by the inductive action of the current on itself at the moment of breaking or mak- ing the circuit. The extra cur- rent induced on breaking flows in the same direct- ion as the original current and acts to strengthen and prolong it. The extra cur- rent induced on making or completing a circuit, is in the opposite direction, tending to oppose or retard the current. Both of these currents are called induced or extra currents. The former is called the direct-induced-current, and the latter the reversed-induced-current. In order to distinguish this induction from that produced in a neighboring conductor by the passage of the electric cur- rent, it is called self-induction. The effect of the self -induced or extra currents on tele- graphic line is to influence the speed of signaling by retard- ing the beginning of a signal, and prolonging its termina- tion. Fig. 127. magnet, and the greater the mass of iron in its core, the greater the strength of the extra current. Currents, X at lira 1 A term sometimes applied to earth currents. (See Earth Currents.) Currents, Negative and Positive A term em- ployed in telegraphy for currents sent over a line in a positive or a negative direction, respectively. (See Telegraph, Single- Needle.) WORDS, TERMS AND PHRASES. 169 Currents, Orders of Induced electric currents named from the order in which they are induced, as currents of the first, second, third, fourth, etc., orders. An induced current can be caused to induce another current in a neighboring- circuit, and this a third current, and so on. Such currents are distinguished by the term, currents of the second, third, fourth, etc., order. (See Coils, Henry's.) Currents, Rectilinear — Currents flowing through straight or rectilinear portions of a circuit. In studying the effects of attraction or repulsion produced by electric currents, the peculiarity of shape of any part of the circuit is often applied to the current flowing through that circuit. Currents, Sinuous A term sometimes applied to currents flowing through a sinuous conductor. Sinuous currents exert the same effects of attraction or repulsion on magnets, or on other circuits, as would a rec- tilinear current whose length is that of the axis of such current. This can be shown by approaching the circuit A'B', Fig. 128, consisting of the sinuous conductor A', and rectilinear conductor B', to the movable conductor ABC on which it produces no effect. The current A', therefore, neutralizes the effects of the current B'; or, it is equal to it in effect. In calculating the effects of sinuous currents, it is convenient to consider them as consisting of a succession of short, straight portions at right angles to one another, as shown in Fig. 129. Currents, ITndulatory Currents the strength and direction of flow of which gradually change. The currents produced by all alternate current dynamos are not of the character generally known as pidsatory, in which the strength and direction change suddenly. In actual practice, such currents differ from undulatory currents more in degree than in kind, since, when sent into a line, the effects 170 A DICTIONARY OE ELECTRICAL of retardation tend to obliterate, to a greater or less extent, the marked differences in intensity on which their undulatory character depends. The currents produced in the coils of the Sie- mens' magneto - electric key, in which the me- chanical to-and-fro mo- tion of the key sends electrical impulses into the line, are, in point of fact, undulatory in character when they fol- low one another rapidly. The currents in most dynamo- electric ma- chines, the number of whose armature coils is comparatively great, are, so far as the variations in their intensity or strength are con- cerned, undulatory in character even when non-commuted. The currents on all telephone lines that transmit articulate speech are undulatory. This is true, whether the transmitter employed merely varies the resistance by variations of pres- sure, or actually employs makes-and-breaks that rapidly fol- low one another. b ^> Jl Fig Curve, Ballistic (See Ballistic Curve.) Curves, Characteristic (See Characteristic Curves.) WORDS, TERMS AND PHRASES. 171 Cut-Out, Automatic for Multiple Connected Electric Lamps. — A device for automatically cutting a lamp out of the circuit of the leads. Automatic cut-outs for incandescent lamps when connected to the leads in multiple-arc, consist of strips of readily melted metal called safety fuses, which on the passage of an abnormal current fuse and thus automatically break the cir- cuit in that particular branch. (See Safety Catch.) Cut-Out, Automatic for Series Connected Lamps. — A device whereby an electric arc lamp is, to all in- tents and purposes, automatically cut out, or removed from the circuit, by means of a shunt of low resistance, which permits the greater part of the current to flow past the lamp. It will be observed that the lamp is still in the circuit, but is to all practical intents cut out from the same, since the pro- portion of the current that now passes through it is too small to operate it. In most series arc lamps the automatic cut-out is operated by means of an electro-magnet placed in a shunt circuit of high resistance around the carbons. If the carbons fail to properly feed, the arc increases in length and consequently in resistance. More current passes through the shunt magnet, until finally, when a certain pre- determined limit is reached, the armature of the electro-mag- net is attracted to the magnet pole and mechanically com- pletes the short circuit past the lamp. In some automatic cut-outs the fusion of a readily fused wire, placed in a shunt circuit around the carbons, permits a spring to complete the short circuit. The automatic cut-out prevents the accidental extinguishing of any single lamp in a series circuit from extinguishing the entire circuit. Cylindrical Carbon Electrodes. — (See Carbons, Cored.) 172 A DICTIONARY OF ELECTRICAL Cymogene. — An extremely volatile liquid which is given off from crude coal-oil during the early parts of its distillation. The two liquids which are obtained from the condensation of the vapors given off during the first parts of the distillation of crude coal oil are called cymogene, and rhigolene. These liquids are employed on account of their extreme volatility for the artificial production of cold. Rhigolene is employed by some for the treatment or flash- ing of the carbons used in incandescent lamps. (See Flashing, Method of.) Damping. — The act of bringing a swinging magnetic needle quickly to rest, so as to determine its amount of deflec- tion, without waiting until it comes to rest after repeated swingings to and fro. Damping devices are such as offer resistance to quick motion, or high velocities. Those generally employed in electrical ap- paratus are either air or fluid friction, obtained by placing vanes on the axis of rotation, or by checking the movements of the needle by means of the currents it sets up, during its motion, in the mass of any conducting metal placed near it. These currents, as Lenz has shown, always tend to produce motion in a direction opposed to that of the motion causing them. Bell-shaped magnets are especially suitable for this kind of damping. (See Magnet, Bell-Shaped.) The needle of a galvanometer is dead-beat, when its moment of inertia is so small that its oscillations in an intense field are very quick, and die out very rapidly, and the needle there- fore moves sharply over the scale from ftoint to point and comes quickly to a dead stop. Darnell's Voltaic Cell— (See Cell, Voltaic.) Dash-Pot. — A mechanical device to prevent too sudden motion in a movable part of any apparatus. The dash-pot of an automatic regulator, or of an arc-lamp, is provided to avoid too sudden movements of the collecting brushes on the commutator cylinder, or the too sudden fall of WORDS, TERMS AXD PHRASES. 173 the upper carbon. Such devices consist essentially of a loose fitting* piston that moves through air or glycerine. Dash-pots are species of damping devices, and, like the damp- ing arrangements on galvanometers or magnetic needles, prevent a too free movement of the parts with which they are connected. (See Damping.) Dead - Beat Galvanometer. — (See Galvanometer, Dead Beat.) Dead Earth.— (See Earths.) Dead Turn§ of Armature Wire, or Dead Wire. — That part of the wire on the armature of a dynamo-electric machine which produces no useful electro-motive force, or resultant current, on movement of the armature through the magnetic field of the machine. The wire on the inside of a Gramme or ring armature, is dead-wire. Dead-Wire§. — Disused and abandoned electric wires. The term dead is often applied to a wire through which no current is passing. The term, however, is more properly applied to a wire formerly employed, but subsequently aban- doned. Dead wires in the neighborhood of active wires are a con- stant menace to life and property, and should invariably be carefully removed. It is often a matter of considerable importance to be able to determine whether or not a current is passing through a wire. When the wire is not inclosed in a moulding, or fastened against a wall, this can readily be ascertained by bringing a small compass needle near the wire, when it will tend to set itself across the wire. The term dead wire, as will be seen, is used in two distinct senses. Death, Electrical Death resulting from the the passage of the electric current through the human body. 174 A DICTIONARY OF ELECTRICAL The exact manner in which an electric current causes death is not known. When the current is sufficiently powerful, as in a lightning flash, or a powerful dynamo current, insensi- bility is practically instantaneous. Death may be occasioned — (1) As the direct result of physiological shock. (2) From the action of the current on the respiratory centres. (3) From the actual inability of the nerves or muscles, or both, to perform their functions. (4) From an actual electrolytic decomposition of the blood or other tissues of the body. (5) From the polarization of those parts of the body through which the current passes. (6) From an actual rupture of parts by a disruptive discharge. The current required to cause death will depend on a variety of circumstances, among which are : (1) The particular path the current takes through the body, with reference to the vital organs that may lie in this path. (2) The freedom or absence of sudden variations of electro- motive force. (3) The time the current continues to pass through the body. In most fatal cases, it is probably the extra-current, or the induced direct current on breaking, that causes death, since, as is well known, its electro-motive force may be many times greater than that of the original current. A comparatively low potential continuous current, cannot, therefore, be properly regarded as entirely harmless, simply because its electro-motive force is comparatively small. Deci (as a prefix). — The one-tenth. Deci-L«ux.— The one-tenth of a lux. (See Lux.) Declination, or Variation of Magnetic Xeedle. — The deviation of the magnetic needle from the true geograph- ical north. This is often called the variation of the magnetic needle. WORDS, TERMS AND PHRASES. 175 The declination of the magnetic needle is either E. or W. (See Angle of Declination.) The declination, or variation, is different for different parts of the earth's surface. Lines connecting' places which have the same value and direction for the declination are called isogonal lines. A chart on which the isogonal lines are marked is called a variation chart. (See Variation Chart.) The value of the declination varies at different times. These variations of the declination are : (1) Secular, or those occurring during [great intervals of time. Thus in 1580, the magnetic needle in London, had a variation of about 11° East. This eastern declination de- creased in 1622, to 6° E., and in 1680, the needle pointed to the true north. In 1692, the declination was 6° W.; in 1730, 13° W.; in 1765, 20° W.; and in 1818, the needle reached its great- est western declination and is now moving eastwards. The declination, however, is still west. (2) Annual, the needle varying slightly in its declination during different seasons of the year. (3) Diurnal, the needle varying slightly in its declination during different hours of the day. (4) Irregular, or those which occur during the prevalence of a magnetic storm. It has been discovered that the occurrence of a magnetic storm is simultaneous with the occurrence of an unusual num- ber of sun spots. (See Sun Spots.) Declinometer. — A magnetic needle suitably arranged for the measurement of the value of the magnetic declination or variation, of any place. Decomposition. — In chemistry, the separation of a mole- cule into its constituent atoms or groups of atoms. (See Mole- cule. Atom.) Decomposition, Electric or Electrolytic — The separation of a molecule into its constituent atoms 176 A DICTIONARY OF ELECTRICAL or groups of atoms by the action of the electric current. These atoms or groups of atoms are either electro-positive or electro-negative in character. (See Electrolysis. Anion. Kathion.) Deflagration of Metals, Electrical The heating of metallic substances by the electric current to a temperature at which they rapidly fuse and volatilize. Deflagral or, Hare's The name given to a voltaic battery, of small internal resistance, employed by Hare in the deflagration of metals by the electric current. Deflection of magnetic Needle— The movement of a needle out of a position of rest in the earth's magnetic field, or in the field of another magnet, by the action of an electric current, or another magnet. Deflection Method. — A method employed in electrical measurements, as distinguished from the zero method, in which a deflection produced on any instrument by a given current, or by a given charge, is utilized for determining the value of that current or charge. The conditions remaining the same, the same current or charge will produce the same deflection at any time. Differ- ent deflections produced by currents or charges, the values of which are unknown, are determined by certain ratios existing between the deflections and the currents or charges. These ratios are determined experimentally by the calibration of the instrument. (See Calibration.) Deflection methods are opposed to zero or null methods, in which latter a balance of opposite electro-motive forces, or a proportionally equal fall of electric potential, is ascertained by the failure of a needle to be moved by a current or a charge. Degradation of Energy. — Such a dissipation of energy as to render it non-available to man. (See Conservation of Energy. Entropy.) Deka (as a prefix). — Ten times. WORDS, TERMS AND PHRASES. 177 Demagnetization. — A process generally directly oppo- site to that for producing a magnet, by means of which the magnet may be deprived of its magnetism. A magnet may be deprived of its magnetism, or be demag- netized — (1) By heating it to redness. (2) By touching to its poles magnet poles of the same name as its own. (3) By reversing the directions of the motions by which its magetism was originally imparted, if magnetized by touch. (4) By exposing it in a helix to the influence of currents which will impart magnetism opposite to that which it origi- nally possessed. Demagnetization of Watche§. — (See. Watches, De- magnetization of.) Density of Charge.— (See Charge, Density of '.) Density of Current. — (See Current, Density of.) Density, Hagnetie (See Magnetic Density.) Dental Mallet, Electro-Hagnetie A mal- let for filling teeth, the blows of which are struck by means of electrically driven mechanism. Electro-magnetism was first employed for this purpose by Bonwill of Philadelphia. Depolarization. — The act of breaking up or removing the polarization of a voltaic cell or battery. (See Polarization of Voltaic Cell.) Deposit, Eleetro-Metallurgieal The deposit of metal obtained by electro-metallurgical processes. To obtain a good metallic deposit the density of the current must be regulated according to the strength of the metallic solution employed. Electro-metallurgical deposits are ejther— - 178 A DICTIONARY OF ELECTRICAL (1) Reguline, or flexible, adherent, and strongly coherent metallic films, deposited when neither the current nor the solution is too strong. (2) Crystalline, or non-adherent and non-coherent deposits. The crystalline deposit may either be of a loose, sandy char- acter, which is thrown down when too feeble a current is used with too strong a metallic solution, or it may consist of a black deposit, which is thrown down when the current is too strong as compared with the strength of the solution. This latter char- q acter of deposit is sometimes technically called burning, and takes place most fre- quently at sharp corners and edges, where the current density is greatest. (See Density of Current.) Derived Circuit.— A term applied to a shunt circuit. If the conductor S, Fig. 130, be connected with the circuit of the battery B, a derived F,g. 130. circuit will thus be established, and a current will flow through S, thus diminishing the current in the gal- vanometer. (See Shunt Circuit.) Derived Units.— (See Units, Derived.) Destructive Distillation.— (See Distillation, Destruc- tive.) Device, Safety for multiple Circuits.— (See Safety Catch.) Device, Safety for Series Circuits.— (See Device, Safety, for Arc Lamps.) Device, Electro-Receptive Various devices placed in an electric circuit, and energized by the passage through them of the electric current. The following are among the more important electro-recep- tive devices, viz. : (1) Electro-Magnet. (2) Electric Motor, WORDS, TERMS AND PHRASES. 179 (3) An Arc or Incandescent Lamp. (4) An Uncharged Storage Cell. (5) An Electric Heater. (6) A Plating Bath, or Voltameter. (7) A Telegraphic or Telephonic Instrument. (8) Electro-Magnetic Signal Apparatus. Dextrorsal Helix. — (See Helix, Dextrorsal.) Diacritical Current. — Such a strength of the magnetiz- ing current as produces a magnetization of an iron core equal to half saturation. Fig. 131. Diacritical Number. — Such a number of ampere-turns at which a given core would receive a magnetization equal to half saturation. Diacritical Point of Magnetic Saturation.— A term proposed by S. P. Thompson for such a value of the coefficient of magnetic saturation, that the core is magnetized to exactly one-half its possible maximum of magnetization, 180 A DICTIONARY OF ELECTRICAL Diagnosis, Electro The determination of the healthy or diseased condition of different parts of the human body by the character and extent of the muscular contrac- tions on electrical excitation of the nerves or muscles. Diagometer, Rousseau's An apparatus in which an attempt is made to determine the chemical com- position and consequent purity of certain substances by their electrical conducting powers. The arrangement of the apparatus is shown in Fig. 131. A dry pile A, has its negative, or — , terminal m', grounded. Its positive, or -f-, terminal is connected to a delicately supported, and slightly magnetized needle M, terminated by a conducting plate L. Opposite L, and at the same height, is a fixed plate of slightly larger size. The needle M, when at rest in the plane of the magnetic meridian, is in contact at L with the fixed plate. If, therefore, the upper plate of the pile is con- nected with the needle M both plates are similarly charged and repulsion takes place, the needle coming to rest at a certain distance from the fixed plate. The substance whose purity is to be determined is placed in the cup G, which is connected through L with the fixed plate. A branch wire from the -\- terminal of the pile is then dipped into the substance in G, and -ts purity determined from the length of time required for the two plates at L to be dis- charged through the material in G, It is claimed that the instrument will detect the difference between pure coffee and chicory. Its practical application, however, is very doubtful. Diagram. Thermo-EIectric A diagram in which the thermo-electric power between different metals is designated for different temperatures. The differences of potential, produced by the mere contact of two metals, varies, not only with the kind of metals, and the physical state of each metal, but also with their temperature. This difference of potential, maintained in consequence of WORDS, TERMS AND PHRASES. 18i Q°c 50°c 100°c 150°c 200°c 250°c 300°c 350°c 400°c 450°c 500 O Lead A' 130 500 ionn B _Cof per V°£ B' A 1734 ' the difference of temperature between the junctions of a thermo-electric couple, is approximately proportional to the differences of temperature of these junctions, if these dif- ferences are not great, and is equal to the product of such differences of temperature and a number dependent on the metals in the couple. This number is called the thermo- electric power. (See Couple, Thermo-Elec- tric. Thermo- Electric Power.) In Fig. 132 (after Tait), the thermo- electric power is shown between lead Fig. 132. and iron, and lead and copper. The numbers at the top of the table represent degrees of the Centigrade thermometer. Those at the sides represent the differences of potential in micro-volts. The thermo-electric power of the lead-iron couple decreases from the freezing point of water, 0° C, to a temperature of 274°. 5 C, when it becomes zero. Beyond that temperature the thermo-electric power increases, but in the opposite direction. The point at which this occurs is called the neu- tral point. Dial Telegraph.— (See Telegraphy, Step-by-Step.) Diamagnetie. — A term applied to the property possessed by substances like bismuth, phosphorus, antimony, zinc and numerous others, which are apparently repelled when placed between the poles q£ powerful magnets. "When diamagnetic substances in the form of rods or bars are placed, as in Fig. 134, between the poles A and B of a powerful electro-magnet, they place themselves at right angles to the poles, or are apparently repelled. 182 A DICTIONARY OF ELECTRiCAL Paramagnetic substances like iron or steel, on the contrary, come to rest under similar circumstances in a straight line joining; the poles, as in the position shown in the annexed /^\ figure. Paramagnetic substances are some- times called ferro - magnetic, or sub- stances magnetic after the manner of iron. This word is unnecessary and ill. advised. The term sidero-magnetic has also been proposed in place of paramag- netic. Paramagnetic substances appear to concentrate the lines of magnetic force on them; that is, their magnetic resist- ance is smaller than that of the air or other medium in which the magnet is Fig. 1SU. placed. They therefore come to rest with their greatest dimensions in the direction of the lines of magnetic force. Diamagnetic substances appear to have a greater magnetic resistance than that of the air around them. They therefore come to rest with their least dimensions in the direction of the lines of magnetic force. The difference between paramagnetic and diamagnetic sub- stances is believed by some to be due to the resistance they thus offer to lines of magnetic force as compared with that offered by air or by a vacuum. The action of magnetism, however, on gaseous media, ro- tating a plane of polarized light to the right, in some gases, and to the left in others, shows that the real nature of these phenomena is yet unknown. Tyndall comes to the conclusion as the result of extended experimentation, " that the diamagnetic force is a polar force, the polarity of diamagnetic bodies being opposed to that of WORDS, TERMS AND PHRASES. 183 paramagnetic ones under the same conditions of excitement." (See Tyndall, on Diamagnetism.) Diamagnetism is also possessed by certain liquid and gas- eous substances. Diamagnetic Polarity. — (See Polarity, Diamagnetic.) Diainagneti§m. — A term applied to the magnetism of dia- magnetic bodies. (See Diamagnetic.) Diameter of Commutation. — In a dynamo-electric machine, a diameter on the commutator cylinder on one side of which the differences of potential, produced by the movement of the coil through the magnetic field, tend to pro- duce a current in a direction opposite to those on the other side. Tims, in Fig. 133, the di- rections of the induced elec- tro-motive forces are indi- cated by the arrows. The diameter of commutation is therefore the line n n' . The term neutral line is also sometimes given to this line. Fig. 133. It lies at right angles to the line of maximum magnetization. In an armature with closed-circuited coils, that is, in an armature in which the armature coils are connected in a closed circuit, the collecting brushes rest on the commutator cylinder at the neutral line, or on the diameter of commuta- tion. In an open circuited armature, however, where the coils are independent of each other, the collecting" brushes must be set at in m, at right angles to the neutral line n n. The term diameter of commutation is, therefore, often applied to this second position. According to this use of the term, the diame- ter of commutation is that diameter on the commutator which joins the points of contact of the collecting brushes. 184 A DICTIONARY OF ELECTRICAL The neutral line n n, Fig. 133, it will be noticed does not occupy a vertical position, but is displaced somewhat in the direction of rotation, thus necessitating the shifting of the brushes forward in the direction of rotation. This necessary shifting of the brushes is known technically as the Lead of the Brushes. (See Angle of Lead.) It will thus be seen that the term diameter of commutation is used in different senses. In reality, the term refers to the position of certain points on the commutator as distinguished from points on the arma*- ture coils. On the commutator, the diameter of commutation is the line drawn through the two commutator bars at which the currents from the two sides are opposed to each other. It is evident that the commutator may be intentionally twisted with respect to the armature, so as to bring its diam- eter of commutation into any desired convenient position. Diaphragm. — A sheet of some solid substance, generally elastic in character and circular in shape, securely fixed at its edges and capable of being set into vibration. The receiving diaphragm of a telephone is generally a rigid plate or disc of iron fixed at its edges, placed near a magnet pole, and set into vibration by variations in the magnetic strength of the pole due to variations in the current that is passed over the line. The diaphragm of the transmitting telephone, or of a pho- nograph, consists of a plate, fixed at its edges and set into vibration by the sound waves striking it. Diaphragm Currents. — Electric currents produced by forcing a liquid through the capillary pores of a diaphragm. (See Osmose, Electric.) Diaphragm of Voltaic Cell.— A term sometimes used for the porous cell of a double fluid voltaic cell. (See Porous Cell. Cell, Voltaic.) Dielectric. — A substance which permits induction to take place through its mass. WORDS, TERMS AND PHRASES. 185 The substance which separates the opposite coatings of a con- denser is called the dielectric. All dielectrics are non-con- ductors. All non-conductors or insulators are dielectrics, but their dielectric power is not exactly proportional to their non-con- ducting power. Substances differ greatly in the degree or extent to which they permit induction to take place through or across them. Thus, a certain amount of inductive action takes place between the insulated metal plates of a condenser across the layer of air between them. Dielectric Capacity, or Dielectric Constant.— A term employed in the same sense as specific inductive capacity. (See Capacity, Specific Inductive.) Dielectric Strain. — The strained condition in which the glass, or other solid dielectric of a condenser, is placed by the charging of the condenser. The stress in this case, i. e., the force producing the defor- mation or strain, is the attraction of the opposite charges. This stress, in the case of a Leyden jar, is often sufficiently great to cause a rupture of the glass. Difference of Potential. — A term employed to denote that portion of the electro-motive force which exists between any two points in a circuit. The difference of potential at the poles of any electric source, such as a battery or dynamo, is that portion of the total elec- tro-motive force which is available, and is equal to the total electro-motive force, less what is lost in the source. (See Potential. Electro-Motive Force.) Differential Galvanometer.— A galvanometer in which the needle is deflected by the action of two parallel coils, the currents in which are opposed to each other. (See Galvanometer, Differential.) 186 A DICTIONARY OF ELECTRICAL Differential Inductometer.— (See Inductometer, Dif- ferential.) Differential Thermo-Pile.— A thermo-pile in which both faces of the pile are exposed to the action of two nearly equal sources of heat in order to determine accurately the difference in their intensities. (See Thermo-Pilc.) Differential Voltameter. — (See Voltameter, Differen- tial.) Diffusion of Electric Current.— A term employed mainly in electro-therapeutics to designate the difference in the density of current in different portions of the human body, or other conductor. When the electrodes are placed at any two given points of the human body, the current branches through various paths, extending in a general direction from one electrode to the other, according to the law of branch or derived circuits, and flowing in greater amount, or with greater density of current, through the relatively better conducting paths. (See Den- sity of Current.) Dimensions of Acceler- a t i © n . — (See Acceleration, Unit of.) Dip, Magnetic The deviation of the magnetic needle from a horizontal posi- tion. The inclination of the mag- netic needle towards the earth. The magnetic needle shown in Fig. 135, though supported at its centre of gravity will not retain a horizontal position in all places on the earth's surface. WORDS, TERMS AND PHRASES. 187 In the Northern Hemisphere its north-seeking end will dip or incline at an angle B O C, called the angle of dip. In the Southern Hemisphere its south-seeking end will dip. The cause of the dip is the unequal distance of the mag- netic poles of the earth from the poles of the needle. The Magnetic Equator is a circle passing around the earth midway (in intensity) between the earth's magnetic poles. There is no dip at the magnetic equator. At either magnetic pole the angle of dip is 90°. Dipping Circle, or Inclination Compass.— A mag- netic needle moving freely in a single vertical plane, and em- ployed for determining the an- gle of dip at any place. The needle M, Fig. 136, is sup- ported on knife edges so as to be free to move only in the vertical plane of the graduated vertical circle C O. This circle is movable over the horizon- tal graduated circle H H. In order to determine the true angle of dip, the vertical plane in which the needle is free to move must be placed exactly in the plane of the magnetic meridian. To ascertain this plane the Fig. 186. vertical circle is moved until the needle points vertically downwards. It is then in a plane 90° from the magnetic meridian. The vertical circle is then moved over the hori- zontal circle 90°, in which position it is in the plane of the magnetic meridian, when the true angle of dip is read off. For an explanation of the reason of this see Component, Horizontal and Vertical, of the Earth's Magnetism. 188 A DICTIONARY OP ELECTRICAL Dipping, Electro-Metallurgical Deposition by The process of obtaining a metallic deposit on a metallic surface by dipping- it in a solution of a readily decom- posable metallic salt. A bright, polished iron surface, when simply dipped into a solution of copper sulphate, receives a coating of metallic cop- per from the electrolytic action thus set up. This process is known technically as dipping. The term dipping is also used in electro-metallurgy to indicate the pro- cess of cleaning the articles that are to be electro-plated by dipping them in various acid or alkaline baths. Direct Current. — (See Current, Direct.) Direct Induced Current.— The current induced in a circuit by induction on itself, or self induction, on breaking the circuit. (See Extra Current.) Direction of Lines of Force. — The direction in which it is assumed the lines of magnetic force pass. It is generally agreed to consider the lines of mag- netic force as coming out of the north pole of a mag- net and passing into its south pole, as shown in Fig. 137. Fig. 137. This is sometimes called the positive direction of the lines of force, and agrees in general with the direction in which the electric current is assumed to flow, which is from the positive to the negative. That is to say, the lines of mag- netic force are assumed to flow or pass out of the north pole and into the south pole of a magnet. Of course there is no evidence of any flow, or any particular direction as character- izing them. (See Field, Magnetic.) WORDS, TERMS AND PHRASES. 189 Directive Power of Magnetic Needle.— The ten- dency of a magnetic needle to move so as to come to rest in the direction of the lines of the earth's magnetic field. The directive power of the needle is due to the attraction of the earth's magnetic poles for the poles of the needle, or to Hie action of the earth's magnetic field. Since the force of the earth's magnetism forms a couple, there is no tendency for the needle to move towards either of the earth's poles, but merely to rotate until it comes to rest with the lines of the earth's magnetic field passing through its poles. (See Couple, Magnetic.) Of course this would be true in the case of a directing mag- not only when it is at a great distance from the needle. Otherwise there would be attraction as well as rotation. Fig. 138. Disc, Arago's A copper or other non-magnetic metallic disc, which, when rapidly rotated under a magnetic needle, supported independently of the disc, causes the needle to be deflected in the direction of rotation, and, when the velocity of the disc is sufficiently great, to rotate with it. Such a disc is shown in Fig. 138, at B. The movement of the needle is due to electric currents, induced by the disc moving through the field of the needle so as to cut its lines of 190 A DICTIONARY OF ELECTRICAL magnetic force. To obtain the best results the disc must move very rapidly, and should be near the needle. Moreover, the needle should be very powerful. This effect was discovered by Arago, in 1824. Since a mag- netic needle moving over a metallic plate produces electric currents in a direction which tend to stop the motion of the needle, a damping of the motion of a magnetic needle is some- times effected by causing it to move near a metal plate. The induced currents which the needle produces in the plate by its motion over it tend to retard the motions of the needle. (See Damping. Lenz's Lair.) Disc Armature.- tures.) Disc, Faraday's -(See Dynamo-Electric Machine, Arma- — A metallic disc movable in a magnetic field on an axis par- allel to the direction of the field. Such a disc is shown in Fig. 139, and moves, as will be seen, so as to cut the lines of magnetic force at right angles. QS^ Fig. 139. The difference of potential generated by the motion of such a disc may be caused to produce a current, by providing a cir- cuit which is completed through the portion of the disc that at any moment of its rotation is situated between spring con- tacts resting on the axis of rotation and the circumference of the disc, respectively. In Barlow's, or Sturgeon's Wheel, Fig. 140, the wheel itself rotates in the direction shown, when a current is sent through it in a direction indicated by the arrows. Discharge. — The equalization of the difference of poten- tial between the terminals of a condenser or source, on their connection by a conductor, WORDS, TESMS AND PHRASES. 191 The removal of a charge from the surface of any charged conductor by connecting it with the earth, or another conduc- tor, effects its discharge. The discharge of an insulated conductor, a cloud, a con- denser, or a Leyden battery, is but momentary, and a cur- rent results which rap- idly passes from its max- imum value to zero. The discharge of a vol- taic battery, or a storage battery, is nearly contin- uous, and furnishes a current which is practi- &W- ll * - cally continuous, as distinguished from the momentary current produced by the discharge of a condenser. A discharge may be Conductive, Convective, or Disruptive. Discharge,. Conductive ■ — A discharge effected by leading the charge off through a conductor placed in con- tact with the charged body. Discharge, Convective The discharge which occurs from the points of a highly charged conductor, through the repulsion by the conductor of air particles that cany off minute charges therefrom. A convective discharge, though often attended by a feeble sound, is sometimes called a silent discharge in order to dis- tinguish it from the noisy, disruptive discharge, which is at- tended by a sharp snap, or, when considerable, by a loud report. A convective discharge is also called a glow or brush dis- charge. The latter is best seen at the small button at the end of the prime, or positive conductor, of a frictional electric machine. The positive discharge from a point or small rounded con- ductor is always brush shaped \ the negative discharge is al- ways star shaped. 192 A DICTIONARY OF ELECTRICAL In rarefied gases, the discharge is convective in character and produces various luminous effects of great beauty, the color of which depends on the kind of gas, and the size, shape, and material of electrodes, and on the degree of the vacuum. Thus, in the rarefied space of the vessel shown in Fig. 141, the discharge, becomes an ovoidal mass of light sometimes called the Philosopher's Egg. When the discharges in rarefied gases follow one another very rap- idly, alternations of light and dark- ness, or stratification, or strioz are produced. The breadth of the dark bands increases as the vacuum becomes higher. The light portions start at the positive electrode, and are hotter than the dark portions. The effects of the luminous con- vective discharge are best seen in exhausted glass tubes, called Geissler Tubes, containing residual atmospheres of various gases. (See Geissler Tubes.) Discharge, Disruptive The sudden, and more or less complete, discharge that takes place across an intervening non-conductor or dielectric. A mechanical strain of the dielectric occurs, which sudden- ly permits the discharge to pass as a spark, or rapid succes- sion of sparks. In air, the spark, when long, generally takes the zigzag path as shown in Fig. 142. These sparks consist of heated gases, and portions of the conductor that are volatilized by the heat. WORDS, TERMS AND PHRASES. 195 The discharge of a Leyden jar or Condenser, may be dis- ruptive, as when the discharging rod is held with one knob con- nected with one coating, and the other near the other coating. It may be gradual, as when the two coatings are alternately connected with the ground. The stress is often sufficient to pierce the glass. Fig. Utf. Discharge, Duration of The time required to effect a complete disruptive discharge. The disruptive discharge is not instantaneous ; some time is required to effect it. Estimates of the duration of a flash of lightning, based on the duration of a Leyden jar discharge, are misleading from the enormous difference in the quantity and the potential in the two cases. Leyden jar discharges, are, however, accomplished in very small periods of time. Discharge Key.— (See Key, Discharge.) Discharge, Lateral (See Lateral Discharge.) Discharge, Oscillating A number of suc- cessive discharges and recharges which occur on the disruptive discharge of a Leyden jar, or condenser. The disruptive discharge of a Leyden jar, or condenser, is not effected by a single rush of electricity. When discharged through a small resistance, a number of alternate partial dis- 194 A DICTIONARY OF ELECTRICAL charges and recharges occur, which produce true oscillations or undulatory discharges. These oscillations are caused by the induction of the dis- charge on itself, and are similar to the mutual induction of a current. Discharger, Universal (See Universal Dis- charger.) Discharging Rod or Tongs.— Metallic rods terminated at one end with balls and connected at the other by a swinging joint, and capable of mo- tion at the free ends towards, or from, one another; employed for the dis- charge of Leyden batteries or con- densers. The insulated handles H, H, Fig. 143, permit the balls at M M to be readily applied to the opposite coatings of the jar or condenser. Disconnections. — A term em- Fig. Ik3. ployed to designate one of the varieties of faults caused by the accidental breaking or disconnection of a circuit. Disconnections of this kind may be : (1) Total; as by a switch inadvertently left open ; or by the accidental breaking of a part of the circuit. (2) Partial; as by a dirty contact; a loose, or badly soldered joint ; a poorly clamped binding screw ; a loose terminal, or a bad earth. (3) Intermittent ; as by swinging joints; alternate expansions or contractions, on changes of temperature; the collection of dust and dirt in dry weather, and their washing out in wet weather. Dispersion Photometer.— (See Photometer, Disper- sion.) WORDS, TERMS AND PHRASES. 195 Dissimulated or Latent Electricity.— The condition of an electric charge when placed near an opposite charge, as in a Leyden jar or condenser. In this case, merely touching one of these charged surfaces will not effect its complete discharge. (See Bound and Free Charge.) Electricity in the condition of a bound charge was formerly called latent electricity. This term is now in disuse. Dissipation of Charge. — The gradual but final loss of any charge by leakage, which occurs even in a well insulated conductor. This loss is more rapid with negatively charged conductors, than with those positively charged. Crookcs, of England, has retained a charge in conductors for years, without appreciable leakage, by placing the conductors in vessels in which a high vacuum was maintained. (See Vacuum, High.) Dissociation. — The separation of a chemica compound into its elementary parts by the action of heat. Distillation, Dry or Destructive The action of heat on an organic substance, while out of contact with air, as a result of which the substance is decomposed into simpler and more stable compounds. The products resulting from the decomposition may be suc- cessively collected by the ordinary processes of distillation. Distillation, Electric The distillation of a liquid in which the effects of heat are aided by an electrifica- tion of the liquid. Beccaria discovered that an electrified liquid evaporates more rapidly than when unelectrified. Distribution Box. — (See Box, Distribution.) Distribution of Electric Charge. (See Charge, Dis- tribution of.) 196 A DICTIONARY OF ELECTRICAL Distribution of Electricity, Systems of.— (See Sys- tems of Distribution by Alternating Currents; — by Direct Currents.) Door-Opener, Electric A device for open- ing a door from a distance by electricity. Various devices consisting of electro-magnets, acting against, or controlling, springs or weights, are employed for this purpose. Double-Carbon Arc Lamp.-An electric arc lamp provided with two pairs of carbon electrodes, so arranged, that when one pair is consumed, the circuit is automatically completed through the other pair. Double-Contact Key.— (See Key, Double- Contact.) Double-Current, or Reverse Current Working. — The employment, in systems of telegraphy, by means of suitable keys, of currents from voltaic batteries, in alternately opposite directions thus increasing the speed of signaling. Double -Fluid Electrical Hypothesis. — (See Elec- tricity, Hypothesis of.) Double-Fluid Voltaic Cells.— (See Voltaic Cells.) Double-Refraction. — (See Refraction, Double.) Double-Refraction, Electric (See Electric, Double Refraction.) Double-Touch, Magnetization by A method for producing magnetization by the simultaneous touch of two magnet poles. (See Magnetization, Methods of. ) Doubler of Electricity. — An early form of continuous elctrophorus. (See Electrophorus.) Drill, Electro-Magnetic A drill, applied especially to blasting or mining operations, operated by means of electricity. Drum, Electro-Magnetic A drum, used in feats of legerdemain, operated by an automatic electro-magnetic make and break apparatus. W6RDS, TERMS AND PHRASES. 197 Brum or Cylinder Armature. — An armature for a dynamo-electric machine, in which the coils are wrapped around the outside of a hollow cylindrical or drum-shaped core. (See Dynamo-Electric Machine, Armatures of.) Dry Pile. — A voltaic pile or battery consisting of numerous cells, the voltaic couple in each of which consists of sheets of paper covered with zinc-foil on one side, and black oxide of manganese on the other. Various modifications of the above are possible. Duplex Telegraphy. — Devices by means of which two messages can be simultaneously sent over a single wire, in opposite directions. (See Telegraphy, Duplex.) Duration of Electric Discharge. — (See Discharge, Duration of.) Dyad. — A dyad or bivalent element, is one which has two bonds by which it can unite or combine with another element. An element whose atomicity is bivalent. Dyeing, Electric The application of electricity to the reduction, or the oxidation, of the aniline salts used in dyeing. Goppelsroder, in his processes of electro-dyeing, forms and fixes aniline black on cloths as follows; viz., the cloth, satu- rated with aniline salt, is placed on an insulated metallic plate, inert to the aniline salt, and connected with one pole of a battery or other electric source. The other pole is con- nected with a metallic plate on which the required design is drawn. On the passage of the current, the design is traced in aniline black on the cloth. A minute or two suffices for the operation. A species of electrolytic writing is obtained on cloths ar- ranged as above by substituting a carbon pencil for the metallic plate. On writing with this pencil, as with an ordinary pencil, the passage of the current so directed, is followed by the de- position of aniline black. 198 A DICTIONARY OF ELECTRICAL By means of a somewhat similar process writing in white on a colored ground is obtained. Dynamic Attraction.— (See Attraction, Dynamic.) Dynamic Electricity. — A term formerly employed for current electricity. Now going out of use. Dynamics, Electro (See Electro Dynamics.) Dynamo Battery.— (See Battery, Dynamo. ) Dynamo-Electric Machine.— A machine for the con- version of mechanical energy into electrical energy, by means of electro-magnetic induction. The term is also applied to a machine by means of which electrical energy is converted into mechanical energy by means of electro-magnetic induction. Machines of the latter class, are generally called motors, those of the former, generators. A dynamo-electric generator, or a dynamo-electric machine proper, consists of the following parts, viz. : (1) The revolving portion, usually the Armaturejin which the electro-motive force is developed, which produces the current. It must be borne in mind that it is not current but differ- ences of electric potential, or electro-motive forces, that are de- veloped by any electric source from which a current is obtained. For ease of reference, however, we will speak of an electric cur- rent as being generated by the armature, or source. No ambig- uity will be introduced if the student bears the above in mind. (2) The Field Magnets, which produce the field in which the armature revolves. (3) The Pole Pieces, or free terminals of the field magnets. (4) The Commutator, by which the currents developed in the armature are caused to flow in one and the same direction. In alternating machines and some continuous current dynamos this part is called the Collector. (5) The Collecting Brushes, that rest on the Commutator Cylinder and take off the current generated in the armature. Dynamo-Electric Machine, Armature. — The coils of insulated wire and the iron core on or around which the coils are wound. WORDS, TERMS AND PHRASES. 199 Armatures are generally divided into the following- classes, viz. : (1) Ring- Armatures, in which the armature coils are wound around a ring shaped core, as shown in Fig. 144. (2) Drum- A r m a- tures, in which the armature coils are w o u n d longitudi- nally over the sur- face of a cylinder or drum, as shown in Fig. 145. (3) Pole or Radial- Armatures, in which ^- lltlu the armature coils are wound on separate poles that project radially from the periphery of a disc, as shown in Fig. 146. (4) Disc Armatures, in which flat coils are supported on the sur- face of a disc. Dynamos are some- times divided into Uni- polar, Bipolar and Mul- ti polar. A unipolar- armature is one whose polarity is never re- versed. A bipolar- ar mature is one in which the polarity is Fig. ii*5. reversed twice in every rotation ; multipolar-armatures have their polarity reversed a number of times in every rotation. Dynamo-Electric machine, Armature Coils.— The coils, strips or bars that are wound on the armature core. To avoid needless resistance the wire should be as short 200 A DICTIONARY OF ELECTRICAL and thick as will enable the desired current to be obtained without excessive speed of rotation. The armature coils should enclose as many lines of force as possible (1 e., they should have as nearly a circular outline as possible). In drum-armatures, the breadth should nearly equal the length, unless other considerations prevent. When the armature wire consists of rods or bars, it should be laminated or slit in planes perpendicular to the lines of force so as to avoid eddy currents. The greater the number of coils, other things being equal, the more uniform the cur- rent generated. The separate coils should be symmetrically disposed, otherwise irregular induction, and consequent spark- ing at the commutator results. The coils of pole-armatures should be wound near the poles rather than on the middle of the cores; In order to avoid undue heating, spaces for air ventilation are not inadvisable. Vari- ous connections of the armature coils are used. In some machines all the coils are connected in a closed cir- cuit. In some, the coils are independent of one another, and, either for the entire revolution, or for a part of a revolution, are on an open circuit. In alternating current dynamos in order to obtain the rapid reversals or alternations of current, whieh in some machines WORDS, TERMS AND PHRASES. 201 are as high at 12,000 per minute, a number of poles of alternate polarity are employed. The separate coils that are used on the armature may be coupled either in series or in mul- tiple-arc. Where a comparatively low electro-motive force is sufficient, such as for incan- descent lamps in multiple- arc, the separate coils are united In parallel; but for purposes where a consider- able electro-motive force is necessary, as, for example, in systems of alternate cur- rent distribution, with con- verters at considerable dis- tances from the generating, alternating current dynamo, the\ series, as shown in the Fisr. 147. Fig. 147. often connected in Dynamo-Electric machine, Armature Core.— The iron core, on, or around which, the armature coils are wound. The armature core is laminated for the purpose of avoiding the formation of eddy currents. In drum, and in ring-armatures, the laminae should be in the form of thin insulated discs or plates of soft iron ; in pole-arma- tures they should be in the form of bundles of insulated wires. The iron in the cores should be of such an area of cross section, as not to be readily oversaturated. Dynamo-Electric machine, Cause of Current generated by The current developed in the arma- ture coils is due to the cutting of the lines of magnetic force of the field by the coils during the rotation of the armature. If a loop of wire, whose ends are connected to the two-part 202 A DICTIONARY OF ELECTRICAL commutator, shown in Fig. 148, be rotated in the magnetic field between the magnet poles N and S, in the direction of the » large arrow, cur- rents will be gen- erated which will flow in the direc- o tion indicated by the small arrows during its motion past the, north Fig. IIS. pole from the top to the bottom, but in the opposite direction during its motion past the south pole, from the bottom to the top. If now the brushes rest on the com- mutator in the position shown in the Fig. 149, the vertical line of the gap between the poles corre- sponding with the vertical gap between the commu- tator segments, the cur- rents generated in the loop will be caused to flow in one and the same direction, and B' will become the positive brush since the end of the loop is connected wit}* it only so long as it is posi- tive. As soon as it becomes negative, from the current in the loop flowing in the opposite direction, the other end, which is then positive, is connected with the positive brush. Fig. 150. A similar series of changes occur at the negative brush, B. Theoretically, the neutral points, where the brushes rest, WORDS, TERMS AND PHRASES. 203 would be in the vertical line coinciding with that of the gap between the poles. An inspection of the figure shows that the Neutral Line, or the Diameter of Commutation, is dis- placed in the direction of rotation. (See Diameter of Com- mutation). The displacement of the brushes, so necessitated, is called the lead. The cause of the lead is the reaction that occurs between the magnetic poles of the field magnets and those of the armature, the result of which is to displace the field magnet poles, and to cause a change in the density in the field. This is shown in Fig. 150, where the density of the lines of force indicates the position of the diameter of commutation as being near n s, or at right angles to the diameter of greatest average magnetic density. The magnetic lag also influences the positive of the neutral line. (See Lead. Angle of Lag.) Dynamo-Electric machine, Collecting Brushes. — Metallic brushes which bear on the commutator cylinder, and take off the current generated by the difference of poten- tial in the armature coils. (See Brushes, Collecting.) Dynamo-Electric Machine, Commutator. — The part of a dynamo-electric machine which is designed to cause the alternating currents produced in the armature to flow in one and the same direction in the external circuit. Fig. 151. Fig. 152. The character of the commutator depends on the shape, arrangement, and number of armature coils, and on the character of the magnetic field. 204 A DICTIONARY OF ELECTRICAL In action, the commutator is subject to wear from the friction of the brushes, and the burning action of destructive sparks. The commutator segments are, therefore, made of compara- tively thick pieces of metal, insulated from one another, and supported on a commutator cylinder usually placed on the shaft of the armature. The enJs of the armature coils are connected to commuta- tor strips or segments. Fig. 153. Figs. 151, 152, and 153, show the connections of an arma- ture coil to the plates of a two-part commutator. (See Com- mutator.) The connections of a four-part commutator for a ring arma- ture, and the connections of the coils are shown in the an- nexed Fig. 154. The commutator strips may either connect the separate coils in one closed circuit, in which the coils are all connected with one another, or, in an open circuited armature, the separate coils are independent of one another. Dynamo-Electric Machine, Field Hagnet§.— The electro magnets employed to produce the magnetic field of a dynamo-electric machine. WORDS, TERM S AND PHRASES. 205 The field magnets consist of a suitable frame, or core, on which the field magnet coils are wound. The field magnet cores are made of thick and solid iron, as soft as possible. They should contain plenty of iron in order to avoid too ready magnetic saturation. All edges and corners are to be avoided, since they tend to cause an irregular distribution of the field. R R R Fig. 155. R R R Fig. 156. The field magnets should have sufficient magnetic strength to prevent the magnetizing effect of the armature from unduly influencing the field, and thus, by causing too great a lead, produce injurious sparking. Dynamo-Electric Machine, Methods of Increas- ing the Electro-Motive Force generated by The electro-motive force of a dynamo-electric machine may be increased in the following ways, viz. : 206 A DICTIONARY OF ELECTRICAL (1) By increasing- its Speed of Rotation. (2) By increasing the Strength of the Magnetic Field be- tween which the armature rotates. (3) By increasing* the Size of the Field through which the armature passes in unit time, the intensity remaining the same. (4) By increasing* the Number of Armature Windings, i. e., by making successive parts of the same wire pass simultane- ously through the field. (5) By increasing the Number of Fields passed through by the same wire. Dynamo-Electric Machine, Pole Pieces.— Massive pieces of iron placed on the poles of the field mag- nets of dynamo-electric machines, to define and limit the magnetic field. The pole pieces should be of massive, soft iron. They are sometimes laminated so as to avoid eddy currents. When de- signed to produce a uni- form field they must ex- tend on each side of the armature, but not too far, else a loss will be occa- sioned by the lines of magnetic force closing directly through the edges of the opposite pole R Fig. 157. pieces, instead of through the armature. Dynamo-Electric Machines, Compound Wound Machines whose field magnets are excited by more than one circuit of coils, or by more than a single electric source. Compound dynamos are of two classes, viz. : WORDS. TERMS AND PHRASES. 207 (1) Those designed to produce a Constant Potential, and (2) Those designed to produce a Constant Current. For Constant Potential. The combination of a Series and Separately Excited ma- The field is in series with the additional and separate excita- chine is shown in Fig. 155. armature, but has also an tion. The combination of a Series and Shunt machine ensures the excitation of the field both by the main and by a shunted current. Such a combination is shown in Fig. 156. For Constant Current. The combination of shunt and separately ex- cited machine is shown in Fig. 157. In this machine the field is excited by means of a shunt to the external circuit, and by a current produced by a sep- arate source. The combination of a Series and Magneto Ma- chine is shown in Fig. 151 constant current. Dynamo-Electric Machines, Varieties of Dynamo-electric machines may be divided into different classes according to the manner in which their field mag- nets are excited. In a Series Dynamo, Fig. 159, the armature circuit is con- nected in series with the field circuit; therefore the entire arm- ature current must pass through the field coils. it -^'-o^'-i- 4'<- S&, ilH^ 4M. -'" Fig. 190, suspended near one another, show by their repulsion the presence of a charge. Two pith balls may be used for the same purpose. Fig. 190. Fig. 191. To use an electroscope for determining the signoi a charge, the gold leaves or pith balls are first slightly repelled by a charge of known name, as, for example, positive, applied to the knob C. They are then charged by the electrified body whose charge is to be determined. If they are farther re- pelled, its charge is positive. If they are first attracted and afterwards repelled, its charge is negative. Similarly, if the pith balls, B B, shown in Fig. 191, re- pelled by a known charge, be approached by a similar charge in S, they will at once be still further repelled, as shown by the dotted liues. Two posts B, Fig. 190, connected with the earth, increase the amount of divergence by induction. 248 A DICTIONARY OF ELECTRICAL Electroscope, Condensing, Volta's.— An electroscope employed for the detection of feeble charges, the leaves of which are charged by means of a condenser. The condensing electroscope, Fig. 192, is formed of two me- tallic plates, placed at the top of the instrument, and separated by a suitable dielectric. The upper plate P, is removable by means of the insulated handle G. To employ the electroscope, as for example, to detect the free charge in an unequally heated crystal of tour- maline the crystal is touched to the lower plate, while the upper plate is connected to the ground by the finger. On the subsequent removal of the upper plate, an enormous decrease ensues in the capacity of the conden- ser, and the charge now raises the potential of the lower plate, and causes a marked divergence of the leaves, L L. (See Pyro-Electricity.) Quadrant Henley's.— An Fig. 192. Electroscope, electroscope sometimes employed to indicate large charges of electricity. A pith ball placed on a light arm A, of straw or other similar material, Fig. 193, is pivoted at the centre of a gradu- ated circle B. The arm C is attached by means of the screw to the prime conductor of an electric machine. The similar charge imparted to A by contact with C, causes a repulsion which may be measured on the graduated arc. This instrument approaches the electrometer in its opera- tion, since by its means simple measurements may be made of the value of the repulsion. It should not, however, be con- founded with the quadrant electrometer. (See Electrometer, Quadrant.) Electrostatic Field. — (See Field, Electrostatic.) WORDS. TERMS AND PHRASES. 249 Electrostatic Induction.— (See Induction, Electro- static.) Electrostatic Induction Machines. — (See Machines, Electrostatic Induction.) Electrostatic Lines of Force. — (See lines of Force, Electrostatic.) Electrostatic Stress.— The force, or pressure in an electric field which produces a strain or deformation in a piece of glass or fcps/g similar body placed therein. (See Optical Strain, Electrostatic.) Electrostatics. — That branch of electric science which treats of the phenomena and measurement of electric charges. The principles of electrostatics are em- braced in the following laws, viz. : (1) Charges of like name, i.. e., either pos- itive or negative, repel each other. Charges of unlike name attract each other. (2) The forces of attraction, or repulsion between two charged bodies are directly pro- portional to the product of the quantities of electricity possessed by the bodies and in- versely proportional to the square of the dis- tance between them. These laws can be demontsrated by the use of Coulomb's torsion balance. (See Bal- ance, Torsion.) p . g m Electro-Therapeutic Bath.— (See Bath, Electro-Ther- apeutic.) Electro-Therapeutics, or Electro-Therapy.— The application of electricity to the curing of disease. (See Elec- ro-Biology). 256 A DICTIONARY OF ELECTRICAL Electro-Therapy, or Electro-Therapeutics.— The application of electricity to the treatment of disease. Electrotonus.— A condition of altered functional activity which occurs in a nerve when subjected to the action of an electric current. This alteration may consist in either an increased or a decreased functional activity. The decreased functional activity occurs in the neighborhood of the anode or the posi- tive terminal, and is called the anelect rotonic state. The in- creased functional activity occurs in the neighborhood of the kathode, or the negative terminal, and is called the kathelec- trotonic state. (See Anelectrotonous. Kathelectrotonous.) Electro typing, or the Electrotype Process. — Ob- taining casts or copies of objects by depositing metals in moulds by the agency of electric currents. The moulds are made of wax, or other substance, rendered conducting by mixing with powdered plumbago. The mould is connected with the negative battery terminal, and placed in a metallic solution, generally copper sulphate, opposite a plate of the same metal, connected with the positive battery terminal. As the current passes, the metal is de- posited on the mould at the kathode, and dissolved from the metallic plate at the anode, thus maintaining constant the strength of the bath. Element, Negative (See Couple, Voltaic.) Element of Current. — (See. Current, Element of .) Element, or Elementary Matter. — Matter which can- not be decomposed into simple matter. Matter that is formed or composed of but one kind of atoms. Oxygen and hydrogen are elements, or varieties of ele- mentary matter. They cannot be decomposed into anything but oxygen or hydrogen. Water, on the contrary, is com- pound matter, since it can be decomposed into its constituent parts, oxygen and hydrogen. WORDS, TERMS AND PHRASES. 251 There are about seventy well known elements, some of which are very rare, occurring in extremely small quantities. The evidence of the true elementary condition of many of the elements is based, to a great extent, on the fact that so far they have resisted all efforts made to decompose them into simpler substances. We should bear in mind, however, that until Davy's use of the voltaic battery, potash, soda and many other similar compounds were regarded as true ele- ments. It is therefore not improbable that many of the now so-called elements, may hereafter be decomposed into simpler constituents. Element, Positive —(See Couple, Voltaic.) The following tables give the names, chemical symbols, equivalents and specific gravities of the principal elements. Simple Substances, with their Symbols, Equivalents and Specific Gravities. Name. Symbol. Equiv. Sp. Grav. Aluminium _. Al Sb As Bi Bi- Cd Ca C CI Co Cu F Au H I Ir Fe Pb Mg Mn 13.7 64.6 37.7 71.5 78.4 55.8 20.5 6.1 35.5 29.5 31.7 18.7 196.6 1.0 126.5 98.5 28.0 103.7 12.7 26.0 2.56 Antimony 6.70 Arsenic _ 5.70 Bismuth 9.82 Bromine 3.00 Cadmium 8.65 Calcium . . 1.58 Carbon 3.50 Chlorine 2.44 Cobalt 8.53 Copper 8.80 Fluorine 1.32 Gold (aurum) . 19.30 Hvdrogen 0.069 Iodine 4.94 Iridium __ 18.68 Iron_. __ 7.75 Lead _. 11.35 Magnesium 1.75 Manganese 8.00 252 A DICTIONARY OF ELECTRICAL Name Mercury Molybdenum Nickel _ Nitrogen Osmium _ _ Oxygen Palladium ___ Phosphorus Platinum _ . . Potassium Rhodium Selenium Silver Sodium Strontium Sulphur Tellurium Tin Titanium Tungsten Uranium Zinc _ Symbol. Equiv. Sp. Grav. Hg Mo Ni N Os O Pd P Pt K R Se Ag Na Sr S Te Sn Ti W U Zn 200.0 47.9 29.5 14.2 99.7 8.0 53.3 15.9 98.8 39.2 52.2 40.0 108.3 23.5 43.8 16.1 64.2 58.9 24.5 92.0 60.0 32.3 13.50 8.60 8.80 0.972 10.00 1.102 11.35 1.77 21.50 0.865 11.00 4.5 10.5 0.972 2.54 1.99 6.30 7.29 5.28 17.00 10.15 7.00 Element, Thermo-Electric Clark & Sabine. -One of the metals or substances which forms a thermo-electric couple. (See Cou- ple, Thermo-Electric.) Element, Voltaic One of the metals or sub- stances which forms a voltaic couple. (See Couple, Voltaic.) Elements, Electrical Classification of A classification of the elements into two groups or classes ac- cording to whether they appear at the anode or kathode when electrolyzed. The chemical elements may be arranged into electro-positive and electro-negative according to whether, during electrolysis, they appear at the negative or positive terminal of the source. The electro-positive elements or radicals are called Jcathions, WORDS. TERMS AND PHRASES. 253 and appear at the kathode or electro-negative terminal. The electro-negative elements are called anions, and appear at the anode or the electro-positive terminal. (See Ions.) The metals generally are electro-positive ; oxygen, chlorine, iodine, fluorine, etc., are electro-negative. Elongation, Magnetic — An increase in the length of a bar of iron on its magnetization. This increase in length is thought to greatly strengthen Hughes' theory of magnetism. (See Magnetism, Hughes' 1 Theory of.) Embosser, Telegraphic An apparatus for re- cording a telegraphic message in raised or embossed characters. E. M. F. — A contraction generally used for the word electro-motive force. Energy. — The power of doing work. The amount of work done is measured by the product of the force, and the space through which it moves. Thus one pound raised vertically through ten feet, ten pounds raised through one foot, or five pounds raised through two feet, all represent the same amount of work, viz., ten foot pounds. If a weight of ten pounds be raised through a vertical height of one foot, by means of a string passing over a pulley, there will have been expended an amount of energy repre- sented by the work of ten foot pounds. If the weight be pre- vented in any way from falling, as by tying the string, it will have stored in it an amount of energy equal to ten foot pounds, and if permitted to fall, is capable of doing an amount of work which, leaving out air resistance and friction, is exactly equal to that expended in raising it to the position from which it falls, viz., ten foot pounds of work. Energy, Actual, Kinetic Energy, Energy of Motion. — Energy employed in doing work, or the power of doing work possessed by bodies that are in motion, 254 A DICTIONARY OF ELECTRICAL Energy, Atomic or Chemical Potential — The potential energy possessed by the elementary chemical atoms. (See Energy, Potential.) Energy, Conservation of —(See Conservation of Energy.) Energy, Degradation of (See Degradation of Energy.) Energy, Electric The power which electricity possesses of doing work. In the case of a liquid surface at different levels, the liquid at the higher level possesses a certain amount of potential energy measured by the quantity of the liquid at the higher level, and the excess of its height over that of the lower level ; or, on the difference of level between them. This difference of level will produce a current from the higher to the lower level, and during the passage of the current, potential energy will be lost, and a certain amount of work will be done. In the case of electricity, the difference of electric level or potential, between any two points of a conductor, causes an electric current to flow between these points from the higher to the lower electric level, during which electric potential energy is lost, and work is accomplished by the current. (See Potential.) The amount of the electric work is measured by the quantity of electricity that flows, multiplied by the difference of poten- tial under which it flows. (See Joule, or Volt- Coulomb.) Electric energy, however, is generally measured in electric power, or rate of doing electric work. Since an ampere is one coulomb per second, if we measure the difference of potential in volts, the product of the amperes by the volts will give the electrical power in volt-amperes, or watts, or units of electric power. CE = The Watts. (See Ampere. Volt. Watt.) Que horse-power equals 550 foot pounds per second. One WORDS, TERMS AND PHRASES. 255 watt or volt-ampere = ^ of a horse-power, or one horse- power equals 746 volt-amperes or watts, therefore : The current in amperes, multiplied by the difference of po- tential in volts, divided by 746, equals the rate of doing work in horse-power. Thus, if .7 ampere is required to operate a 16 candle, 110 volt, incandescent lamp, it requires 4.8 watts per candle. One Watt = 44.2394 foot-pounds per minute. One Watt = .737324 foot-pounds per second. The Heat Activity, or the heat per second produced by an electric current, is also proportional to the product C E, or the watts, for the heat is proportional to the square of the current in amperes multiplied by the resistance in ohms, or C 2 R = the Heat. (See Calorimeter, Electric.) By Ohm's Law (See Ohm's Law), E C - — (1), or C R = E , (2), R but the electric power or the watts = CE (3). If, now, we substitute the value of E, taken from equation (2) in equation (3) we have CE = C X CR = C 2 R; therefore C 2 R = watts. To determine the heating power of a current in small cal- ories, calling- H, the amount of heat required to raise 1 gramme of water through 1° Cent., and C, the current in amperes. H = C 2 R X .24. Or, for any number of seconds, t, H = C 2 ~Rt X -24, Therefore, one watt = .24 calories per second. (See Calorie.) But from Ohm's law, E C = - (1), R and the formula for electric power or the watts = CE , (2) 256 A DICTIONARY OF ELECTRICAL By substituting in equation (2) and the value of C in equation (1), E E 3 CE = EX — = — = watts. R R That is to say, the electric power, in any part of a circuit varies directly as the square of the electro-motive force. We therefore have three expressions for the value of the watt or the unit of electric power, viz. : CE= watts. (1) C 2 R = watts. (2) E 2 — == watts. (3) R (1) C E = Watts ; or the electric power is proportional to the product of the quantity of electricity per second, that passes, in amperes, and the difference of electric poten- tial or level, through which it passes, in volts. (2) C 2 R = Watts ; or the electric power varies directly as the resistance R, when the current is constant, or as the square of the current, if the resistance is constant. That is to say, if with a given resistance, the power of a given current has a certain value, and the current flowing through this same resistance be doubled, the power is four times as great, or is as the square of the current. E 2 (3) — = Watts, or the electric power is inversely as the re- R sistance R, ivhen the electro-motive force is constant. A circuit of one ohm resistance will have a power of one watt, when under an electric motive force of one volt, since it would then have a current of one ampere flowing through it, and C E = 1. If, however, the resistance be halved or becomes .5 ohm, then two amperes pass, or the power equals 2 watts. The power varies as the square of the electro-motive force in any part of a circuit, when the resistance is constant in WORDS, TERMS AND PHRASES". 257 that part. Thus 2 amperes, and 2 volts, in a circuit of one ohm resistance, give a power, CE = 2 X 2 =4 walls. If now, R, remaining the same, the electro-motive force be raised to 4 volts, then since E is doubled, (', or the amperes are doubled, E a 16 and CxE = 4x4 = l(i watts, or — = — = 16. R 1 Energy, Electric Transmission of ■ — The transmission of mechanical energy between two distant points connected by an electric conductor, by converting- the mechanical energy into electrical energy at one point, send- ing the current so produced through the conductor, and recon- verting the electrical into mechanical energy at the other point. A system for the electric transmission of energy embraces : (1) A Conducting Circuit between two stations. (2) An Electric Source, or battery of electric sources, or machines, at one of the stations, generally in the form of a dynamo-electric machine, for converting mechanical energy into electric energy. (3) Electro-Receptive Derives, generally electric motors, at the other station for reconverting the electric into mechanical energy. (See Motors, Electro- Magnetic.) Energy, Potential, Energy of Position, Static Energy, or Energy of Stress. — Stored energy ; potency or capability of doing work. The capacity for doing work possessed bj- a body at rest, arising from its position as regards the earth, or from the pos- ition of its atoms as regards other atoms. A pound of coal if raised vertically one foot, possesses, as a mere weight, an amount of energy capable of doing an amount of work equal to one foot pound. The atoms of carbon, how- ever, of which it is composed, have been raised or separated from those of oxygen, or some other elementary substance, and when the coal is burned, or the carbon atoms fall towards 258 A DICTIONARY OF ELECTRICAL the oxygen atoms (i.e., unite with them), the coal gives up the potential energy of its atoms in the form of heat. All elementary substances possess in the same way atomic, or chemical potential energy, or the energy with which they tend to fall together. This energy varies in amount in differ- ent elements and becomes kinetic, as heat, on combination with other elements. Engine, Electro-Magnetic A motor whose driving power is electricity. (See Motor, Electric.) Engraving, Acoustic Engraving by the human voice. In the Phonograph, Grapliophone, and Gramophone, a dia- phragm is set in vibration by the speaker's voice so that it cuts or engraves a record of its to-and-fro movements on a sheet of tin foil, on a cylinder of hardened wax, or on a specialty coated plate of metal or glass. This record is em- ployed in order to reproduce the speech. (See Phonograph.) Engraving, Electric ■ or Electro-Etching. — A method for electrically etching or engraving a metallic plate by covering it with wax, tracing the design on the wax so as to expose the metal, connecting it with the positive ter- minal of a battery, and placing it in a bath opposite another plate of metal. By the action of electrolysis the metal is dissolved from the exposed portions and deposited on the plate connected with the other terminal of the battery. (See Electrolysis.) By connecting the waxed plate to the negative terminal, the metal will be deposited on the exposed portions, thus pro- ducing the design in relief. This latter method is not, how- ever, apt to produce a sufficiently uniform deposit to enable the plate so formed to be used for printing from. Entropy. — In thermo-dynamics the non-available energy in any system. (Clausius and Mayer.) WORDS, TERMS AXD PHRASES. 250 The available energy in any system. (Tait, Thomson, and Maxwell.) As will be noticed this term is used in entirely different and opposite senses by different scientific men. The latter sense is, perhaps, the one most generally taken. Heat energy is available for doing" useful external work only when the source of heat is hotter than surrounding- bodies, that is, when the heat is transferred from a hotter to a colder body. When all bodies acquire the same temperature no more external work can be done by them. In the various transformations of energy some of the energy is converted into heat, and this heat is gradually diffused through the universe and thus becomes non-available to man. There- fore, the entropy of our earth is decreasing-. "Entropy, in Thermodynamics," says Maxwell, "is a quantity relating to a body such that its increase or diminu- tion implies that heat has entered or left the body. The amount of heat which enters or leaves the body is measured by the product of the increase or diminution of entropy into the temperature at which it takes place." Entropy, Electric A term proposed by Maxwell in thermo-electric phenomena to include the doctrine of en- tropy in electric science. " When an electric current," says Maxwell, "passes from one metal to another heat is emitted or absorbed at the junc- tion of the metals. We should, therefore, suppose that the electric entropy has diminished or increased when the elec- tricity passes from one metal to the other, the electric entropy being different according to the nature of the medium in which the electricity is, and being affected by its temperature, stress, strain, etc." Equator, Geographical An imaginary great circle passing around the earth midway between its poles. Equator, Magnetic — The magnetic parallel, or circle on the earth's surface where a magnetic needle free to more stands horizontal. 260 A DICTIONARY OP ELECTRICAL i \ LL' / / An irregular line passing around the earth approximately midway between the earth's magnetic poles. (See Dip, Angle of.) Equator of Magnet.— A point midway between the poles of a bar magnet. This term was proposed by Dr. Gilbert. It is now almost entirely displaced by the term neutral point or points. Equipotential Surfaces.— Surfaces, all the points of which are at the same electric potential. (See Potential, Electric.) Electric surfaces perpendicular to the lines of electric force over which aquantity of electricity, considered as being con- centrated at a point, may be moved without doing work. (See Field, Electrostatic.) In electrostatics, equipotential surfaces correspond with a water level, over which a body may be moved horizontally against the force of gravity without doing any work. In the case of the charged in- sulated sphere, shown in the Fig. 194, the equipotential surfaces, represented by the circles, are concentric. Equipotential Surfaces, Magnetic Surfaces surrounding thejpoles of a magnet, or system of mag- nets, where the magnetic potential is the same. (See Poten- tial, Magnetic.) Magnetic equipotential surfaces extend in a direction per- pendicular to the lines of magnetic force. (See Field, Mag- netic.) Therefore work is required in order to move a unit pole WORDS, TERMS AND PHRASES. 261 across equipotential magnetic surfaces, because in so doing it cuts the lines of magnetic force. Equipotential surfaces, whether electric or magnetic, cannot intersect one another since their potential is the same at all points. Eqaivalciil, Chemical The quotient obtained by dividing the atomic weight of any elementary substance by its atomicity. (See Atomic Weight. Atomicity.) The chemical equivalent is different from the atomic weight. The atomic weight of gold is 190.0. but since in chemical com- bination one atom of gold is capable of combining with three atoms of hydrogen, the weight of the gold, equivalent to that of one atom of hydrogen is one-third of 190.0, or 05.5. Equivalent, Electro-Chemical.— A number represent- ing the weight of an elementary substance Liberated during electrolysis by the passage of one coulomb of electricity. (See Electrolysis. ( 'oulomb.) It may be determined experimentally that one coulomb of electricity expended electrolytically will liberate .0000105 grammes of hydrogen. Therefore a current of one ampere, or one coulomb per second, will liberate .0000105 gramme of hydrogen per second. The number .0000105 is the electro- chemical equivalent of hydrogen. The electro-chemical equivalents of the other elements are obtained by multiplying tbe electro-chemical equiv- alent of hydrogen by the chemical equivalent of the sub- stance. Thus, the chemical equivalent of potassium is 39.1, therefore its electro-chemical equivalent is 39.1 x .0000105 = .00041055. By multiplying the strength of the current that passes by the electro-chemical equivalent of any substance., we obtain the weight of that substance liberated by electrolysis. The following Table of Electro-Chemical Equivalents is col^ lected from different authorities, mainly Hospitalier. 262 A DICTIONARY OF ELECTRICAL Electro- Chemical Eq uivalents. Names of Elements. 5 M 2 o < o a a' W '« o a .£3 O J! g- || £ So o> A V" 5 o ?> ° !§ 23 S2 O (D a a o— < £° • C] W o r a 1 i o n . — The < hange from the liquid to the vaporous state. Wet clothes exposed to the air are dried by the evapora- tion of the water. Evaporation is greater : (1) The more extended the surface exposed. (2) The higher the temperature of the air. (3) The dryer the air, or the smaller the quantity of vapor already in it. (4) The stronger the wind. (5) The smaller the pressure of the air. Fig, 1V5. 266 A DICTIONARY OF ELECTRICAL Evaporation, Electrification by Electrifica- tion resulting from the condensation of a mass of vapor. The free electricity of the atmosphere is believed by some to be due to the condensation of the vapor of the air that results in rain, hail, clouds, etc. It is probable, however, that the true effect of condensation is mainly limited to the increase of a feeble electrification already possessed by the air or its contained vapor. The small difference of potential of the exceedingly small drops of water in clouds, is enor- mously increased by the union or coalescing- of many thous- ands of such drops into a single rain drop. (See AtmospJieric Electricity.) Exchange, Telephonic System of —A com- bination of circuits, switches and other devices, by means of which any one of a number of subscribers connected with a telephonic circuit, or a neighboring telephonic circuit or cir- cuits, may be placed in electrical communication with any other subscriber connected with such circuit or circuits. A telephone exchange consists essentially of a multiple switch-board, or a number of multiple switch-boards, fur- nished with spring-jacks, annunciator drops, and suitable con- necting cords. A call bell, or bells, is also provided. The annunciator drops are often omitted. (See Board, Multiple Sivitch.) Excitability, Electric of tferve or Muscular Fibre. — The effect produced by an electric current in stimu- lating the nerve of a living animal or producing an involun- tary contraction of a muscle. Du Bois-Reymond has shown that these effects depend ; (1) On the strength of the current employed, and that they occur only when the current begins to flow, and when it ceases flowing, or, when the electrodes first touch the nerves, and when they are separated from it. Subsequent investiga- tion have shown that this is true only for the frogs nerves, WORDS, TERMS AND PHRASES. 267 and is true for the human nerves only in the case of moderate currents, strong' currents producing- tetanus. (2) On the rapidity with which the current used readies its maximum value, that is, on the rapidity of change of current density. (See Current Density.) Excitability, Faradic Muscular or nervous excitability following the employment of the rapidly intermitt- ent current produced by induction coils. (See Induction Coils.) Faradic excitability is different from galvanic excitability, produced by means of a continuous voltaic current. Excitation, Electro Muscular (See Electro M use u la r Excitation.) Exciter of Field. — In a separately excited dynamo- electric machine, the dynamo-electric machine, voltaic bat- tery, or other electric source employed to produce the field of the field magnets. (See Dynmuo-Electric Machines.) Execution, Electric Causing the death of a criminal, in cases of capital punishment, by means of the electric current. Electric execution has been adopted by the State of New York, in accordance with the following law : "The Court shall sentence the prisoner to death within a certain week, naming no day or hour, and not more than eight nor less than five weeks from the day of sentence. The execution must take place in the State prison to which con- victed felons are sent by the court, and the executioner must be the agent and warden of the prison."' "No newspaper may print any details of the execution, which is to be inflicted by electricity. A current of electricity is to be caused to pass through the body of the condemned of sufficient intensity to kill him, and the application is to be continued until he is dead." Exhaustion, or Prostration Electric— (See Sun Stroke, Electric.) 208 A DICTIONARY OF ELECTRICAL I x 1 1 . Million of Voltaic Cell.— The condition of a voltaic cell in which, on account of having all its active elec- trolyte decomposed, or its positive plate dissolved, it will furnish no difference of potential and therefore no current. An exhausted secondary cell is revivified or charged, by the passage through it of a charging current. A primary cell is revivified by the addition of fresh electro- lyte or battery liquid, or a new positive plate. Expansion, Electric The increase in vol- ume produced in a body on giving- such body an electric charge. A Leyden jar increases in volume when a charge is im- parted to it. This result is due to an expansion of the glass due to the electric charge. According to Quincke, some sub- stances, such as resinous or oily bodies, manifest a contrac- tion <>f volume on the reception of an electric charge. Expansion Join I*. — (See Joints, Expansion.) Explof iron filings on a sheet of paper held in a magnetic held. (.See Field. Magnetic.) Filament. — A slender thread or Jibre. The term is applied generally to threads or fibres varying considerably in diameter. 278 A DICTIONARY OF ELECTRICAL Filament of Incandescent Electric Lamp.— A term now generally applied to the incandescing- conductor of an incandescent electric lamp, whether the same be of very small cross section, or of comparatively large cross section. The term filament is properly applied to a conductor con- taining fibres or filaments extending in the general direction of the length of the incandescing conductor. Such a con- ductor is made of carbonizable fibrous material, cut or shaped prior to carbonization, so as to have the fibres extending with their greatest length in the direction of length of the filament. Filament, Magnetic — A chain or thread of magnetized particles. This is sometimes called a uniform magnetic filament. A bar-magnet possesses but two free poles, which when broken at its neutral point or equat or will develop free poles at the broken ends. This is explained by considering the magnet to be composed of a number of separate particles, separately magnetized. A single chain or filament of such particles is called a magnetic filament. (See Neutral Point of a Magnet. Magnetism, Hughes' Theory of.) Fire Alarm, Electric A system for telegraph- ically sending an alarm of fire from stations in different portions of a district to the engine houses. (See Alarm, Elec- tric, Fire.) Such alarms are automatic when the alarm is sounded by the completion of the circuits by means of a thermostat. (See Thermostat.) Fire Extinguisher, Electric A thermo- stat, or a mercury contact, which automatically completes the circuit and turns on a water supply for extinguishing a fire, on a certain predetermined increase of temperature. Fi§lies, Electric (See Animal Electricity. Eel, Electric.) WORDS, TERMS AND PHRASES. 27\) Flashing of Carbons, Process for the — A process for improving- the electrical uniformity of the carbon conductors employed in incandescent lighting, by the deposition of carbon in their pores, and over their surfaces at those places where the electric resistance is comparatively great. The carbon conductor is placed in a vessel usually filled with the vapor of a hydro-carbon liquid called rhigolene, or any other readily decomposable hydro-carbon liquid, and gradually raised to electrical incandescence by the passage through it of an electric current. A decomposition of the hydro-carbon vapor occurs, the carbon resulting therefrom being- deposited in and on the conductor. If the current is gradually increased, those parts of the conductor which are first rendered incandes- cent, that is in those parts where the resistance is the highest, and practically those parts only, receive the deposits of carbon. As the current gradually increases, other portions become successively incandescent and receive a deposit of carbon, until at last the filament glows with a uniform brilliancy, in- dicative of its electric homogeneity. A carbon whose resistance varies considerably at different parts could not be successfully employed in an incandescent lamp, since if heated by a current sufficiently great to render the points of comparatively small resistance satisfactorily in- candescent, the temperature of the points of high resistance would be such as to lower the life of the lamp, while if only those portions were safely heated, the lamp would not be economical. The flashing process is therefore of very great value in the manufacture of an incandescent lamp. Flashing of Dynamo Electric Machine.— A name given to long, flashing sparks at the commutator, usually due to the short circuiting- of the external circuit at the commu- tator. Floating Battery, De la Rive's A floating voltaic cell, the terminals of which are connected with a coil 280 A DICTIONARY OF ELECTRICAL of insulated wire, employed to show the attractions and re- pulsions between magnets and movable electric circuits. The cell, shown in Fig. 206, consists of a voltaic couple of zinc and copper, the terminals of which are connected to the circular coil of insulated wire, as shown, and the whole floated by means of a cork, in a vessel containing- dilute sulphuric acid. When the current flows through the coil in the direction shown by the arrows, the approach of the N-seeking pole of a magnet will cause the cell to be attracted or to move to- wards the magnet pole, since the south face or end of the coil is nearer the north pole of the magnet. If the other end were nearer, repulsion would occur, the cell turning around until the south face is nearer the magnet, when attraction oc- curs. Flow. — In hydraulics, the quantity of water or other fluid which escapes from an orifice in a containing vessel in a given time. Flow Fig. 206. Direction of Cm •ent- — The direc- tion the current is assumed to take, i. e., from the positive pole of the source through the circuit to the negative pole of the source. The electricity is assumed to come out of the source at its positive pole, and to return or flow back into the source at its negative pole. (See Current, Direction of.) Flow of Line* of Electrostatic Force. — A mathe- matical conception in which the phenomena of electricity are compared with the similar phenomena of heat. In heat no flow of heat occurs over isothermal surfaces, or surfaces at the same temperature. Over different isothermal WORDS, TERMS AND PHRASES. 281 surfaces the flow will vary with the power of heat conduc- tion. In electricity no flow occurs over equipotential sur- faces. Specific Inductive Capacity corresponds to heat con- ductivity, and the lines of force to the lines of heat conduction. (See Capacity, Specific Inductive.) FIuore§cence. — A property, possessed by certain solid or liquid substances of becoming self luminous while exposed to the light. Canary glass, or glass colored yellow by oxide of uranium, and a solution of sulphate of quinine, possess fluorescent prop- erties. The path of a pencil of light brought to a focus in either of these substances is rendered visible, by the particles lying in this path becoming self luminous. The path of a beam of light, entering the dusty air of a darkened chamber, is visible from the light being diffused or scattered in all directions by the floating dust particles. So in a tiuoreseent substance the path of the light is also ren- dered visible by the particles which lie in its path, throwing out light in all directions. There is, however, this difference, that in the case of the dust particles the light which conies directly from the beam is reflected, while in the case of the fluorescent body the light is from the particles themselves, which are set into vibrations by the light that is passing through, and has been absorbed by their mass. Fluorescence is, therefore, a variety of phosphorescence. (See Phosphorescence.) Flush Boxes. — A box or space, flush with the surface of a road bed, provided in a system of underground wires or conduits, to facilitate the introduction of the conductors into the conduit, or for the examination of the conductors. Flyer, Electrie Electric Fly, or Electric Re- action Wheel. — A wheel arranged so as to be set into rota- tion by the escape of convection streams from its points when placed on a charged conductor. 38S A DICTIONARY OF ELECTRICAL A wheel formed of light radial arms P, P, shaped as shown in Fig. 207, and capable of rotation on the vertical axis A, is set into rapid rotation when connected with the prime conduc- tor of a machine, through the convection streams of air parti- cles which are shot off from the points or extremities of the radial arm. The wheel is driven by the reaction of these streams in a direction opposite to that of their escape. (See Discharge, Convectivc.) Focus. — The point in front or back of a lens, or mirror, where the rays of light meet. (See Achromatic Lens.) Fog, Electric Dense fogs which occur on rare occasions when there is an unusual quantity of free electricity in the atmosphere. During these electric fogs the free electricity of the atmosphere changes its polarity at frequent intervals. Following Horns of Dynamo- Electric Machine. — (See Horns, Folio iv ing , of Dynamo- Electric Machine.) Foot Candle— (See Candle, Foot.) Foot-Found.— A unit of work. (See Work.) The amount of work required to raise one pound vertically through a distance of one foot. The same amonnt of work is done by raising one pound through a vertical distance of three feet, or three pounds through a vertical distance of one foot, viz., three foot- pounds. Apart from air friction, the amount of work done in raising one pound through one foot, viz., one foot-pound, is the same whether this work be done in one second, or in one clay. The power, however, or the rate of doing work is very different in the two cases. (See Power.) Fig. 207. AVORDS, TERMS AND PHRASES. 283 For another unit of work, see the Erg. Force. — Any cause which changes the condition of rest or motion of a body. Force, Centrifugal (See Centrifugal Force.) Force, Coercive or Cocrcif ive or Magnetic Retentivitv. — The power of resisting magnetization or de- magnitization. (See Coercive Force.) Force, Composition of (See Components.) Force, Electrostatic The force producing the attractions or repulsions of charged bodies. Force, Lines of Electrostatic (Sec Field, Fleetro-Stotic.) Force, Eincs of Magnetic (See Field, Mag- netic.) Force, Magnetic The force which causes the at- tractions or repulsions of magnet poles. (Sec Magnetic Force. ) Force, Resolution of —(See Resultants.) Force, Tubes of or Tubes of Induction.— Tubes bounded by lines of electrostatic or magnetic force. Lines of force never intersect one another. Hence a tube of force may be regarded as containing the same number of lines of force at any and every cross section. Tubes of electrostatic force always terminate against equal quantities of positive and negative electricity respectively. They terminate when they meet a conducting surface. The term tubes of force is somewhat misleading, since such so-called tubes are in general cones rather than tubes. Force, Unit of ■ or Dyne— A force, which acting for one second, on a mass of one gramme, will give it a ve- locity of one centimetre per second. (See Dyne.) Forces, Parallelogram of —A parallelogram constructed about the two lines that represent the direction and intensity with which two forces are simultaneously acting 284 A DICTIONARY OF ELECTRICAL on a body, in order to determine the direction and intensity of the resultant force with which it moves. If the two forces A C and A B, Fig. 208, simultaneously act in the direction of the arrows on a body at A, the direction and intensity of the resultant, A D, is determined by draw- ing D C and B D, parallel respectively to A B, and A C. The diagonal A D, of the parallelogram A C D B, thus pro- duced, gives this resultant. (See Components.) Forming Plates of Secondary or Storage Cells.— Obtaining a thick coating of lead monoxide on the plates of a storage cell, by repeatedly sending the charging current through the cell alternately in opposite directions. (See Storage of Electricity.) I D ^ Forninlie. — Mathematical expressions B f"" —~pfr f or S ome general rule or principle. ^s^ Formulae are of great assistance in ^^ science in expressing the relations wbicli A ' exist between certain forces or values, Fig. 208. am j ^ ne e ff ec t s t] ia t result from their oper- ation, since they enable us to express these relations in clear and concise forms. Thus, in the formulation of Ohm's law, E C = — , R we see that the current C, in any circuit is equal to the elec- tro-motive force E, divided by the resistance R. Again, we see that the current is directly proportional to the electro- motive force, and inversely proportional to the resistance. Formulae are usually written in the form of an equation, and therefore contain the sign of equality or =. Formulae, Photometric —(See Photometric Formulae.) Foucault Currents, Eddy Currents, Parasitical Currents, Local Action,— (See Currents, Eddy.) WORDS, TERMS AND PHRASES. 285 Fraiiklinie Electricity. — A term, sometimes employed in electro therapeutics, for the electricity produced by a fric- tional or an electrostatic induction machine. Free Charge, Free Electricity.— (.See Charge, Bound and Free.) Frictioiial Electricity. — Electricity produced by fric- tion. This term as formerly employed to indicate static charges as distinguished from currents, is gradually falling into dis- use, and the frictional electric machines, are being generally replaced by continuous induc- tion machines, like those of Holtz, Topler-Hdltz, orWims- hurst. Frog, Qalvanoscopic The hind legs of a re- cently killed frog, employed as an electroscope or galvano- scope by sending an electric current from the nerves to the muscles. (See Electro- scope. ) In 1786, Luigi Galvani, made the observation that when the Fig - ~ 09 - legs of a recently killed frog were touched by a metallic con- ductor connecting the nerves with the muscles, the legs were convulsed as though alive. He repeated this experiment, and found the movements were more pronounced when two dissimilar metals, such as iron and copper, were employed in the manner shown in Fig. 209. This classic experiment created intense excitement in the scientific world, and Galvani at first believed that he had dis- covered the true vital fluid of the animal, but afterwards 286 A DICTIONARY OF ELECTRICAL recognized it as electricity, which he believed to be obtained from the body of the animal. Volta, claimed that the move- ments were due to electricity caused by the contact of dissi- milar metals, and thus produced his famous voltaiepile. (See Pile, Voltaic.) Fulgurite. — A tube of vitrified sand, believed to be formed by a bolt of lightning-. The fulgurite consists of an irregular shaped tube of glass formed of sand which has been melted by the electric dis- charge. Fulminate.— The name of a class of highly explosive compounds. Fulminating gold, silver, and mercury, are highly explos- ive substances. Fulminates are employed on percussion caps. Functions, Trigonometric (See Trigonomet- ric Functions.) Fundamental Units. — (See Units, Fundamental.) Furnace, Electric A furnace in which heat, generated electrically, is employed for the purpose of effect- ing difficult fusions, for the extraction of metals from their ores, or for other metallurgical operations. In electric furnaces the heat is derived either from electric incandescence, or from the voltaic arc. The latter form is frequently adopted. The substance to be treated is exposed directly to the vol- taic arc. In some forms of furnace the crushed ore is per- mitted to fall through the arc, and the melted matter received in a suitable vessel, in which the separation of the substances so formed, is afterwards completed. In other forms of furnace, the ore is placed between two electrodes of carbon or other refractory substances, between which a powerful current is passed. In the Cowles furnace, when aluminium is reduced, molten copper forms an alloy with the aluminium as soon as it is separated. WORDS, TERMS AND PHRASES. 287 Very numerous applications of electricity to furnace opera- tions have boon made, for details of which, standard works should be consulted. Fuse, Electric A device for electrically igniting a charge of powder. Electric fuses are employed both in blasting operations and for firing cannon. Electric fuses are operated either by means of the direct spark, or by the incandescence of a thin wire, placed in the circuit. They are therefore either high tension, or low tension fuses. The advantages of an electric fuse consist in the fact that its use permits the simultaneous firing of a number of charges in a mining operation, thus obtaining a greater effect from the explosion. A fulminate of mercury is frequently employed in connection with some forms of electric fuses. A form of fuse in which the ignition is effected by the electric spark is shown in Fig. 210, and is known as Strathcnns fuse. The spark passes through a break A B, in the insulated leads D. Since gunpowder is not readily ignited by an electric spark, a peculiar priming material is em- ployed at A B, in the place of ordinary powder. Fu§c, Safety Safety Strip, or Safety Plug. — A strip, plate, or bar of lead or some readily fusible alloy, that automatically breaks Fi V- ~ 10 - the circuit in which it is placed on the passage of a current of sufficient power to fuse such strip, plate, or bar, when such current would endanger the safety of other parts of the circuit. Safety fuses are made of alloys of lead, and are placed in boxes, lined with non-combustible material, in order to pre- vent fires from the molten metal. Fig. 211, shows a fusible strip F, connected with leads L, L. Safet}' fuses are placed 288 A DICTIONARY OP ELECTRICAL on all branch circuits, and are made of sizes proportionate to the number of lamps they guard. Since incandescent lamps are generally connected with the circuit in multiple-arc, or in multiple-series, one or more of the circuits can be opened by the fusion of the plug with- out interfering with the continuity of the rest of the circuit. In series circuits, however, such as arc light circuits, when a lamp is cut out, a short circuit or path around it must be pro- vided to avoid the extinguishing of the rest of the lights. Fig. 211. Galvanic Battery — Two or more voltaic cells so ar- ranged as to form a single source. (See Battery, Voltaic.) Galvanic Cell.— (See Cell, Voltaic.) Galvanic Circle. — (See Circle, Galvanic.) Galvanic Circuit. — A term sometimes employed instead of the term voltaic circuit. The term galvanic in place of voltaic is unwarranted by the facts of electric science. ( See Circuit, Voltaic.) Gal vani thought he had discovered the vital fluid of animals . Volta first pointed out the true explanation of the phenomena observed in Galvani's frog, and devised the means for produc- ing electricity in this manner. The terms voltaic battery, cell, circuit, etc., are therefore preferable. WORDS, TERMS AND PHRASES. 289 Galvanic Polarization. — A term sometimes applied to the polarization of a voltaic cell. (See Polarization of Vol- taic Cell.) Galvanism. — A term sometimes employed to express the effects produced by voltaic electricity. Galvanization. — In electro therapeutics the effects pro- duced on nervous or muscular tissue by the passage of a voltaic current. In electro-metallurgy, the process of covering any con- ducting surface with a metallic coating by electrolytic de- position, such, for example, as the thin copper coating deposited on the carbon pencils or electrodes used in systems of arc lighting. This term is borrowed from the French, in which it has the above signification. It is preferably replaced by the term electro-plating. (See Electro-Plating.) It is never correctly applied to the process for covering iron with zinc or other metal by dipping the same in a bath of molten metal. Galvanized Iron.— Iron covered with a layer of zinc by dipping in a bath of molten zinc. The process of galvanizing iron is designed to prevent the corrosion or rusting of the iron on exposure to the air. (See Metals, Electrical Protection of.) Galvano-Canterj .— (See Cautery, Electric.) Galvano-Faradization.— In electro therapeutics the simultaneous excitation of a nerve or muscle by both a voltaic and a farad ic current. Galvanometer.— An apparatus for measuring the strength of an electric current by the deflection of a magnetic needle. The galvanometer depends for its operation on the fact that a conductor, through which an electric current is flowing, 290 A DICTIONARY OF ELECTRICAL will deflect a magnetic needle placed near it. This deflection is due to the magnetic field caused by the current. (See Field, Magnetic, of Current.) This action of the current was first discovered by Oer- sted. A wire conveying a current in the direction shown by the straight arrow, Fig. 212, or from -f to — , will deflect a magnetic needle in the direction shown by the curved arrows. Fi $>- m - If the wire be bent in the form of a hollow rectangle F D E G, Fig. 213, and the needle, M, be placed inside the circuit, the upper and lower branches of the current, will deflect the needle in the same direction, and the effect of the current will thus be multiplied. Mercury cups are provided at A, B and C, for a ready change in the direction of the circuit. (See Astatic Needle.) This principle of the multiplication of the deflecting power of the current was applied to galvanometers by Ftg - m - Schweigger, who used a number of turns of insulated wire for the greater deflection of the needle. He called such a device a multiplier. In extremely sensitive galvanometers very many turns of wire are employed, in some cases amounting to many thousands. Such galvanometers are of a high resist- WORDS, TERMS AND PHRASES. 291 a nee. Others, of low resistance, often consist of a single turn of wire and are used in the direct measurement of large currents. A Schweigger's multiplier or coil C C, of many turns of insulated wire, is shown in Fig. 214. The action of such a coil, on the needle M, is comparatively great, even when the current is small. In the case of any galvanometer, the needle when at rest, and no current is passing, should in general, occupy a posi- tion parallel to the length of the coil. On the passage of the c u r rent t h e needle tends to place itself in a position at right angles to the di- rection of the cur- rent, or to the length of the con- ducting wire in the coil. The strength of the current passing is Fig. 81U. determined hy observing the amount of this deflection as measured in degrees on a graduated circle over which the needle moves. The needle is deflected by the current from a position of rest, either in the earth's magnetic field, or in a field obtained from a permanent, or an electro magnet. In the first case, when in use to measure a current, the plane of the galvano- meter coils must coincide with the plane of the magnetic meri- dian. In the other case, the instrument may be used in any position in which the needle is free to move. Galvanometers assume a variety of forms according either to the purposes for which they are employed, or to the manner in winch their deflections are valued. Galvanometer, Absolute A galvanometer with an absolute calibration. (See Calibration, Absolute.) 292 A DICTIONARY OF ELECTRICAL Such a galvanometer is called absolute because if the dimen- sions of its coil and needle are known, the current can be de- termined directly from the observed deflection of the needle. Galvanometer, Aperiodic (See Galvanometer, Dead Beat.) Galvanometer, Astatic A galvanome- ter, the noedle of which is astatic. (See Astatic Needle.) Nobili's astatic galvanometer is shown in Fig. 215. The astatic needle, suspended by a fibre b, has its lower needle placed inside a coil «, consisting of many turns of insulated wire, its upper needle moving over the graduated dial. The current to be measured is led into and from the coil at the binding posts x and y. In this instrument, if small de- flections only are employed, the deflections are sensibly proportion- al to the strength of the deflecting ^ currents. Galvanometer, Ballistic A galvanometer Fi '9- 215 - designed to measure the strength of currents that last but for a moment, such for example, as the current caused by the discharge of a condenser. The quantity of electricity passing in any circuit is equal to the product of the current and the time Since the cur- rent caused by the discharge of a condenser lasts but for a small time, during which it passes rapidly from zero to a maximum and back again to zero, the magnetic needle in a ballistic galvanometer takes the form of a ballistic pendulum, i. e., it is given such a mass, and acquires such a slow mo- tion, that its change of position does not practically begin until the impulses have ceased to act. "WORDS, TERMS AND PHRASES. 293 In the ballistic galvanometer of Siemens and Halske, the coils R, R, Fig. 216, have a bell-shaped magnet M, suspended Fig. 316. inside them by means of an aluminium wire. The magnet is 294 A DICTIONARY OF ELECTRICAL provided with a mirror S, for measuring the deflections. The bell-shaped magnet is shown in elevation at M, and in plan at n, s. In using the ballistic galvanometer it is necessary to see that the needle is absolutely at rest before the discharge is sent through the coils. Galvanometer, Dead Beat A galvanometer, the needle of which comes quickly to rest, instead of swinging re- peatedly to and fro. (See Damping.) Galvano meter, Differential A galvanometer con- taining two coils so wound as to tend to de- flect the needle in op- posite directions. The needle of a differ- e n t i a 1 galvanometer shows no deflection when two equal cur- rents are sent through the coils in opposite directions, since, under these conditions each coil neutralizes the other's effects. Such instruments may be used in comparing re- sistances. The Wheatstone Bridge, however, in most cases, affords a preferable method for such purposes. (See Balance, Wheatstone'' s.) A form of differential galvanometer is shown in Fig. 217. WORDS, TERMS AND PHRASES. 295 Sometimes the current is sent through the two coils so that each coil deflects the needle in the same direction. In this case, the instrument is no longer differential in action. If the magnetic needle, in such cases, is suspended at the exact centre of the line which joins the centres of the coils, the advantage is gained of obtaining a field of more nearly uni- form intensity around the needle. Galvanometer, Figure of Merit of —(See Figure of Merit of Galvanometer.) Galvanometer, Marine A galvanometer devised by Sir Wm. Thomson for use on steamships where the motion of magnetized masses of iron would seriously dis- turb the needles of ordinary instruments. Fig. 218. The needle of the marine galvanometer is shielded or cut off from the extraneous fields so produced, by the use of a magnetic screen or shield, consisting of an iron box with thick sides, inside of which the instrument is placed. The needle is suspended by means of a silk fibre attached both above and below, and passing through the centre of gravity of the needle. In this manner the oscillations of the ship do not affect the needle. 296 A DICTIONARY OF ELECTRICAL Galvanometer, Mirror A galvanometer in which, instead of reading the deflections of the needle directly by its movement over a graduated circle, they are read by the movements of a spot of light reflected from a mirror attached to the needle. This spot of light moves over a graduated scale, or its movements are observed by means of a telescope. A form of mirror galvanometer designed by Sir Wm. Thomson, is shown in Fig. 218. The needle is attached directly to the back of a light, sil- vered glass mirror, and consists of several small magnets made of pieces of a watch spring. The needle and mir- ror are suspended by a single silk fibre and are placed inside the coil. A com- pensating magnet N S, movable on a vertical axis, is used to vary the sen- sitiveness of the instrument. The lamp L, placed back of a slot in a wide screen, throws a pencil of light on the mirror Q, from which it is reflected to the scale K. Galvanometer Shunt.— A shunt Fig. 219. placed around a sensitive galvanometer for the purpose of protecting it from the effects of a strong current, or for altering its sensibility. (See Shunt.) The current which will flow through the shunt wire depends on the relative resistance of the galvanometer and of the shunt. In order that only T V, x£o or nn> o of tne total current shall pass through the galvanometer, it is necessary that the re- sistances of the shunt shall be the |, -^ or ¥ £ F of the galvanome- ter resistance. Fig. 219, show r s a shunt, in which the resistances, as com- pared with that of the galvanometer are those above referred to. The galvanometer terminals are connected at N N. Plug WORDS, TERMS AND PHRASES. 297 keys are used to connect one or another of the shunts into the circuit. (See Multijrfying Poiver of Shunt.) Galvanometer, Sine A galvanometer in which a vertical coil is movable around a vertical axis, so that it can be made to follow the magnetic needle in its deflections. Fig. 320. In the sine galvanometer the coil is moved so as to follow the needle, until it is parallel with the coil. Under these cir- cumstances the strength of the deflecting currents in any two different cases is proportional to the sine of the angle of de- flection. 298 A DICTIONARY OF ELECTRICAL A form of sine galvanometer is shown in Fig. 220. The vertical wire coil is seen at M. A needle, of any length less than the diameter of the coil M, moves over the graduated circle N. The coil M, is movable over the graduated horizontal circle H, by which the amount of the movement necessary to bring the needle to zero is measured. The current strength is proportional to the sine of the angle measured on this circle, through which it is necessary to move the coil M from its position when the needle is at rest in the plane of the earth's magnetic meridian, until the needle is not further deflected by the current, although parallel to the coil M. Galvanometer, Tangent An instrument in which the deflecting coil consists of a coil of wire within which is placed a needle very short in pro- portion to the diameter of the coil, and supported at the centre of the coil. A galvanometer acts as a tan- gent galvanometer only when the needle is very small as compared with the diameter of the coil. The length of the needle should be less than one-twelfth the diameter of the coil. Fig. m. A form of tangent galvanometer is shown in Fig. 221. The needle is supported at the exact centre of the coil C. Under these circumstances the strengths of two different de- flecting currents are proportional to the tangents of the angles of deflection. Tangent galvanometers are sometimes made with coils of wire containing many separate turns. Galvanometer, Tangent, — Ohach's.— A form of galvanometer in which the deflecting coil, instead of being in a fixed vertical position, is movable about a horizontal "WORDS, TERMS AND PHRASES. 299 axis, so as to decrease the delicacy of the instrument, and thus increase its range of work. Galvanometer, Torsion A galvanometer in which the strength of the deflecting current is measured by the torsion exerted on the suspension system. A bell-shaped magnet, shown at the right of Fig. 222, is suspended by a thread and a spiral spring between two coils of high resistance, placed parallel to each other in the positions shown. On the deflection of the magnet, by the cur- rent to be measured, the strength of the current is determined by the amount of the torsion required to bring the m a g n e t back to its zero point. The angle of torsion is measured on the horizontal scale at the top of the instrument. In the torsion gal- vanometer, unlike the electro-dynamometer, the action between the coils and the movable magnet is as the cur- rent strength causing the deflection. In the electro dynamometer, Fig. 222. such an increase in the deflecting coil produces a corresponding- increase in the deflected coil ; the mutual action of the two is as the square of the current strength causing the deflection. Galvanometer, Vertical A galvanometer, the needle of which is capable of motion in a vertical plane only. 300 A DICTIONARY OF ELECTRICAL In the vertical galvanometer the north pole is weighted so that the needle assumes a vertical position when no current is passing. In the form shown, in Fig. 223, two needles are some- times employed, one of which is placed inside the coils C, C. The vertical galvanometer is not as sensitive as the ordinary forms. It is employed, however, in various forms for an electric current indicator or even for a rough current measurer. Galvanometer, Volt-Meter ■ — An instrument devised by Sir Wm. Thomson, for the measurement of differ- ences of electric potential. This instrument is so arranged that by a simple correction for the varying strength of the earth's field in any place, the results are read at once in volts. A coil of insulated wire, shown at A, Fig. 224, has a resist- ance of over 5,000 ohms. A magnetic needle, formed of short parallel needles placed above one another and called a magnetome- ter needle, is attached to a long but light aluminium index, moving over a grad- uated scale. A mov- Fig- MS- able, semi-circular magnet B, called the restoring magnet, is placed over the needle, and is used for varying the effect of the earth's field WORDS, TERMS AND PHRASES. 301 at any point. The sensitiveness of the instrument may be varied either by the restoring- magnet, or by sliding the mag- netometer box nearer to, or further away from the coil. The volt-meter galvanometer depends for its operation on the fact that when a galvanometer of sufficiently high resistance is introduced between any two points in a circuit, the current that passes through it, and hence the deflection of its needle, is directly proportional to the difference of potential between such two points. Galvanometers for the commercial measurement of cur- rents assume a variety of forms. They are generally so con- structed as to read off the amperes, volts, ohms, watts, etc., directly. They are called amperemeters or ammeters, volt- meters, ohmmeters, wattmeters, etc. For their fuller descrip- tion reference should be had to standard electrical works. Fig. 22k. Galvano-Plastics.— A term formerly employed to ex- press electrotyping or electro-metallurgical processes, but now generally abandoned. (See Electro- Met all urgy .) Galvaiio-Puncture. — In electro therapeutics the treat- ment of diseased parts of the body by the introduction therein of electrolytic needles. (See Electro-Puncture.) Galvanoscopic Frog.— (See Frog, Galvanoscopic.) Ga§-Battery.— A battery in which the elements consumed are gases as distinguished from solids. 302 A DICTIONARY OF ELECTRICAL The electrodes of a gas battery generally consist of plates of platinum, or other solid substance which possesses the power of occluding oxygen and hydrogen, the lower parts of which plates dip into dilute sulphuric acid, and the upper parts are respectively surrounded by oxygen and hydrogen gas derived from the electrolytic decomposition of the dilute acid. Fig. 225. A gas battery consisting of plates of platinum dipping below into acid liquid, and surrounded in the space above the liquid by hydrogen and oxygen H, H' and O, O', etc., respect- ively, is shown in Fig. 225. In charging this battery an electric current is sent through it until a certain quantity of the gases has been produced. If, then the charging current be discontinued, a current in the opposite direction is produced by the battery. The gas battery is in reality a variety of storage battery. (See Storage of Electricity. Storage Cells.) Gas batteries can also be made by feeding continually a gas capable of acting on the positive elements. Gas Burner, Automatic matic.) — (See Burner, Auto- WORDS, TERMS AND PHRASES. 303 Gas Jet Photometer. — A photometer for determining the intensity of gas light by measuring- the length of the gas jet producing the light when burning under certain circum- stances. Gas Lighting, Electric Various devices employed for the simultaneous electric ignition of a number of gas jets from a distance. Such devices are operated by moans of minute electric sparks which are caused to pass through the escaping- gas jets. The spark for this purpose is obtained either by means of the extra current from a, spark coil, by means of an induc- tion coil or by static discharges. (See Extra Current. Sj)ark Coil. Induction Coil.) Gases, Oeelusion of (See Occlusion of Gases,) Gastroseopc. — An electric apparatus for the illumination and Inspection of the human stomach. The light is obtained by means of a platinum spiral in a glass tube surrounded by a layer of water to prevent undue heating - . The platinum spiral is placed at the extremities of a tube, provided with prisms, and passed into the stomach of the patient. A separate tube for the supply of air for theextensior of the stomach is also provided. Gauge, Electrometer A device employed in connection with some of Sir Wm. Thomson's electrometers to ascertain whether the needle connected with the layer of acid that acts as the inner coating of the Leyden jar used in con- nection therewith, is at its normal potential. The gauge consists, as shown in Fig. 226, of an attracted disc electrometer. The attracted disc is shown above in the cover plate at S, and the attracting disc at B, insulated by rod A, but electrically connected by the wire C to the sulphuric acid in the Leyden jar. Gauge, Wire (See Wire Gauge.) Gauss. — The unit of intensity of magnetic field. 304 A DICTIONARY OF ELECTRICAL The term gauss for unit of intensity of magnetic field was proposed by S. P. Thompson as being that of a field whose in- tensity is equal to 10 8 C. G. S. units. J. A. Fleming pro- poses for the value of the gauss such a strength of field as would develop an electro-motive force of one volt, in a wire one million centimetres in length, moving through such a field with unit velocity. Fleming's value for the gauss was assumed on account of the small value of the gauss proposed by S. P. Thompson. It is 100 times greater in value than Thompson's gauss. Sir Wm. Thomson proposes for the value of the gauss such an intensity of magetic field as is produced by a current of one (ampere) weber at the distance of one centimetre. Fig. gse. Geissler Tubes. — Vacuum tubes of glass, provided with platinum electrodes which are passed through and fused into the glass, and designed to show the various luminous effects of electric discharges through comparatively low vacua. Geissler tubes are made of a great variety of shapes, and often include tubes, spirals, spheres, etc,, within other tubes. These inclosed tubes are made either of ordinary glass, or of uranium glass in order to obtain the effects of fluor- escence, or some of the inclosed tubes are filled with fluor- escent liquids. WORDS, TERMS AND PHRASES. 305 The vacuum in Geissler tubes is by no means what might be called a high vacuum. Indeed, if the exhaustion of the tube be pushed too far, much of the brilliancy of the luminous effects are lost. Two of the many forms of Geissler tubes is shown in Fig. 227. Generator, Dynamo-Elect ric An appa- ratus in which electricity is produced by the mechanical move- ment of conductors in a magnetic field so as to cut the lines of force. A dynamo-electric machine. (See Dynamo-Electric Ma- chine. ) Generator, Pyro-Hagnctic An appara- tus in which electricity is produced by the combined action of heat and magnetism. (See Pyro-Magnetic Generator.) Fig. 227. Generator, Secondary (See Secondary Gene- rator.) Geographical Equator. (See Equator, Geographical.) Geographical Meridian. (See Meridian, Geograph- ical.) Gilding, Electric The electrolytic deposition of gold on any object. The object to be gilded is rendered a conductor on its sur- face and connected to the negative terminal of a voltaic cell or other source, and immersed in a plating bath containing a so- 306 A DICTIONARY OF ELECTRICAL lutionof a salt of gold, opposite a plate of gold connected with the positive terminal of the source. The objects to be plated thus becomes the kathode, and the plate of gold the anode of the plating bath. On the passage of the current, the gold is dissolved from the plate at the anode and deposited on the ob- ject at the kathode. (See Kathode. Anode.) Gimbals. — Concentric rings of brass, suspended on pivots in a compass box, and on which the compass card is supported so as to enable it to remain horizontal notwithstanding the movements of the ship. (See Azimuth Compass.) Each ring is suspended on two pivots which are directly opposite each other, that is, at the ends of a diameter, but this diameter in one ring is at right angles to that in the other. Fig. 228. Globular Lig lit iiinj;.— A variety of lightning in which the electricity appears in the form of a ball or globe which floats quietly about, and at last explodes with a loud detonation. Its cause is but little understood. The actual existence of these balls or globes is doubted by some, who regard them as optical effects produced by the per- sistence of the optical impression of a discharge. Glow Discharge. (See Discharge, Conveetive.) Gold Bath. (See Baths, Gold, etc.) Gold-Leaf Electroscope. — An electroscope in which two leaves of gold are used to detect the presence of an electric charge, or to determine its character whether positive or ne- gative. When a charge is imparted to the knob C, Fig. 228, the WORDS, TERMS AND PHRASES. 307 gold leaves n, n, diverge. This will occur whether the charge be positive or negative. To determine the polarity of an unknown charge, the leaves are first caused to diverge by means of a known positive or negative charge. The unknown charge is then given to the leaves. If they diverge still further, then the charge is of the same name as that originally possessed by the leaves. If, however, they first move together and are then repelled, the charge is of the opposite name. Governor, Centrifugal (See Centrifugal Gov- ernor.) Governor, Electric Steam A device used in connection with a valve to so electrically regulate the supply of steam to an engine, that the engine shall be driven at such a speed as will maintain either a constant current or a constant potential. In the electric governor the steam valve is operated by an electro magnet, whose coils, in the case of a constant current machine, are of thick wire and are in the main circuit, and in that of a constant potential machine are of thin wire and are in a shunt around the mains. Governors, Electric ■ Devices for electrically controlling the speed of a steam engine, the direction of cur- rent in a plating bath, the speed of an electric motor, the re- sistance of an electric circuit, the flow of water or gas into or from a vessel, or for other similar purposes. The particular form assumed by the apparatus varies with the character of the work it is intended to accomplish. In some cases ordinary ball centrifugal governors are employed to open or close a circuit ; or, a mass of mercury in a rotating vessel is caused at a certain speed to open or close a circuit ; or, the resistance of a bundle of carbon discs is caused to vary, either by pressure produced by centrifugal force; or by the movement of an armature. 308 A DICTIONARY OF ELECTRICAL Gramme.— A weight equal to 15.43235 grains. (See Metric System of Weights and Measures.) Gramme Atom.— (See Atom, Gramme.) Gramme Moleenlc.— (See Molecule, Gramme.) * Gramophone— An apparatus for the recording and re- production of articulate speech. (See Phonograph.) Graphite. — A soft variety of carbon suitable for writing on paper or similar surfaces. Graphite is the material that is employed for the so-called black lead of lead pencils. It is sometimes called plumbago. Strictly speaking the term graphite is only applicable to the variety of plumbago suitable for use in lead pencils. Graphite is used for rendering surfaces to be plated electric- ally conducting, and also for the brushes of dynamos and motors. Graphophone. — An apparatus for the recording and re- production of articulate speech. (See Phonograph.) Gravitation. — A name applied to the force which causes masses of matter to tend to move towards each other. This motion is assumed to be that of attraction, that is, the bodies are assumed to be drawn together. It is not impos- sible, however, that they may be pushed together. Gravitation, like electricity, is well known, so far as its effects are concerned ; but, as to the true cause of either, par- ticularly the former, we are in comparative ignorance. The general facts of gravitation may be succinctly stated by the following law : Every particle of matter in the universe is attracted by every other particle of matter, and itself attracts every other particle of matter, with a force which is directly proportional to the product of the masses of the two quantities of matter and inversely proportional to the square of the distance between them. WORDS, TERMS AND PHRASES. 309 -The centre of weight of a Gravity, Centre of - body. Bodies supported at their centres of gravity are in equili- brium, since their weight is then evenly distributed around the point of support. Greiict's Voltaic Cell.— {Cell, Voltaic.) Grid. — A lead plate in the form of a gridiron, i. e., pro- vided with perforations, _, and employed in storage cells for the support of the active material. (See Secondary Cells.) Grotliiiss' Hypo- thesis. — A hypothesis devised by Grothuss to account for the electroly- tic phenomena that occur on closing the circuit of a voltaic cell. T h i s hypothesis as- sumes (1) That before the cir- cuit is closed, the mole- cules of the electrolyte are arranged in an ir- regular or unpolarized condition, asrepresented in Fig. 229. These molecules are shaded, as shown in Fig. 230, to indicate their composition and polarity. (2) When the circuit is closed, and a current begins to pass, a polariza- tion of the electrolyte, as shown at (2), Fig. 230. ensues, whereby all the negative ends of the molecules of hydrogen sulphate, or sulphuric acid r are turned towards the positive, or the zinc plate, and Fig. 229. 310 A DICTIONARY OF ELECTRICAL the positive ends, towards the negative, or the copper plate. This, as will be seen, will turn the S0 4 ends toward the zinc, and the H 2 ends towards the copper. (3) A decomposition of the polarized chain whereby the S0 4 unites with the zinc, forming Zn S0 4 , and the H 2 liberated reunites with the S0 4 of the molecule next to it in the chain, and its liberated H 2 with the one next to it, until the last liberated H 2 is given off at the surface of the copper or negative plate. This leaves the chain of molecules as shown at (3). (4) A semi-rotation of the molecules of the chain as at (3), until they assume the position shown at (4). This rotation is required since the molecules in (3) are turned with their similar poles towards similarly charged battery plates. Ground or Earth-Grounded Wire.— The earth or ground which forms part of the return path of an electric cir- cuit. A circuit is grounded when it is completed in part by the ground or earth. Grounded Circuit.— (See Circuit, Grounded.) Grove's Voltaic Cell.— (See Cell, Voltaic.) Giltta-Perclia. — A resinous gum obtained from a tropical tree, and valuable electrically for its high insulating powers. Gutta-percha readily softens by heat, but on cooling be- comes quite hard and tough. Unlike india rubber, it possesses but little elasticity. Its specific inductive capacity is 4.2, that of air being 1, and of vulcanized india rubber 2.94. (See Capacity, Specific Inductive.) Gym no tu* Electricus.— The electric eel. (See Eel, Elec- tric.) Hail, Assumed Electric Origin of — A hypothesis, now generally rejected, framed to explain the origin of the alternate layers of ice and snow in a hail stone, WORDS, TERMS AND PHRASES. 311 by the alternate electric attractions and repulsions of the stones between neighboring-, oppositely charged, snow and rain clouds. It is now generally recognized that the electric manifesta- tions attending hail storms, are the effects and not the causes of the hail. (See Paragrelcs.) Hair, Electrolytic Removal of The per- manent removal of hair by the electrolytic destruction of the hair follicles. A negative platinum electrode is inserted in the hair follicle and the positive electrode, covered with moist sponge or cotton, is held in the hand of the patient. A current of two to four milliamperes from a battery of from eight to ten Leclanche elements is then passed for from ten to thirty sec- onds. A few bubbles of gas appear, and the hairs are then removed from the follicle by a pair of forceps. (See Milliam- p&res.) When the work is properly done there is no destruction of the skin and therefore no marks or scars. In the removal of hair from the face, it is preferable that the current should slowly reach its maximum strength. Hall EfTeet.— (See Effect, Hall.) Hanger-Board of Electric Lamp.— A board furnished with a hand switch and hooks for connecting it with a circuit, and provided with means for readily placing an arc lamp in the circuit. The lamp is connected by the mere act of hanging it in position, though binding posts are generally connected with the board, for the purpose of more thoroughly connecting the lamp terminals with the circuit. Hanger, Cable or Clip.— (See Cable Clip.) Harmonic Receiver. — (See Receiver, Harmonic.) Harmonic Telegraphy. — (See Telegraphy, Harmonic.) Head Eight, Locomotive Electric An 312 A DICTIONARY OF ELECTRICAL electric light placed in the focus of a parabolic reflector in front of a locomotive engine. (See Light House Illumina- tion.) Heat. — A form of energy. The phenomena of heat are due to a vibratory motion im- pressed on matter by the action of some form of energy. Heat in a body is due to the vibrations or oscillations of its molecules. Heat is transmitted through space by means of a wave motion in the universal ether. This wave motion is the same as that causing light. A hot body loses its heat by producing a wave-motion in the surrounding ether. This process is called radiation. Radiant Energy, or energy transmitted by means of ether waves, is of two kinds, viz. : (1) Obscure Heat, or heat, which does not affect the eye, although it can impress a photographic image on a sufficiently sensitive photographic plate. (2) Luminous Heat, or heat which accompanies light. Heat is conducted, or transmitted through bodies, with different degrees of readiness. Some bodies are good conductors of heat, others are poor conductors. Heat is transmitted through the mass of liquids by means of currents occasioned by differences in density caused by differ- ences of temperature. These currents are called convection currents. Heat is measured as to its relative degree of intensity by the thermometer. It is measured as to its amount or quantity by the calorimeter. (See Thermometer. Calorimeter.) The heat unit is the calorie, or the amount of heat required to raise one gramme of water one degree centigrade. Another heat unit, very generally employed in the United States and England, is the quantity of heat required to raise one pound of water 1° Fahrenheit. (See Calorie, Heat Unit, English. Joule. Volt- Coulomb.) WORDS, TERMS AND PHRASES. 313 Heat, Absorption and Generation of in Voltaic Cells. — The heat effects which attend the action of a voltaic cell. The chemical solution of the positive plate or element of a voltaic cell, like all cases of chemical combination, is attended by a development of heat. "When, however, the circuit of the cell is closed, the energy liberated during the chemical combination, appears as elec- tricity, which develops heat in all parts of the circuit. (See Heat, Electric. Cell, Voltaic.) Heat, Atomic A constant product obtained by multiplying the specific heat of an elementary substance by its atomic weight. (See Atomic Weight.) The product of the specific heat of all elementary substances by their atomic weights is nearly the same. This product is called the atomic heat, and is about equal to C.4. If, therefore, a number of grammes of any substance, such for example as chlorine, be taken numerically equal to its atomic weight, viz., 35.5, this number, called the gramme atom of chlorine, will represent the number of small calories of heat required to raise one gramme-atom of such substance through 1° C. (See Calorie.) Heat, Electric The heat developed by the pass- age of the electric current through any conductor. Heat is developed by the passage of the current through any conductor, no matter what its resistance may be. If the conductor is of considerable length, and of good con- ducting power, the heat developed is not very sensible since it is spread over a considerable area, and is rapidly lost by radiation. (See Heat.) H, the heat generated in any conductor of a resistance R, by the passage through it of an electric current C, is equal to H = C 2 R, in watts. But one watt = .24: small calorie per second. H =°'(i) 314 A DICTIONARY OF ELECTRICAL Therefore, the heat which is generated, H=C 2 Rx .24 calories per second. For the case of a uniform wire of circular cross section the resistance R, in ohms, is directly proportional to the length 7, and inversely proportional to, the area of cross section 7tr 2 , or 7 R = ; that is, 7TV 2 , ' nr The temperature to which a wire of a given resistance is raised, will of course vary with the mass of the wire, its radia- ting surface, and its specific heat capacity. If the same num- ber of heat calories are generated in a small weight of a conduc- tor, whose radiating surface is small, the resulting temperature will of course be far higher than if generated in a larger mass provided with a much greater radiating surface. In general, however, its temperature increases as the square of the current strength, and as the resistance of the wire per unit of length is greater. The temperature a wire acquires by the passage of a current through it varies with the third power of the radius. If two wires of the same material have the same lengths, but differ- ent radii, the temperature acquired by the passage of an elec- tric current wiH. depend on the heat developed per second less that radiated per second. Since the former varies as 1 — , and the latter as r, that is, as 7 x 27tr, the temperature r 2 1 1 attained varies as — , and not as — , as frequently stated. {Larden.) The current required to raise the temperature of a bare copper wire a given number of degrees above the tempera- ture of the air is given in the following table WORDS, TERMS AND PHRASES. 315 Bare Copper Wires, Current required to increase the temperature of a copper wire t° centigrade above the surrounding air, the copper wire being bright polished, or blackened. Diameter in Centimetres CURRENT IN AMPERES. (thousanths of an inch.) t. = L°c. t. = 9° c. t. = 25° c. t. = 49° c. t. = 81° c. Cm. Mills. Brght Black Brght Black Brght Black Brght Black' Brght Black .1 40 1.0 1.4 3.0 4.1 4.8 6.6 6.5 8.9 7.9 11.0 .2 80 2.8 3.9 8.3 11.5 13.5 18.7 18.3 25.3 22.4 31.0 .3 120 5.2 7.2 15.3 21.2 24.9 34.4 33.5 46.4 41.2 57.0 .4 160 8.0 11.0 23.6 32.7 38.3 53.0 51.7 71.5 63.4 87.8 .5 200 11.1 15.4 33.0 45.7 53.5 74.1 72.2 99.9 88.6 123 .6 240 14.6 20.3 43.4 60.0 70.3 97.4 94.9 131 116 161 .; 280 18.5 25.6 54.6 75.6 88.7 123 119 165 147 203 .8 310 22.6 31.2 66.7 92.4 108 150 146 202 179 248 .9 350 26.9 37.3 79.6 110 129 179 T74 241 214 296 1.0 390 31.5 43.6 93.3 129 151 210 304 283 251 347 2.0 790 89.2 123 264 365 428 593 577 799 709 981 3.0 1180 164 227 485 671 787 1090 1061 1468 1303 1805 4.0 1570 252 349 746 1035 1211 1675 1633 2260 2006 2776 5.0 1970 353 488 1043 1441 1692 2343 2283 3160 2802 3880 6.0 2360 463 642 1371 1898 2225 3080 3000 4154 3685 5100 7.0 2760 584 808 1728 2392 2803 3882 3781 5233 4642 6426 8.0 3150 714 988 2110 2922 3422 4741 4620 6396 5671 7850 9.0 3540 851 1178 2519 3186 4088 5659 5511 7630 6769 9370 10.0 3940 997 1380 2950 4084 4788 6626 6425 8935 7926 10973 34.4 70000 (Forbes.) 316 A DICTIONARY OF ELECTRICAL Heat, Molecular The number of calories of heat required to raise the temperature of one gramme-molecule of any substance 1° C. (See Heat, Atomic.) Heat, Specific The capacity of a substance for heat as compared with the capacity of an equal quantity of water for heat. Different amounts or quantities of heat are required to raise the temperature of a given weight of different substances through one degree. The specific- heats of substances are generally compared with water or with hydrogen, the capa- city of these substances for heat being very great. The specific heat of all elementary atoms is the same. For example, the heat energy of an atom of hydrogen is equal to that of an atom of oxygen, but since the latter weighs sixteen times as much, a given mass of hydrogen contains sixteen times as many atoms as an equal mass of oxygen ; therefore, when compared weight for weight, hydrogen lias a specific heat sixteen times greater than that of oxygen. Or, in general, comparing equal iveights, the specific heat of an elementary substance is inversely proportional to its atomic ivcight. (See Calorimeter.) Heat, Specific of Electricity.— (See Specific Heat of Electricity.) Heat Unit, English, or British Thermal Unit.— The quantity of heat required to raise the temj>erature of one pound of water 1° F. This heat unit represents an amount of work equivalent to 772 foot-pounds. (See Mechanical Equivalent of Heat.) 1 Foot Pound = 13,562,600 Ergs. (See Erg.) Heat Unit, or Calorie. — The quantity of heat required to raise the temperature of one gramme of water 1° C. The calorie is sometimes taken as the amount of heat re- quired to raise the temperature of 1,000 grammes of water 1° C. These are termed, respectively, the Small Calorie and the Large Calorie. (See Calorie.) WORDS, TERMS AND PHRASES. 317 Heat Unit, or Joule. — The quantity of heat developed by the passage of a current of one ampere through a resis- tance of one ohm. (See Joule.) 1 Joule = .24 Calorie. 1 Foot Pound = 1.356 Joule. Heater, Electric A device for the conversion of electricity into heat for the purposes of artificial heating-. Electric heaters consist essentially of coils or circuits of some refractory substance of high resistance, through which the current is passed. These coils or circuits are surrounded by air or finely divided solids, and placed inside metallic boxes, or radiators, which throw oil' or radiate the heat produced. When employed for the heating of liquids the coils are placed directly in the liquid to be heated, or are surrounded by radiating boxes that are placed in the liquid. Heating Effects of Currents.— (See Heat, Electric. Calorimeter, Electric. Joule's Laws.) Hecto (as a prefix.) — One hundred times. Helices, Sinistrorsal and Dcxlrorsal Coils of wire so wrapped or wound that when traversed b}^ an elec- tric current they acquire all the properties of magnets. (See Solenoids, Sinistrorsal and Dextrorsal.) Heliograph, — An instrument for telegraphic communica- tion bj r means of flashes of light, which represent the dots and dashes of the Morse alphabet, or the movements of the needle of the needle telegraph to the right or left. (See Alphabet Telegraphic.) The flashes of light are thrown from the surface of a plane mirror. Motions to the right or left may be used to distinguish between the dots and dashes, or the same purpose may be effected by the relative durations of the flashes of light, or by the intervals between successive flashes. Similar telegraphic communication has been carried on be- tween steamers during foggy weather by means of their fog horns, or between locomotives, by their steam whistles. 318 A DICTIONARY OF ELECTRICAL Herinel ical Seal.— Such a sealing of a vessel, designed to hold a vacuum, or gaseous atmosphere under pressures greater or less than that of the atmosphere, as will prevent either the entrance of the external atmosphere into the vessel, or the escape of the contained gas into the atmosphere. Hermetical sealing may he accomplished either by the use of suitable cements, or by the direct fusion of the walls of the containing vessel. Heterostatic.— A term applied by Sir William Thomson to an electrometer in which the electrification is measured by determining the attraction exerted by the charge to be measured and that of an opposite charge imparted to the instru- ment by a source independent of the charge to be measured. This term distinguishes this electrometer from an idiostatic instrument, or one in which the measurement is effected by determining the repulsion between the charge to be measured and that of a charge of the same sign imparted to the instru- ment from an independent source. (See Electrometer.) Hicks 9 Automatic Button Repeater.— (See Re- peater, Telegraphic). Holders for Brushes of Dynamo Electric Ma- chines. — A device for holding the collecting brushes of a dynamo-electric machine. (See Dynamo-Electric Machines.) Holders for Carbons of Arc Lamp.— (See Lamp, Electric Arc.) Holders for Safety Fuse.— (See Fuse, Safety.) Hood for Electric Lamp.— A hood provided for the double purpose of protecting the body of an electric lamp from rain or sun, and for throwing its light in a general d o wnward direction. Hoods for arc lamps are generally conical in shape. Horizontal Component of Magnetism. (See Com- ponent, Horizontal, of Earth's Magnetism.) WORDS, TERMS AND PHRASES. 319 Horns, Following and namo-Electric Machines. - Leading, — ■The ed^es or of terminals of the pole-pieces of a dynamo-electric machine from or towards which the armature is carried during its rotation. According- to S. P. Thompson, the following horns, b, d, Fig. 231, are those towards which the armature is carried ; the leading horns, a, c, those from which it is carried. As the change in the magnetic intensity is more sudden when the armature is moved from the pole pieces, and least when moved towards them, it is clear that the leading horns in a dynamo-electric machine, and the following horns in an elec- tric motor, become heated during rotation by the production of eddy currents. (See Currents, Eddy. Dy- namo Electric Ma- chines. ) Horse Power. — A commercial unit for / rate of doing work. Fig. 231. A rate of doing work equal to 33,000 pounds raised one foot per minute, or 559 pounds raised one foot per second. A careful distinction must be drawn between ivork and power. The same amount of work is done in raising one pound through ten feet, whether it be done in one minute or in one hour. The power expended, or the rate of doing work is, however, quite different, being in the former case sixty times greater than in the latter. Horse-Power, Electric — Such a rate of doing electric work as is equal to 33,000 foot-pounds per minute, or 550 foot-pounds per second. Just as one pound of water raised through a vertical dis- tance of one foot requires the expenditure of a foot-pound of energy, so one coulomb of electricity acting through the differ- 320 A DICTIONARY OF ELECTRICAL ence of potential of one volt requires a certain amount of work to be done on it. (See Coulomb. Volt. Potential.) This amount is called a volt-coulomb or joule and, measured in foot-pounds, is equal to .737324 foot-pounds. The volt- coulomb, or the joule, is therefore the unit of electric work, just as the foot-pound is the unit of mechanical ivork. The electric work of any circuit is equal to the product of the volts by the coulombs. If we determine the rate per second at which the coulombs 2)ass, and multiply this product by the volts, we have a quantity which represents the electrical power, or rate of doing electrical ivork. But one ampere is equal to one coulomb per second; therefore, if we multiply the current in amperes by the difference of potential in volts, the product is equal to the electrical power or rate of doing- electrical work. The product of an ampere by a volt is called a volt-ampere, or a watt. One Watt = .0013406 Horse-power, or One Horse-power = 745.941 Watts. Therefore the Electrical Horse-power = , 1 746 where C = the current in amperes, and E = the difference of potential in volts. Hor§eslioe Magnet. — A magnetized bar of steel or iron bent in the form of a horseshoe, or letter U. A compound horseshoe magnet is shown in Fig-. 232. It consists of separately magnetized plates placed with their similar poles together. A horseshoe magnet possesses greater portative power than a straight bar magnet. (See Portative Power.) (1) Because its opposite poles are nearer together, and (2) Because the magnetic resistance of its circuit is less, the lines of magnetic force closing through the armature, and thus concentrating the magnetic attraction on the armature. Electro-magnets are generally made of the horseshoe shape. WORDS, TERMS AND PHRASES. 321 Human Body, Electric Resistance of The electric resistance offered by the human body. Accurate data concerning- the resistance of the human body are yet to be obtained. When the electrodes of any source are applied to the skin, the resistance will necessarily vary with the size and position of the contacts, the nature of the con- tacts, the condition both of the skin and the contacts, whether dry or moist, and the pathological or other condition of the portion acted on. The chief resistance offered by the human body to the passage of an elec- tric current is the skin. It may be regarded as a protective covering so far as electric currents are concerned. The body is composed, generally speaking, of solids and liquids. The liquids offer paths of less resistance than the solids. The blood and nerves are probabty the best conducting media in the body. The muscles offer a fair conducting path from the quantity of saline fluids they contain. Since the human body, like that of all animals, is itself a source of electric currents, it is possible that the pas- ■*%• 2S2 - sage through it of a current generated from without, would of itself greatly alter its electric resistance. "Wolfenden found the resistance in fifty healthy persons, measured under exactly similar conditions, to vary from 4,000 to 5,000 ohms. Certain diseased conditions of the body appear to cause a marked variation in what may perhaps be regarded as a nor- mal electric resistance. Charcot made measurements in which 322 A DICTIONARY OF ELECTRICAL it appears that the resistance fell below the normal in certain cardiac affections, and in Graves' Disease, Wolfenden cor- roborates this, and in eighteen cases of undoubted Graves' Disease the resistance was but 500 to 1,500 ohms. In eight of these it was less than 1,000 ohms. In ordinary goitre, unlike Graves' Disease {Exophthalmic Goitre), no variation of the resistance was found. In a case of malignant thyroid it was as high as 8,000 ohms. In some cases of hemiplegia, it varied from 1,300 to 4,000 ohms. In some of epilepsy, from 1,000 to 4,000. In three cases of cerebral softening, the resistance was about 3,000 ohms and in one case of paraplegia, it was 6,500 ohms, and in one case of chorea (adult), 350 ohms. (Wolfenden.) Hydro-Electric machine, Armstrong's A machine for the development of electricity by the friction of condensed steam passing over a water surface. Steam generated in a suitable boiler, Fig. 233, which is insulated, is allowed to escape through a tortuous nozzle, from a series of apertures opposite a pointed comb, attached to an insulated conductor. The cooling of the steam during its passage through a flat box, termed the cooling box, connected with the nozzles, causes a partial condensation, so that the box always contains a small quantity of water. The friction of the drops of water against the orifice and possibly their friction against the water surface itself are the cause of the electricity. A conductor connected with the pointed comb furnishes positive electricity. The boiler furnishes negative electricity. The hydro-electric machine is not a very economical source of electricity, and is only employed for experimental purposes. It was discovered accidentally through a shock given to an engineer, who placed his hand in a jet of steam escaping from a leaking boiler he was endeavoring to mend. The causes were first studied by Mr., now Sir Wm., Armstrong, who, in. 1840, devised the apparatus just described. WORDS, TERMS AND PHRASES. 323 Hydrometer or Areometer.— An apparatus for de- termining the specific gravity of liquids. (See Areometer.) Fig. 233. Hydrotasimeter, Electric -An elec- trically operated apparatus designed to show at a distance the exact position of any water level. In most forms a float placed in the liquid and connected 324 A DICTIONARY OF ELECTRICAL with an electric circuit, breaks this circuit, and, at intervals, sends positive impulses into the line when rising, and negative impulses when falling. These are registered by means of an index moved by a step-by-step motion, positive currents moving it in one direction, and negative currents moving it in the opposite direction. Hygrometer.— An apparatus for determining the amount of moisture in the air. Hypothesis.— A provisional assumption of facts or causes, the real nature of which is unknown, made for the purpose of studying the effects of such causes. A theory is a more or less accurate expression of some phys- ical truth which has been deduced from independently derived laws and principles. Our notions concerning the causes of electricity have, in reality, only reached the stage of hypotheses ; they cannot yet be properly considered as having attained the dignity of theories. Hypothesis, Double Fluid Electric (See Double Fluid Electric Hypothesis.) Hypothesis, Single Fluid Electric (See Single Fluid Electric Hypothesis. ) Hypsometer. — An apparatus for determining the eleva- tion of a mountain or other place, by obtaining the exact tem- perature at which water boils at such elevation. The use of a thermometer to measure the height of a moun- tain or other elevation is based on the fact that a given de- crease in the temperature of the boiling point of water inva- riably attends a given decrease in the atmospheric pressure. Therefore, as the observer goes further above the level of the sea, the boiling point of water becomes lower, and from this decrease, the height of the mountain or other elevation may be calculated. WORDS, TERMS AND PHRASES. 325 Idio-Electrics. — A name formerly applied to such bodies as amber, resins, glass, etc., which are readily electrified by friction and which were then supposed to be electric in them- selves. This distinction was based on an erroneous conception, and the word is now obsolete. Idiostatic. — A term employed by Sir Wm. Thomson, to designate an electrometer in which the measurement is effected by determining" the repulsion between the charge to be measured and that of a charge of the same sign imparted to the instrument from an independent source. (See Hetero- statie.) Igniter, Jablochkoff A small strip of carbon, or carbonaceous paste of readily ignitable material, placed at the free ends of the parallel carbons of a Jablochkoff candle, for the establishment of the arc on the passage of the current. The igniter is necessary in the Jablochkoff electric candle, since the parallel carbons are rigidly kept at a constant distance apart by the insulating material placed between them, and cannot therefore be moved together as in the case of the ordinary lamp. (See Candle, Jablochkoff.) Ignition, Electric The ignition of a combus- tible material by heat of electric origin. The electric ignition of wires is generally accomplished by electric incandescence. Ignition may be accomplished by the heat of the voltaic arc. (See Heat, Electric. Furnace, Electric.) The ignition of combustible gases is accomplished by the heat of the electric spark. (See Burner, Automatic Electric.) Illumination, Artificial The employment of artificial sources of light to render objects visible. A good artificial illuminant should possess the folio wing- properties, viz.: (1) It should give a general or uniforn illumination as dis- tinguished from sharply marked regions of light and shadow. 326 A DICTIONARY OF ELECTRICAL To this end, a number of small lights well distributed are pre- ferable to a few large lights. (2) It should give a steady light, uniform in its brilliancy, as distinguished from a flickering, unsteady light. Sudden changes in the intensity of a light injure the eyes and prevent distinct vision. (3) It should be economical, or not cost too much to produce. (4) It should be safe, or not likely to cause loss of life or property. To this intent it should, if possible, be inclosed in or surrounded by a lantern or chamber of some incom.bustible material, and should preferably be lighted at a distance. (5) It should not give off noxious fumes or vapors, when in use, nor should it unduly heat the air of the space it illumines. (6) It should be reliable, or not apt to be unexpectedly extingished when once lighted. The claims of the electric incandescent lamp as a cheap safe, reliable and steady, artificial illuminant, will be evident if these points are examined seriatim, viz. : (1) The incandescent light is capable of great sub-division, and can therefore produce a uniform illumination. (2) It is steady and free from sudden changes in its intensity. (3) It compares favorably in point of economy with coal oil or gas. (4) It is safer than any known illuminant, since it can be entirely inclosed and can be lighted from a distance, or at the burner, without the use of the dangerous friction match. The leads, however, must be carefully insulated and pro- tected by safety fuses. (See Fuse, Safety.) (5) It gives off no gases, and produces far less heat than a gas burner of the same candle power. It perplexes many people to understand why the incandes- cent electric light should not heat the air of a room as much as a gas light, since it is quite as hot as the gas light. It must be remembered, however, that a gas burner, when lighted, not only permits the same quantity of gas to enter WORDS, TERMS AND PHRASES. 327 the room which would pass if the gas were simply turned on and not lighted, but that this bulk of gas is still given off, and is even considerably increased, by the combination of the illu- minating gas with the oxygen of the atmosphere, and which moreover, it is given off as highly heated gases. Such gases are entirely absent in the incandescent electric light, and con- sequently its power of heating the surrounding air is much less than that of gas lights. (6) It is quite reliable and will continue to burn as long as the current is supplied to it. Illumination, Light House Electric— (See Light House Illumination, Electric). I Hum in at ion, Unit of — — A standard of illumina- tion proposed by Preece, equal to the illumination on a sur- face such as a street, given by a standard candle at the dis- tance of 12.7 inches. According to Preece, the illumination for the average streets of London, where gas is emploj'ed, is equal to about one-tenth this standard, in the neighborhood of a gas lamp, and about one-fiftieth, in the middle space between two lamps. The term, unit of illumination, in place of the intensity of light, was proposed by Preece, in order to avoid the very great difficulty in determining the intensity of a light in a street or space where there were a number of luminous sources, and where the directions of incidence of the different lights vary so greatly. A carcel standard at the distance of a metre will illumine a surface to the same intensity of illumination as a standard candle at the distance of 12.7 inches. Images, Electrie A term sometimes applied to the charge produced in a neighboring surface by induction from a known charge. A positive charge produces by induction, in a flat metallic surface near it, a negative charge which is distributed with 328 A DICTIONARY OF ELECTRICAL varying density over the surface, but acts electrically as would an equal quantity of negative electricity placed back of the plate, at the same distance the positive charge is in front of it. The correspondence of this charge with the image of an object seen in a plane mirror has led to the term electrical image. Maxwell defines electric image as follows: "An electric image is an electrified point, or system of points, on one side of a surface, which would produce on the other side of that surface the same electrical action which the actual electrification of that surface really does produce." Imponderable. — That which possesses no weight. A term formerly applied to the luminiferous or universal ether, but now generally abandoned. It is very questionable whether it is possible for any form of matter to be actually imponderable, or to possess no attraction for other matter An imponderable fluid, as for example the universal ether, as the term is now generally employed, is a fluid whose weight is comparatively small and insignificant, and not a fluid, an indefinite quantity of which would be entirely devoid of weight. Ineaiideseenee, Electric The electric heating of a substance, generally a solid, to luminosity. Electric incandescence of solid substances differs from ordinary incandescence, in the fact that unless the sub- stance is electrically homogeneous throughout, the tempera- ture is not uniform in all parts, but is highest in those por- tions where the resistance is highest and the radiation small- est. The deposition of carbon in and on a carbon conductor by the flashing process is quite different as performed by electrical incandescence, than it would be if the carbons were heated by ordinary furnace or other heat. (See Flashing of Carbons.) Inclination Compass, or Inclinometer.— A mag- netic needle so arranged as to readily permit the measurement WORDS, TERMS AND PHRASES. 320 of the magnetic dip at any place. (See Dipping Circle or In- clination Compass.) Inclination, Magnetic —(See Magnetic Inclina- tion.) Inclination Map or Chart. — A chart or map on which lines are drawn showing - the lines of equal dip or inclination, or the isoclinic lines. An inclination chart is shown in Fig - 234. It will be seen that the magnetic equator, or line of no dip, does not correspond with the geographical equator, being generally north of the equator in the eastern hemisphere, and south of it in the western. The figures attached to the lines indicate the value of the angle of dip. Inclination or Dip of Magnetic Needle.— The deviation of an evenly weighted magnetic needle from a horizontal position. The direction of a magnetic needle in all parts of the earth, except at the magnetic equator, differs from a level or hori- zontal position. One of its ends inclines or dips towards the ground. (See Dip, Magnetic. Dipping Needle.) India Rubber. — A resinous substance obtained from the milky juices of several tropical trees. India rubber is quite elastic and possesses high powers of electric insulation. When vulcanized or combined with sulphur, instill retains its powers of electric insulation in a high degree. In this state it is readily electrified by friction. (See Caoutchouc). Indicating Bell. — (See Bell, Indicating.) Indicators, Electric Various devices, generally operated by the deflection of a magnetic needle, or the ring- ing of a bell, or both, for indicating at some distant point the condition of an electric circuit, the strength of current that is flowing through it, the height of water or other liquid, the pressure on a boiler, the temperature, the speed of an engine 330 A DICTIONARY OF ELECTRICAL WORDS, TERMS AND PHRASES. 331 or line of shafting, the working of a machine, or other similar events or occurrences. Indicators are of various forms. They are generally electro- magnetic in character. Indicators, Electric Circuit Various devices, generally in the form of vertical galvanometers, employed to indicate the presence and direction of a current in a circuit, and often to roughly measure its strength. (See Galvanometer, Vertical.) Induced Current, Direct Induced Current. — (See Current, Extra.) Induced Current, Reverse Induced Current. — (See Current, Extra.) Induction Balance, Hughes' (See Balance, Induction, Hughes'.) Induction, Dynamo Electric (See Induction, Electro-Dynamic.) Induction, Electro-Dynamic Electro motive forces set up by induction in conductors which are either actually or practically moved so as to cut the lines of magnetic force. These electro-motive forces, when permitted to act or neutral- ize themselves, produce a current. Electro-dynamic induction occurs only in a magnetic field, the intensity of which is either increasing or decreasing. It may be produced in the following ways, viz. : (1) By the use of an inducing field of varying magnetic in- tensity. Varying the strength of the current and consequently the intensity of its magnetic field, will produce an in- duction of the circuit on itself, or a self-induction, and will result in extra currents, which are in the opposite direction on closing and in the same direction on opening the circuit ; or it will produce induction in neighboring conductors which are 332 A DICTIONARY OF ELECTRICAL within the field of the inducing current. (See Self -Induction, Mutual Induction. Currents, Extra.) (2) By using an inducing field of practically unvarying intensity, and varying the number of lines of magnetic force that pass through a conductor, by moving the conductor through the inducing field so as to cut its lines of force. Or, the conductor remaining fixed in position, the inducing field is moved past the conductor by moving the electro-mag- net, or electric circuit, or permanent magnet producing the field. Electro-dynamic induction, therefore, includes . (1) Self-induction. (2) Mutual Induction, or, as it is sometimes called, Voltaic or Current Induction. (3) Electro-Magnetic Induction, or Dynamo-Electric Induc- tion. (4) Magneto-Electric Induction. The coil B, Fig. 235, consists of two parallel coils of insu- lated wire, the terminals of one of which, called the primary coil, are connected with the battery cell P N, and those of the other, called the secondary coil, with the galvanometer G. Under these circumstances it is found : (1) That at the moment of closing the circuit, through the primary coil, a momentary current is produced in the second- ary coil in a direction opposite to that of the current through WORDS, TERMS AND PHRASES. 333 the primary, as is shown by the direction of deflection of the needle of the galvanometer. (2) At the moment of breaking- the circuit through the primary coil an induced current is produced in the secondary coil in the same direction as that flowing through the primary coil. (3) These induced currents are momentary, and only con- tinue in the secondary while the intensity of the current in the primary is varying, i.e., while variations are occurring in the strength of the magnetic field in which the secondary coil is placed. If, for instance, when the current is established in the primary coil, and no current exists in the secondary, the intensity of the current in the primary be varied by establish- ing a shunt circuit across the battery terminals, as by placing a short wire d, Fig. 236, in the mercury cups g, g, thus decreas- ing the intensity of the current in the primary, an induced current will be set up in the secondary circuit in the same direction as the primary current. Fig. 236. From all of these phenomena we see that an increase of cur- rent in a conductor produces in a neighboring conductor an induced inverse current, or one in the opposite direction to the inducing current, while a decrease of such current pro- 334 A DICTIONARY OF ELECTRICAL duces a direct induced current, or one in the same direction as ihe inducing current. If the induction coil be made, as in Fig. 237, with its primary coil movable into and out of the secondary coil, then the fol- lowing' phenomena will occur: (1) When the primary coil is moved towards the secondary coil an inverse current is induced in the secondary, and, (2) When the primary coil is moved away from the second- ary coil a direct current is induced in the secondary. The movements of permanent magnets towards or from a coil will also produce an induced current. If, for example, the apparatus be arranged, as in Fig. 238, then : Fig. 237. (1) A motion of the magnet towards the coil produces an induced current in the coil in one direction, and (2) Its motion away from the magnet produces an induced current in the coil in the opposite direction. WORDS, TERMS AND PHRASES. 335 These induced currents are respectively inverse and direct as compared with the direction of the arnperian currents which are assumed to produce the magnetic poles of permanent mag- nets, or of the currents that actually produce electro magnets. (See Magnetism, Ampere's Theory.) Induction, Electro-Magnetic (See Induction Electro-Dynamic. ) These facts may be expressed by the following laws : (1) Any decrease in the number of lines of force which pass through a circuit produces a direct current in that circuit, while any increase in the number of such lines of force which pass through any circuit produces an inverse current in that circuit. Fig. 23S. (2) The induced current has an intensity, or more correctly, the differences of potential produced are proportional to the rate of increase or decrease of lines of force passing through the circuit. Any conductor therefore, w T hen moved through a magnetic field so as to cut the lines of magnetic force, will have a current produced in it by induction. 336 A DICTIONARY OF ELECTRICAL A simple but effective manner of remembering the direction of such currents is that proposed by Fleming*. If the hand be held with the fingers extended, as in Fig. 239, and the direction of the fore finger represent the positive direc- tion of the lines of force, i. e., those coming out of the N. pole of a magnet, then, if a wire or other conductor be moved in the direction in which the thumb points, so as to cut these lines of force at right angles, that is if the conductor have its length moved directly across these lines, it will have an induced current developed in it m the direction in which the middle finger points. (See Direction of Lines of Force). Or, the same thing* can, perhaps, be e v e n more eadily remembered by cut- ting a piece of paper in the shape shown in Fig. 240, marking it as shown, and then bending the arm P, upwards at the dotted line, so as to form three axes at right angles to one an- other. As has been already re- marked, a differ ence of potential is produced by the motion of a conductor through a magnetic field so as to cut its lines of force, and not a current. It can be shown that in order to generate a differ- ence of potential of one volt, 100,000,000 C. G. S. lines of force must be cut per second. In electro-magnetic induction the induced current is pro- duced by the energy absorbed by moving the conductor through JJfrectcons of Current. WORDS, TERMS AND PHRASES. 33T the field. Lenz has shown that in all cases of electro-magnetic induction, produced by the movement either of the circuit or of the magnet, the current induced in the circuit is in such a direction as to produce a magnet pole which would tend to oppose the motion. For mutual attraction and repulsion of currents see Electro-Dynamics. X c Induction, Electrostatic P .2 3 -The production of an electric o . Ml Direction of Motion. M. charge in a conductor brought into an electrostatic field. If the insulated conductor A B, Fig. 241, be brought into the positive elec- trostatic field of the insulated conductor C, then, (1) A charge will be produced on A B, as will be indicated by the divergence of the pith balls. (2) This charge is negative at the end A, nearest C, and positive at the end C, furthest from B, as can be shown by an electroscope. (See Electroscope.) Fig. %0. Fig. 2kl. (3) The charges at A and B, are equal to each other; for, if the conductor A B, be removed from the field of C, without touch- ing it, the opposite charges completely neutralize each other, 338 A DICTIONARY OF ELECTRICAL (4) If, however, the conductor A B, be touched at any place by a conductor connected with the earth, it will lose its positive charge, and will remain negatively charged when removed from the field of C. It is in this manner that the electrophones is charged. (See Electrophones.) (5) The amount of the charges produced in the conductor, A B, can never be greater than that in the inducing body C. That is to say, the negative electricity at A, may be sufficient in amount to neutralize the positive charge on C, if allowed to do so. In point of fact the Fig. 21 amount than the inducing charge, according to the distance between C and A, and the nature and condition of the medium which separates them. The attractions of light bodies by charged surfaces is due to the opposite charge produced on those parts of the light bodies that are nearest the charged body. , The pith ball B, Fig. 242, suspended by a silk thread between an insulated positively charged conductor A, and the unin- sulated conductor C, will receive by induction a negative charge on the side nearest to A, and a positive charge on the side nearest to C. It is therefore attracted to A, where, re- ceiving a positive charge, it is repelled to C, where it is dis- charged and again assumes a vertical position. Induction again occurs, and consequent attraction and repulsion. These movements follow one another so long as a sufficient charge remains in A. Induction Coils. — Parallel coils of insulated wire em- ployed for the production of currents by electro-magnetic in- duction. (See Induction, Electro-Magnetic.) WORDS, TERMS AND PHRASES. 339 A rapidly interrupted battery current sent through a coil of wire called the primary coil, induces intermittent currents in a coil of wire called the secondary coil. As heretofore made, the primary coil consists of a few turns of a thick wire, and the secondary coil of many turns, often thousands, of fine wire. Such coils are generally called Ruhmkorff Coils, from the name of a celebrated manufacturer of them. In the form of Ruhmkorff coil, shown in Fig. 243, the pri- mary wire is wound on a core formed of soft iron wires, and its ends brought out as shown at/, f ' . The fine wire is wrapped around an insulated cylinder of vulcanite, or glass, surround- ing the primary coil. This wire is very thin, and in some coils is over one hundred miles in length. The ends of the secondary coil are connected to the insu- lated pillars A and B. The primary current is rapidly broken by means of a mer- cury break, shown at L, and M, 340 A DICTIONARY OF ELECTRICAL The commutator, shown to the right and front of the base, is provided for the purpose of cutting off the current through the primary, or for changing its direction. "When a battery w 1 deli produces a comparatively large current of but a few volts electro-motive force, is connected with the primary, and its current rapidly interrupted, a torrent of sparks will pass be- tween A and B, having an electro-motive force of many thou- sands of volts. In such cases, excepting losses during conversion, the energy in the primary current, or C E, is equal to the energy in the secondary current, or C E'. As much therefore as E', the electro-motive force of the secondary current exceeds E, the electro-motive force of the primary current, the current strength C, of the secondary will be less than the current strength C, of the primary. (See Converter, or Trans- former.) Fig. 244, shows diagramatically the arrangement and con- nection of the different parts of an induction coil. The core I, I' consists of a bundle of soft iron wires, each of which is covered with a thin insulating layer of varnish or ox- ide. A primary wire P, P, consisting of a few turns of com- paratively thick wire is wound around the core, and a greater length of thin wire S, S, is wound upon the primary. This is called the secondary. So as not to confuse the details of the figure it is represented as a few turns. The ends of the battery B are connected to the primary wire, through the automatic interrupter, in the manner shown. It will be seen that the attraction of the core 1 1', for the vi- brating armature H, will break contact at the point o, and cause a continued interruption of the battery current. The condenser C, C, is connected as shown. It acts to di- minish the sparking at the contact points on breaking contact, and thus, by making the battery current more sudden, to con- sequently make its inductive action greater. WORDS, TERMS AND PHRASES. 841 Induction Coils, Inverted Conver- ters. Transformers. — An inverted induction coil is an in- duction coil in which the primary coil is made of a long-, thin wire, and the secondary coil of a short, thick wire. Fig. 2hU. By the use of an inverted coil, a current of high electromo- tive force and comparatively small current strength, i. c, bui of few amperes, is converted or transformed into a current of comparatively small electromotive force and large current strength. For the advantages of this see System of Dis- tribution by Alternating Currents. Inverted induction coils are called converters or transfor- mers. (Converter or Transformer.) Induction, Lateral Induction, Magnetic (See Lateral Induction.) The production of mag- netism in a magnetizable substance by bringing it into a mag- netic field. When a magnetizable body is brought into a magnetic field the following phenomena occur, viz.: 342 A DICTIONARY OF ELECTRICAL (1) The lines of magnetic force pass through the body and are condensed upon it. (See Field, Magnetic. Paramagnetic.) (2) If the body is free to move around an axis, but not bodily towards the magnet pole, it will come to rest with its greatest extent or length in the direction of the lines of force ; i. e., in the direction in which it will offer the least resistance to the lines of force that thread through it. (3) The body will therefore become a magnet, its south pole being situated where the lines of force enter it, and its north pole where they pass out from it. (4) The intensity of the induced magnetism will depend on the number of lines of force that pass through it. (5) The direction of the axis of magnetism will depend on the directions in which the lines of force thread through the body. (See Axis of Magnetism). If a bar of iron N, S, Fig. 245, be brought near the magnetized bar, N, S, poles will be produced in N S" n' it by induction, as may be Fig. U5. shown by throwing iron filings on it. Since the nearer the body to be magnetized is brought to the magnetizing pole, the greater will be the number of lines of force that thread through it, the greater will be the inten- sity of its induced magnetism. This will be greatest when the two actually touch each other. The production of magnetism therefore by contactor touch is only a special case of magnetization by induction. The attraction of a magnetizable body by a magnet pole, is caused by the mutual attraction which exists between the un- like pole produced by induction in the parts of the piece of iron nearest the attracting magnet pole. This, it will be seen, is the same as the attraction caused by an electric charge. Induction, Magneto Electric (See Induction, Electro Dynamic.) WORDS, TERMS AND PHRASES. 343 Induction, Mutual Induction produced by two neighboring' circuits on one another by the mutual interac- tion of their magnetic fields. (See Currents, Extra.) Induction, Self Induction produced in a circuit at the moment of starting or stopping the currents therein, by the induction of the current on itself. (See Cur- rent, Extra.) Induction Top. — A top consisting of an iron disc sup- ported on a vertical axis, which, when spun before the poles of a steel magnet assumes an inclined position, through the influence of the currents induced in the disc. The top maintains the inclined position so long only as the strength of the induced currents is sufficiently great ; that is while speed of rotation is sufficiently great. Induction, Tubes of (See Force, Tubes of, or Tubes of Induction.) Inductive Capacity, Specific (See Capac- ity, Specific Inductive.) Inductonieter, Differential An appa- ratus for measuring by means of a galvanometer the momen- tary currents produced by the discharge of a cable. Currents produced by the discharge of a cable are of so short a duration that they do not produce much effect on a galvanometer needle. The inductive charge in a cable, or the quantity of elec- tricity produced in it by induction, is (1) Directly as the electromotive force of the charging bat- tery. (2) Inversely as the square root of the thickness of the coating of gutta-percha or other insulating material between the conducting wires and the metallic sheathing, and (3) Directly as the square root of the diameter of the copper wire of the conductor. In order to cause the cable discharge to more thoroughly affect the galvanometer needle, Mr. 344 A DICTIONARY OF ELECTRICAL Latimer Clark employed a differential instrument with a large battery, and three reversing- keys, by means of which he gave a rapid successsion of charges to the cable. He called the instrument a Differential Inductometer. Incluctophone. — A device suggested by Mr. Willoughby Smith for obtaining electric communication between trains in motion and fixed stations by means of the induction currents developed in a spiral of wire fixed on the moving engine, in its motion past spirals on the line, into which intermittent currents are passed. The spiral on the engine is placed in the circuit of a tele- phone. (See Telegraphy, Inductive.) I ml ii< t oriu m. — A name sometimes applied to a jRuhm- korff induction coil. (See Induction Coils.) Inertia. — The inability of a body to change its condition of rest or motion, unless some force acts on it. The inertia of matter is expressed in Newton's first law of motion, as follows : " Every body tends to preserve its state of rest or of uniform motion in a straight line, unless in so far as it is acted on by an impressed force." All matter possesses inertia. Inertia, Magnetic or Lag. — The inability of a magnet core to instantly lose or acquire magnetism. The magnet core tends to continue in the magnetic state in which it was last placed. To decrease the magnetic inertia the strength of the mag- netizing current is increased and the length of the iron core decreased. The iron should also be quite soft. (See Coercive Force. Lag, Magnetic.) Infinity Plug. — A plug, in a box of resistance coils, in which the two pieces of brass it connects are not connected by any resistance coil and which, therefore, leaves on unplugging, an open circuit or an infinite resistance. WORDS, TERMS AND PHRASES. 345 Ink-Writer, Telegraphic, or Recorder. (See Balance, Wheat stone's Electric, Box, Form of.) — A de- vice employed for recording the dots and dashes of a tele- graphic niessag-e in ink on a fillet or strip of paper. Insolation, Electric. — (See Sun Stroke, Elective.) Installation. — A term embracing the entire electric plant and its accessories required to perform any specified work. Insulating Cements.— (See Cements, Insulating.) Insulating' Materials. — Non-conducting substances which surround a conductor, in order that it may either retain an electric charge, or permit the passage of an electric current through the conductor without sensible leakage. Various gases, liquids, or solids may be employed as insu- lators. A high vacuum affords the best known insulation. Insulating Stool. — A stool provided with insulating legs, on which a person, or other body, maybe placed in order to receive an electric charge. Insulating Tape.— (See Tape, Insulating.) Insulating Varnish.— (See Varnish, Insulating,) Insulators, Telegraphic or Telephonic. Non-conducting supports, by means of which telegraphic, telephonic, electric light wires, or other wires are attached to the objects by which they are supported. The insulators are generally made of glass, earthenware, porcelain, or hard rubber, and assume a variety of forms, some of which are shown in Figs. 246, 247, and 248. Of what- ever material they are made, it is necessary that the surface on which the wire rests, or around which it is wrapped, should be smooth so as to avoid abrasion either of its insulat- ing covering or of the wire itself. Two things are to be considered in the selection of an insu- lator, viz. : 346 A DICTIONARY OF ELECTRICAL (1) The insulating power of the material of which it is com- posed, so as to reduce the leakage as much as possible. (See Electric Leakage). And, (2) The tensile strength of the material, so that in case of heavy wires no breaks may result from the fracture of the insulator. Intensity of Current.— A term some- times employed to indicate current strength. ■Fig. 2h6. (See Amp $ re j Intensity of Field. — The strength of a field as meas- ured by the number of lines of force that pass through it per unit of area of cross section. (See Field, Electrostatic. Field, Magnetic.) Intensity of Light. — The brilliancy or illuminating power of a light as measured by a photometer in standard candles. (See Photometer.) Intensity of Magnetization, or Magnetic Density.— The strength of Fig. 2hi. magnetism as measured by the number of lines of magnetic force that pass through a unit of area of cross section of the magnet, i. e., a section taken at right angles to the lines of force. (See Magnetic Density.) Interlocking Apparatus. — Devices for me- chanically operating railroad switches, and sema- phore signals for indicating the position of such switches, from a distant signal tower, by means of a system of interlocking levers, so constructed that the signals and the switches are interlocked, so as to render it impossible, after a route has Fig. 2hs. once been set up and a signal given, to clear a signal for a route that would conflict with the one previously set up. WORDS, TERMS AND PHRASES, 847 Intermittent Eartli. — (See Earths.) Interrupter. — Any device for interrupting or breaking a circuit. Interrupter, Automatic -(See Automatic Con- tact Breaker.) Interrupter, Tuning Fork or Reed An interrupter in which the makes and breaks are caused to follow one another by the vibrations of a tuning fork or reed. The tuning fork or reed is maintained in vibration by any suitable means. Such interrupters are applied to various uses. Synchronous multiplex telegraphy is an example of such uses. Inverted Induction Coil*. — (See Converters or Trans- formers.) Ions. — Groups of atoms or radicals which result from the electrolytic decomposition of a molecule. The ions are respectively electro-positive and electro-ne- gative. The electro-positive* ion appears at the plate con- nected with the electro negative terminal, or at the kathode, and is called the kathion. The electro-negative ion appears at the plate connected with the electro-positive terminal, or at the anode, and is called the anion. (See Electrolysis. Kathion. Anion.) Iron-Clad Magnet.— A magnet in which the magnetic resistance is lowered by a casing of iron connected with the core and provided for the passage of the lines of magnetic force. (See Magnet, Tubular.) Isobars, or Isobaric Lines. — Lines connecting places on the earth's surface which have at any time the same barometric pressure. A study of the isobaric lines, or isobars, is of great assist- ance in making forecasts or predictions of coming changes in the weather. Isochronism. — Equality of time of vibration. 348 A DICTIONARY OF ELECTRICAL Isochronous Vibrations or Oscillations.— Vibra- tions which perform their to and fro motions on either side of the position of rest in equal times. The vibrations of a pendulum are isochronous, no matter what the amplitude of the swing may be, that is, whether the pendulum swings through a large arc or a small arc, provided this arc be not very great. All vibrations, therefore, that produce musical sounds may be regarded as isochronous. lsoclinic Charts. — (See Inclination Map or Charts.) Isoclinic Lines. — Lines connecting places that have the same angle of magnetic dip or inclination. (See Dip, Mag- netic.) Isodynamic Lines. — Lines connecting places which have the same magnetic intensity. The magnetic intensity of a place is determined by the number of oscillations that a small magnetic needle, moved from its position of rest in the magnetic meridian of any place, makes in a given time. This method is similar to that employed for determining the intensity of gravity at any place by observing the number of oscillations that a pen- dulum of a given length makes in a given time at that place. If, for example, a magnetic needle at one place makes 211 os- cillations in ten minutes, and 245 in the same time at another place, the relative magnetic intensities at these places are as the squares of these numbers or as 44521 : 60025, or as 1 : 1.348. Isodynamic Map or Chart — A map of the earth on a Mercator's projection on which isodynamic lines are drawn. An isodynamic chart is shown in Fig. 249. It will be ob- served that the isodynamic lines do not exactly coincide with the isoclinic lines, since the line of least magnetic intensity, does not correspond with the line of the magnetic equator. The point of least magnetic intensity is found at about lat. 20° S, and long. 35° W. The point of greatest magnetic in- tensity, is found at about lat. 52° N. and long. 92° W. WORDS, TERMS AND PHRASES. 349 350 A DICTIONARY OF ELECTRICAL. Another though weaker point of great magnetic intensity is found in Siberia. These are distinguished from the true magnetic poles by the term Poles of Intensity. The Poles of Verticity, as determined by the dipping needle, and the poles of intensity as determined by the needle of os- cillation, therefore do not coincide in the northern hemisphere. Isogonal Ones. — Lines connecting places that have the same magnetic variation or declination. (See Declination, Magnetic.) Isotonic or JOeclination Map or Chart.— A chart on which the isogonal lines are marked. In the declination or variation chart, shown in Fig. 250, the region of western declination is indicated by the shading. There is a remarkable oval patch in the northeastern part of Asia, in which the declination is west. A similar oval of de- creased declination is seen in the southern Pacific. The entire earth acts as a huge magnet with an excess of south magnetic polarity in the northern hemisphere. It is not known whether the earth possesses more than a single pair of magnetic poles, or what is the exact cause of its magnetism. The variations in the declination, and in the intensity of its magnetism, due to the position of the sun, as well as the marked magnetic disturbances that accompany the occurrence of sun spots, would appear to con- nect the earth's magnetism with the solar radiation. It is believed by some that the earth possesses in reality the two magnetic poles, viz., a south pole in the northern hemisphere, and a north pole in the southern hemisphere. (See False Poles, Magnetic.) Isotropic Conductor. — A conductor which possesses the same powers of electric conduction in all directions. An electrically homogeneous medium. Isotropic Medium. — A transparent medium which pos- sesses the same optical or electric properties in all directions. An optically homogeneous, transparent medium. WORDS, TERMS AND PHRASES. 351 352 A DICTIONARY OF ELECTRICAL An electrically isotropic medium possesses the same powers of electric conduction or spe- cific inductive capacity in all directions. (See Anistropic Medium.) I, W. Cr. — A contraction for Indian Wire Gauge. Jar, L.eyden A condenser in the form of a jar, in which the metallic coatings are placed opposite to each other on the outside and the inside of the jar. The metal coatings should not extend to more than two- Fi 9- 251 - thirds the height of the jar, the rest of the glass being varnished to avoid the creeping of the charge over the glass in damp weather. The inside coating is connected by means of a metallic chain, to a rounded knob on the top of the jar, as shown in Fig. 251. The conductor supporting the knob passes through a dry cork or plug of some insulat- ing material. To charge the jar the outside coating is connected with the earth, as by holding it in the hand, and the inside coating is con- nected with the conductor of a machine. Jar, Unit A small Leyden jar sometimes employed to measure approxi- mately the quantity of electricity passed into a Leyden battery or condenser. As shown in Fig. 252, the unit jar consists of a small Leyden jar/, whose outer coating is connected with a sliding metallic WORDS, TERMS AND PHRASES. 353 rod o, provided at each end with a rounded knob, and the inner coating- of which is connected with a metallic knob c, placed, and as shown, inside a glass jar d, opposite the ball on the long end of b. When now the inside of the unit jar, or the end connected with c, is connected with the charging source, such as a machine, and the outside at a is connected with the battery that is to be charged, for every spark that passess between d and c, a definite quantity has passed at a. The value of this unit charge, may be varied by varying the distance between d and c. The smaller the unit jar in proportion to the jar to be charged, and the shorter the distance between c and d, the more reliable are the comparative results obtained. Jet Photometer. — An apparatus for determining the candle power of a luminous source. (See Carcel, Standard.) Jewelry, Electric The substitution of minute incandescent electric lamps for the rarer gems in articles of jewelry. The lamps are lighted by means of small, primary storage batteries, carried in the pocket. Joint Re§i§tance of Parallel Circuits— The joint resistance of two parallel circuits is determined by means of the following formula : R r -\-r' Where R = the joint resistance of any two circuits whose separate resistances are respectively r and r'. When there are three resistances r, r' and r", in parallel, the joint resistance, -. r r V K = r r' -J- r r" -\- r' r" (See Circuits, Varieties of.) 354 A DICTIONARY OF ELECTRICAL Joint Testing. — Ascertaining the resistance of the in- sulating material around the joint in a cable. The resistance of a cable at its joint is necessarily high, since the joint forms but a small part of length of the cable. It should not, however, be large as compared with an equal length of another part of the cable with a perfect core. Two methods for the testing of cable joints are generally employed, viz.: (1) A condenser is charged through the joint for a given time, and the deflection obtained by its discharge is compared with the discharge of the same condenser charged for an equal length of time through a few feet of perfect cable. (2) A charged condenser is permitted to discharge itself through the joint, and the amount lost after a given time noted. For description of methods, see Kempe's "Handbook of Electrical Testing." Joints, Butt End to end joints. Butt joints are formed by bringing the ends to be joined together and securing them while in such position. Joints, Butt and Lap for Wires.— Joints effected in wires either by placing the wires end on, or by overlapping the ends, and subsequently soldering. Joints, Butt and Lap of Belts.— The joints in a leather belt, employed for transmitting power from a line of shafting, where the ends are simply brought together and laced, is called a, butt joint, in contradistinction to a lap joint, or a joint formed by placing one end of the belt over the other and lacing or riveting the two. In delicate galvanometers the slightest change in the speed of the engine driving the dyna mo-electric machine producing the current, causes an annoying fluctuation of the needle that prevents accurate reading, when lap joints are used in the belt instead of butt joints, unless the former are very carefully made. It also causes a flickering in the lights, WORDS, TERMS AND PHRASES. 355 Joint §, Expansion Joints for underground con- ductors, tubes or pipes, exposed to considerable changes of temperature, in which a sliding joint is provided to safely permit a change of length on expansion or contraction. Joints, Lap Joints effected by overlapping short portions near the ends of the two things to be joined, and secur- ing them while in such position. Joints, Telegraphic, Telephonic, etc. Methods adopted for joining the ends of electric conductors so as to insure a permanent junction whose resistance shall not be appreciably greater per unit of length than that of the rest of the wire. In making a joint care should always be taken to clean and scrape the insulating material from the wires before twisting them together. Telegraph wires were formerly joined by the ordinary bell- hanger's joint ; that is, the wires were simply looped together. The constant vibrations to which the wires are subject caused such a joint to be abandoned and an improvement introduced by bolting the ends together, as shown in Fig. 253. This latter method is now replaced by the following, viz. : In the Britannia Joint, shown in Fig. 254, the wires to be joined are placed side by side for about two inches, bound with No. 16 (British gauge) binding wire, in the manner shown, and then carefully soldered. The American Twist Joint, shown in Fig. 255, is made by twisting the wires together in the manner shown and sub- sequently soldering. This joint is easily made and is quite serviceable. All joints should be soldered, but in so doing care must be taken that the soldering liquid or solid employed is free from acids or other corrosive materials, and that ail traces of such materials are removed before the joint is covered with insulat- ing material. 356 A DICTIONARY OF ELECTRICAL Kerite, Okonite, or other insulating- Tape, should preferably be wrapped around the joint after it is soldered. In making a joint in a gutta-percha covered wire, such as a submarine cable wire, or wires, the following method may be employed : The bared and cleansed wires are ^^Bi^feBKStt Fig. 253. twisted together and soldered. The soldered joint is then covered with a layer of plastic insulating material made of a mixture of gutta-percha, tar and rosin. (See Chatterton's Compound.) In order to insure a good junction between this and the gutta-percha covering on the rest of the wire, the Fig. 25k. outer surface of the gutta-percha is removed for about two inches from each side of the joint so as to remove its oxidized surface. After the coating is put on, it is warmed gently by a warm joining tool and not by the flame of a lamp. A sheet of warmed gutta-percha is then wrapped around the Fig. 255. joint, and while it and the joint are still hot, another coating of the plastic, insulating material is applied. Successive layers of gutta-percha and insulating material are generally applied in the case of submarine cables. (Culley.) JouSad. — A term proposed for the Joule, but not gener- ally adopted. (See Joule.) tfrORDS, TERMS AND PARASES. 357 Joule. — The unit of electric energy or work. The volt-coulomb. The amount of electric work required to raise the potential of one coulomb of electricity one volt The joule may be regarded as a unit of work or energy in general, apart from electrical work or energy. 1 joule = 10,000,000 ergs. 1 joule. = .73732 foot pound. 1 joule =1 volt-coulomb. 4.2 joules = 1 small calorie. 1 joule per second = 1 watt. The British Association recently proposed to call one joule the work done by one watt per second. Joule Effect. — The heating effect produced by the passage of an electric current through a conductor, arising merely from the resistance of the conductor. (See Effect, Joule.) Kaolin. — A variety of white clay sometimes employed for insulating purposes. Jablochkoff employed kaolin between the parallel carbons of his electric candle for the purpose of insulating them. He also devised an electric lamp in which a spark of considerable difference of potential, obtained from an ordinary induction coil, was caused to raise a surface of kaolin to incandescence by its passage over it. Katheleetrotonus, or Katelectrotonus.— In elec- tro therapeutics the condition of increased functional activity that occurs in a nerve in the neighborhood of the negative electrode, or the kathode applied in medical electricity. (See Electrotonus.) Kathion. — The electro positive ion, atom, or radical into which the molecule of an electrolyte is decomposed by electro- lysis. (See Electrolysis. Ions.) Kathion is sometimes improperly written cation. 358 A DICTIONARY OP ELECTRICAL Kathode. — The conductor or plate of a decomposition cell connected with the negative terminal or electrode of a battery or other source. The word kathode is sometimes applied to the negative terminal of a battery or source, whether connected with a decomposition cell or not. It is preferable, however, to restrict its use to a decomposition cell. (See Anode.) The word kathode is often improperly written cathode. ■ PER! POLAR (KA1 "ELECTRCf ro iM OZONE •--- : __polar(ane uECTROTQ 1 1 N c ZONE _ : j ! ACTUAL A\ f *N DE j \ Fig. 256. Kathodic and Anodic Electro-Diagnostic Re- actions. — The reactions which occur at the kathode or anode of an electric source placed on or over any part of a living body. Fig. 256, from DeWatteville's Medical Electricity, represents what he assumes takes place at the points of entrance and exit of the current in a nerve submitted to the action of the anode of an electric source. Two zones are formed, an anodic and kathodic; the virtual anode is formed by the portion of the skin nearer the nerve, and the virtual kathode in the adjoin- ing muscles. There are thus formed two zones of influence, WORDS, TERMS AND PHRASES. 359 one, immediately around the anode, called the polar, or anelec- trotonic zone, and one, surrounding this and including- the virtual kathode, and called the peripolar, or katelectrotonic zone. K. C C — In electro therapeutics, a brief method of writing kathodic closure contraction, or the effects of muscular con- traction observed by the closure of a circuit at the kathode. K. I>. C — In electro therapeutics, a brief method of writing kathodic duration contraction, or the effects of muscular con- traction observed at the kathode after the current has been passing for some time. Keeper of Magnet. — A mass of soft iron applied to the poles of a magnet through which its lines of magnetic force pass. (See Field, Magnetic.) The keeper of a magnet differs from its armature in that the keeper while acting as such is always kept on the poles to prevent loss of magnetization while the armature, besides act- ing as a keeper, may be attracted towards, or repelled from, the magnet poles. While performing its functions the keeper is always fixed; the armature generally, though not always, is in motion. Opinion is divided, however, on the efficacy of the keeper. Key-Board.— (See Board, Switch.) Key, Discharge. — A key employed to enable the dis- charge from a condenser to be readily passed through a galvanometer for purposes of measurement. Key, Discharge, Kempe's A discharge key constructed as shown in Fig. 257. The solid lever, hinged at one extremity, plays between two contacts connected to two terminals, and has two finger triggers at its free end marked "Discharge" and "Insulate," con- nected to two ebonite hooks respectively. The hook at- tached to that marked "Discharge" is a little higher than the other, so that when the lever is caught against it, the 360 A DICTIONARY OF ELECTRICAL key rests in an intermediate position between the two con- tacts, and when caught against the lower trigger, it rests against the bottom contact. When in the last position, a de- pression of the ''Insulate" trigger causes the lever to spring up against the second hook, thus insulating it from either con- tact, and on the depression of the "Discharge" trigger, the lever springs up against the top contact. Fig. 257. Key, Discharge, Webb's — A discharge key con- structed as shown in Fig. 258. A horizontal lever L, Fig. 258, passing between two contacts and hinged at J, is pressed upwards by a spring. The free end of this lever terminates in two steps 1 and 2. A vertical lever H, provided with an insulating handle, is jointed at J', and has, at C a projecting metallic tongue that engages in the upper step when the lever H, is vertical, and on the lower step when it is slightly moved from the free end. When the projection C rests on the lower step 2, the lever L is intermediate between the top and bottom contacts, and is therefore disconnected from either of them ; but, when it rests on the upper step, it is in contact with the lower contact. When the lever H is so moved as to have the projection C, away from both contacts, the lever L is pressed by its spring against the upper contact. WORDS, TERMS AND PHRASES. 361 The battery terminals are connected with the condenser terminals when the lever L, is touching the lower contact, but when the lever L, touches the top contact, the condenser is connected with the galvanometer terminals. Fig. 258. Key, Double-Contact Form of Bridge Key, Sprague's A key designed to close two separate circuits successively. On depressing K, Fig. 259, the contacts c, c, are first closed and then those ate', c'. Metallic pieces 1, 2, 3 and 4, serve to make contacts with appar- atus used in connec- tion therewith. The battery circuit is connected to 1 and 2, and the galvanome- ter to 3 and 4, so that the battery circuit is closed first, and the galvanometer afterwards. Used in connection with the Wlu>atstone Bridffe. Fig. 362 A Dictionary of electrical Key, Double-Contact -, Lambert's.— A key used in cable work, and constructed as shown in Fig. 260. F. .ft* In Thomson's method for the determination of electrostatic capacity, the capacity of the cable is compared with that of a condenser containing- a known charge. These two charges are so connected electrically as to discharge into and neutralize each other if equal, but if not, to produce a gal- vanometer deflection by a charge equal to their difference. The connections are such that the pushing ~ forward of K, depresses Fig.S6l. k e y S that permit a bat- tery to simultaneously charge the condenser and the cable. On drawing K, back, the difference of the two charges are allowed to mix. Then, on depressing k, the difference of the charge, if any, is discharged through the galvanometer. Key, Magneto-Electric A telegraph key for sending an electric impulse into a line, so arranged that the WORDS, TERMS AND PHRASES. coil of wire on an armature connected with the key lever, is, by the movements of the key, moved towards or from the poles of a permanent magnet, the movements of the key thus producing the currents sent into the line. Key, Plug A simple form of key in which a con- nection is readily made or broken by the insertion of a plug of metal between two metallic plates that are thus introduced into a circuit. A form of plug-key is shown in Fig. 261. Key, Reversing - -A key, inserted in the circuit of a galvanometer for obtain- ing deflections of the needle on either side of the galvano- meter scale. The galvanometer termin- als are connected to the bind- ing posts 2 and 3, Fig. 262, and the circuit terminals to the other two posts. On de- pressing K, the current flows in one direction and on de- pressing K', in the opposite direction. Clamps, operated by handles, are provided so as to close either of the keys per- manently, if so desired. Key, Sliort-Circuit A key, which in its normal condition short-circuits the galvanometer. Such a short-circuit key is provided for the purpose of pro- tecting the gavanometer from injury by large currents being accidentally passed through its coils. In the form shown in Fig. 263, the spring S, rests against a platinum contact, but when depressed by the insulated head at K, it rests against an ebonite contact, and throws the galvanometer into the de- sired circuit. The key is provided with double binding posts at P and N, Fig. 262. 864 A DICTIONARY OF ELECTRICAL for convenience of attachment to resistance coils, batter- ies, etc. In the form of short-circuit key shown in Fig. 264 a catch is provided for the purpose of keeping the key down when once depressed. Its arrangement will be understood from an inspection of the figure. Fig. 263. Key, Sliding-Contaet - slide form of Wheatstone's The key employed in the bridge, to make contact with the wire over which the sliding contact passes. (See Balance, Wheatstone's, Slide Form of .) Key, Telegraphic Fig. 26h- The key employed for send- ing over the line the successive makes and breaks that pro- duce the dots and dashes of the Morse alphabet, or the deflections of the needle of the needle telegraph. (See Tele- graphy, American or Morse System of.) WORDS, TERMS AND PHRASES. 365 Kilo (as a prefix). — One thousand times. Kilodyne. — One thousand dynes. (See Dyne.) Kilogramme. — One thousand grammes, or 2.2046 lbs. av- oirdupois. (See Weights, French System of.) Kilojoule. — One thousand joules. Kilometre. — One thousand metres. Kilowatt. — One thousand watts. Kine. — A unit of velocity proposed by the British Asso- ciation. A kine equals one centimetre per second. Kinetie Energy. — Energy which is actually doing work, as distinguished from energy that only possesses the power of doing work, or potential energy. (See Energy.) Kite, Franklin's A kite raised in Philadelphia, Pa., in June, 1752, by means of which Franklin experiment- ally demonstrated the identity between lightning and elec- tricity, and which, therefore, led to the invention of the light- ning rod. It is true that Dalibard, on the 10th of May, 1752, prior to Franklin's experiment, succeeded in drawing sparks from a tall iron pole he had erected in France. This experiment was, however, tried at the suggestion of Franklin, and must prop- erly be ascribed to him. The following description of this kite is given by Franklin in the following letter : Letter XI., from Benj. Franklin, Esq., of Philadelphia, to Peter Collinson, Esq., F.R.S., London. " Oct. 19, 1752. "As frequent mention is made in public papers, from Europe, of the success of the Philadelphia experiment for drawing the electric fire from clouds by means of pointed rods of iron erected on high buildings, etc., it may be agreeable to the dbb A DICTIONARY OF ELECTRICAL curious to oe informed that the same experiment has succeeded in Philadelphia, though made in a different and more easy- manner, which is as follows : " Make a small cross, of two light strips of cedar, the arms so long, as to reach to the four corners of a large thin hand- kerchief, when extended ; tie the corners of the handkerchief to the extremities of the cross, so you have the body of a kite ; which, being properly accommodated with a tail, loop, and string, will rise in the air, like those made of paper ; but this, being of silk, is fitter to bear the wet and wind of a thunder gust without tearing. To the top of the upright stick of the cross is to be fixed a very sharp pointed wire, rising a foot or more above the wood. To the end of the twine, next the hand, is to be tied a silk ribbon, and where the silk and twine join, a key may be fastened. This kite is to be raised when a thunder gust appears to be coming on, and the person who holds the string must stand within a door or window, or under some cover, so that the silk ribbon may not be wet ; and care must be taken that the twine does not touch the frame of the door or window. As soon as any of the thunder clouds come over the kite, the pointed wire will draw the electric fire from them, and the kite, with all the twine will be electrified, and the loose filaments of the twine will stand out every way, and be attracted by an approaching finger. And when the rain has wet the kite and twine, so that it can conduct the electric fire freely, you will find it stream out plentifully from the key on the approach of your knuckle. At this key the phial may be charged ; and from electric fire, thus obtained, spirits may be kindled, and all the other electric experiments be performed, which are usually done by the help of a rub- bed glass globe or tube, and thereby the sameness of the electric matter with that of lightning completely demon- strated. B. Franklin." Kyanizing". — A process employed for the preservation of wooden telegraph poles by injecting a solution of corrosive WORDS, TERMS AND PHRASES. 367 sublimate into the pores of the wood. (See Poles, Tele- graphic.) Lag:, Magnetic The tendency of the iron core of a magnet, or of the armature of a dynamo-electric machine, to resist and therefore retard magnetization. This retardation, or lag, is called the magnetic lag. The lead necessary to give the brushes of a dynamo-electric machine to ensure quiet action has by some been erroneously ascribed to the magnetic lag. The lead, though due to lag in part, is, in reality, mainly due to the resultant magnetization of the armature by both the field magnets and by its own cur- rent. (See Angle of Lead.) This displacement is measured by an angle sometimes called the angle of lag. (See Angle of Lag.) Lamination of Core. — The subdivision of the core of the armature of a dynamo-electric machine into separate in- sulated plates or strips for the purpose of avoiding eddy cur- rents. This lamination must always be perpendicular to the direc- tion of the eddy currents that would otherwise be produced. (See Eddy Currents). Lamellar Di§tribntion of Magneti§ni, Magnetic Shell. — The distribution of magnetism in magnetic shells. A magnetic shell is a thin sheet or disc of magnetized mate- rial whose opposite extended faces are of opposite magnetic polarities, and the extent of whose surface is very great as compared with its thickness. The field produced by a magnetic shell is exactly similar to that produced by a closed voltaic circuit, the edges of the space inclosed by which correspond to the edges of the mag- netic shell. Magnetic Density or Intensity, or the number of lines of force per unit area of cross section, is equal over all parts of the surface of a simple magnetic shell. The strength of such 368 A DICTIONARY OF ELECTRICAL a shell will therefore be equal to its thickness multiplied by- its surface density. A magnetic shell may be conceived as consisting of a very- great number of exceedingly short, straight, magnetic needles placed side by side, with their north poles terminating at one of the faces of the sheet and their south poles at the opposite face, the breadth of the sheet being very great as compared with its thickness. Such a distribution of magnetism is known as a lamellar dis- tribution. Lamp, Arc, Electric An electric lamp in which the light is pro- duced by a voltaic arc formed between two or more carbon electrodes. The carbon electrodes are placed in various positions, either parallel, horizon- tal, inclined, or vertically one above the other. The latter is the form most gen- erally adopted, since it permits the ready feeding of the upper carbon. The carbons are maintained during their consumption, at a constant distance apart, by the aid of various feeding devices. Such devices consist generally of trains of wheelwork, mechanical or electric motors, or are operated by the simple action of a spring, gravity or a solenoid. The carbon pencils or electrodes are held in carbon holders, consisting of clutches or clamps, attached to the ends of the lamp rods. When the lamp is not in operation the carbons are usually in contact with one another ; but, on the passage of the current, they are separated the required distance by the action of an electromagnet whose coils are traversed by the direct current. Fig. 265. WORDS, TERMS AND PHRASES. 369 In order to maintain the electrodes a constant distance apart, the upper carbon is held in position by the operation of a clutch in some lamps, or, in others, by a detent, that en- gages in a toothed wheel. The position of this clutch or detent is controlled by the action of an electro-magnet whose coils are usually situated in a shunt or derived circuit, of high resis- tance, around the electrodes. When the carbons are at their normal distance apart, the shunt current is not of sufficient strength to move the clutch or detent from the position in which it prevents the downward motion of the upper carbon rod. When, however, by the burning or consumption of the carbons, the resistance of the arc has increased to an extent which can be predetermined, the increased current that is thereby passed through the shunt circuit is now sufficiently strong to release the clutch or detent, thus permitting the fall or feed of the upper carbon. In a well designed lamp this occurs so gradually as to produce no perceptible effect on the steadiness of the light. Arc lamps are generally placed in series circuits, that is, the current passes successively through all the lamps in the circuit, and returns to the source. In order to avoid the breaking of the entire circuit, an automatic safety device is provided. This consists essentially of an electro- magnet placed in a shunt circuit, so that, when the resist- ance of the arc becomes very great, the increased current, flowing through the coils of the electro-magnet, produces a movement of its armature which closes a short circuit around the lamp, and thus cuts it out of the circuit. (See Device, Safety.) Arc lamps assume a great variety of forms. A well known form is shown in Fig. 265. Lamp Bracket, Electric (See Bracket, Lamp.) Lamp, Carcel (See Car eel Lamp.) Lamp, Differential Arc An arc lamp in which the movements of the carbons are controlled by the different 370 A DICTIONARY OF ELECTRICAL tial action of two magnets opposed to each other, one of whose coils is in the direct, and the other in a shunt circuit around the carbons. Sometimes the differential coils are placed on the same magnet core. Lamp-Hours.— The number of lamp-hours is obtained by multiplying the number of lamps by the average number of hours during which they are burning. A method of estimating the current supplied to a consumer by counting the number of hours each lamp is in service. To convert lamp-hours to ivatt-hours multiply the number of lamp-hours by the number of watts per lamp. The watt- hours, divided by 746, will then give the electrical horse-power hours. (See Watt-Hours.) Lamp, Incandescent Electric An electric lamp in which the light is produced by the electric incan- descence of a strip or filament of some refractory substance, generally carbon. The carbon strip or filament is usually bent into the form of a horseshoe or arc, and placed inside a glass vessel, called the lamp chamber. This vessel is exhausted by means of a mercury pump, generally to a fairly high vacuum. In order to insure the complete removal from the lamp chamber of all the air it originally contained, both it and the carbon strip that is placed within it are maintained at a high temperature during the process of exhaustion. This tempera- ture in practice is obtained by sending the current through the carbon strip as soon as the air is nearly all removed. Towards the end of the pumping operation the current is increased so as to raise the carbons to their full brilliancy. This latter operation is termed the occluded-gas process, and is essential to the successful sealing of an incandescent lamp. By its means, a considerable quantity of air or other gaseous substances shut up or occluded by the carbon, is WORDS, TERMS AND PHRASES. 371 driven out of the carbon, which it would be impossible to get rid of by the mere operation of pumping. In order to insure the success of the operation it is necessary that the heating mast take place while the lamp is being exhausted, since otherwise the expelled gases would be reabsorbed. (See Gases, Occlusion of.) The exhaustion continues up to the moment the lamp cham- ber is hermetically sealed. The lamp chamber is usually hermetically sealed by the fusion of the glass, in the manner adopted in the sealing of Geissler tubes, or Crooke's radio- meters. For the preparation of the carbon strip, its carbonization, and the flashing of the strip see Carbonization, Processes of, and Flashing of Carbons, Process for. The ends of the carbon strip, or arc, are attached to leading-in wires of platinum that, pass through the glass walls of the lamp chamber, and are fused therein by melting the glass around them, in the same manner as are Fig. 266. the leading-in wires in Geissler tubes and other similar ap- paratus. Incandescent lamps are generally connected to the leads or circuits, in multiple-arc, or in multiple-series circuits; they are, however, sometimes connected to the line in series. (See Circuits, Varieties of.) In the former case their resistance is comparatively high ; in the latter case, comparatively low. Incandescent electric lamps assume a variety of different forms. One of them is shown in Fig. 266. The lamp chamber conforms in general shape to the outline of the filament. Lamp, Semi-Incandescent Electric An electric lamp, in which the light is due to the combined effects 372 A DICTIONARY OF ELECTRICAL of a voltaic arc, and electric incandescence. In the Reynier semi-incandescent lamp, shown in Fig. 267, a thin pencil of carbon C, is gently pressed against a block of graphite B. A lateral contact is provided at L, through a block of graphite I, by means of which the current is conveyed to the lower part only of the movable rod C, which part alone is rendered incandescent. In this lamp the light is due to both the incandescence of q the rod C, and to the small arc formed at J, between its lower end and the contact block B, though mainly from the latter. L- a t e n t Electricity.— A term formerly applied to bound electricity. Now in disuse. (See Bound, Dissimulated or Dis- guised Electricity.) Lateral Discharge.— A small discharge observed on the discharge of a Leyden jar, be- tween parts of the jar not in the circuit of the main discharge. If a charged Leyden jar is placed on an insulating stool, and is then discharged by the dis- charging rod, the lateral discharge is seen as a small spark that passes between the outside coating of the jar and a body connected with the earth at the moment of the discharge through the rod. This lateral discharge is due to a small excess of free electricity on the outside, that is not neutralized by the opposite charge. A lateral discharge is also seen in the sparks that can be taken from a conductor in good connection with the earth, by holding the hand near the conductor, while it is receiving Words, terms and phrases. 373 large sparks from a powerful machine in operation. These discharges are due to induction. Lateral Induction. — Induction observed between closely approached portions of a circuit, through which the disruptive discharge of a Leyden jar is passed as a long spark, thereby making the resistance of the circuit high. A long copper wire, bent in the form of an open rectangle, has its free ends bent near their extremities so as to approach each other until but half an inch apart. The extreme end of one of the extremities is provided with a metallic ball, and the other end connected with the earth. If, now, a Leyden jar charge is passed through the wire, by connecting the outer coating with the end of the earth connected wire, and holcl- ingthe inside coating near the knob, a spark will pass through the half inch of air space between the approached portions of the circuit. This discharge is clue to what was called formerly lateral induction. The discharge from the approached parts of the wire is probably to be regarded as a branch discharge, or shunt current, due to the fact that the accumulated resistance of the wire to the current of the disruptive discharge, becomes greater than that of the air space between the approached pails of the wire. Law, Natural — A correct expression of the order in which the causes and effects of natural phenomena follow one another. The law of gravitation, for example, correctly expresses the order of sequence of the phenomena which result when unsup- ported bodies fall to the earth. It should be carefully borne in mind, however, that natural laws cannot be regarded as explaining the ultimate causes of natural phenomena, but merely express their order of occurrence or sequence. We are, ignorant, for example, of the true cause of gravita- tion and are only acquainted with its effects. This is true of 374 A DICTIONARY OF ELECTRICAL all ultimate physical causes, save for the belief in their origin in a Divine will. Laws, Ampere's or Laws of Electro-Dyna- mic Attraction and Repulsion.— Laws expressing the attractions and repulsions of electric circuits on one another. Laws, Beequerel's or Laws of Magneto- Optic Rotation. — Laws of the magneto-optic rotation of the plane of polarization of light. (See Magneto- Optic Rota- tion.) Laws of Coulomb, or Laws of Electrostatic and magnetic Attractions and Repulsions. — Laws for the force of attraction and repulsion between charged bodies or between magnet poles. The fact that the force of electrostatic attraction or repul- sion between two charges, is directly proportional to the product of the quantities of electricity of the two charges and inversely proportional to the square of the distance between them, is known as Coulomb' 's Law. Coulomb also ascertained that the attractions and repulsions between magnet poles is directly proportional to the product of the strength of the two poles, and inversely proportional to the square of the distance between them. This is also called Coulomb's Law. Laws of Faraday, or Laws of Electrolysis.— Laws for the effects of electrolytic decomposition. (See Electrolysis.) Law* of Kirchoff, or Laws of Shunt-Circuits.— The laws of branched or shunted circuits. These laws may be expressed as follows : (1) In any number of conductors meeting at a point, if cur- rents flowing to the point be considered as -f-, and those flow- ing away from it as — , the algebraic sum of the meeting cur- rents will be zero. This is the same thing as saying as much electricity must flow away from the point as flows toward it. WORDS, TERMS AXD PHRASES. 375 (2) In any system of closed circuits the algebraic sura of the products of the currents into the resistances is equal to the electro-motive force in the circuit. Iu this case all currents flowing in a certain direction are taken as positive, and those flowing in the opposite direction as negative. All electro-motive forces tending to produce currents in the direction of the positive current are taken as positive, and those tending to produce currents in the oppo- site direction, as negative. E This follows from Ohm's law; for, since C = — , the electro- R motive force E = CR, and this is true no matter now often the circuit is branched. Laws of Lenz. — Laws for determining the directions of the cm-rents produced by electro magnetic or electro dynamic induction. (See Lenz's Lair.) Law of Ohm, or Law for Current Strength.— A fundamental law for determining the current strength in any circuit. The strength of the current in any circuit is directly pro- portional to the electro-motive force, and inversely propor- tional to the resistance of the circuit. E C = — , or E = C R. (See Ohm's Laiv.) R Law of Volta, or Law for Contact-Series.— A law for the differences of electric potential produced by the con- tact of dissimilar metals or other substances. " The difference of potential between any two metals is equal to the sum of the differences of potential between the intervening substances in the contact-series.''' (See Contact Electricity. Contact-Series.) Layer, Crookes' A layer, or stratum, in the residual atmosphere of a vacuous space, in which the mole- cules recoiling from a heated or electrified surface do not 376 A DICTIONARY OF ELECTRICAL meet other molecules, but impinge on the walls of the vessel directly opposite to such heated surface. A Crookes' layer may result as the effect of two different causes, viz. : (1) The rarefaction of the gas is such that the distance be- tween the walls of the vessel and the heated surface is less than the mean free path of the molecules. (2) The wall is so near the heated surface that the distance between the two is less than the actual mean free path of the molecules. Under these last named circumstances, Crookes' layers may result whatever be the density of the gas. Lead of Brus1ie§ of Dynamo-Electric Machine. (See Angle of Lead.) Leading Horns of Dynamo-Electric Machine. (See Horns, Leading, of Dynamo Electric Machine.) Leads. — The main conductors of any system of electric dis- tribution. The leads, or main conductors in a multiple system of incan- descent lighting, must maintain a constant potential at the lamp terminals. The dimensions of the leads are therefore so proportioned as to absorb as small an amount of potential as possible. Since in incandescent lighting, where the lamp is connected to the leads in multiple-arc, the total resistance of the lamps is comparatively small, the resistance of the leads must necessarily be quite small in order to avoid a marked drop of potential. Comparatively large conductors must therefore be used. The main conductor for series circuits, such as for arc lights, has in all parts the same current strength. Since the resist- ance of the lamp in such a circuit is quite high, a compara- tively high resistance in the conductor can be employed with- out a proportionally large absorption of potential. Com- paratively small conductors can therefore be used. (See Sys- tems of Current Distribution by Constant and by Alternating Currents.) WORDS, TERMS AND PHRASES. 377 Leakage, Electric The gradual dissipation of a charge or current due to insufficient insulation. Some leakage occurs under nearly all circumstances. On telegraph lines, during wet weather the leakage is often so great as to interfere with the proper working of the lines. The leakage of a well insulated conductor, placed in a high vacuum, is almost inappreciable. Crookes has maintained electric charges in his high vacua for years without appre- ciable loss. Leakage Conductor. — A conductor placed on a tele- graph circuit, to prevent the disturbing effects of leakage into a neighboring line by providing a direct path for such leakage to the earth. The leakage conductor, as devised by Varley, consists of a thick Avire attached to the pole. The lower end of the con- ductor is well grounded, and its upper end projects above the top of the pole. There exists some doubt in the minds of experienced tele- graph engineers whether it is well to apply leakage conductors to telegraphic or telephonic lines of over 12 or 15 miles in length, since such conductors greatly increase the electro- static capacity of the line, and thus cause serious retardation. Leakage, Magnetic A useless dissipation of the lines of magnetic force of a dynamo-electric machine, or other similar device, by their failure to pass through the armature. (See Magnetophone.) Leclanche'§ Voltaic Cell. (See Cell, Voltaic.) Legal Ohm. — The resistance of a column of mercury one square millimetre in cross-section and 106 centimetres in length, at the temperature of 0° C. or 32° F. (See B. A. Unit.) 1 Ohm = 1.00112 B. A. Unit. This value of the ohm was adopted by the International Electric Congress, in 1884, as a value that should be accepted internationally as the true value of the ohm. B78 A DICTIONARY OF ELECTRICAL Length of Spark.— The length of spark that passes between two charged conductors depends : (1) On the difference of potential between them. (2) On the character of the gaseous medium that separates the two conductors. (3) On the density or pressure of the gaseous medium be- tween the conductors. Up to a certain pressure, a decrease in the density causes an increase in the length of the distance the spark will pass. When this limit is reached, a farther decrease of density decreases the length of spark. A high vacuum prevents the passage of a spark even under great differences of potential. (4) On the kind of material that forms the electrodes be- tween which the charges pass. (5) On the shape of the charged conductor. (6) On the direction of the current. Sparks from the prime conductor are denser and more powerful than those from the negative conductor. It will be observed that the length of the spark practically depends mainly on two circumstances, viz., on the differences of potential of the opposite charges, and the conducting power of the medium that separates the two bodies. Lenz' Law. — The direction of the currents set up by electro-mag'netic induction is always such as to tend to op- pose the motion producing them. Letter-Boxes, Electric Various devices that announce the deposit of a letter in a box, by the ringing of a bell or the movement of a needle or index. These devices generally act by the making or opening of an electric circuit by the fall of the letter in the box. Ley den Jar. (See Jar, Ley den.) Ley den- Jar Battery. (See Battery, Ley den Jar.) Lichtenberg's Figures. (See Figures, Lichteriberg.) WORDS, TERMS AND PHRASES. 379 Life of Electric Incandescent Lamps. — The num- ber of hours that an incandescent electric lamp, when traversed by the normal current, will continue to afford a good com- mercial light. The failure of an electric incandescent lamp results either from the volatilization or rupture of the carbon conductor, or from the failure of the vacuum of the lamp chamber. Since the employment of the flashing' process, and the process for removing the occluded gases it is not unusual for incandes- cent lamps to have a life of several thousand hours. (See Flashing Carbons, Process for.) Light, Electro-Magnetic Hypothesis of A hypothesis for the cause of light proposed by Maxwell, based on the relations existing between the phenomena of light and those of electro-magnetism. Maxwell's electro-magnetic theory of light assumes that the phenomena of light and magnetism are each due to cer- tain motions of the ether. Electricity and magnetism being due to its rotations or oscillations, and light to its to-and-fro motions. He proposed this theory to show that the phenomena of light, heat, electricity and magnetism could all be explained by one and the same cause, viz., a vibratory or oscillatory motion of the particles of the hypothetical ether. Maxwell died before completing his hypothesis, and it has never since been sufficiently developed to thoroughly entitle it to the name of a theory. There are, however, numerous considerations which render it probable that electric and magnetic phenomena, like those of light and heat, have their origin in a vibratory or oscillatory motion of the luminiferous ether. A few of these, as pointed out by Maxwell, S. P. Thompson, Lodge, Larden and others, are as follows : (1) It is quite possible that the thing called electricity is the ether itself ; negative electrification consisting in an excess of 880 A DICTIONARY OF ELECTRICAL the ether, and positive electrification in a deficit. (See Hy- potheses of Electricity.) (2) It is possible that electrostatic phenomena consist in a strain or deformation of the ether. A dielectric may differ from a conductor in that the former may have such an attrac- tion for the ether as to give it the properties of an elastic solid, while in the latter the ether is so free to move that no strain can possibly be retained by it. (See Dielectric. Con- ductor.) (3) Dielectrics are transparent and conductors are opaque. There are exceptions to this in the case of vulcanite and man} T other excellent dielectrics. Nor should this similarity be expected to be general in view of the difference between diathermancy and transparency. (4) It is possible that an electric current consists of a real motion of translation of the ether through a conductor. (5) It is possible that electro-motive force results as differ- ences of ether pressures, this would of course follow from (4). (6) The vibrations of light are propagated in a direction at right angles to the direction in which the light is moving. The magnetic field of a current is propagated in planes at right angles to the direction in which the current is flowing. (7) It is possible that lines of electrostatic and magnetic force consist of chains of polarized ether particles. (8) The velocity of propagation of light agrees very nearly with the velocity of propagation of electro-magnetic induc- tion. (See Velocity Ratio.) (9) In certain axial crystals the difference of transparency in the direction of certain axes, corresponds with the direc- tion in which such crystals conduct electricity. Light-House Illumination, Electric The application of the electric arc light to the illumination of light houses. A powerful arc light is placed in the focus of the dioptric lens now commonly employed in light houses. Since the con- WORDS, TERMS AND PHRASES. 331 sumption of the carbon electrodes would alter the position of the focus of the light, electric lamps for such purposes are constructed to feed both of their carbons instead of the upper carbon only, as in the case of the ordinary arc lamp. Light, Intensity oi* (See Intensity of Light. Photometer.) Lighting, Central Station The lighting of a number of houses or other buildings from a single station, centrally located. Central station lighting is distinguished from isolated lighting, by the fact that a number of separate buildings, houses, or areas are lighted by the current produced at a single station, centrally located, instead of from a number of separate electric sources located in each of the houses, etc., to be lighted. (See Systems of Electric Distribution.) Lightning.— The spark or bolt that results from the dis- charge of a cloud to the earth, or to a neighboring cloud. (See Atmospheric Electricity. Kite, Franklin's.) Lightning Arrester.— A device, by means of which the apparatus placed in any electric circuit are protected from the destructive effects of a flash or bolt of lightning. In the phenomena of lateral induction we have seen the tendency of a disruptive discharge to take a short cut across an intervening air space, rather than through a longer though better conducting path. Most lightning arresters are depend- ent for their operation on this tendency to lateral discharge. (See Induction, Lateral. Discharge, Disruptive.) A form of lightning arrester is shown in Fig. 268. The line wires A and B, are connected by two metallic plates to C and D, respectively. These plates are provided with points, as shown, and placed near a third plate, connected to the ground by the wire G. Should a bolt strike the line, it is discharged to the earth through the wire G, A DICTIONARY OF ELECTRICAL Lightning, Back or Return Stroke.— (See Back or Return Stroke of Lightning.) Lightning, Globular A rare form of light- ning, in which a globe of fire appears for a while, quietly floats in the air, and then explodes with great violence. The exact cause of globular lightning is unknown. Phe- nomena allied to it, however, have been observed by Plants during the discharge of his rheostatic machine, when dis- charged in series, or for a great difference of electric potential. Similar phenomena, are sometimes, though rarely, observed during the discharge of a powerful Leyden battery. Sir Wm. Thomson ascribes the effect to an optical illusion. .Lightning, Heat or Sheet, Volcanic and Zigzag Heat or sheet lightning is the name given to a dis- charge unaccompanied by any thunder audible to the observer, in which the entire surfaces of the clouds are illumined. Its cause has been ascribed to the reflection from the clouds of lightning flashes too far below the horizon to permit them to be directly seen, or the thunder to be audible, WORDS, TERMS AND PHRASES. 383 If a Geissler tube, which contains several concentric tubes, be charged by a Holtz machine, and then touched at different parts by the hands, a succession of luminous discharges will be seen in the dark, that bear a remarkable resemblance to the flashes of heat or sheet lightning. Lightning Rods. — A rod, or wire cable of good conduct- ing material, placed on the outside of a house or other struc- ture,^ order to protect it from the effects of a lightning dis- charge. Lightning rods were invented by Franklin. The result of a very extended inquiry recently made on the subject, leaves no room for doubt that a lightning rod, properly constructed and placed, affords an efficient protection to the buildings on which it is placed. To insure this protection, however, all the following con- ditions must be carefully fulfilled, else the rod may prove a source of danger rather than a protection, viz.: (1) The rod, generally of iron or copper, should have such an area of cross section as to enable it to cany without fusion the heaviest bolt it is liable to receive in the latitude in which it is located. When of iron, the area of cross section should be about seven times greater than when of copper. (2) The rod should be continuous throughout, all joints being carefully avoided. If these be used they should be made of as low resistance as possible and should be protected against corrosion. (3) The upper extremity of the rod should terminate in one or more points formed of some metal that is not readily cor- roded, such as platinum or nickel. (4) The lower end of the rod should be carried down into the earth until it meets permanently damp or moist ground, where it should be attached to a fairly extended metallic sur- face buried in the ground. Metallic plates will answer for the purpose, but, if gas or water pipes are available, the rod should 384 A DICTIONARY OF ELECTRICAL be placed in good electrical connection therewith, by wrapping it around and soldering it to such pipes. This fourth requirement is of great importance to the pro- per action of a lightning rod, and unless thoroughly fulfilled may render the rod worthless, no matter how carefully the other requirements are attended to. When a bolt strikes a light- ning rod which is not properly grounded, the discharge is almost certain to destroy the building to which the rod is connected. (5) The rod should not be insulated from the building, un- less to prevent stains from the oxidation of the metal. On the contrary it should be directly connected with all masses of metal in its path, such as tin roofs, gutter-spouts, metallic cornices, etc. In this way only can dangerous disruptive lateral dis- charges from the rod to such masses of metal be avoided. (6) The rod should project above the roof or highest part of the building, or, in other words, the height of the rod should bear a certain proportion to the size of the building to be pro- tected. A rod will protect a conical space around it, the radius of whose base is equal to the vertical height of the rod above the ground, but whose sides are curved inwards instead of being straight. Where the building is very high, a num- ber of separate rods all connected to one another should be employed. (7) A stranded conductor is much better than an equal cross section of a solid rod of the same metal. A lightning rod more frequently acts to quietly discharge an impending cloud by convective discharge, than by an ac- tual disruptive discharge of the same. (See Discharge, Con- vective. Discharge, Disruptive.) Lightning rods should be frequently tested to see that no breaks or oxidation of their joints have occurred. Lightning Rods for Ships.— A system of rods designed to afford electric protection for vessels at sea. Since the lightning discharge takes place between the points of greatest difference of potential, and these are gener- WORDS, TERMS AND PHRASES. 385 ally between the cloud and the nearest point of the earth, tall objects are especially liable to be struck. Ships at sea should, therefore, be thoroughly protected from lightning. In Harris' system of lightning protection for ships, the rods are connected with a series of copper plates and rods so placed on the masts as to readily yield to strains. These are elec- trically connected with the copper sheathing of the vessel and with all large masses of metal in the vessel. This latter precau- tion is especially necessary in the case of men-of-war, in order to protect the powder magazine. Harris' method for the light- ning protection of ships, which was adopted only after very considerable opposition, proved so efficacious in practice that serious effects of lightning on vessels so protected are now almost unknown. In 1845, Harris received the honor of knighthood from the English Government for his services in this respect. A lightning rod sometimes fails to protect a house or barn from the fact that a heated, ascending current of air from a fire in the house, or from the gradual heating of green hay or grain in the barn, increases the virtual height of the house beyond the ability of its rod to protect it. Lightning, Volcanic — The lightning dis- charges that attend most volcanic eruptions. Volcanic lightning is probably due to the friction of volcanic dust particles against one another, or against the air, but par- ticularly to the sudden condensation of the vapor that is gen- erally disengaged during volcanic eruptions. Lightning, Zigzag, Chain or Forked The commonest variety of lightning flashes in which the dis- charge apparently assumes a forked zigzag, or even a chain- shaped path. This form is seen in the discharge of a Holtz machine, or of a Ruhmkorff Induction Coil. d»b A DICTIONARY OF ELECTRICAL The irregular shape of the path is probably due to the resistance of solid particles in the air, which are piled up in front of the discharge, or to the effects of the lateral induc- tion that is produced during the discharge. (See Induction, Lateral.) Line, Neutral of a Magnet.— A line joining the neutral points of a magnet, or the points approximately mid- way between the poles. This is sometimes called the equator of the magnet. The neutral point is the point where the lines of force out- side the magnet are parallel to the surface of the magnet. (Hering.) Line, Neutral of Commutator Cylinder.— A line on the commutator cylinder of a dynamo-electric machine, connecting the neutral points, or the points of maximum posi- tive and negative difference of potential. (See Dynamo- Electric Machine.) Line, Telegraphic, Telephonic, etc. The conducting circuit provided for the transmission of the elec- tric impulses or currents employed in any system of electric transmission. Lines, Aclinic, or Isoclinic Lines connecting places that have the same magnetic inclination. (See Aclinic Line. Isoclinic Line.) Lines, Agonic, or Isogonic Lines connecting places that have an equal magnetic declination. (See A gone.) Lines, Isodynamic (See Isodynamic Lines.) Lines of Electrostatic Force. — Lines extending in the direction in which the force of electrostatic attraction or re- pulsion acts. Lines of electrostatic force pass through dielectrics; whether the force acts by means of a polarization of the dielectric, or by means of a tension set up in it, is not known. (See Field, Electrotastic.) WORDS, TERMS AND PHRASES. 387 Lines of Force, Direction of Lines extending in the direction in which the lines of magnetic force are assumed to pass. The lines of magnetic force are assumed to come out of the north pole of a magnet, and to pass in at its south pole. The lines of electrostatic force are assumed to pass out of a positively charged surface, and into a negatively charged sur- face. Lilies of Magnetic Force.— Lines extending in the direction in which the force of magnetic attraction or repul- sion acts. (See Field, Magnetic.) Liquids, Specific Resistance of The resist- ance of a given length (one centimetre) and cross section (one square centimetre) of any liquid as compared with the resist- ance of an equal length and cross section of pure silver. The resistance of a few common liquids and solutions is here given from Lupton : Water, pure at 75° C 1.188 X 10 8 ohms i. e., 118,800,000. Water at 4° C 9.100 X 10 6 " Water at 11° C 3.400 X 10 5 " Dilute hydrogen sulphate (sulphuric acid) at 18° C. 5 per cent, acid 4.88 Dilute hydrogen sulphate at 18° C. 3 per cent.acid 1.38 " Nitric acid, at 18° C. density 1.32 1.61 " Saturated solution of copper sulphate (blue vitriol) at 10° C 29.30 Saturated solution of zinc sulphate at 14° C. 21.50 " Hydrochloric acid, 20 per cent, acid, at 18° C. 1.34 " Sal ammoniac, 25 per cent, salt 2.53 " Common salt, saturated, at 13° C 5.30 " It will be observed that the resistance varies considerably with differences of temperature. 388 A DICTIONARY OF ELECTRICAL Local Action. — In a battery, the loss of energy by the irregular and wasteful solution of the zinc or positive element by the electrolyte. The local action of a battery is caused by the solution of the zinc or positive plate by the action of local voltaic couples formed by couples of zinc and minute particles of carbon, lead, or other impurities. It is remedied by the amalgamation of the zinc. (See Zinc, Amalgamation of.) In a dynamo electric machine, the loss of energy by the setting up of eddy currents in the conducting masses of the pole-pieces, cores, etc. (See Currents, Eddy.) In a dynamo electric machine local action is obviated by a lamination of the pole pieces, armature core, etc. (See Lamination of Cores. ) Local Battery. — (See Battery, Local.) Local Currents. — (See Currents, Eddy.) Localization of Faults. — Determining the position of a fault in a telegraph line or cable by calculations based on the fall in the potential of the line measured at different points or by loss of charge, etc. For description see standard works. Locomotive, Electric A railway engine whose motive power is electricity. (See Railroad Electric.) Locomotive Head-Light, Electric (See Head-Light, Electric.) Lodes tone. — A name applied by the ancients to an ore of iron (magnetic iron ore), that naturally possesses the power of attracting light pieces of iron to it. Lodestone, or magnetic iron ore, must be regarded as a magetizable substance that has become permanently magnetic from its situation in the earth's magnetic field. Such beds of ore concentrate the lines of the earth's magnetic field on them, and thus become magnetic. WORDS, TEHMS AND PHRASES. 389 Log, Electric An electric device for measuring the speed of a vessel. Any log- that operates by the rotation of a wheel is caused to register the number of rotations by a step-by-step recording- apparatus operated by breaks in the circuit, made during- the rotation of the wheels, at any given number of turns, say 100, or any other convenient multiple. Such a log* may he kept constantly in the water, and observed when required, or it can be made to register a permanent record of its actual speed at any lime during the entire run. Logarithm*. — The logarithm of any given number, is the exponent of the power to which it is necessary to raise a fixed number, in order to produce the given number. A table of logarithms enables the operations of multiplica- tion, division, and the extraction of roots, to be readily per- formed by simple multiplication, division, addition or subtrac- tion. When thoroughly understood, logarithms greatly re- duce the labor of mathematical calculations. For the manner in which they are used the student is referred to any standand work on mathematics. Longitude, Electrical Determination of The determination of the longitude of a place, by differ- ences in time between it and a place on the prime meridian, as simultaneously determi ned telegraphically. In determinations of this character allowance must be made for the retarding effects of long telegraphic lines, or cables. Loop, Electric A portion of a main circuit consisting of a wire going out from one side of a break in the main circuit and returning to the other side in the break. Loops are employed for the purpose of connecting a branch telegraph office with the main line ; for placing* one or more electric arc lamps on the main line circuit ; for connecting a messenger call, or telephone circuit with a main line; and for numerous similar purposes. 390 A DICTIONARY OF ELECTRICAL Loxodrograpn. — An apparatus for electrically recording 1 on paper the actual course of a ship by the combined action of magnetism and photography. Luces. — Plural of lux. (See Lux.) Lux. — A name proposed by Preece for the unit of inten- sity of illumination. One lux is the illumination given by a standard candle at the distance of 12.7 inches. One lux is the illumination given by a carcel at the distance of one metre. One lux is the illumination given by a lamp of 1,000 candles at 105.8 feet. (See Illumination, Unit of.) Machine, Frictional Electric A machine for the de- velopment of electric- ity by friction. A frictional electric machine consists of a plate or cylinder of glass A, Fig. 271, ca- pable of rotation on a horizontal axis. A rubber formed of a chamois skin, covered with an amalgam of tin and mercury, is placed at B. By the rotation of the plate the rubber becomes negatively, and the glass positively excited. An insulated conductor D, called the prime or positive conductor, provided with a comb of points, becomes positively charged by induction. The machine will develop electricity best if a conductor attached to the 271. WORDS, TERMS AND PHRASES. 391 rubber is connected with the ground, as by a chain, as shown. Machines, Electrostatic Induction or Influence Machines. — Machines in which a small initial charge produces a greatly increased charge by its in- ductive action on a rapidly rotated disc of glass. An excellent type and example of such a machine is found in the Holtz machine which consists of the following parts, as shown in Fig. 272, viz. : (1) A stationary glass plate A, fixed at its edges to insulated supports. (2) A movable plate B, capable of rapid rotation on a hor- izontal axis, by a driv- ing pulley. (3) Armatures of var- n i s h e d paper/,/', placed on opposite sides of the fixed plate at holes or windows P, P', cut in the plate. The armatures are placed on the side of the fixed plate away from the moving plate, or on the back of the plate, so that the plate, on its rotation, moves towards tongues of paper attached to the middle of the armature. (4) Metal combs placed in front of the movable disc oppo- site the armatures, and connected with the brass balls m, n, one of which is movable towards and from the other by means of a suitably supported insulating- handle connected with it. 892 A DICTIONARY OP ELECTRICAL A small initial charge is given to one of the armatures by holding a plate of electrified vulcanite on it, and rotating the machine while the balls m, n, are in contact. As soon as the machine is charged the balls are gradually separated, when a torrent of sparks will pass between them so long as the plate is rotated. When the balls are separated too far the sparks cease to pass. The balls must then be again brought into contact and gradually separated as before. The Holtz machine can be regarded as a revolving electro- phones provided with means for constantly discharging and recharging the upper metallic plate. (See Electrophorus). The action of the machine is well described by S. P. Thomp- son in his " Elementary Lessons on Electricity and Magnetism," as follows : ' ' Suppose a small -f- charge to be imparted at the outset to the right armature /; this charge acts inductively across the discs upon the metallic comb, repels electricity through it, and leaves the points negatively electrified. They discharge negatively electrified air upon the front surface of the mov- able disc ; the repelled charge passes through the brass rods and balls, and is discharged through the left comb upon the front side of the movable disc. Here it acts inductively upon the paper armature, causing that part of it which is opposite itself to be negatively charged and repelling a -f- charge into its farthest part, viz., into the tongue, which being" bluntly pointed, slowly discharges a -j- charge upon the back of the movable disc. If now the disc be turned round, this -|- charge on the back comes over from the left to the right side, in the direction indicated by the arrow, and, when it gets opposite the comb, increases the inductive effect of the already existing -f- charge on the armature, and therefore repels more electricity through the brass rods and knobs into the left comb. Mean- time the — charge, which we saw had been induced in the left WORDS, TERMS AND PHRASES. armature, has in turn acted on the left comb, causing a -\- charge to be discharged by the points upon the front of the disc ; and, drawing electricity through the brass rods and knobs, has made the right comb still more highly — , increasing the dis- charge of — ly electrified air upon the front of the disc, neu- tralizing the -f- charge w hi c h is being con- veyed over from the left. These actions re- sult in causing the top half of the moving - disc to be — ly electrified. The charges on the front serve as they are carried round, to neu- tralize the electricities let off by the points of tht» combs, while the charges on the back, in- Fi 0- -75. duced respectively in the neighborhood of each of the arma- tures, serve, when the rotation of the disc conveys them round, to increase the inductive influence of the charge on the other armature." The student will be aided in following Prof. T.s explanation by the diagrammatic sketch, shown in Fig. 273. Here the rotat- ing plate is shown for convenience in the form of a cylinder. The armatures are shown on the back of the plate at /' and/, opposite the brass collecting combs P' and P, with their dis- charging rods and balls a a. The effect of the positive charge given to the right hand armature/, directly through the combs P , rods a a, comb P, to left hand armature /, is readily seen. The rotation of the plate being In the direction of the curved arrows, the charging of the front of the plate by convection streams from the combs, and the back of the plate from the points 394 A DICTIONARY Off ELECTRICAL of the paper armatures, as well as the character of the charge will he understood. There thus results, as is shown, a positive charge on both the front and back of the upper half of the rotating plate, and a negative charge on both sides of its lower half. A reversal of polarity of the plate occurs at the line PaaF, Sometimes the reversal does not occur and the machine either loses its charge entirely, or in part. A conductor S S, furnished with points, is sometimes provided to lessen the chances of lack of reversal. Machines, Faradic (See Faradic Machines.) Made Circuit.— (See Circuit, Closed.) Magnc-Crystallic Action. — A term proposed by Fara- day to express the differences in the action of magnetism on ciystalline bodies in different directions. A needle of tourmaline if hung with its axis horizontal is no longer paramagnetic as usual, but diamagnetic. The same is true of a crystal of bismuth. Faraday concluded from these experiments that a force existed distinct from the paramag- netic or diamagnetic force. He called this the magne-crys- tallic force. Plucker infers from these phenomena that a definite relation exists between the ultimate form of the particles of matter and their magnetic behavior. The subject may be regarded as yet somewhat obscure. (See Diamagnetic Polarity.) Magnet. — A bod}' possessing the power of attracting the unlike poles of another magnet or repelling the like poles ; or of attracting readily magnetizable bodies like iron filing's to either pole. A body possessing a magnetic field. — (See Field, Magnetic.) The lines of force are assumed to pass through the magnetic field out at the north pole and in at the south pole. All lines of force form closed magnetic circuits. If a magnetizable body is brought into a magnetic field, the lines of magnetic force WORDS, TERMS AND PHRASES. 395 are concentrated on it and pass through it. The body there- fore becomes magnetic. The intensity of the resulting magnetism depends on the number of lines of force that pass through the body, and the polarity on the direction in which they pass through it. Magnet, V nomalou§ A magnet which pos- sesses more than two poles. — (See Anomalous Magnet.) Magnet, Artificial A magnet produced by induction from another magnet, or from an electric current. Any magnet not found in nature is called an artificial magnet. Magnet, Bell Shaped A modification of a horseshoe shaped magnet in which the approached poles are semi-annular in shape, and form a split tube. Bell magnets are. used in many galvanometers, because they can be readily dampened by surrounding them by a mass of copper. The needle in its motion produces currents that tend to oppose and therefore to stop its motion. (See Lenz's Law.) Magnet Coils. — The coils of insulated wire surrounding" the core of an electro magnet, and through which the mag- netizing current is passed. — (See Magnetism, Ampere's Theory of. Dynamo Electric Machine, Field Magnets.) Magnet, Compensating — —A magnet placed over a magnetic needle, generally over the magnetic needle of a galvanometer, for the purpose of varying the direction and intensity of the magnetic force of the earth on the needle. — (See Galvanometer, Reflecting.) A magnet, called a compensating magnet, is sometimes placed on a ship, near the compass needle, for the purpose of neutral- izing the local variation produced on the compass needle by the magnetism of the ship. 896 A DICTIONARY OF* ELECTRICAL Magnet, Compound •A number of single magnets, placed parallel and with their similar poles facing one another, as shown in Fig. 274. Compound magnets are stronger in proportion to their weight than single magnets. Magnet, Electro A magnet produced by the passage of an electric current around a core of soft iron.— (See Electro-Magnet. ) Magnet, Horse§lioe (See Horseshoe Magnet.) Magnet, Keeper of (See Keeper of Magnet. ) Magnet, Permanent A magnet of hardened steel or other sub- stance which retains its magnetism for a long time after being magnetized. A permanent magnet is distinguished, in this respect, from a temporary magnet of soft iron which loses its magnetization very shortly after being taken from the magnetizing- field. NkZ= Magnet, Portative Power of °' 27lt ' The lifting power of a magnet. The portative, or lifting power of a magnet, depends on the form of the magnet, as well as on its strength. A horseshoe magnet, for example, will lift a much greater weight than the same magnet if in the form of a straight bar. This is due not only to the mutual action of the approached poles, but also to the decreased resistance of the magnetic circuit, and to the greater number of lines of magnetic force that pass through the armature. The portative power increases as the area of contact in- creases. Magnet, Receiving or Relay. — (See Relay.) WORDS, TERMS AND PHRASES. 397 Magnet, Simple A single magnetized bar. Magnet, Solenoidal A long, thin, uniformly magnetized straight bar of steel, with its poles at its extremi- ties, that acts on external objects as if equal and opposite quan- ties of magnetism were collected at its extremities. It derives its name solenoidal, from the similarity between its action and that of a solenoid. Unless very carefully mag- netized a magnet will not act as a solenoidal magnet. (See Electro-Magnet. Solenoidal Distribution of Magnetism. ) Magnet, Tubular or Iron-Clad Magnet. — A form of horseshoe magnet in which one pole is brought near the opposite pole by a hollow cylinder or tube, which is placed in contact with one of the magnetic poles, so as to completely surround the other, except in the plane of cross section of that pole. There is thus obtained a magnet, with two concentric poles, one solid and one annular, the portative power of which is much greater than that of a horseshoe magnet of equal di- mensions. Magnetic Attraction. — (See Attraction, Magnetic.) Magnetic Axis. — (See Axis, Magnetic.) Magnetic Azimuth.— (See Azimuth, Magnetic.) Magnetic Battery. — (See Battery, Magnetic.) Magnetic Bridge.— (See Bridge, Magnetic.) Magnetic Circuit. — (See Circuit, Magnetic.) Magnetic Couple.— (See Couple, Magnetic.) Magnetic Curves. — Curved lines, formed by sprinkling iron filings on a sheet of paper or glass held in the field of a magnet, and gently tapping the same so as to permit the fil- ings to arrange themselves in the direction of the lines of magnetic force. (See Figures, Magnetic.) OVO A DICTIONARY OF ELECTRICAL Magnetic Declination.— The angular deviation of the magnetic needle to the east or west of the true geographical north. (See Needle, Declination of. Declination Chart.) magnetic Density.— (See Density, Magnetic.) Magnetic Dip.— (See Dip, Magnetic.) Magnetic Explorer.— (See Explorer, Magnetic.) Magnetic Field.— The atmosphere of magnetic influence which surrounds the poles of a magnet. Any space traversed by lines of magnetic force, forms a magnetic field. (See Field, Magnetic.) Magnetic Figures.— (See Figures Magnetic. Field, Mag- netic.) Magnetic Filament.— A polarized line or chain of ulti- mate magnetic particles. (See Filament, Magnetic.) Magnetic Force. — The force which causes magnetic at- tractions and repulsions. Magnetic Inclination.— The angular deviation from a horizontal position of a freely suspended magnetic needle. (See Dip of Needle. Inclination Chart.) Magnetic Induction. — The magnetization of magnetiz- able substances by bringing them into a magnetic field. (See Induction, Magnetic.) Magnetic Inertia. — (See Inertia, Magnetic. Lag, Magnetic.) Magnetic Intensity. — (See Intensity of Magnetiza- tion.) Magnetic Lag. — (See Lag, Magnetic.) Magnetic Leakage. — Useless dissipation of lines of magnetic force outside that portion of the field of a dynamo electric machine through which the armature moves. Magnetic leakage will result in a low efficiency of the dyna- mo. (See Coefficient, Economic of Dynamo.) WORDS, TERMS AND PHRASES. 399 Magnetic Lines of Force. — (See Lines of Force, Mag- netic.) Magnetic Masses. — (See Masses, Magnetic.) Magnetic Memory. — A term proposed by J. A. Fleming for coercive force. Y Soft iron has but a feeble memory of its past magnetization. Magnetic Meridian. — The magnetic meridian of any place is the meridian which passes through the poles of a mag- netic needle, when in a position of rest under the free influence of the earth's magnetism at that place. The plane of the magnetic meridian of a place is a vertical plane passing through the poles of a magnetic needle in a position of rest under the free influence of the earth's mag- netism at that place. Magnetic Moment. — The magnetic moment of a mag- netic needle is the product of one of the two forces of the directive couple, multiplied by the perpendicular distance be- tween the directions of these forces ; or, in other words, the moment of a magnet is equal to its length multiplied by the intensity of the magnetism of one of its poles. -(See Couple, Magnetic). Magnetic Observatory. — (See Observatory, Magnetic.) Magnetic Permeability. — Conductibility for lines of magnetic force. Iron is a substance which possesses great magnetic permea- bility. When placed in a magnetic field the lines of force are concentrated on and readily pass through its mass, or, in other words, its magnetic resistance is low. All paramag- netic bodies, have a high magnetic permeability. (See Par- amagnetic) Magnetic Pole§, False (See False Poles, Mag- netic.) Magnetic Reluctance. — A term recently proposed in place of magnetic resistance, to express the resistance offered 400 A DICTIONARY OF ELECTRICAL by a medium to the passage through its mass of the lines of magnetic force. Magnetism, Residual The small amount of magnetism retained by soft iron when removed from a mag- netizing field. Magnetic Resistance.— Resistance offered by a medium to the passage of the lines of magnetic force through it. The magnetic resistance of the circuit of the lines of force is reduced by forming the circuit of a medium having a high magnetic permeability, such as soft iron. This is accomplished by the armature or keeper of a magnet, or by the iron in an ironclad magnet. (See Iron- Clad Magnet.) Magnetic Retentivity.— (See Retentivity, Magnetic.) Magnetic Saturation. — The condition of iron, or other paramagnetic substance, when its intensity of magnetization is so great that it fails to be further magnetized by any magnetic force however great. When the core of an electro-magnet is saturated by the passage of an electric current, the only further increase of its magnetization that is possible, is that due to the magnetic field of the increased current which may be sent through its coils. This is comparatively insignificant. A magnet is sometimes said to be super-saturated, that is, to have received more magnetism than it can retain for any considerable time after its magnetization. Magnetic Screen, or Shield. — A hollow box whose sides are made of thick iron, placed around a magnet or other body so as to cut it off or screen it from any magnetic field external to the box. Magnetic screens are placed around delicate galvanometers to avoid any variations in their field due to extraneous masses of iron, or neighboring magnets. They are also sometimes placed around watches to shield or screen the works from the effects of magnetism. WORDS, TERMS AND PHRASES. 401 To act effectively, when the external fields are at all power- ful, magnetic screens must be made of thick iron. They differ in this respect from electrostatic shields, which will afford protection against electrostatic charges although they may be but mere films. (See Shields, Electrostatic.) Magnetic Shells. — A sheet or layer consisting of mag- netic particles, all of whose north poles are situated in one of the flat surfaces of the sheet, and the south poles in the oppo- site surface. (See Shell, Magnetic. Lamellar Distribitt ion of Magnetism.) Magnetic Solenoids. — A spiral coil of wire which acts like a magnet when an electric current passes through it. (See Solenoids, Electro- Magnetic.) Magnetic Sounds. — Faint clicks heard on the magneti- zation of a readily magnetizable substance. One of the earlier forms of Reis' telephone operated by means of a rapid succession of these faint, magnetic sounds. Magnetic Storms. — Sudden, but small and irregular variations in the intensity of the earth's magnetism that simultaneously affect all parts of the earth. Magnetic storms have been observed to accompany auroral displays, and to be coincident with the occurrence of sun sjjots, or unusual outbursts of solar activity. Magnetic Susceptibility. — The relation which exists be- tween the strength of the magnetizing field and that of the magnetized body, or the intensity of the magnetism induced, divided by the intensity of the inducing field. When the inducing field has unit strength of magnetiza- tion the magnetic susceptibility will measure directly the strength of the magnetization. When a bar of iron is placed in a magnetic field, it is threaded by the lines of magnetic force, and thus becomes magnetized by induction. This induction will necessarily 402 A DICTIONARY OF ELECTRICAL depend both on the number of lines of force in the magnet- izing field, and on the magnetic permeability of the magnet- ized body ; or, in other words, the induction is equal to the product of the intensity of the magnetizing field and the magnetic permeability of the body in which the induction occurs. Magnetic Variations.— Variations in the value of the magnetic declination, or inclination, that occur simultaneously over all parts of the earth. These variations are : (1) Secular, or those occurring at great cycles of time. (2) Annual, or those occurring at different seasons of the year. (3) Diurnal, or those occurring at different hours of the day, and, (4) Irregular, or those accompanying magnetic storms. The first three are periodical ; the last is irregular. (See Angle of Declination. Variation Chart. Inclination Chart.) Magnetite. — Magnetic oxide of iron, or Fe 3 4 . Lodestone consists of pieces of magnetized magnetite. Magneto-Electricity. — Electricity produced by the mo- tion of magnets past conductors, or of conductors past mag- nets. Magneto-Electric Call Bell.— An electric call bell operated by currents produced by the motion of a coil of wire before the poles of a permanent magnet. Magneto-Electric Induction. — Electric induction pro- duced by the motion of a conductor past a permanent magnet, or vice versa. (See Induction, Electro Magnetic.) Magneto-Electric Machine. — A dynamo in which currents are produced by the motion of armature coils past permanent magnets. (See Dynamo Electric Machine.) Magnet ograph, or Self-Recording Magnetome- ter. — A self-recording apparatus by means of which the daily WORDS, TERMS AND PHRASES. 403 and hourly variations of the magnetic needle are continuously registered. The magnetograph, as employed in the observatory at Kew, consists essentially of a photographic record of a spot of light reflected from a mirror attached to the needle whose varia- tions are to be record- ed. The photographic record is received on a strip of sensitized paper, maintained in uniform and continu- ous motion by means of suitable clockwork. The record so obtained is called a magneto- graph. Magnelomct e r . — An apparatus for the measurement of magnetic force by the torsion balance. The principles of the operation of the magnetometer are the same as those of the torsion balance. (See Balance, Coulomb's T o r s ion.) A mag- net N S, Fig. 275, is suspended by a single wire, and the magnet FiQ- % 75 - N, whose strength is to be measured is introduced in an open- ing at the top of the glass cage, in place of the proof plane which is used when the apparatus is employed for measuring the force of electrostatic attraction and repulsion, 404 A DICTIONARY OF ELECTRICAL In delicate magnetometers, the construction of which differs considerably from the form shown in Fig. 275, the deflection of the magnet is measured by a beam of light reflected from a mirror attached to the axis of suspension. Magneto-Optic Rotation.— The rotation of the plane of polarization of a beam of light on its passage through a transparent medium placed in a strong magnetic field, which medium only p6ssesses such properties while in the field. In a ray of ordinary light the vibrations of the ether parti- cles are at right angles to the direction of the ray, or to the direction in which the light is moving. Successive ether particles that lie along the path of the ray, do not, however, perform their vibrations in the same plane. Each successive particle moves in a plane which, though at right angles to the ray, is slightly inclined to the neighboring particle. The motion of the particles therefore, would describe a screw-like path through space. Under certain circumstances, all the ether particles may be caused to move in planes that are parallel to one another. Such a beam of light is called a plane polarized beam. A plane polarized beam, when passed through many trans- parent substances, will have its ether particles vibrating in the same plane when it emerges from the medium, as it had before it entered. Other substances possess the property of rotating or turning the plane of polarization of the light to the right or to the left. This property is called respectively right-handed rotary polarization, and left-handed rotary polarization. Many substances that ordinarily possess no power of rotary polarization acquire this power when placed in a magnetic field. This property of a magnetic field was discovered by Faraday. The effect is to be ascribed to the strain produced in the transparent medium by the stress of the magnetic field. It may be caused in solid bodies by mechanical forc§, WORDS, TERMS AND PHRASES. 405 The apparatus for demonstrating the rotation of the plane of polarization by a magnetic field is shown in Fig. 276. A powerful electro-magnet M, N, is provided with a hollow core. The substance c, is placed in the field thus produced by the approached poles, and its action on the light of a lamp, placed opposite at I, is observed by suitable apparatus at a. Magnetophone. — An apparatus for measuring the num- ber of breaks or interruptions of a circuit by the pitch of the musical note heard in an electro-magnetic telephone placed in such circuit. (See Telephone, Electro-Magnetic.) Fig. €76. A similar apparatus is useful in studying the distribution of the magnetic field of a dynamo electric machine. In this case, a small thin coil of insulated wire is held in the different regions around the machine, while the telephone is held to the ear of the observer. Magnetic leakage, or useless dissipation of lines of magnetic force outside the field proper of the machine, is at once rendered manifest by the musical note caused by variations in the intensity of the field. Since the intensity of the note heard will vary according to 406 A DICTIONARY OF ELECTRICAL the intensity of the field, and also according to the position in which the coil is held, such a coil becomes a magnetic explorer, and by its use the distribution and varying- intensity of an irregular field can be ascertained. Its use is especially advan- tageous in proportioning dynamo-electric machines, and elec- tric motors. Magnetism. — That branch of science which treats of the properties of a magnetic field. (See Field, Magnetic.) Magnetism, Ampere's Theory of.— A theory or hypo- thesis proposed to account for the cause of magnetism by the presence of electric currents in the ultimate particles of matter. Unmagnetize.d Fig. 277. Magnetized Fig. 278. This theory assumes . (1) That the ultimate particles of all magnetizable bodies have closed electric circuits in which electric currents are con- tinually flowing. (2) That in an unmagnetized body these circuits neutralize one another because they have different directions. (3) That the act of magnetization consists in such a polariza- tion of the particles as will cause these currents to flow in one and the same direction, magnetic saturation being reached when all the separate currents are parallel to one another. (4) That the coercive force is due to the resistance these circuits offer to a change in the direction of their planes. WORDS, TERMS AND PHRASES. 40*7 Figs. 277 and 278, show the circular paths of some of these circuits. Fig\ 277 shows the assumed condition of an unmag- netized bar. Fig-. 278 the assumed condition of a magnetized bar. A careful inspection of the figures will show that in a magne- tized bar all the separate currents flow in the same direction. All the circuits except those on the extreme edge of the bar will, therefore, have the currents flowing in them in opposite directions to that in their neighboring circuits, and, therefore, will neutralize one another. There will remain .however, a current in a circuit on the outside of the bar, which must therefore be regarded as the magnetizing circuit. Guided by these considerations, Ampere produced a coil of wire, called a solenoid, which is the equivalent of the magnetiz- ing circuit assumed by his theory. It therefore follows that an electric current sent through a coil of insulated wire surrounding a rod or bar of soft iron, or other readily magnetizable material, will make the same a magnet. A magnet so produced is called an electro-magnet. (See Electro-Magnet.) The magnetizing coil is called a helix or solenoid. (See Solenoid, Electro-Magnet ie.) The polarity of the magnet depends on the direction of the current, or on the direction of winding of the helix or sole- noid. (See Solenoids, Sinistro?*sal and Dextrorsal.) Magnetism, Electro Magnetism produced be means of electric currents. The discovery of Oersted, in 1820, of the action of an elec- tric current on a magnetic needle, was almost immediately followed by the simultaneous and independent discoveries of Arago and Davy, of the method of magnetizing iron by the passage of an electric current around it. These observations were first reduced to a theory by Am- pere. (See Magnetism, Ampere's Theory of. Electro-Mag- net.) »/ 408 A DICTIONARY OF ELECTRICAL Magnetism, Hughes' Theory of A theory pro- pounded by Hughes to account for the phenomena of magnet- ism apart from the presence of electric currents. Hughes' theory, or, more strictly speaking, hypothesis of magnetism, though very similar to that of Ampere, does not assume the improbable condition of a constantly flowing- electric current. Hughes' hypothesis assumes : (1) That the molecules of matter, and probably even the n s n s n s atoms, possess naturally op- n^ ^ 00t "^^s p o s i t e magnetic polarities >? 1 which are respectively -f- and \« — > or N. and S. I J s (2) That these molecules, n * in when arranged in closed S V y's chains or circuits, are capable s^^ ^^ ^ of neutralizing one another so n s n s n s n far as external action is con- Fig. 279. cerned. Two such arrangements or groupings are shown in Figs. 279 and 280. It will be observed that the magnetic chain or circuit is complete, and that, therefore, the substance can possess no magnetic properties so far as external action is concerned. n s n s n s n s n .s have been constructed, in which a chemical or mechanical record is made of the notes struck by the per- former, as well as the musical value of these notes. By such a device the musical creations of a composer are permanently recorded in characters that are capable of interpretation by a compositor skilled in musical notation. Oscillating Discharge.— (See Discharge, Oscillating.) Oscillating Needle.— (See Needle of Oscillations.) 444 A DICTIONARY OF ELECTRICAL Oscillation, Centre of The point, in a body- supported so as to swing like a pendulum, which is neither accelerated nor retarded during its oscillations. The centre of oscillation is always below the centre of grav- ity. The vertical distance between the centre of oscillation and the point of support of a pendulum, determines the virtual length of the pendulum and hence, its number of vibrations per second. (See Pendulum, Laws of.) Oscillations Electric The series of par- tial, intermittent discharges, of which the apparent instan- taneous discharge of a Leyden jar through a small resistance actually consists. These partial discharges produce a series of electric oscilla- tions of the current in the circuit of the discharge, which con- sist of a true to and fro, or backward and forward motion of the electricity. Osmose. — The unequal mixing of liquids of different dens- ities through the pores of a separating medium. If a solution of sugar and water be placed in a bladder, the neck of which is tied to a straight glass tube, and the bladder is then immersed in a vessel of pure water with the tube in a vertical position, the two liquids will begin to mix, the sugar and the water passing through the bladder into the pure water, and the pure water passing into the sugar and water in the bladder. This latter current is the stronger of the two, as will be shown by the water rising in the vertical glass tube. The stronger of the two currents is called the endosmotic current, and the weaker the exosmotic current. Osmose, Electric A difference of liquid level produced in two liquids placed on opposite sides of a diaph- ragm on the passage of a strong electric current through the liquids between two electrodes placed therein. The higher level is on the side towards which the current flows through the diaphragm, thus apparently indicating an WORDS, TERMS AND PHRASES. 445 onward motion of the liquid with the current, cm* in other words, the liquid is higher about the kathode than the anode. The difference of level is the more marked when poorly con- ducting liquids are employed. As a converse of this, Quincke has shown that electric cur- rents arc set up when a liquid is forced by pressure through a porous diaphragm. The term diaphragm currents has been proposed for these currents. Their electro-motive force de- pends on the nature of the liquid, on the material of the dia- phragm, and on the pressure that forces the liquid through the diaphragm. (See Electro- Capillary Phenomena.) Output of Dynamo-Electric Machines. — The elec- tric power of the current generated by a dynamo-electric machine expressed in volt-amperes, or watts. S. P. Thompson suggests that dynamo-electric machines be rated as to their practical safe capacity in units of output of 1,000 watts, or one kilo-watt. According to this, an 8-unit machine might give, say 100 amperes at a difference of poten- tial of 80 volts, or 2,000 amperes at a difference of potential of four volts. Such a unit would be far more expressive than the usual method of rating a machine as having a capacity of such and such a number of lights. Overtones. — Additional, faint tones, accompanying nearly every distinct musical tone, by the presence of which its pecu- liarity or quality is produced. (See Quality, or Timbre.) Ozone. — A peculiar modification of oxygen which pos- sesses more powerful oxydizing properties than ordinary oxygen. Ozone is now generally believed to be tri-atomic oxygen, or oxygen in which the bonds are closed, thus : O A o — o The peculiar smell observed when a torrent of sparks 446 A DICTIONARY OF ELECTRICAL passes between the terminals of a Holtz machine, or a Ruhm- korff coil, is caused by the ozone thus formed. In a similar manner ozone is formed in the atmos- phere during the passage through the air of a flash of lightning. During the so-called electrolysis of water, some of the oxy- gen is given off in the form of ozone. The volume of the oxygen liberated is, therefore, somewhat less than half the volume of the hydrogen. Palladium. — A metal of the platinum group. Metallic palladium has a tin-white color, and, when polished, a high metallic lustre. It is tenacious and ductile, and, like iron, can be welded at a white heat. It is very refractory and possesses in a marked degree the power of absorbing or occluding hydrogen and other gases. It is not affected by oxygen at any temperature, nor readily affected by ordinary corrosive agents. Palladium Alloys.— Alloys of palladium with other metals. Palladium forms a number of useful alloys with various metals. Some of the alloys are as elastic as steel, are un- affected by moisture or ordinary corrosive agencies, and are entirely devoid of paramagnetic properties. These properties have been utilized by their discoverer, Paillard, in their employment for the hair-springs, escape- ments and balance wheels of watches, in order to permit the watches to be carried into strong magnetic fields without any appreciable effects on the rate of the watch. A number of careful tests made by the author, by long continued ex- posure of watches, thus protected by the Paillard alloys, in extraordinary fields, show that the protection thus given the watches enables them to be carried into the strongest possible magnetic fields without appreciably affect- ing- their rate, WORDS, TERMS AND PHRASES. 447 The Paillarcl palladium alloys have the following- composi- tion, viz.: Alloy No. 1. Palladium _ 60 to 75 parts. Copper 15 to 25 " Iron.. 1 to 5 Alloy No. 2. Palladium.. .50 to 75 " Copper 20 to 30 Iron 5 to 20 Alloy No. 3. Palladium. ..65 to 75 Copper.. 15 to 25 " Nickel lto 5 " Gold.. lto 2% " Platinum % to 2 Silver 3 to 10 " Steel.... lto 5 " Alloy No. 4. Palladium 45 to 50 " Silver.. 20 to 25 •« Copper _ 15 to 25 Gold... 2to 5 " Platinum 2 to 5 " Nickel. 2to 5 " Steel 2to 5 " The great value of these alloys, when employed for the hair- springs of watches, arises not only from their non-magnetiz- able properties, and, their inoxidizability, but particularly from the fact that their elasticity is approximately the same for comparatively wide ranges of temperature. Pane, Magic A sheet of glass covered with pieces of tin foil with small spaces between them pasted in some de- sign on the glass. On the discharge of a Leyden jar through these metallic 448 A DICTIONARY OF ELECTRICAL pieces, the design is seen as a series of minute sparks that bridge the spaces between the adjacent pieces of foil. Pantelegraphy, or Facsimile Telegraphy.— A system for the telegraphic transmission of charts, diagrams, sketches or written characters. (See Telegraphy, Facsi- mile.) Paper Carbons. — Carbon, of textile or fibrous origin, obtained from the carbonization of paper. The carbonization of paper is readily effected by submitting it to the prolonged action of a high temperature while out of contact with air. For this purpose the paper is packed in retorts or crucibles, and covered with lamp-black, or powdered plumbago, in order to exclude the air. Since paper consists of a plane of material uniformly thin in one direction, formed almost entirely of fibres of pure cel- lulose, the greatest length of which extend in a direction nearly parallel to that in which the paper is uniformly thin, it is clear that sheets of this substance, when carbonized, should yield flexible carbons of unusual purity and electrical homogeneity, since such carbons are structural in character, and are uniformly affected by the heat of carbonization, to an extent that would be impossible by the carbonization of any material in a mass. Paper Perforator. — An apparatus employed in systems of automatic telegraphy for punching in a fillet of paper, circular or elongated spaces that produce the dots and dashes of the Morse alphabet, when the fillet is drawn between metal terminals that form the electrodes of a battery. (See Teleg- raphy, Automatic.) Parabolic Reflector. — A reflector, or mirror, the reflect- ing surface of which is a paraboloid, or such a surface as would be obtained by the revolution of a parabola about its axis. WORDS, TERMS AND PHRASES. 449 A parabolic curve, which may be regarded as a section of a parabola, is shown in Fig. 294. A parabola has the following- properties : If lines F P, F P, etc., be drawn from the point F, called the focus, to any point, P, P, etc., in the curve, and the lines Pp, Pp, Pp, etc., be then drawn severally parallel to the axis, V M, then all such angles, F Pp, F Pp, will be bisected by verticals to tangents at the point P, P, and P. Therefore, if a light be placed at the focus of a parabolic reflector, all the light reflected will pass off sensibly parallel to the axis V M. In locomotive head lights, a lamp is placed at the focus of a parabolic reflector, and the parallel beam so obtained utilized for the illumination of the track. In a search light, an electric arc lamp is placed in a para- bolic reflector, or at the focus of a lens. A parabolic reflector, such as is used for search lights, is shown in Fig. 295. A fo- cussing arc lamp must be used for this pur- v ' pose, so as to maintain the voltaic arc at ' the focus of the parabolic reflector, notwith- standing the consumption of the carbons. Parafflnc. — The name given to various solid hydrocarbons, of the marsh-gas series, Fig. 2%. that are derived from coal oil or petroleum by the action of nitric acid. Parafine possesses excellent powers of insulation, and forms a good dielectric medium. Dried wood, boiled in melted par- afhne, forms a fair insulating material. Paragreles. — Lightning rods, intended to protect fields against the destructive action of hail. (See Hail, Assumed Electrical Origin of.) It was formerly believed that hail is caused by electricity. It is now generally believed that the electricity in hail storms is caused by the hail. It will therefore readily be understood that paragreles can afford no real protection. pz w P w ^7 P p p'AI p P \i v V M f \ p p r \ P p )A p p w 450 A DICTIONARY OF ELECTRICAL Parallax. — The apparent angular displacement of an ob- ject when seen from two different points of view. In reading the exact division on a scale to which a needle points, care must be taken to look directly down on the needle, and not sideways, so as to avoid the error of displace- ment due to parallax. Parallel Circuit. — A name sometimes applied to circuits connected in multiple- arc. (See Circuits, Varieties of.) Parallelogram of Forces. — (See Forces, Par- allelogram of.) Paramagnetic. -Sub- stances possessing the proper- ties ordinarily recognized as magnetic. Substances possessing the power of concentrating the lines of magnetic force on them. Paramagnetic is a term em- ployed in contra-distinction to diamagnetic. (See Dia- magnetic.) A paramagnetic substance, cut in the form of a bar whose length is much greater than its breadth and thickness, when suspended in a magnetic field in the manner shown in Fig. 296, will take up a position of rest with its greatest length in the direction of the lines of force, i. e., will point axially. In other words the lines of force will so pass through the paramagnetic substance as to reduce the magnetic resistance of the circuit as much as possible, Fig. 295. WORDS, TERMS AND PHRASES. 451 Paramagnetic substances, therefore, concentrate the lines of force on them. (See Resistance, Magnetic.) Diamagnetic substances, on the contrary, placed as shown in Fig. 296, assume a position of rest with their least dimen- sions in the direction of the lines of force, i. e., the}' point equatorially. This is the position in which they are placed by the lines of force, in order to ensure the least magnetic resist- ance in the circuit of these lines. The magnetic resistance of diamagnetic substances is great as compared with that of paramagnetic substances. - The term ferro-magnetic has been proposed for paramag- netic. If another term be required, which is doubtful, sidero-magnetic proposed by f^\ S. P. Thompson, would be far prefer- able. (See Ferro-Magnetic. Sidero-Mag- netic.) Tyndall believes that the magnetic po- larity possessed by diamagnetic substances is a distinct polar force, different in its nature from ordinary magnetiism. (See Polarity, Diamagnetic.) Paramagnetism. — The magnetism of a paramagnetic substance. Parasitical Currents.— (See Cur- rents, Eddy, Foucault, or Local.) Paratoniieres.— A French term for lightning rods, sometimes employed in English technical works. Lightning rod would appear to be the preferable term. Partial Earth. (See Earths.) Passive State. — The condition of a metallic substance in which it may be placed in liquids that would ordinarily Fig. 296. 452 A DICTIONARY OF ELECTRICAL chemically combine with it, without being attacked or cor- roded. It is very doubtful whether metallic bodies can be properly regarded as possessing an actual passive state. Iron, for example, which is one of the metals that is said to be capa- ble of assuming this so called passive state, can be placed in this condition by immersing it for a few moments in concen- trated nitric acid, and subsequently washing it. It will then, unlike ordinary iron, neither be attacked by concentrated nitric acid, nor will it precipitate copper from its solutions. This condition is now generally believed to be due to the for- mation of a thin coating of magnetic oxide on its surface. Many of the instances of the so-called passive state are simply cases of the well known electrical preservation of metals that form the negative element of a voltaic combina- tion, under which circumstances the positive element only of the voltaic couple is chemically attacked by the electrolyte. (See Cell, Voltaic. Metals, Electrical Preservation of.) P. D. or p. d. — A contraction frequently employed for difference of potential. (See Difference of Potential.) Peltier E fleet. —(See Effect, Peltier.) Pendulum, Electric A pendulum so arranged that, in its to-and-fro motions, it sends electric impulses over a line, either by making and breaking contacts, or such in which the to and fro movements are maintained by electric impulses. Such pendulums are employed in systems for the electrical distribution of time. Sometimes, instead of using true pendulums for such pur- poses, coils, or contact points, mounted on the ends of flexible bars of steel called reeds, or on tuning forks, are often used for the purpose of establishing currents, or modifying the cur- rents that are already passing in a circuit. The movement of a magnetic diaphragm, as in the case of a telephone WORDS. TERMS AND PHRASES. 453 diaphragm, towards and from a coil of wire is another illustra- tion of an electric pendulum. Pendulum, Laws of The laws which ex- press the peculiarities of the motion of a simple pendulum. A simple pendulum is one in which the entire weight is con- sidered as concentrated at a single point, suspended at the end of a weightless, inflexible, and inextensible line. The following are the laws of the simple pendulum : (1) Oscillations of small amplitude are approximately isochronous: that is, are made in times that are sensibly equal. (See Amplitude of Vibration. Isochronism.) (2) In pendulums of different lengths, the duration of the oscillations is proportional to the square root of the length of the pendulum. (3) In the same pendulum, the length being preserved invariable, the duration of the oscillation is inversely proportional to the square root of the intensity of gravity. The intensity of gravity at any latitude, may be determined by the number of oscillations of Fig . 297. a pendulum of a given length. In the same manner the inten- sity of a magnetic field, or the intensity of magnetization of a magnet, may be determined by the needle of oscillation. by observing the number of oscillations a needle makes in a given time when disturbed from its position of rest. (See Needle of Oscillation.) Since a simple physical pendulum is a physical impossibility, the virtual length of a pendulum, that is, the vertical distance between its point of support to the centre of oscillation is taken as the true length of the pendulum. If the irregularly shaped body, shown in Fig. 297, whose cen- tre of gravity is at G, is made to swing like a pendulum, either on S, or O, its oscillations will be performed in equal times, and 454 A DICTIONARY OF ELECTRICAL the body will act as a simple pendulum, whose virtual length is S O. If, while suspended at S, it be struck at O, it will oscillate around S, witbout producing- any pressure on the supporting- axis at S, on which it turns. If floating entirely submerged in a liquid, a blow at O would cause it to move in a straight line, in t lie direction of tbe blow, without rotation. The point O, is called the centre of percussion, or the centre of oscillation. The centre of oscillation is always below the centre of gravity. Pen, Electric A device for manifold copying, in which a sheet of paper is made into a stencil by minute per- forations obtained by a needle driven by a small electric motor. The stencil is afterwards employed in connection with an inked roller for the production of any required number of copies. Mechanical pens are constructed on the same principle, the perforations being obtained by mechanical instead of by electric power. Percussion, Centre of That point in a body, suspended so as to move as a pendulum at which a blow would produce rotation, but no forward motion, or motion of translation. Periodicity ol Auroras and Magnetic Storms. — Observed coincidences between the occurrence of auroras and magnetic storms, and sun spots. The periodical occurrence of auroras, or magnetic storms, both as to frequency and intensity, which, occuring at periods of about eleven years apart, corresponds to the well-know eleven-year sun-sjjot period. It also agrees with a variation in the magnetic declination of a place which, according to Sabine, occurs once in every eleven years. Permanent Magnet. — (See Magnet, Permanent.) WORDS, TERMS AND PHRASES. 455 Permanent State of Charge of Telegraph Line. —(See State, Permanent.) Permeability, Magnetic The ease afforded by any substance to the passage through it of lines of mag- netic force. The magnetic permeability of paramagnetic substances is much less than that of diamagnetic substances. A substance of great magnetic permeability has small magnetic resistance, or possesses small magnetic reluctance to magnetization. (Sec Paramagnetic. Diamagnetic. Magnetic Reluctance.) HIIIIIIIIHIIIIIIIIIIIIIIIIIHIIIIIIIIIIIIIIII Ullllllllll Illllllll lllllllllllllllllllllllMllllllllllDIIIIIIIIIIIIIIHim -(See Elec- Fig. 298. Phenomena, Electro Capillary tro-Capillary Phenomena.) Pherope or Telephote.— (See Telephote.) Phial, Ley den (See Jar, Ley den.) Philosopher's Egg.— (See Discharge, Convective.) Phonantograph.— An apparatus for the automatic pro- duction of a visible tracing of the vibrations produced by any sound. 456 A DICTIONARY OF ELECTRICAL PhonautogTaphic apparatus consists essentially of devices by which the sound waves are caused to impart their to-and- fro movements to a diaphragm at the centre of which a pencil or tracing' point is attached. The record is received on a sheet of paper, or wax, or on a smoked glass or other suitable sur- face. Leon Scott's Phonautograph, which is among* the forms best known, consists of a hollow conical vessel A, Fig. 298, with a diaphragm of parchment stretched tightly like a drum-head over its smaller aperture B. A tracing point, attached to the Fig. 299. centre of the diaphragm, traces a sinuous line on the surface of a soot-covered cylinder 0, that is uniformly rotated under the tracing point. As the cylinder is advanced a short dis- tance with every rotation, a sinuous spiral line is traced on the surface. Phonic Wheel. — A wheel to which is attached a circular table of contact points, that is maintained in synchronous rotation by means of a timed series of electric impulses sent over a line. WORDS, TERMS AND PHRASES. 45? The phonic wheel was invented by La Cour, but was first put into successful operation in multiplex telegraphy by Delany in his system of Synchronous Multiplex Telegraphy. (See Telegraphy, Synchronous, Multiplex.) Delany obtains the exact synchronism of the phonic wheel by a series of cor- recting electric impulses, automatically sent over the line on the failure of the phonic wheel at either end of the line to exactly synchronise with that at the other. Phonograph. — An apparatus for the reproduction of articulate speech, or of sounds of any character, at any in- definite time after their occurrence and for any number of times. In Edison's phonograph the voice of the speaker, received by an elastic diaphragm of thin sheet iron, or other similar material, is caused to indent a sheet of tin-foil placed on the surface of a cylinder C, Fig. 299, that is maintained at a uni- form rate of rotation by the crank at W. In the form shown, the motion is by hand, In a later improved form the cylinder is driven by means of an electric motor, or b} T clockwork. In order to reproduce the speech or other sounds the phono- gram record is placed on the surface of a cylinder similar to that on which it was received, (or is kept on the same surface), and the tracing point, placed ai the beginning of the record and being maintained against it by gentle pressure, is caused, by the rotation of cylinder, to follow the indentations of the pho- nogram record. As the point is thus moved up and down the hills and hollows of the record surface, the diaphragm to which it is attached is given a to-and-fro motion that exactly corres- ponds to the to-and-fro motion it had when impressed originally by the sounds it has recorded on the phonogram record. A person listening at this diaphragm will therefore hear an exact reproduction of the sounds originally uttered. In this manner, the voices of relatives, distinguished sing- ers, or statesmen can be preserved for future generations. 458 A DICTIONARY OF ELECTRICAL In Edison's improved phonograph, the record suuface con- sists of a cylinder of hardened wax. The motion of the cylin- der is obtained by means of an electric motor. Two diaphragms are used, one for recording, and one for reproducing. As shown in Fig. 300, the recording diaphragm is in position against the cylinder. The recording diaphragm is made of malleable glass. The reproducing diaphragm is formed of bolting silk covered with a thin layer of shellac. Fig. 300. In the Graphophone of Bell and Tainter, the point at- tached to the diaphragm is caused to cut or engrave a cylinder of hardened wax. Two separate diaphragms are employed, one for speaking, and the other for hearing. The surface is made of a mixture of beeswax and paraffine. A uniformity of rotation of the cylinder is obtained by means WORDS, TERMS AND PHRASES. 459 Fig. 301. 460 A DICTIONARY OF ELECTRICAL of a motor provided with a suitable governor. An ordinary conversation of some five minutes, it is claimed, can be recorded on the surface of a cylinder 6 inches long and l 1 ^ inch in diameter. In the Gramophone of Berliner, a circular plate of metal, covered with a film of finely divided oil or grease, receives the Fig. 303. record in a sinuous, spiral line. This record is subsequently etched into the metal by any suitable means, or is photog- raphically reproduced on another sheet of metal. Glass covered with a deposit of soot is sometimes employed for the latter process. The apparatus is shown in Fig. 302, as arranged for the reproduction of speech. In Mr. Berliner's apparatus, the record surface is impressed by a point attached to the transmitting* diaphragm, in a direc- tion parallel to the record surface, and not, as in the instrument WORDS, TERMS AND PHRASES. 461 of Mr. Edison, in a direction at right angles to the same. This method, would appear to be the best calculated for the more exact reproduction of articulate speech, since it permits comparatively loud speaking or singing, without interfer- ing with the quality of the reproduced sounds. Since the re- sistance to indentation, or vertical catting, increases more rapidly than the increase in the amplitude of vibration (See Amplitude of Vibration) of the cutting point, it follows that the louder the sounds recorded by the phonograph or grapho- phone, the less complete would be the quality of the repro- duced sounds, or the less the probability of the peculiarities of the speaker's voice being recognized. In order to avoid this, the speaker in the phonograph and the graphophone speaks in an ordinary conversational tone only. For purposes of dictation, and most commercial purposes, this is rather an advantage than otherwise. Phonograph, Graphophone, or Gramophone Rceords. — Records produced in a phonograph, grapho- phone, or gramophone, for the subsequent reproduction of audible, articulate speech. Phonozenograph. — An instrument devised by De Feltre to indicate the direction of a distant sound. A Deprez-D' Arson val galvanometer, a Wheatstone's bridge, and a microphone of peculiar construction, are placed in the circuit of a voltaic battery, and a receiving telephone. The observer determines the direction of the distant sound by means of the sounds heard under different conditions in the telephone. PhoiUograph. — A name proposed for an electro-thermal recording telephone devised by Irish. Phosphore§cenee. — The power of emitting light, or be- coming luminous by simple exposure to light. Bodies that possess the property of phosphorescence, when exposed to a bright light acquire the power of continuing 462 A DICTIONARY OF ELECTRICAL to emit light, when carried into the dark, for periods varying from a few seconds to several hours. The diamond, barium and calcium sulphides, dry paper, silk, sugar, and compounds of uranium, are examples of phosphorescent substances. A phosphorescent body generally emits light of the same character as that it absorbed when exposed to the exciting light, That there is an actual absorption, is seen from the fact that the light which has passed through a fluorescent solution, fails to produce fluorescent effects in a similar solu- tion. A selective absorption has, therefore, been effected. The effects of phosphorescence appear to be due to sympa- thctic vibrations set up in the molecules of the phosphores- cent body by the exciting light. (See Sympathetic Vibrations.) In some cases, however, that are not exactly understood, the wave length of the emitted light is more rapid than that of the exciting light. The phenomena of fluorescence are now generally believed to be due to the phosphorescence of the body during its ex- posure to the light, The portions traversed by the light are thus temporarily rendered luminous. (See Fluorescence.) The fire-fty, the glow-worm, and decaying animal or vege- table matter, exhibit a species of phosphorescence, that ap- pears to be due to the actual oxidation, or gradual burning of a peculiar, specific, chemical substance. Phosphorescence may therefore be divided into two classes, viz. : (1) Physical Phosphorescence, or that produced, by the actual impact of the light, and, (2) Chemical Phosphorescence, or that caused by an actual chemical combination, or the combustion of a specific sub- stance. Phosphorescent paints for rendering the position of a push button, electric call, match safe, or other similar object visible at night, consist essentially of sulphides of calcium or barium, or of mixtures of the same. WORDS, TERMS AND PHRASES. 463 Phosphorescence, Electric -Phospho- rescence caused in a substance by the passage of an electric discharge. The phosphorescent material is placed in an exhausted glass tube, as shown in Fig. 303, and submitted to the action of a series of discharges, as from a Ruhmkorff coil, or Holtz machine. The violet blue light of such discharge is very efficient in producing phosphorescence. Phosphorescence is thus effected by subjecting the phosphorescent material to the molecular bombardment which thus occurs in a high vacuum. (See Bombardment, Molecular.) Photometer. — An apparatus for measuring the intensity of the light emitted by any luminous source. There are vari- ous methods for measuring the in- tensity of a beam of light passing through any giv- en space, or emitt- ed from any lum- inous source; these methods are embraced in Fig. SOS. the use of the following apparatus : (1) Calorimetric Photometer, in which the light to be meas- ured is absorbed by the face of a thermo-electric pile and the electric current thereby produced is carefully measured. Since obscure radiation, or heat will also thus produce an electric current, it is necessary to first absorb all the heat by passing the beam of light through an alum cell. (2) Actinic, or Chemical Photometers, in which the intensity of the light is estimated by a comparison of the depth of oloration produced on a fillet of photographic paper under 464 A DICTIONARY OF ELECTRICAL similar conditions of exposure to a standard light, and the light to be measured. The combination of pure hydrogen and chlorine, or the de- composition of pure mercurous chloride, have been employed for the purpose of determining the intensities of two lights by measuring th« amount of chemical decomposition effected. (3) Shadoiv Photometers, in which a shadow produced by the light to be measured is compared with a shadow produced by a standard candle. (See Candle, Standard.) Fig. SOU. Rumford's photometer, shown in Fig. 304, is an example of this form of instrument. The standard candle, shown at L, casts a shadow C", of an opaque rod C, on the screen at B. The light to be measured L', is moved away from the screen until its shadow C, on the screen at A, is judged by the eye to be of the same depth. The distance between the screen and the lights is then measured in straight lines. The relative in- tensities of the two lights are then proportional to the squares of their distances. If, for example, the candle be at 10 inches WORDS, TERMS AND PHRASES. 465 from the screen, and the lamp at 40 inches, then the intensities are as 10 3 : 40 2 or as 100 : 1600, or the lamp is a 16 candle-power lamp. This photometer is based on the fact that the shadow of each source is illumined by the light of the other source. (4) Translucent Disc Photometers. — The light to be meas- ured and a standard candle are placed on opposite sides of a sheet of paper the centre of which contains a grease spot. The standard candle is kept at a fixed distance from the paper and the other light is moved towards or from the paper until both sides of the paper are judged to be equally illu- mined. In Bunsen's photometer a vertical sheet of paper with a grease spot at its centre, is exposed to the illumination of a standard candle on one side, and the light to be measured on the other. The sheet of paper is placed inside a dark box provided with two plane mirrors placed at such an angle to the paper that an observer can readily see both sides of the paper at the same time. This box can be slid along a graduated, horizontal scale, towards, or from, the light to be measured, and carries with it the standard candle mounted on it at a constant distance of 10 inches. If the box is too near the light to be measured, the grease spot appears brighter on the side of the sheet of paper nearest the candle. If too near the candle, it appears brighter on the side of the sheet of paper nearest the light to be measured. The position in which the spot appears equally bright on both sides, is the position in which it is equally illumined, and the relative intensities of the two lights are then directly as the squares of their distances from the sheet of paper. Shadow, and translucent disc, photometers being dependent on equal illumination, are reliable only when the color of the lights compared is the same. For the determination of the 466 A DICTIONARY OF ELECTRICAL photometric intensity of very bright lights, the standard candle is replaced by a carcel lamp, a standard gas jet, or by the light emitted by a given mass of platinum, heated by a given current of electricity. (See Carcel Lamp. Carcel Standard Gas Jet. Platinum Standard Light.) Preece's photometer belongs to the class of translucent disc photometers. A tiny incandescent lamp is placed in a box, the top of which has a white paper screen on which is a grease spot. The box is placed in the street where the in- tensity of illumination is to be measured, and the intensity of the light of the incandescent lamp is varied until the grease spot disappears. The current of electricity then passing through the incandescent lamp acts as the measure of the illumination. In the case of the shadow photometer, or of Bunsen's photo- meter, if the intensity of illumination is the same, the relative intensities of the two lights may be determined as follows : Calling I, and i, respectively the relative intensities of the standard light, and the light to be measured, and D, and d, their respective distances from the screen, then I : % : : D 2 : d 2 , or I x d* = i x D 2 ; / d 2 \ that is, i = I ( — ) • VD 2 / /d 2 \ Or, the intensity of the light to be measured is (— J times the intensity of the standard light. If for example D, and d, represent 10 and 100 inches, respec- tively, the intensity of i is 100 times the intensity I, the standard light. (5) Dispersion Photometers. — A class of photometers in which, in order to more readily compare or measure a very bright or intense light, like that of an arc lamp, the intensity of the light is decreased by dispersion by a readily measurable amount. Ayrton & Perry's Dispersion Photometer. — A photometer in which, in order to bring an intensely bright light, like WORDS, TERMS AND PHRASES. 467 an electric arc light, to such an intensity as will permit it to be readily compared with a standard candle, its intensity is weakened by its passage through a diverging (concave) lens. Ayrton & Perry's dispersion photometer is shown in two different positions, Figs. 305 and 306. The apparatus is supported on a tripod stand E, arranged so as to obtain exact levelling. A plane mirror H, movable around a pin placed directly under its centre, can be rotated and thus reflect the light after its passage through the diverging lens, while still maintaining its distance from the electric light. Fig. 305. The horizontal axis of this mirror is inclined 45° to its reflecting surface in order to avoid errors arising from varying absorption at different angles of reflection. The inclination of the beam to the horizontal is indicated by means of an index attached to the' mirror and moving over the graduated circle G. A black rod A, casts its shadow on a screen of white blot- ting paper B, A standard candle, placed in the holder D, 468 A DICTIONARY OF ELECTRICAL casts its shadow alongside the shadow cast by the electric light. The lens is now displaced until the shadow of the electric light is of the same intensity as that of the candle, when viewed successively through sheets of red and green glass. A graduated scale serves to mark the distance of the candle and of the lens from the screen, from which data the intensity of the electric light may be calculated. Fig. 306. (6) Selenium Photometers. — Instruments in which the rela- tive intensities of two lights are determined by the effects pro- duced on a selenium resistance. In Siemens' selenium photometer a selenium cell is em- ployed in connection with an electric circuit for determining the intensity of light. The tube A B, Fig. 307, is furnished at A with a dia- phragm, and at B with a selenium plate, connected by wires, G G, with the circuit of a battery and a galvanometer. A graduated scale L M, bears the standard candle N. WORDS, TERMS AND PHRASES. 469 The tube A B is capable of rotation on the vertical axis F. A reflecting- mirror-galvanometer is used in connection with the selenium photometer. The light to be measured is placed at right angles to the scale L M, and the tube A B directed towards it, and the galvanometer deflection com- pared with the deflection obtained when turned towards the standard candle. (7) Gas-Jet Photometers.— Instruments in which the candle power of a gas jet is determined by measuring the height at which the jet burns when under unit conditions of volume and pressure. Fig. 807. In determining the candle power of an intense light like the electric arc light, a large gas light is used intsead of a standard candle, and the photometric power of this gas light is carefully determined by comparison with a gas-jet pho- tometer. (See Car eel, Standard, Gas Jet.) Photoplione.— An instrument invented by Bell for the telephonic transmission of articulate speech along a ray of light instead of along a conducting wire. A beam of light, reflected from a diaphragm against which 470 A DICTIONARY OF ELECTRICAL the speaker's voice is directed, is caused to fall on a Selenium resistance inserted in the circuit of a voltaic battery, and a telephone. The changes thus effected in the resistance of the circuit by the varying amounts of light reflected on the selenium from the moving diaphragm, produce in the receiving telephone, a series of to-and-fro movements, similar to those impressed on the transmitting diaphragm. One listening at the telephone can hear whatever has been spoken at the transmitting diaphragm. Telephonic communication can therefore by such means be carried on along a ray or beam of light, theoretically through any distance. (See Selen- ium, Resistance.) A block of vulcanite and many other substances may be used as the receiver, since it has been discovered that a rapid succession of flashes of light produces an audible sound in small masses of these substances. The term Sonorescence has been proposed for such a property. (See Sonorescence.) Photophore, Trouve's An apparatus in which the light of a small incandescent electric lamp is em- ployed for purposes of medical exploration. A small incandescent lamp is placed in a tube containing a concave mirror and a converging lens. Phototelegraphy, or Telephotography.— The elec- tric production of pictures, writing, charts, or diagrams at a distance. (See Telejrfwtograjihy.) Photo- Voltaic Effect. — The change in the resistance of selenium or other substances effected by their exposure to light. (See Selenium Cell.) Physiology, Electro (Sec Electro-Physi- ology.) Piano, Electric A piano in which the strings are struck by hammers actuated by means of electro-mag- nets, instead of by the usual mechanical action of levers. WORDS, TERMS AND PHRASES. 471 Electric piano-action is mainly useful in permitting* the in- strument to be played at any distance from the performer. It is also of value from the ease it affords in recording the piece played. It fails, however, to properly preserve the various modula- tions of force so requisite for brilliant instrumentation. Pickle. — An acid solution in which metallic objects are dipped before being galvanized, or electroplated, in order to thoroughly cleanse their surfaces. The pickle used for the preparation of iron for galvaniza- tion is a weak solution of sulphuric acid in water. Vari- ous acids, or acid liquids, are employed for that thorough cleansing of metallic surfaces so necessary in order to ensure an even, uniform, adherent coating of metal by the process of electro-plating. (See Electro-Plating.) Pile, Dry ■ — A voltaic battery, consisting of numerous voltaic couples formed of discs of paper co veved on one side with zinc-foil, and on the other with black oxide of manganese. (See Dry Pile.) Pile, Matteucci's Muscular (See Muscular Pile, Matteucci's.) Pile, Thermo-Electric A battery consisting "of a number of thermo-electric couples connected so as to form a single electric source. (See Thermo-Electric Battery.) Pile, Voltaic A battery consisting of a number of voltaic couples connected so as to form a single electric source. A form similar to Volta's original pile, consisting of alternate discs of copper and zinc, separated from each other by discs of wet cloth, and piled on one another, so as to form a number of separate voltaic couples connected in series, is showfi in Fig. 308. The thick plates marked Zn, are of zinc ; the copper plates, marked Cu are much thinner. The discs of moistened cloth are shown at d d. One end of such a 472 A DICTIONARY OF ELECTRICAL pile, would then be terminated by a plate of copper, and the other by a plate of zinc. The copper end forms the positive electrode, and the zinc end the negative electrode. (See Cell, Voltatic, Polarity of Electrodes.) Pith.— A light, cellular ma- terial forming- the central por- tions of most exogenous plants. An excellent pith, suitable for electrical purposes, is furnished by the dried wood of the elder- berry. Pith-Ball Electroscope. — An electroscope which shows the presence of a charge by the repulsion of two similarly charged pith balls. (See Elec- troscope.) Any two pith balls, suspended by conducting threads, but in- sulated from the earth, will serve as an electroscope. Pith Balls.— Two balls of pith, suspended by conducting threads of cotton to insulated conductors, and employed to show the electrification of the same,by their mutual repulsion. The pith balls connected with Fig. 308. the insulated cylinder A B, Fig. 309, not only show the electrification of the cylinder, but serve also to roughly indicate the peculiarities of distribution of the charge thereon. Pivot Suspension. — The suspension of a needle or mag- net, by a pivot, as distinguished from suspension by a thread. (See Suspension, Methods of.) WORDS, TERMS AND PHRASES. 473 Plant ». Electricity of —Electricity produced naturally by plants during- their vigorous growth. DuBois-Reymond and others, have shown that plants while in a vigorous vital state, are active sources of electricity. If one of the terminals of a galvanometer be inserted into a fruit near its stem, and the other terminal into the opposite part of the fruit, the galvanometer at once shows the presence of an electric current. Buff has shown that the roots and interior portions of plants are always negatively charged, while the flowers, fruits and green twigs are positively charged. Plant tissue or fibre, like the muscular fibre of animals, exhibits in many cases a true contraction on the passage through it of an electric current. This is seen in the mimosa sensitiva, or sensitive fern ; in the Venus' fly trap ; and in several other species of plants. Fig. 309. Plate Condenser. — (See Condenser or Accumulator.) Plating Bath, Electro (See Bath, Electro- Plating.) Plating, Electro The depositing of a plating or coating of one metal on the surface of another metal, or on any conducting surface, by the action of electricity. — (See Electro-Plating. ) Platinoid. — An alloy consisting of German silver with one or two per cent, of metallic tungsten. 474 A DICTIONARY OF ELECTRICAL This alloy is suitable for use in resistance coils on account of the comparatively small influence produced on its electric resistance by changes of temperature. (See Coils, Resistance), Its resistance is 60 per cent, higher than that of German silver. Platinum. — A refractory and not readily oxidizable metal, of a tin white color. The coefficient of expansion of platinum by heat is nearly that of ordinary glass. Platinum is, therefore, much employed for the leading-in conductors of an incandescent lamp. Platinum Black.— Finely divided platinum that pos- sesses, in a marked degree, the power of absorbing or occlud- ing gases. Platinum black is obtained by the action of potassium hy- drate on platinum chloride. Unlike metallic platinum it is of a black color. Platinum-Silver Alloy.— An alloy used for resistance coils, consisting of one part of platinum and two parts of silver. Platinum Standard Light.— The light emitted by a surface of platinum, one square centimetre in area, at its tem- perature of fusion. Plow. — The sliding contacts connected to the motor of an electric streetcar, and placed within the slotted underground conduit, and provided for the purpose of taking off the current from the electric mains placed therein, as the contacts are pushed forwards over them by the motion of the car. Similar contacts, placed in the rear of the motor car and drawn after the train, form what is technically known as the sled, or when rolling on overhead wires as trolleys. (See Rail- ways, Electric.) Plow, Electric A plow driven by an electric motor placed either on a wagon to which the plow is attached, WORDS, TERMS AND PHRASES. 475 or by a stationary electro motor, by the aid of cords or other flexible belts. One of the first practical applications of the electric trans- mission of energy was for the operation of a plow, driven electrically, by an electric current generated at some distance, and transmitted to the field by suitable conductors. PliicRer Tubes. — (See Tubes, Plucker.) Plug, Infinity (See Infinity Plug.) Plumbago. — An allotropic modification of carbon. Plumbago, the material commonly known as black lead, is the same as graphite. Powdered plumbago is employed in electrotyping processes for rendering non-conducting surfaces electrically conducting. For this purpose powdered plumbago is dusted on the surfaces which thus acquire the power of re- ceiving a metallic lustre by friction. Stove polishes are formed of mixtures of plumbago and other cheaper materials. (See Graphite.) Strictly speaking the term graphite is properly applied to such varieties of plumbago as are suitable for direct use for writing purposes as in lead pencils. Plunge Battery.— (See Battery, Plunge.) Pneumatic Perforator. — (See Perforator, Pneumatic.) Pneumatic Signals, Electro —(See Signals, Electro-Pneumatic.) Poggendorff's Voltaic Cell.— (See Cell, Voltaic.) Points, Electric Action of The effect of points placed on an insulated, charged conductor, is to slowly dis- charge the conductor by electric convection. (See Convection, Electric.) The cause of this action is the increased density of a charge on the surface of a conductor in the neighborhood of points. (See Charge, Distribution of.) 476 A DICTIONARY OF ELECTRICAL Points or Rhumbs, of Compass.— The thirty -two points into which a compass card is divided. Sixteen of these points are shown in Fig. 310. The position of the remaining will be readily seen by an inspection of the figures. These points are as follows : 1. North. 2. N. by E. 3. N. N. E. 4. N. E. by N. 5. N. E. 6. N. E. by E. 7. E. N. E. 8. E. by N. 9. East. 10. E. by S. 11. E. S. E. 12. S. E. by E. 13. S. E. 14. S. E. by S. 15. S. S. E. 16. S. by E. Boxing the Compass, consists in naming all these points con- secutively from any one of them. The direction in which the ship is sailing is determined by means of a point fixed on the inside of the compass box, directly in the line of the vessel's bow. Points on Lightning Rod.— Points of inoxidizable material, placed on lightning rods, to effect the quiet discharge of a cloud by convection streams. (See Lightning Rods. Convection, Electric.) Polarity, IMamagnetic — A polarity, the re- verse of ordinary magnetic polarity, assumed by Faraday to explain the phenomena of diamagnetism. (See Diamagnet- ism.) 17. South. 13. S. by W. 19. S. S. W. 20. S. W. by S. 21. S. W. 22. S. W. W. 23. W. S. W. 24. W. by S. 25. West. 26. W. by N. 27. W. N. W. 28. N. W. by W. 29. N. W. 30. N. W. by N. 31. N. N. W. 32. N. bv W. WORDS, TERMS AND PHRASES. 477 Faraday assumed that diamagnetic substances, when brought into a magnetic field, such, for example, as north, acquired north magnetism in those parts that were nearest the north pole, instead of south magnetism as with ordinary magnetic substances. The north pole thus obtained, would, he thought, explain the apparent repul- sion of a slender rod of any diamagnetic material, deli- cately suspended in a strong magnetic field, and cause it to point equatorially, or with the lines of force passing through its least dimen- sions. This supposition was subsequently abandoned by Faraday. It has recently been revived by Tyndall. (See Diamagnetic.) Polarity, magnetic The polarity acquired by a magnetizable substance when brought into a magnetic field. The direction of magnetic polarity, acquired by a substance when brought into a magnetic field, depends on the direction in which the lines of magnetic force pass through it. Where these lines enter the substance a south pole is produced, and where they pass out, a north pole is produced. The axis of magnetization lies in the direction of the lines of force as they pass through the body, and the intensity of magnetization, depends on the number of these lines of force. The cause of magnetic polarity is not definitely known. Hughes's hypothesis attributes it to a property inherent in all matter. Ampere attributes it to closed electric circuits in the ultimate particles. Whatever its cause, it is invariably manifested by a magnetic field, the lines of force of which are assumed to have the direction already mentioned. Fig. 810. 478 A DICTIONARY OF ELECTRICAL Polarization of Dielectric. — A molecular strain pro- duced in the dielectric of a Leyden jar, by the attraction of the electricities on its opposite faces, or by electrostatic stress. (See Dielectric Strain.) The polarization of the glass of a Leyden jar, and the ac- companying strain, are seen by the frequent piercing of the glass, and by the residual charge of the jar. (See Charge, Residual.) Polarization of Electrolyte. — The formation of mole- cular groups or chains, in which the poles of all the molecules of any chain are turned in the same direction, viz. , with their positive poles facing the negative plate, and their negative poles facing the positive plate. (See Cell, Voltaic. Grothuss , Hypothesis.) Polarization of Xerves.— (See Electrotonus.) Polarization of Voltaic Cell.— The collection of a gas, generally hydrogen, on the surface of the negative elo^ ment of a voltaic cell. The collection of a positive substance like hydrogen on the negative element or plate of a voltaic cell, sets up a counter electromotive force, which tends to produce a current in the opposite direction to that produced by the cell, and thus to decrease the normal current of the cell. (See Counter Elec- tromotive Force. ) The causes of the decrease of the normal current of a vol- taic cell by its polarization, are as follows : (1) The Increased Resistance of the cell owing to the bubbles of gas, which form part of the circuit. (2) The Counter Electromotive force, produced by the film of gas on the negative plate. There are three ways in which the ill effects of this polariz- ation can be avoided. These are : (1) Mechanical. — The negative plate is furnished with a roughened surface which enables the bubbles of gas to escape WORDS, TERMS AND PHRASES. 479 from the points on such surface ; or, a stream of gas, or air, is blown through the liquid against the plate to brush the bubbles off. (2) Chemical. — The surface of the negative plate is sur- rounded by some powerful oxydizing substance, such as chromic or nitric acid, which is capable of oxidizing the hy- drogen, and thus thoroughly removing it from the plate. The oxidizing substance may form the entire electrolyte, as is the case of the bichromate solution employed in the zinc-carbon couple. Generally, however, it has been found preferable to employ a separate liquid, like nitric acid to completely sur- round the negative plate, and another liquid for the positive plate, the two liquids being generally kept from mixing by a porous cell, or diaphragm. Such cells are called double fluid cells. (See Cell, Voltaic, Double Fluid.) (3) Electro Chemical. — This also necessitates a double fluid cell. The negative element is immersed in a solution of a salt of the same metal as the negative plate. Thus, a copper plate, immersed in a solution of copper sulphate, cannot be polarized since metallic copper is deposited on its sur- face by the action of the hydrogen which tends to be liberated there. The constancy of action of a Daniell cell depends on a deposition of metallic copper on its copper plate as well as on the formation of hydrogen sulphate, and the solution of additional copper sulphate. (See Cell, Voltaic, DanielVs.) Polarized Armature.— (See Armature, Polarized.) Polarized Relay.— (See Relay, Polarized.) Pole, Antilogous That pole of a pyro-electric substance, like tourmaline, which acquires a negative electrifi- cation w T hen the temperature is rising, and a positive electrifi- cation when it is falling, (See Pyro- Electricity.) Pole I'll any it. — A switch or key for changing or re vers- 480 A DICTIONARY OF ELECTRICAL ing the direction oi current produced by any electric source, such as a battery. The commutator of a Buhmkorff coil is a simple form of pole changer. (See Induction Coils.) Pole Piece§. — Pieces of soft iron placed at the ends of the poles of electro magnets for the purpose of concentrating- and directing their magnetic fields. Pole Pieces of Dynamos. — Masses of iron connected with the poles of the field magnet frames of dynamo-electric machines, and shaped to conform to the outline of contour of the armature. The pole pieces are made in a variety of forms, but in all cases are so shaped as to conform to the outline of the space in which the armature rotates. They are brought as near as possible to the armature so as to increase the intensity of the magnetic induction. The in- tervening air space should be as thin as possible, but of as large an area as convenient. The opposite pole pieces should not have their extensions brought too near together, as this will permit of serious loss through magnetic leakage. The distance between them should be as many times the depth of the armature windings as possible. (See Magnetic Leakage.) Rounded edges are preferable to sharp edges for the same reason. Poles, Consequent of Magnet.— (See Con- sequent Magnet Poles.) Poles, False (See False Poles.) Poles of Magnetic Intensity. — The earth's magnetic poles as determined by means of the needle of oscillation. The points of the earth's greatest magnetic intensity. (See Inclination Chart.) Poles of Verticity, Magnetic. — The earth's magnetic poles as determined by means of the dipping needle. WORDS, TERMS AND PHRASES. 481 The points of the north where the angle of dip is 90°. (See Inclination Chart.) Poles, Telegraphic Wooden or iron uprights on which telegraphic or other wires are hung. Wooden poles are generally round. The terminal pole, or the last pole at each end of the line, or where the wires bend at an angle of nearly 90°, is gener- ally cut square. The holes for the poles must be dug in the true line of the wires, and not at an angle to such line. As little ground should be disturbed in the digging as possible. Earth borers, or modifications of the ordinary ship auger, are generally employed for this purpose. When the pole is placed in posi- tion the ground should be rammed, or punned around the pole. In setting the pole, it is generally set at least five feet in the ground. In England the poles are planted to a depth of about one-fifth of their length. In embankments and loose ground, they are planted deeper than in more solid earth. On curves, the poles should be inclined a little so as to lean back against the lateral strain of the wire, since by the time the ground has completely set, the strain of the wire will have pulled them into an erect position. Care must be taken to so plant the poles on that side of a road or railway, that the prevailing winds will blow them off the same, should it overturn them. As to location, the top of steep cuttings is preferable to the slope. In all exposed posi- tions, it is preferable to strengthen the poles by stays attached to both sides. Where the number of wires is unusually large, heavy timber, or in case of its absence, double poles suitably braced together, must be employed. In long lines the poles should all be numbered in order to afford ease for reference or repair. When, even with the best punning, and other precautions, the pole is judged to be unable to resist the strain on it, stays 482 A DICTIONARY OF ELECTRICAL and struts are employed. A stay is used when it is desired to remove the pull or tension from the pole ; a strut, when it is desired to remove the thrust or pressure. Fig. $11. The arms or brackets, or the cross pieces that support the insulators, should all be placed on the same side of the poles. Some common forms of arms or brackets are shown in Fig. 311. Saddle Brackets should be placed on alternate sides of the pole. When the strain on an insulator is too great, on ac- ^Kb ms* — **> . count of the wire going off at a sharp angle, a Shackle is used. This is a spec- ial form of insulator which confines the Fig. 812. strain to one spot. A form of Double Shackle is shown in Fig. 312. The wire passes around the recess at B, between the two insulators. On curves, or in any situation when there is a probability, in WORDS. TERMS AND PHRASES. case of the breaking of an insulator, of a wire getting into a dangerous position Guards should be employed. Guards are of two kinds, viz.: Hoop Guards and Hook Guards. A form of hook guard is shown in Fig. 313. When wooden poles are employed various preservative methods are adopted to protect the wood from decay, which is very apt to occur, especially at the line of the pole enters the ground. Some of these forms are as follows, viz. : (1) Charring and Tarring the ^^^ butt end of the pole where it en- /^^^ ters the ground, so as to expel the /Y sap and destroy injurious plants or // animal germs. The charred end is then cleansed and dipped in a mixture of tar and slaked lime. (2) Burnetising, or the introduc- tion of chloride of zinc into the pores of the wood, by placing the poles in an open tank filled with a solution of this salt. (3) Kyanising, or the similar in- troduction of corrosive sublimate, ^3" or mercuric chloride. Fig ' 313 ' (4) Boucherising, or the injection of a solution of copper sul- phate, into the pores of the wood. (5) Creosoting, or the application of creosote to well -sea- soned poles. Porous Cells. — Jars of unglazed earthenware, employed in double-fluid voltaic cells, to keep the two liquids separated. The use of a porous cell necessarily increases the internal resistance of the cell, from the decrease it produces in the area of cross section of liquid between the two elements. When the battery is dismantled, the porous cells should be kept under water, otherwise the crystallization of the zinc sulphate or 484 A DICTIONARY OF ELECTRICAL other salt is apt to produce serious exfoliation, or even to crumble the porous cell. A porous cell is sometimes called a diaphragm. (See Cell, Voltaic.) Portative Power. — The lifting- power of a mag-net. (See Lifting Power of Magnet.) Fig. Slh. Portrait, Electric A portrait formed on paper by the electric volatilization of gold or other metal. An electric portrait, is obtained by cutting on a thin card a portrait, in the form of a stencil. A sheet of gold leaf is then placed on one side of the paper stencil, and a sheet of paper on the other side ; sheets of tin foil are then placed on the outside, as shown in Fig. 314, and the whole firmTy p'-essed WORDS, TERMS AND PHRASES. 485 together. If now a disruptive discharge is passed through from one sheet of tin foil to the other, the gold leaf is vo- latilized, and a purplish stain is left on the paper on the outlines of the stencilled card, thus forming an electric por- trait. Positive Electricity. — One of the phases of electrical excitement, rather than one of the kinds of electricity. (See Negative Electricity.) Positive Direction of Lines of Magnetic Force. — The direction the lines of magnetic force are assumed to take, viz. : out of the north pole of a magnet and into the south pole. (See Field, Magnetic. Direction of Lines of Force.) Posts, Binding or Binding Screws, — (See Binding Posts.) Potential, Constant -A potential which remains constant under all conditions. A machine or other electric source is said to have a con- stant potential when it is capable, while in operation, of main- taining a constant difference of electric pressure between its two terminals. (See Circuit, Constant Potential.) Potential, Difference of (See Difference of Potential.) Potential, Difference of Methods of Meas- uring Methods employed for determin- ing difference of potential. These methods are as follows : (1) By the Method of Weighing, that is, by obtaining the weight required to overcome the attraction between two op- positely charged plates, or oppositely energized coils ; or by measuring the repulsion between similarly charged surfaces, or similarly energized coils. (2) By the use of Electrometers, or apparatus designed for measuring differences of potential. (See Electrometers.) (8) By the use of Galvanometers. 486 A DICTIONARY OF ELECTRICAL Difference of potential, in the case of currents, may be determined from the quantity of electricity which flows per second through a given circuit, that is, by the number of amperes, just as the pressure of water at any point in the side of a containing vessel can be determined by the quantity of water that flows per second. Difference of potential in the case of currents, therefore, may be measured by any galvano- meter which measures the current directly in amperes, and knowing the resistance of the circuit. Potential, Electric The power of doing electric work. Electric level. Electric potential can be best understood by comparison with the case of a liquid such as water. The ability of a water supply or source to do work depends: (1) On the Quantity of Water. (2) On the Level of the Water, as compared with some other level, or, in other words on the difference between the two levels. In a like manner the ability of electricity to do work de- pends : (1) On the Quantity of Electricity. (2) On the Electric Potential at the place where the elec- ricity is produced, as compared with that at some other place, r, in other words on the Difference of Potential. In the case of water flowing through a pipe, the quantity which passes in a given time is the same at any cross section of the pipe. In the case of electricity, the quantity of electricity flowing through any conductor, or part of a circuit, is the same at any cross section. A galvanometer introduced into a break in any part of the conductor would show the same strength of current. But, though the quantity of water which passes is the same at any cross section of a pipe, the pressure per square inch is WORDS, TERMS AND PHRASES. 487 not the same, even in the case of a horizontal pipe of the same diameter throughout, but becomes less, or suffers a loss of head, or difference of pressure, at any two points along the pipe, that causes the flow between these two points against the resistance of the pipe. So too, in the case of a conductor carrying an electric cur- rent, though the quantity of electricity that passes is the same at all cross sections, the electric pressure or potential is by no means the same at all points in the conductor, but suffers a loss of electric head or level in the direction in which the electricity is flowing. It is this loss of electric head or level, or difference of electric potential, that causes the electricity to flow against the resistance of the conductor. a a ^6 d_ z: e f '-- Fig. 815. These analogies can be best shown by the following illus- tration : In Fig. 315, a reservoir, or source of water, at C, communi- cates with the horizontal pipe A B, furnished with open vertical tubes at a, b, c, d, e, f, g, and B. If the outlet at B is closed, the level of the water in the communicating vessels is the same as at the source ; but if the liquid escape freely from B, the level of the water in the branch pipes, will be found on the inclined dotted line or at a', b', c' , d', e' , f, a 1 , or on the hydraulic gradient. 488 A DICTIONARY OF ELECTRICAL The pressure per square inch, at any cross section of the horizontal pipe, which is measured by the height of the liquid in the vertical pipe at that point, decreases in the direction in which the liquid is flowing. The force that urges the liquid through the pipe between any two points, may be called the liquid-motive force (Fleming) and is measured by the differ- ence of pressure between these points. In Fig. 316, the dynamo electric machine at D, has its nega- tive pole grounded, and its positive pole connected to a long lead, A B, the postive end of which is also grounded. A fall of potential, represented by the inclined dotted line, occurs be- tween A and B, in the direction in which the electricity isflow- in 9> n fv^a> -x: *-«.• 0" [El Fig. 316. I — I The dynamo electric machine may be regarded as a pump that is raising the electricity from a lower to a higher level, and passing it through the lead A B. The electric pressure or potential producing the flow is greatest near the dynamo and least at the further end, the differences at the points a, b, c, d, e, f, and g, being represented by the vertical lines a a', b b', c c', d d', e e', ff, and g g'. The electricity flows between any two points as a, and b, in the conductor A B, in virtue of the difference of electric pressure or potential between these two parts, or the differ- ence between a a', and b b'. Differences of potential must be distinguished from differ- WORDS, TERMS AND PHRASES. 489 ences in electric charge, or electrostatic density. If two con- ductors at different potentials are connected by a conductor, a current will flow through this conductor. When their potential is the same no current flows. The density of a charge is the quantity of electricity per unit of area. The electric potential is the same at all points of an insulated charged conductor ; the density is different at different points, except in the case of a sphere. The potential, however, is the same, since no current flows, or the charge does not redistribute itself. The density on an insulated, isolated sphere is uniform over all parts of the surface, and its potential is the same at all points. If now the sphere be approached to another body, its density will vary at different parts of its surface, and while the charge is redistributing itself so as to produce these differ- ences in density the potential will vary. As soon, however, as this redistribution is effected and no further current exists, the potential is the same over all parts, though the density differs at different points. Potential, Electrostatic The power of doing work possessed by a unit quantity of positive electricity charged on an insulated body. The electric potential of any point may also be defined as being equal to the work required to be exerted on a unit of positive electricity in bringing it to that point from zero poten- tial, i. e., from an infinite distance. Potential Energy. — Energy possessing the power or po- tency of doing work, but not actually performing such work. (See Energy, Potential.) Potential, Fall of (See Potential, Electric.) Potential, Magnetic The amount of work re- quired to bring up a unit north-seeking magnetic pole from an infinite distance to another unit north-seeking magnetic pole. Potential of Conductor, Methods of Varying 490 A DICTIONARY OF ELECTRICAL — The potential of a conductor may be varied in the following ways : (1) By varying its electric charge. (2) By varying its shape without altering its charge. (3) By varying its position as regards neighboring bodies. This resembles the case of a gas whose tension or pressure may be varied as follows, viz. : (1) By varying the quantity of gas. (2) By varying the size of the gas holder in which it is kept, and, (3) By varying the temperature. Difference of potential, therefore corresponds, (1) With difference of level in liquids. (2) "With difference of pressure in gases. (3) With difference of temperature in heat. (Ayrton.) Potential, Zero An arbitrary level from which electric potentials are measured. As we measure the heights of mountains from the arbitrary mean level of the sea so we measure electric levels from the arbitrary level of the potential of the earth. The true zero potential would be situated at a point infinitely distant from any electrified body. Potentiometer. — An apparatus for the galvanometric measurement of electro-motive forces, or differences of poten- tial by a zero method. (See Null, or Zero Methods.) In the potentiometer the difference of potential to be measured is balanced, or opposed, by a known difference of potential, and the equality of the balance is determined by the failure of one or more galvanometers, placed in shunt circuits, to show any movement of their needles. The principle of operation of the potentiometer will be understood from an inspection of Fig. 317. A secondary bat- tery S, has its terminals connected to the ends of a uniform wire A B, of high resistance called the Potentiometer Wire. There will therefore occur a regular drop or fall of WORDS, TERMS AND PHRASES. 491 potential along this wire, which, since the wire is uniform, will be equal per unit of length. This drop of potential can be shown by connecting the terminals of a delicate high resis- tance galvanometer to different parts of the wire, when the deflection of the needle will be proportional to the drop of potential between the two points of the wire touched. If now the terminals of a Standard Cell be inserted in the circuit of the galvanometer, so as to oppose the current taken from the potentiometer wire, and the contacts of the potentiometer wire be slid along it until no deflection of the galvanometer needle is produced, the drop of potential between these two points on the potentiometer wire will be equal to the difference of poten- tial of the standard cell. (See Standard Cell.) Suppose now it be desired to measure the difference of poten- tial between two points a and 6, on the wire C, through which a current is flowing. Connect the points b and d, and a and c, as Ftg ' 317 ' shown, with the delicate high resistance galvanometer G, in either of them. Now slide c towards d, until the needle of G shows no deflection. The potential between a and b, is then equal to that between c and d. Potentiometer Wire.— The wire of a potentiometer which has been calibrated for its drop of potential. (See Potentiometer.) Power. — Rate of doing work. Mechanical power is generally measured in horse power, which is equal to work done at the rate of 550 foot-pounds per second. The C. G. S. Unit of Power is one Erg per Second. The practical unit of power is the Watt, or 10,000,000 ergs per second. 1 Watt = 7 £ F H. P. 492 A DICTIONARY OF ELECTRICAL Power, Absorptive Power, Stray -(See Absorptive Power.) -(See Stray Power.) Power, Thermo-EIectric -A number which, when, multiplied by the difference of temperature of a ther- mo-electric couple, will give the difference of potential thereby generated in micro-volts. (See Diagram, Thermo- EIectric.) Power, Unit§ of — measurement of power. The following table of taken from Herimr's worl Units of Work, and of Power on Dynamo Electric Machines : Work erg = 1. dyne-centimetre. " = .0000001 joule. gram-centimetre = 981.00 ergs. " = . 00001 kilogram-metre. = 1937.5 ergs. \ = 10,000,000 ergs. = .737324 foot-pound. foot-grain _. joule, or .- volt-coulomb, or watt during every sec- ond, or. 1 volt-ampere d u r i n g every second 1 foot-pound .101937 kilogram-metre. /= .0013592 metric horse power for one second. = .0013406 horse power for one second. = .0009551 pound-Fah., heat unit. = .0005306 pound-Centig., heat unit. = .0002407 kilogr. - Centig. heat unit. = .0002778 watt-hour. = 13562600 ergs. = 1.35626 joules. WORDS, TERMS AND PHRASES. 493 1 foot-pound = .13825 kilogram-metre. " = .0018434 metric horse-power for one second. " =.00181818 horse-power for one second. " = .0012953 pound-Fah., heat unit, = .0007196 pound - Centig., heat unit. =.0003264 kilogr. -Centig., heat unit. = . 0003767 watt-hour. 1 kilogram-metre _ . = 98100000 ergs. = 9.81000 joules. = 7.23314 foot-pounds. " = .01333 metric horse-power for one second. " =.013151 horse - power for one second. = .009369 pound-Fah. , heat unit, " = .005205 pound-Centig., heat unit. = . 002361 kilogr. -Centig. heat unit. = . 002725 watt-hour. 1 watt-hour = 3600. joules. = 2654.4 foot-pounds. - . . = 366. 97 kilogram-metres. = 3.4383 pound-Fah., heat units. " .= 1.9102 pound-Centig., heat units. " = .8664 kilogr. -Centig., heat units. " -.. = .0013592 metric horse - power- hour. " = .0013406 horse-power-hour. 1 metric horse-power-hour = 2648700 joules. = 1952940 foot-pounds. " = 270000 kilogram-metres. " = 2529.7 pound-Fah., heat units. 494 A DICTIONARY OF ELECTRICAL 1 metric horse-power-hour = 1405.4 pound-Centig., heat units. = 637. 5 kilogr. -Centig. , heat units. " = 735.75 watt-hours. " = .98634 horse-power-hour. 1 horse-power-hour = 2685400 joules. = 1980000. foot-pounds. " =273740 kilogram-metres. " = 2564.8 pound-Fan., heat units. " = 1424.9 pound-Centig., heat units. " = 646.31 kilogr. -Centig. , heat units. = 745.941 watt-hours. " =1.01385 metric horse - power - hour. Heat. 1 gram -Centigrade = .001 kilogram-Centigrade. 1 pound-Fahrenheit = 1047.03 joules. « ' = 772 foot-pounds. " ...._= 106.731 kilogram-metres. " = .55556 pound-Centigrade. " = . 25200 kilogram-Centigrade. " = . 29084 watt-hour. " = .0003953 metric horse- power - hour. " = .0003899 horse-power-hour. 1 pound-Centigrade = 1884.66 joules. = 1389.6 foot-pounds. " = 192.116 kilogram-metres. " = 1.8000 pound-Fahrenheit. " = .4536 kilogram-Centigrade. " = .52352 watt-hour. " =.0007115 metric horse -power- hour. " = .0007018 horse-power-hour. 1 kilogram-Centigrade = 4154.95 joules. « = 3063.5 foot-pounds. WORDS, TERMS AND PHRASES. 495 1 kilogram-Centigrade. 1 erg per second 1 watt, or 1 volt-ampere, or 1 joule per second, or 1 volt-coulomb per second 1 foot-pound per min. 1 kilogram metre per min 1 metric horse-power . or 1 French horse-power or. = 423.54 kilogram-meters. = 3.9683 pound-Fahrenheit. = 2.2046 pound-Centigrade. = 1.1542 watt-hours. = .001569 metric horse - power - hour. = .0015472 horse-power-hour. Power, = .0000001 watt. = 10000000. ergs per second. = 44.2394 foot-pounds per min. = 6.11622 kilogram - metres per min. = .0573048 lb. -Fan., heat unit per min. = .0318360 lb.-Cent., heat unit per min. = .0144402 klgr.-Cent. heat unit per mm. = .0013592 metric horse-power. = .0013406 horse-power. = 226043 ergs per second. = .0226043 watt. = . 13825 kilogram-metre per min. = .00003072 metric horse-power. = .000030303 horse-power. = 1635000. ergs per second. = .163500 watt. = 7.23314 foot-pounds per min. = .0002222 metric horse-power. = .0002192 horse-power. = 735.75 x 10 7 ergs per second. = 735.750 watts. = 32549.0 foot-pounds per min. = 4500 kilogram-metres per min. 496 A DICTIONARY OF ELECTRICAL 1 cheval-vapeur, or ... ... = 42.162 lb.-Fah., heat units per min. 1 force de cheval, or = 23.423 lb. -Cent, heat units per min. 1 Pferdekraft = 10.625 klg.-Cent., heat units per min. " = .98634 horse-power heat units per min. 1 horse-power = 745.94 x 10 7 ergs per second. = 745.941 watts. " = 33000 foot-pounds per min. " .„_„ =4562.33 kilogram - metres per min. " =42.746 lb.-Fah., heat units per min. « =23.748 lb. -Cent., heat units per min. " = 10. 772 klg. -Cent. , heat units per min. " = 1.01385 metric horse-power. 1 lb. Fah., heat unit per min = 17.45 x 10 7 ergs per second. " = 17.4505 watts. " = .23718 metric horse-power. " = .023394 horse-power. 1 lb. Cent., heat unit per min = 31.41 x 10 7 ergs per second. " = 31.4109 watts. " = .04269 metric horse-power. " = .042109 horse-power. 1 klgr. -Cent. , heat unit per min = 69.25 x 10 7 ergs per second. " = 69.249 watts. " = .09412 metric horse-power. *' - .092835 horse-power. (Hering.) WORDS, TERMS AND PHRASES. 497 Practical Units. — (See Units, Practical) Primary Battery.— (See Battery, Primary. ) Prime Conductor. — The positive conductor of a frac- tional electric, or electrostatic machine. (See Machine, Elec- tric, Fractional.) Prime Motor.— (See Motor, Prime.) Probe, Electric Metallic conductors, inserted in the body of a patient, to ascertain the exact position of a bullet or other metallic body. The conductors are placed parallel, and are separated at the extremity of the probe by any suitable insulating- material. On contact with the metallic substance, an electric bell is rung- by the closing of the circuit, or the same thing is more readily detected by the deflection of the needle of a galvano- meter, or by a telephone placed in the circuit. Process, Electrotype (See Electrotype Process.) Processes of Carbonization.— (See Carbonization, Processes of. ) Prony-Brake.— (See Brake, Prony.) Proof-Plane. — A small insulated conductor employed to take test charges from the surface of an insulated, charged conductor. The proof-plane is used in connection with some forms of electrometer. — (See Balance, Torsion, Coulomb's.) Proof-Plane, Magnetic A small coil of wire placed in the circuit of a delicate galvanometer, and used for the purpose of exploring a magnetic field. When the coil is suddenly inverted in a magnetic field, if a long coil galvanometer provided with a heavy needle is used, the number of lines of force which pass through the area of cross section of the coil, will be proportional to the sine of half the angle of the first swing of the needle. 498 A DICTIONARY OF ELECTRICAL Proportionate Arms of Electric Bridge.— A term applied to two of the arms of an electric bridge or balance. (See Balance, Whealstone's Electric, Box Form of.) Prostration, Electric (See Sun Stroke, Elec- tric.) Protection, Electric of Houses, Ship* and Buildings Generally. (See Lightning Rods.) Protection, Electric of Metals.— (See Metals, Electric Protection of.) Protector, Lightning (See Lightning Ar- rester.) Protector, Vacuum Lightning A protec- tor consisting of a glass vessel in which the line wires and an earth wire are fused, and in which a partial vacuum is maintained. Vacuum protectors are employed on the lines of submarine cables, or underground lines, in order to protect them from lightning discharges. A discharge of high potential passes more readily through this partial vacuum to the ground ohan through the line wires. Protoplasm, Effects of Electric Currents on — Contractions observed in all protoplasm on the passage of an electric current through it. Protoplasm, the basis of plant and animal life, or the jelly like matter that fills all organic cells, whatever may be the origin of such cells, suffers contraction when traversed by an electric current. An increased activity of the movements of the amoeba is occasioned by slight shocks from an induction coil ; stronger discharges produce tetanic contractions, with, in some cases, expulsion of food or even of the nucleus. A uniform strength of current produces contraction and imperfect tetanus. WORDS, TERMS AND PHRASES. 499 Pump, Mechanical Air- — A mechanical device for exhausting or removing the air from any vessel. An excellent form of air pump is shown in Fig. 318, which is a drawing of Bianchi's pump. Three valves, all opening upwards, are placed at the top and bottom of the cylinder, and in the piston, respectively. These valves are mechanically opened and closed at the proper moment by the movements of the piston, i. e., their action is automatic. This enables tained than when the valves open and close by the tension of the air. Mechanical pumps are unable to readily produce the high vacua employed in most electric lamps. Mercury pumps are employed for this purpose. Pumps, Mercurial Air — Devices for obtaining Fig. 318. high vacua by the use of mercury. Mercury pumps are, in general, of two types of construction, viz. : (1) The Geissler Pump. (2) The Sprengel Pump. In the Geissler Mercury Pump, Fig. 319, a vacuum is obtained by means of the Torricellian vacuum produced m a large glass bulb that forms the upper extremity of a barometric column. (See Barometric Column.) The lower end of this tube or column is connected with a reservoir of mercury by means of a flexible rubber tube. To fill the bulb with mercury the reservoir is raised above its level, i. e., above thirty inches, the air it contains being allowed to escape through an open- ing governed by a stop-cock. The vessel to be exhausted is 500 A DICTIONARY OF ELECTRICAL Fig. 319. WORDS, TERMS AlJD PHRASES. 501 connected with the bulb, and by means of a two-way exhaus- tion cock, communication can be made with the bulb, when it contains a Torricellian vacuum, and shut off from it while its air is being expelled. In actual practice the mercury is mechanic- ally pumped into the barometric column, and the valves are opened either by hand, or, au- tomatically by suitable mechanism, or by elec- trical means. In the Sprengel Mer- cury Pump, Fig. 320, a vacuum is obtained by means of the fall of a stream of mercury in a vertical tube of compar- atively fine bore, which dips below a mercury level. The fall of a mer- cury stream causes the exhaustion of a reser- voir connected with the vertical tube, by the me- chanical action of the mercury in entangling babbles of air. These bubbles are largest at the beginning of the Fig. 320. exhaustion, but become smaller and smaller near the end, until, at last, the characteristic metallic click of mercury or 502 A DICTIONARY OF ELECTRICAL other liquid falling in a good vacuum is heard. The exhaust- ion may be considered as completed when the bubbles entirely disappear from tue column. The Sprengel pump produces a better vacuum than the Geissler pump, but is slower in its action. In actual practice, the mercury that has fallen through the tube is again raised to the reservoir connected to the drop tube by the action of a mechanical pump. Punning of Telegraph Poles.— Ramming or packing the earth around the base of a telegraph pole for the purpose of more securely fixing it in the ground. Push Button. — (See Button, Push.) Pyro Electricity.— Electricity de- veloped in certain crystalline bodies by heating or cooling them. Tourmaline possesses this property in a marked degree. When a crystal of tourmaline is heated or cooled, it acquires opposite electrifications at opposite ends or poles. In the crystal of tourmaline shown in Fig. 321, the end A, called the analogous pole, acquires a positive electrification, and the end B, called the antilogous pole, a negative electrification, while the tem- perature of the crystal is rising. While cooling the opposite electrifications are produced. A heated crystal of tourmaline, suspended by a fibre, is at- tracted or repelled by an electrified body or by a second heated tourmaline, in the same manner as an electrified body. Many ciystalline bodies possess similar properties. Among these are the ore of zinc known as electric calamine or the silicate of zinc, boracite, quartz, tartrate of potash, sulphate of quinine, etc. ^ A Fig. , WORDS, TERMS AND PHRASES. 503 Pyromagnetic Motor.— A motor driven by the attrao tion of magnet poles on a movable core of iron unequally heated. Fig. sn. The intensity of magnetization of iron decreases with an in- crease of temperature, iron losing most of its magnetization at 504 A DICTIONARY OF ELECTRICAL a red heat. A disc of iron, placed between the poles of a magnet so as to be capable of rotation, will rotate if heated at a part nearer one pole than the other, since it becomes less powerfully magnetized at the heated part. Fig. 323. In the form of pyromagnetic motor devised by Edison, and shown in Fig. 322, in elevation, and in Fig. 323, in vertical sec- WORDS, TERMS AND PHRASES. 505 tion, the disc of iron is replaced by a series of small iron tubes, or divided annular spaces, heated by the products of combustion from a fire placed be- neath them. In order to render this heating local, a flat screen is placed dissymetrically across the top to pre- vent the passage of air through the portion of the iron tubes so screened. The air is supplied to the furnace by passing down from above through the tubes so screened. This is shown in the drawings, the direction of the heating and the cooling air currents being in- dicated by the arrows. The supply of air from above thus insures the more rapid cooling of the screened portion of the tubes. Pyromagnetic Generator or Dy- namo. — An apparatus for producing electric- ity directly from the burning of fuel. Fig. s%. The operation of the generator is dependent on the fact, 506 A DICTIONARY OF ELECTRICAL that any variation in the number of lines of magnetic force that pass through a conductor, will develop differences of electric potential therein. Such variations may be effected either by varying the position of the conductor as regards the magnetic field, or by varying the intensity of the magnetic field itself. The latter method qf generating differences of potential is utilized in the pyromagnetic generator, and is effected in it by varying the magnetization of rolls of thin iron by the action of heat. A form of pyromagnetic generator devised by Edison is shown in Figs. 324 and 325. Eight electro-magnets are provided each with an armature, consisting of a roll of corrugated iron. Each of these arma- tures is provided with a coil of insulated wire wound on it and protected by asbestos paper. These armatures pass through two iron discs as shown. The armature coils are con- nected in series in closed circuit, the wires from the coils being connected with metallic brushes that rest on a commutator, supported on a vertical axis. A pair of metallic rings is provided above the commutator to carry off the current gene- rated. The vertical axis is provided below with a semi- circular screen called a guard plate which rotates with the axis and cuts off or screens one-half the iron armatures from the heated air. When the axis is rotated, the differences in the magnetiza- tion of the armatures, when hot and cold, develop differences in electromotive force which result in the production of an electric current. Pyrometer. — An instrument for determining tempera- tures higher than those that can be readily measured by ther- mometers. Pyrometers are operated in a variety of ways. A common method is by the expansion of a metal rod. Pyrometer, Siemen§> Electric An WORDS, TERMS AND PHRASES. 507 apparatus for the determination of temperature by the meas- urement of the electric resistance of a platinum wire exposed to the heat whose temperature is to be measured. Fig. 325. The platinum wire is coiled on a cylinder of fire-clay, so that its separate convolutions do not touch one another. It is protected by a platinum shield, and is exposed to the tempera- ture to be measured while inside a platinum tube. The resistance of the platinum coil at 0° C. having been 508 A DICTIONARY OF ELECTRICAL accurately ascertained, the temperature to which it has been exposed can be calculated from the change in its resistance when exposed to the unknown temperature. Pyrometer, Siemens' Water A pyrometer employed for determining the temperature of a furnace, or other intense source of heat, by calorimetric methods, i. e., by the increase in the temperature of a known weight of water, into which a metal cylinder of a given weight has been put, after being exposed for a given time to the source of heat to be measured. When copper cylinders are employed, the instrument pos- sesses a range of temperature of 1800° F.; when a platinum cylinder is used, it has a range of 2700° F. Quadrant Electroscope, Henley's (See Electroscope, Quadrant, Henley's.) Quadrant Electrometer.— (See Electrometer, Quad- rant.) Quadruplex Telegraphy.— A system of telegraphy by means of which four messages can be simultaneously trans- mitted over a single wire, two in one direction, and two in the opposite direction. — (See Telegraphy, Quadruplex.) Qualitative Analysis. — (See Analysis.) Quality of Disruptive Discharge, How Affected. — The appearance of the disruptive discharge as affected by a variety of circumstances. — (See Discharge, Disruptive.) Quality or Timbre of Sound.— That peculiarity of a musical note which enables us to distinguish it from another musical note of the same tone or pitch, and of the same in- tensity or loudness, but sounded on another instrument. The middle C, for example of a pianoforte, is readily dis- tinguishable from the same note on a flute, or on a violin ; that is to say, its quality is different. The differences in the quality of musical sounds are caused by the admixture of additional WORDS, TERMS AND PHRASES. 509 sounds called overtones which are always associated with any musical sound. Briefly, nearly all so-called simple musical sounds, are in reality chords or assemblages of a number of different musical sounds. One of these notes is far louder than all the others and is called the fundamental tone or note, and is what is recognized by the ear as the note proper. The overtones are too feeble to be heard very distinctly, but their presence gives to the note proper its own peculiar quality. In the case of a note sounded on the flute, these overtones are different either in number or in their relative intensities from the same note sounded on another instrument. Their fundamental tones, however, are the same. The peculiarities which enable us to distinguish the voice of one speaker or singer from another are due to the presence of these overtones. The over-tones must be correctly repro- duced by the diaphragm of the telephone, or phonograph, graphophone, or gramophone, if the articulate speech is to be correctly reproduced with all its characteristic peculiarities. Quantitative Analysis — (See Analysis.) Quantity, Arrangement of Voltaic Cell§ for — A term, now generally in disuse, to indicate the grouping of voltaic cells, technically known as parallel or multiple-arc. The arrangement or coupling of a number of voltaic cells in multiple-arc being an arrangement that reduces the internal resistance of the battery, and thus permits a greater current, or quantity of electricity to pass ; hence the origin of the term. Quantity, Unit of Eleetric A definite amount or quantity of electricity called the coulomb. — (See Coulomb.) Although the exact nature of electricity is unknown, yet it acts like a fluid (a liquid or gas) and can be accurately measured as to quantity. A current of one ampere, for example, is a current in which one coulomb of electricity passes in every second. 510 A DICTIONARY OF ELECTRICAL A condenser of the capacity of one farad is large enough to hold one coulomb of electricity if forced into the vessel under an electro-motive force of one volt.— (See Capacity. Farad. Volt.) Quiet Discharge.— (See Discharge, Convective.) Radiant Energy. — Energy transferred to, or charged on, the universal ether. Radiant energy is of two forms, viz. : (1) Obscure Radiation, or Heat. (2) Luminous Radiation, or Light. Radiant Matter.— (See Matter, Radiant.) Radiophony. — The production of sound by a body cap- able of absorbing radiant energy, when an intermittent beam of light or heat falls on it. The action of radiant energy, when absorbed by matter, is to cause its expansion by the consequent increase of temper- ature. This occurs even when the body is but momentarily exposed to a flash of light, but the instantaneous expansion, thus produced, immediately dies away, and by itself is indis- tinguishable. If, however, a sufficiently rapid succession of such flashes fall on the body, the instantaneous expansions and contractions produce an appreciable musical note. The sounds so produced have been utilized by Bell and Tainter in the construction of the Photophone. (See Photo- phone.) Radiation. — The transference of energy by means of ether waves. Radicals. — Unsaturated atoms or molecules, in which one or more of the bonds are left open or free. Radicals are either Simple or Compound. The radical may be regarded as the basis to which other elements may be added, or as the nucleus around which they may be grouped. WORDS, TERMS AND PHRASES. 511 Thus H 2 forms a complete chemical molecule, because the bonds of all its constituent atoms are saturated, thus H — O — H. But H — O — , or hydroxyl, is a radical, because its oxygen atom possesses one unsaturated or free bond. By- combining with the radical, (N0 2 ), it forms nitric acid, thus H — O — (NO,) = HN0 8 . During electrolysis, the molecule of the electrolyte is de- composed into two simple or compound radicals, called ions. These ions are respectively electro-positive or electro-negative, and are called kathions and anions. (See Ions. Electrolysis.) Radiometer, Crookes' An apparatus for showing the action of radiant matter in producing motion from the effect of the reaction of a stream of molecules escap- ing from a number of easily moved heated surfaces. (See Matter, Radiant.) Rail Road, or Railway, Electric A rail- road, or railway, the cars on which are driven or propelled by means of electric motors connected with the cars. The electric current that drives the electric motor is either derived from storage batteries placed on the cars, or from a dynamo-electric machine or battery of dynamo-electric machines, conveniently situated at some point on the road. (See Storage of Electricity.) The current from the dynamo is led along the line by suitable electric conductors. This current is passed into the electric motor as the car runs along the tracks, in various ways, viz. : (1) Placing one or both rails in the circuit of the dynamo and taking the current from the tracks by means of sliding or rolling contacts connected with the motor. (2) By placing the conducting wires parallel to each other in a longitudinally slotted undergroumd conduit in the road bed, and taking the current by means of a traveling brush or roller, called a plow, sled or shoe, and provided with two cen- tral plates, insulated from one another and connected re- spectively to the motor terminals. On the movement of the 512 A DICTIONARY OF ELECTRICAL car over the track, these traveling contacts touch the two parallel line conductors in the conduit, and take the electric current therefrom. (See Plow, Sled.) (3) By placing the line conductors on poles, along the road, and taking the current therefrom by means of suitable travel- ing contacts called trolleys or by sliders. (See Trolleys.) The first method, viz., that of using the tracks alone as con- ductors is not much employed. The use of the track and ground as a return for the current is now very generally employed. In some systems the track is divided into sections which are successively brought into action with the main conductors by contacts effected by the attraction between magnets carried on the car and contact pieces of magnetic material placed be- low the surface. The rail section thus temporarily energized is placed in connection with the motor. In order to regulate the speed, various devices are employed to vary the current strength in the motor circuit. These devices consist essentially in rheostats or resistances intro- duced into, or removed from, the motor circuit by the move- ment by hand of a lever that forms part of the circuit, over contact plates connected to the resistance coils. In order to change the direction of the car, the direction of rotation of the electric motor is changed. This is effected by some form of reversing gear or mechanism that changes the direction of rotation of the motor, either by shifting the brushes, by changing the field, or by any other means. (See Telpherage. Electric Motor. Rheostat.) Ray, Electric (See Fishes, Electric.) Rays, Actinic (See Antinic Rays.) Reaction Principle of Dynamo-Electric Ma- chines o — The reaction of the field magnets and the armature of a dynamo-electric machine on each other until the full work- ing current which the machine is capable of developing is pro- duced. WORDS, TERMS AND PHRASES. 513 When the armature of a series or shunt dynamo commences to rotate, the differences of potential generated in its coils are very small, since the field of the magnet is so weak. The cur- rent so produced in the armature, however, circulating through the field magnet coils, increases the intensity of the mag- netic field of the machine, and this reacting on the arma- ture results in a more powerful current through it. This cur- rent again increases the strength of the magnetic field of the machine, which again reacts to increase the current strength of the armature coils, and this continues until the machine is producing the full current it is designed to produce. A dynamo-electric machine very rapidly "builds up," or reaches its maximum current after starting. The reaction principle was discovered by Soren Hjorth, of Copenhagen. Reaction Telephone. — An electro-magnetic telephone in which the currents induced in a coil of wire attached to the diaphragm are passed through the coils of the electro- magnet and thus react on and strengthen it. Reaetion Wheel, Electric (See Flyer, Electric.) Reactions, Anodic and Kathodic (See Kath- odic and Anodic Reactions.) Reading Telescope. — (See Telescope, Reading.) Receiver, Harmonic A receiver, employed in systems of harmonic telegraphy, containing an electro- magnetic reed, tuned to vibrate to one note or tone only. (See Telegraphy, Harmonic.) Receiver, Phonographic, Telephonic, Grapho- phonic, Grainophonic The apparatus employed in' a telephone, phonograph, graphophone, or gramophone, for the reproduction of articulate speech. (See Phonograph.) Reciprocals. — The quotient arising from dividing unity by any number. The reciprocal of 4 is }-± or .250. 514 A DICTIONARY OF ELECTRICAL The conducting power of any circuit is equal to the re- ciprocal of its resistance, or, in other words, the conducting power is inversely proportional to the resistance. The following table contains the reciprocals of the numerals up to 100 : Table of Reciprocals. No. Recip- rocal. No. Recip- rocal. No. Recip- rocal. No. Recip- rocal. No. Recip- rocal. 2 0.5000 22 0.0455 42 0.0338 62 0.0161 82 0.0122 3 0.3333 23 0.0435 43 0.0233 63 0.0159 83 0.0120 4 0.2500 24 0.0417 44 0.0227 64 0.0156 84 0.0119 5 0.2000 25 0.0400 45 0.0222 65 0.0154 85 0.0118 6 0.1667 26 0.0385 46 0.0217 66 0.0152 86 0.0116 7 0.1429 27 0.0370 47 0.0213 67 0.0149 87 0.0115 8 0.1250 28 0.0357 48 0.0208 68 0.0147 88 0.0114 9 0.1111 29 0.0345 49 0.0204 69 0.0145 89 0.0112 10 0.1000 30 0.0333 50 0.0200 70 0.0143 90 0.0111 11 0.0909 31 0.0323 51 0.0196 71 0.0141 91 0.0110 12 0.0833 32 0.0313 52 0.0192 72 0.0139 92 0.0109 13 0.0769 33 0.0303 53 0.0189 73 0.0137 93 0.0108 14 0.0714 34 0.0294 54 0.0185 74 0.0135 94 0.0106 15 0.0667 35 0.0286 55 0.0182 75 0.0133 95 0.0105 16 0.0625 36 0.0278 56 0.0179 76 0.0132 96 0.0104 17 0.0588 37 0.0270 57 0.0175 77 0.0130 97 0.0103 18 0.0556 38 0.0263 58 0.0172 78 0.0128 98 0.0102 19 0.0526 39 0.0256 59 0.0169 79 0.0127 99 0.0101 20 0.0500 40 0.0250 60 0.0167 80 0.0125 100 0.0100 21 0.0476 41 0.0244 61 0.0164 81 0.0123 {Clark & Sabine.) Record, Gramophonic, Graph ©phonic, or Phon- ographic The irregular indentations, cuttings, or tracings made by a point attached to the diaphragm spoken against, and employed in connection with the receiving diaphragm for the reproduction of articulate speech. Record, Telephonic A permanent record pro- duced by the diaphragm of a telephone. WOKDS, TERMS AND PHRASES- 515 Various methods have been proposed for telephone records, but none of them have yet been introduced into actual com- mercial use. Recorder, Bain's Chemical An apparatus for recording the dots and dashes of a Morse telegraphic dispatch, on a sheet of chemically prepared paper. A fillet of paper soaked in some chemical substance, such as ferro-cyanide of potassium, is moved at a uniform rate between the two terminals of the line, one of which is iron tipped, so that on the passage of the current, a blue dot, or dash, will be made on the paper according to the length of time the current is passing. In order to ensure a moist condition of the paper fillet some deliquescent salt, like ammonium nitrate, is generally mixed with the ferro-cyanide of potas- sium. A Bain Recorder is shown in Fig. 326. A, is a drum of brass, tinned on the outside. The paper fillet is drawn from the roll and kept pressed against the cylinder A, by a small wooden roller B. The needle, which is a metallic point, is in connection with one end of the line wire, and the brass drum is connected with the other end through the earth. Care must be observed to connect the needle point with the positive electrode, as otherwise the paper will not be marked. The Bain Recorder is now almost entirely replaced by the Morse Sounder. Recorder, Morse or Morse Register.— An apparatus for automatically recording the dots and dashes of a Morse telegraphic dispatch, on a fillet of paper drawn 516 A DICTIONARY OF ELECTRICAL under an indenting or marking point on a striking lever, con- nected with the armature of an electro-magnet. The Morse registering or recording apparatus is shown in Fig. 327. The paper fillet passes between a pair of rollers r. driven by the clockwork W. The upper roller is provided with a groove, so that the depression of the stylus at the bent end of the lever L, by the electro-magnet M, moving its arma- ture attached to the lever L, may indent or emboss the paper fillet. When no current is passing, the armature of the magnet and the lever L, are drawn back by the action of an adjustable spring at n. 9 Eig. 327. In the drawing, the ordinary Moi'se sounder is shown on the right. The sounder has almost entirely replaced the record- ing apparatus. Recorder, Siphon An apparatus for re- cording in ink on a sheet of paper, by means of a fine glass siphon supported on a fine wire, the message received over a cable. One end of the siphon dips in a vessel of ink. The record is received on a fillet of paper moved mechanically under the siphon. The ink is discharged from the siphon by electric charges imparted to the ink by a static electric machine. WORDS, TERMS AND PHRASES. 517 In the annexed sketch of the siphon recorder, Fig. 328, a light rectangular coil b b, of very fine wire, is suspended by a fine wire//', between the poles N, S, of a powerful com- pound permanent magnet, and moving on the vertical axis of the supporting wire//', adjustable as to tension, at h. A stationary soft iron core a, is magnetized by induction Fig. and strengthens the magnetic field of N, S. The cable cur- rent is received by the coil b b, through the suspending wire //', and is moved by it to the right or the left, according to its direction, to an extent that depends on the current strength. The fine glass siphon n, which dips into a reservoir of ink at m, is capable of movement on a vertical axis I, and is moved backwards or forwards, in one direction by a thread k, 518 A DICTIONARY OF ELECTttlCAF attached to b, and in the opposite direction by a retractile spring- attached to an arm of the axis /. As the paper is moved under the point of the siphon, an irregular curved line is marked thereon. Two records as actually received by a siphon recorder are shown in the Figs. 329 and 330. Movements upwards corre- spond to the dots, and downwards to dashes. Rectilinear Currents. (See Currents, Rectilinear.) Reflecting Galvanometer.— (See Galvanometer, Re- flecting.) Reflector, Parabolic Hector.) — (See Parabolic Re- S I PHON RECORDER Fig. 329. Refraction, Double Reflectors. — Plane or curved sur- faces capable of regu- larly reflecting light. (See Parabolic Re- flectors.) The property possessed by certain bodies of splitting up by refraction a ray of light passed into it, into two separate rays, and thus doubly refract- " "¥Dl . ' J SETTLE D ing it. Certain specimens of calc spar ig - ' m possess the property of double refraction. Each of the two rays into which the original ray is separated is polarized. Refraction, Double Electric The prop- erty of doubly refracting light acquired by some transparent substances when placed in an electrostatic or electro-magnetic field. (See Double Refraction, Electric.) Register, Watchman's Electric —(See Watch- man's Register, Electric.) Registering Apparatus, Electric -De- vices for obtaining permanent records by electrical means. (See Recorders.) WORDS, TERMS AND PHRASES. 519 Regulation, Automatic — (See Automatic Regulation.) Relative Calibration.— (See Calibration, Absolute and Relative.) Relay Bell.— (See Bell, Relay.) Relay, Microphone (See Microphone Relay.) Relay, or Receiving Magnet. — An electro-magnet employed in systems of telegraphy provided with contact- points, placed on a delicately supported armature, the move- ments of which throw a battery, called the local battery, into or out of circuit, for the operation of the recording apparatus. Fig. 331. The use of a relay permits much smaller currents to be used than could otherwise be done, since the electric impulses, on reaching a distant station, are required to do no other work than attracting a delicately poised movable contact, and thus, by throwing a local battery into the circuit of the receiving- apparatus, to cause such local battery to perform the work of 520 A DICTIONARY OF ELECTRICAL registering. Its use is especially required in the Morse system of telegraphy in order to cause the Sounder to be distinctly heard. A form of relay much used is shown in Fig. 331. The electro-magnet M, is wound with many turns of very fine wire. In the form used by the Western Union Telegraph Company, there are about 8,500 turns, having resistance of 150 ohms. A screw m, is provided for moving the electro- magnet M, a slight distance in or out for the purposes of ad- justment. A semi-cylindrical armature A, of soft iron, is attached to the insulated armature lever a, the lower end of which is supported by a steel arbor, which is pivoted between two set screws. A retractile spring S', regulable at S, is pro- vided for moving the armature away from the electro-magnet. There are four binding posts, two of which are placed in the circuit of the electro-magnet, and two in that of the local battery. The ends of the line wire are connected with the former, and the receiving instrument placed in the circuit of the latter. A platinum contact is placed on the end of a screw supported at F, opposite a similar contact, near the end a, of the armature lever. The contact is regulable by means of a screw c. On the the energizing of the electro-magnet, the attraction of its armature closes the platinum contact, and by thus com- pleting the circuit of the local battery causes an attraction of the armature of the receiving apparatus. On the cessation of the current in the main line, the spring S', pulls the armature away from the magnet, breaks the current of the local battery, and thus permits a similar spring on the receiving instrument to pull its armature away. Thus all the movements of the armature of the relay are reproduced with increased intensity by the armature of the receiving instrument. The connections of the relay to the local battery and the registering apparatus, will be better understood from an in- spection of Fig. 332, which represents a form of relay much WORDS, TERMS AND PHRASES. 521 used in Germany. The retractile spring /, is regulated by the up-and-down movements of its lower support, which slides in the vertical pillar S. The line wire is shown at m ra, con- nected at one end to earth by the ground wire. The register- ing apparatus, R, is connected in the circuit of the local bat- tery L, as shown. The contacts are made by the end B, of the lever B B', attached to the armature A, of the electro- magnet M M. Fig. 332. -A telegraphic relay provided Relay, Polarized with a permanently magnetized armature in place of the soft iron armature of the ordinary instrument. In the form of polarized relay shown in Fig. 333, N S, is a steel magnet, whose magnetism is consequently permanent, with its north and south poles at N and S, respectively. The cores of the electro-magnet m m', are of soft iron, and, since they rest on the north pole N of the permanent steel magnet o22 A DICTIONARY OF ELECTRICAL the poles, brought very near together by the armatures at n, n', will be of the same polarity as N, when no current is passing through the coils m, m' ; but when such current does pass, one of these poles becomes of stronger north polarity, while the other changes its polarity to south. By this means to-and-fro movements of the armature lever with its contact point are effected without the use of a retractile spring ; movement in one direction occurring on the closing of the circuit through the electro-magnetism developed by the coils Fig. 333. m, w! , and movement in the opposite direction, on the losing of this magnetism on breaking the circuit, by the permanent magnetism of the steel magnet N S. These movements are imparted to the soft iron lever c c', pivoted at B, and passing between the closely approached soft iron poles at n, n'. This lever rests at the end c' against a contact point when moved in one direction, and against an insulated point when moved in the opposite direction. It rests against the insulated point when no current is passing through the coils m, m'. If the armature lever were placed in a position exactly mid- WORDS, TERMS AND PHRASES. 523 way between the poles n and n', it would not move at all, being- equally attracted by each ; but if moved a little nearer one pole than the other, it would be attracted to, and rest against, the nearer pole. When alternating currents are employed on the line, the lever c c' must be adjusted as nearly as possible in the middle of the space between nand n', in which case it will remain on the side to which it was last attracted, until a current in the opposite direction moves it to the other side. LB Fig. 33U. The space between „ne magnet poles n, n' , and the contacts of the armature lever at D and D', are shown in detail in Fig. 334, which is a plan of the preceding figure. The bind- ing posts, for the line battery are shown at LB, and those for the local battery at O, B. The dotted lines show the con- nections. Since the polarized relay dispenses with the retractile spring, it is far more sensitive than the ordinary instrument. 524 A DICTIONARY OP ELECTRICAL Once adjusted no further regulation is required, in which re- spect, it differs very decidedly from non-polarized relays. Reluctance, Magnetic (See Magnetic Re- luctance.) Repeaters, Telegraphic — Teregraphic de- vices, whereby the relay, sounder, or registering apparatus is caused to repeat the signals received, by opening and clos- ing another circuit with which it is suitably connected. Fig. 385. Repeaters are employed to establish direct communication between very distant stations, or to connect branch lines to the main line. Fig. 335, shows Wood's Button Repeater. This repeater consists simply of a three-point-switch L, capable of being WORDS, TERMS AND PHRASES. 525 placed on the points 1, 2 and 3 ; and a ground switch at 4. The circuits are arranged between the sounders S, S', relays M, M', main batteries B, B', and the two main lines E and W, in the manner shown. If the lever L, is in the position shown in the drawing, the lines E and W, form inde- pendent circuits. If the ground switch 4 is closed, and the lever L is placed on 2, 2, the eastern line re- peats into the western. If the lever L is placed on the plates 3, 3, the western line repeats into the eastern. This repeater is non- automatic and can be worked in but one di- rection ; morever, it re- quires the services of an attendant. The automatic repeat- er can be operated in both directions, and dis- penses with the con- stant services of an at- tendant at the repeat- ing station. In sending a dispatch through a repeater, the dots and dashes are prolonged so as to 526 A DICTIONARY OF ELECTRICAL give the lever of the repeating instrument time in which to move backwards and forwards. In Hi'cks 1 Automatic Button Repeater, shown in Fig. 336, the switch or circuit changer is automatic in its action. The relay magnets are shown at M, M', the sounders at R, and R' ; /, /', are platinum contacts operated by levers I and V, and L and L' are Extra Local Magnets, that act on armatures placed directly opposite the armatures of the relay magnets. The extra local magnet L is cut out of the circuit of B', the Extra Local Battery, when the main cir- cuit is broken, and the armature is in contact with c. As soon as this happens, however, the spring s, drawing away the armature, and thus opening the short circuit of no resistance between c and a, establishes a circuit through L. On a coming in contact with c, the circuit is again broken. The tension of the spring s is so regu- lated that a very rapid vibration of a is so constantly maintained, that it is impossible to close the main circuit when L is not cut out. The armature a will there- fore respond to very weak impulses of the relay magnet. On breaking the western main circuit N, the lever a vibrates I, of the sounder R, first breaks the circuit of L, and afterwards that of the eastern main circuit E, which passes though M. Both L' and M', be- ing broken, a slight tension of s', will hold a, in place, thus avoiding the breaking of the western main circuit through Fig. 837. very rapidly. The lever WOUDS, TERMS AND PHRASES. 527 the closing- of the local circuit through R. On the closing- of the western circuit, the reverse of these operations occur. The author has taken the above explanation mainly from Pope's work on " Modern Practice of the Electric Tele- graph." Replenisher, Thomson's A static influ- ence machine devised by Sir Wm. Thomson for charging- the quadrants of his quadrant electrometer. Two brass carriers C and D, shown in Fig. 337, are ec- centrically fixed to the end of the vulcanite rod E, which is capable of rotation by the thumb screw at M, in the direction shown by the arrow. Hollow metal half cylinders, A and B, act as inductors, a strip of brass fixed around the edges of a piece of vulcanite P, connecting the metallic springs S and S', as shown. The action of the replenisher is readily understood from the following considerations, as suggested by Ayrton in his " Practical Electricity" : A and B, Fig. 338, are two insulated hollow metallic vessels having a small difference of potential between them, A, being the higher. C and D, are two small uncharged conductors held by insulating strings. If C and D be held near A and B, as shown, the potential of C will, by induction, be raised somewhat above that of D, so that when connected by a con- ductor, such as the metallic wire W, a small quantity of positive electricity will flow from C to D, thus leaving D positively, and C negatively charged. If, now, C and D, are removed from W and placed in the bottom of B and A, as shown in Fig. 339, the difference of potential between A and B, will be thereby increased, and if they are then withdrawn, and totally discharged, and again placed in the first position shown, an additional charge can be given to A and B, and this can be repeated as often as desired. In the replenisher, A and B correspond to the vessels A and B; the brass carriers C and D, to the balls C and D, 528 A DICTIONARY OF ELECTRICAL and the spring S S, and M, to the wire W. No initial charge need be given to A and B, since they are invariably found to be at a sufficient difference of potential to build up the charge. Residual Atmosphere.— (See Atmosphere, Residual.) Residual Charge.— (See Charge, Residual.) Residual Magnetism. — The magnetism remaining in the core of an electro-magnet on the opening of the magnetiz- ing circuit. Resin. — A general term applied to a variety of dried juices of vegetable origin. Resins are, in general, transparent, inflammable solids, soluble in alcohol, and are non-conductors of electricity. Rosin is one of the varieties of resin. Fig. 338. Resinous Electricity. — A term formerly employed in place of negative electricity. It was at one time believed that all resinous substances are negatively electrified by friction. This we now know to be untrue, the nature of electrification depending as much on the character of the rubber, as on the character of the thing WORDS, TERMS AND PHRASES. 529 rubbed. Thus resins rubbed with cotton, flannel or silk, be- come negatively excited, but rubbed with sulphur or gun- cotton, positively excited. The terms positive and negative are now exclusively employed. Resistance Box. — A box containing a number of coils of known resistances employed for determining the value of an unknown resistance. (SeeBo.v, Resistance. Balance, Electric, Box Form of.) Resistance Coil. — A coil of insulated wire of known the external effects of its own magnetic field. sistance.) Resistance Coil, Standard (See Coils, Re- coil the resistance of which is that of the standard ohm. The standard ohm, as issued by the Electric Standards Com- mittee of England, has the form shown in Fig. 340. The coil of wire is formed of an alloy of platinum and silver, insulated by silk covering and melted paraffine. Its ends are soldered to thick copper rods r, ?•', for ready connection with mercury cups. The coil is at B. The space above it at A is filled with paraffin, except at the opening t, which is provided for the insertion of a ther- mometer Resistance, Effect of Heat on Electric Nearly all metallic conductors have their electric resistance increased by an increase of temperature. The carbon conductor of an electric incandescent lamp on the contrary, has its resistance decreased when raised to electric Fig. SAO. 530 A DICTIONARY OF ELECTRICA, incandescence. The decrease amounts to about three-eighths of its resistance when cold. The effects of heat on electric resistance may be sum- marized as follows : (1) The electric resistance of metallic conductors increases as the temperature rises. (Carbon is an exception). (2) The electric resistance of electrolytes decreases as the temperature rises. (3) The electric resistance of dielectrics and non-conductors decreases as the temperature rises. Resistance and Conductivity of Pure Copper at Different Temperatures. Centigrade Centigrade Tempera- Resistance. Conductivity. Tempera- Resistance. Conductivity. ture. ture. 0° 1.00000 1.00000 16° 1.06168 .94190 1 1.00381 .99624 17 1.06563 .93841 2 1.00756 .99250 18 1.06959 .93494 3 1.01135 .98878 19 1.07356 .93148 4 1.01515 .98508 20 1.07742 .92814 5 1.01896 .98139 21 1.08164 .62452 6 1.02280 .97771 22 1.08553 .92121 7 1.02663 .97406 23 1.08954 .91782 8 1.03048 .97042 24 1.09365 .91445 9 1.03435 .96679 25 1.09763 .91110 10 1.03822 .96319 26 1.10161 .90776 11 1.04199 .95970 27 1.10567 .90443 12 1.04599 .95603 28 1.11972 .90113 13 1.04990 .95247 29 1.11382 .89784 14 1.05406 .94893 30 1.11782 .89457 15 1.05774 .94541 (Latimer Clark.) The following table from Matthiessen's measurements giv( the relative resistances of equal lengths and cross sectioi WORDS, TERMS AND PHRASES. 531 of different substances as compared with silver. The sub- stances are chemically pure. Legal Microhms. Resistance in Microhms atO° C. Relative Resistance. Names op Metal. CenUmetre. J Cubic inch. Silver, annealed Copper, annealed Silver, hard drawn Copper, hard drawn... Gold, annealed Gold, hard drawn Aluminium, annealed. Zinc, pressed . 1.504 1.598 1.634 1.634 2.058 2.094 2.912 5.626 9.057 9.716 12.47 13.21 19.63 20.93 35.50 94.32 131.2 0.5921 0.6292 0.6433 0.6433 0.8102 0.8247 1.1470 2.215 3.565 3.825 4.907 5.202 7.728 8.240 13.98 37.15 51.65 1. 1.063 1.086 1.080 1.369 1.393 1.935 3.741 Platinum, annealed... Iron, annealed Nickel, annealed Tin, pressed.. Lead , p ressed German Silver Antimony, pressed Mercury 6.022 6.460 8.285 8.784 13.05 13.92 23.60 62.73 Bismuth, pressed 87.23 (Ayrton.) The above resistances are for chemically pure substances only. Slight impurities produce very considerable changes in the resistance. Re§istance, Electric The ratio between the electro-motive force of a circuit and the current that passes therein. Ordinarily the resistance of a circuit may be conveniently regarded as that which opposes or resists the passage of the 532 A DICTIONARY OF ELECTRICAL current. Strictly speaking, however, this is not true, since from Ohm's law (See Ohm's Law), E C = — , from which we obtain R E R = — , which shows that resistance is a ratio between C the electro-motive force that causes the current and the current so produced. Resistance may be expressed as a velocity. The dimensions of resistance in terms of the electro-magnetic units are L T ' (See Units, Electro-Magnetic.) But these are the dimensions of a velocity which is the ratio of the distance passed over in unit time. Resistance may therefore be expressed as a velocity. " The resistance known as ' one ohm ' is intended to be 10 9 absolute electro-magnetic units, and therefore is represented by a velocity of 10 9 centimetres or ten million metres (one earth-quadrant) per second " — Sylvanus Thompson. Resistance may be represented by a velocity, one ohm being the resistance of a wire, which, if moved through a unit field of force at the rate of ten million (10 9 ) centimetres per second will have a current of one ampere generated in it. (See Ohmic Resistance. Spurious Resistance. The unit of resistance is the ohm. Its true value, as has been shown by careful measurements, is not exactly equal to 10 9 centimetres per second. Resistance, Electric of Liquids.— The resist- ance offered by a liquid mass to the passage of an electric current. As a rule the electric resistance of a liquid is enormously higher than that of metallic bodies, with the single exception of mercury. To determine the resistance ®f a liquid, a section is taken WORDS, TERMS AND PHRASES. 533 between two parallel metallic plates A and B, Fig. 341, placed as shown in the figure, and an electric current is passed between them. In order to avoid the effect of a spur- ious resistance, due to a counter electro-motive force, it is necessary to use plates at A and B, of metals that are not acted on chemically by the liquid on the passage of the current. (See Counter Electro-Motive Force. Spurious Resistance.) In order to more accurately vary the size of the plates immersed in the liquid, and hence the area of cross section of the liquid conductor, as well as the distance between the plates, the apparatus shown in Fig. 342 may be used, in which these distances are readily adjustable, as shown. Resistance, Magnetic (See Magnetic Resistance.) Resistance, Measurement of Methods em- ployed for determining the resistance of any circuit or part of a circuit. Numerous methods are employed for this purpose. Among these are : (1) The use of a Resistance Box with a Wheatstone's Bridge, by opposing or bal- ancing the unknown resistance against a known resistance. (See Balance, Wheat- stone's.) (2) With the Differential Galvanometer. (See Galvanometer, Differential.) (3) By the Method of Substitution. (4) By a Comparison of the Deflections of a Galvanometer. Method of Substitution — A resistance box R, Fig. 343, galvanometer G, and the resistance x, that is to be measured, Fig. Ski. are placed in the direct circuit of the battery B by means of conductors of such thick wire that their resistance can be neglected. The deflection of the gal- vanometer is first measured with x in circuit, and no resist- 534 A DICTIONARY OF ELECTRICAL ance in the box R. The resistances is then cut out of the circuit by placing a thick copper wire across the terminals of the mercury cups at m, m', and resistances unplugged in R, until the same deflection is obtained. Then, if the electro- Fig. 3U2. motive force of the battery has remained constant, the resist- ances unplugged equal the unknown resistance. For full description of the various methods of determining resistance the reader is referred to " Ayr-ton' 8 Practical Elec- tricity," "Kempe's Handbook of Testing," or other standard electrical books. x 9 I I o o o o "\ m' M'lt Resistance, Olim- i c (See Ohmic Resistance.) Resistance, Spur- (See Fig. 3h3. equal lengths and cross sections of given in ohms, or other units of resistance : ious Spurious Resistance.) Resistance, Tab- les of Tables in which the resistance of different substances is WORDS, TERMS AND PHRASES. 535 Resistance. Resistance of Wires of Pure Annealed Copper at O r {Density = 8.9.) a . _, U fl>^~. Resistance of Wire of Pnre Annealed *i i .£&££ Copper at 0° C. 3 ^ fee « 2 5=0 |fe e£3 M® l| Ohms Metres Ohms £^1 J *3B per per per 5S £ O Kilometre. Ohm. Kilogramme. 5 175 5.7 .8 1230.5 .00456 4.4 135.28 7.4 1.06 944.38 .00784 3.9 106.35 9.5 1.35 722 .0128 3.4 80.8 12.5 1.80 563.92 .0222 3 62.93 16 2.3 439.07 .0365 2.7 51 19.8 2.8 355.65 .0557 2.4 40.23 25 3.6 281 .088 2.2 33.82 29 4.2 236.08 .123 2 27.95 36 5.1 195.15 .185 1.8 22.7 44 6.3 158.08 .278 1.6 17.89 56 8 124.9 .448 1.5 15.75 63 9.1 109.75 .574 1.4 13.7 73 10.5 95.651 .763 1.3 11.84 85 12 82.42 1.03 1.2 10.06 100 14 70.247 1.42 1.1 8.47 119 17 59.024 2.02 1 6.99 144 20 48 782 2.95 .9 5.66 178 25 39.515 4.19 .8 4.47 225 32 31.225 7.21 .7 2.83 294 42 23.9 12.3 .6 2.52 400 57 17.56 22.78 .5 1.74 576 81 12.305 46.81 .4 1.175 902 122.4 8.173 110.41 .34 .808 1251 177.9 5.622 222.55 .3 .7181 1607 228.5 4.377 367.2 .24 .4026 2508 357 2.801 895.36 .2 .2797 3614 514 1.945 1,857.6 .16 .179 5590 803.1 1.245 4,489 .12 .1007 9929 1428 .7 14,179 .1 .0699 14369 2056 .486 29,549 .08 .0447 24570 3213 .311 78,943 .06 .0252 39824 5713 .173 227,515 .04 .0112 88878 12848 .078 1,142,405 (Hospitalier.) 536 A DICTIONARY OF ELECTRICAL Table of Conducting Powers and Resistances in Ohms. a> v *S bo" O c 5 o o a a o o p— 1 a £ o a> -1 o a> be CD b£ £S 8 J SPSS t-, £2 bt &-P * o *| a si t- £ os 3 83 4> S3 o o3 a) S322 Names of Metals. O ._ £ £ "N. <*- o . ft"g, a 1 ■a o be a> p %S . -2^ 2 .2 o'S O bfl a Is! o IIS 2 - § bc- Silver, annealed 0.2214 0.1544 9.936 0.01937 0.377 Silver, hard drawn... 100.00 0.2421 0.1689 9.151 0.02103 Copper, annealed 0.2064 0.1440 9.718 0.02057 0.388 Copper, hard drawn. . Gold, annealed 99.55 0.2106 0.1469 9.940 0.02104 0.5849 0.4080 12.52 0.02650 0.355 Gold, hard drawn 77.96 0.5950 0.4150 12.74 0.02697 Aluminium, annealed 0.06822 0.05759 17.72 0.03751 Zinc, pressed 29.02 0.5710 0.3983 32.22 0.07244 0.365 Platinum, annealed. . 3.536 2.464 55.09 0.1166 Iron, annealed 16.81 1.2425 0.7522 59.40 0.1251 Nickel, annealed. .. 13.11 1.0785 0.8666 75.78 0.1604 Tin, pressed 12.36 1.317 0.9184 80.36 0.1701 0.365 Lead, pressed 8.32 3.236 2.257 119.39 0.2527 0.387 Antimony, pressed. . . 4.62 3.324 2.3295 216.0 0.4571 0.389 Bismuth, pressed.. . Mercury, liquid . . 1.24 5.054 3.525 798.0 1.689 0.354 18.740 13.071 600.0 1.270 0.072 Platinum-silver, a 1 - loy, hard or annealed 4.243 2.959 143.35 0.3140 0.031 German silver, hard or annealed 2.652 1.850 127.32 0.2695 0.044 Gold, silver, alloy, hard or annealed. . . 2.391 1.668 66.10 0.1399 0.065 (Jenkin.) When several resistances are placed in series in any circuit, by measuring the difference of potential at their terminals, their values can be determined by simple calculation, being directly proportional to these differences of potential. This method in especially applicable to the measurement of such low resistances as the armatures of dynamo electric machines. Resultant. — In mechanics, a single force that represents WORDS, TERMS AND PHRA.SES. 537 in direction and intensity the effects of two or more forces acting in different directions. Retardation. — A decrease in the speed of telegraphic signaling caused by the induction of the line conductor on itself, and the induction between it and neighboring con- ductors. Retardation in signaling is produced by the following causes : (1) Self-induction which produces extra currents. (See Self-induction. Currents, Extra.) The extra current on making, retards the beginning of the signal, and the extra current on breaking, retards its stopping. (2) Mutual Induction between the line conductor and neigh- boring conductors. The line must receive a certain charge before a current sent into it at one end can produce a signal at the other end. This charge will depend on the length and surface of the wire, on its neighborhood to the earth or other wires, and on the nature of the insulating material between it and the neighboring' conductor. This results in a charg'e given to the wire which is lost as a current for signaling. The greater the electrostatic capacity of the line wire, the greater will be the retardation in signaling. (See Capacity, Specific Inductive. Dielectric. Electrostatic Capacity.) (3) The Magnetic Inertia or Lag, or the time required to magnetize or demagnetize the core of the electro-magnetic receptive devices used on the line. Retentivity, Magnetic A term proposed by Lamont in place of coercive force, or the power possessed by a magnetizable substance of resisting magnetization or demagnetization. (See Coercive Force.) Return Shock or Stroke. (See Back Stroke.) Reverse Induced Current. — The current produced by self-induction in a circuit at the moment of completing the circuit. (See Extra Current.) 538 A DICTIONARY OF ELECTRICAL Reversing Gear of Electric Motor.— Apparatus for reversing the direction of the current through an electric motor, and, consequently, the direction of its rotation. (See Railroad or Railway, Electric.) Reversing Key.— (See Key, Reversing.) Rheochord.— (See Rheostat.) Rlieometer.— A term formerly employed for any device for measuring the strength of a current. (Now obsolete and replaced by the word Galvanometer.) Rheomotor. — A term formerly employed to designate any electric source. (Now obsolete and replaced by the various names of the different electric sources. (See Source, Electric.) Rheophore. — A term formerly employed to indicate a portion of a circuit conveying a current and capable of deflect- ing a magnetic needle placed near it. (Now obsolete.) Rheoscope. — A term formerly employed in place of the present word Galvanoscope, for an instrument intended to show the presence of a current, or its direction, but not to measure its strength. (Now obsolete.) Rheostat. — A term signifying any adjustable resistance. A rheostat enables the resistance to be brought to a stand, i. e., to a fixed value ; hence the name. The term rheostat is applied generally to a readily variable resistance, the varying values of which are known. Rheostat, Wheats tone's A form of appa- ratus sometimes employed for an adjustable resistance. This apparatus is very seldom employed in accurate work. The parallel cylinders A and B, Fig. 344, are respectively of conducting and non-conducting materials, the bare wire on which can be wound from either cylinder to the other. When introduced into a circuit, only the resistance of the portions of the wire on B is introduced into the circuit, since the bare wire on A is short circuited by the metallic cylinder. This WORDS, TERMS AND THRASES. 539 rheostat is seldom employed in accurate measurements ow- ing to the difficulty of invariably obtaining- reliable contacts. Rheostatic Machine. — A machine devised by Plant e in which continuous static effects of considerable intensity are obtained by charging a number of condensers in multiple arc and discharging them in series. The condensers are charged by connecting them with a number of secondary or storage batteries- Rlieo tome .—A term formerly em- ployed for any device by means of which a circuit could be peri- odically interrupted. (Now obsolete and re- placed by Interrupt- er.) Rlieotrope. — A term formerly em- ployed for any device by which the current m &- 3kU - could be reversed. (Now obsolete and replaced by Commuta- tor or Current Reverser.) Rhigolene. — A volatile hydro-carbon obtained during the distillation of coal oil, and emploj'ed in the flashing, or treat- ment of carbons. (See Flashing of Carbons.) Rhumbs of Compass. — The thirty-two points of the mariners' compass. (See Points of Compass.) Rigidity, Molecular -Resistance offered by the molecules of a substance to rotation, or displacement. The molecular rigidity of a magnetizable substance is now generally considered to be the cause of differences of coercive 540 A DICTIONARY OF ELECTRICAL force or magnetic retentivity. (See Coercive Force. Reten- tivity, Magnetic.) Rings, Nobili's (See Metallochromes.) Rods, Lightning (See Lightning Rods.) Rotation, Electro magnetic (See Accumu- lator. Disc, Arago's. Disc, Faraday's. Motors, Electric.) Rotation, Magneto-Optic (See Magneto- Optic Rotation. Rubber of Electrical Machine.— A cushion of leather, covered with an electric amalgam, and employed to produce electricity by its friction against the plate or cylin- der of nfrictional electric machine. (See Machine, Frictional. ) Ruhmkorff Coils.— (See Induction Coils.) Saddles, Telegraphic Brackets placed on the top of telegraph poles, for the support of the insulators. Saddle brackets are usually employed for the wire attached to the top of a telegraph pole. (See Poles, Telegraphic.) Safety Catch, Safety Device, Safety Fuse, Safety Plug or Safety Strip for Multiple Circuits.— A wire, bar, plate, or strip of readily fusible metal, capable of conduct- ing, without fusing, the current ordinarily employed on the circuit, but which fuses, and thus breaks the circuit, on the passage of an abnormal current. (See Lamp, Incandescent.) Safety Device for Arc Lamp, or Series Circuits.— Mechanism which automatically provides a path for the current around a lamp, or other faulty electro-receptive de- vice in a series circuit, and thus prevents the opening of the entire circuit on the failure of such device to operate. (See Lamp Arc, Electric.) Safety Lamp, Electric An incandescent electric lr,mp, with thoroughly insulated leads, employed in WORDS, TERMS AND PHRASES. 541 mines, or other similar places, where the explosive effects of readily ignitable substances are to be feared. Such lamps are often directly attached to a portable battery. Salts, Electrolysis of The decomposition of a salt into its electro positive and negative radicals or ions. (See Electrolysis.) Saturation, Magnetic The maximum mag- netization which can be imparted to a magnetic substance. In an electro-magnet, such a degree of magnetization, that any further increase of the magnetizing current, increases the magnetic intensity only to the comparatively small extent of the increase of the magnetic field due to the current itself. (See Magnetic Saturation.) Scratch Brush. — A brush furnished with metallic bristles, and employed for cleansing the surfaces of metallic objects prior to their being electro-plated. Screen, Methven's Standard (SeeMethven's Standard Screen.) Screen or Shield, Electric A closed con- ductor, placed over a charged body to screen or protect it from the effects of external electrostatic fields, The ability of a closed, hollow conductor to act as a screen, arises from the fact that all points on its inner surface are at the same potential, and therefore are not affected by an in crease or decrease in the potential of the outside of the con- ductor as compared with that of the earth. (See Net. Fara- day's.) No considerable thickness is required for the efficient opera- tion of an electric screen. Screen or Shield, Magnetic (See Magnetic Screen or Shield.) Screws, Binding or Binding Posts — (See Binding Posts.) 542 A DICTIONARY OF ELECTRICAL Seal, Hcrmetical (See Hermetical Seal.) Search- Lights, Electric (See Lighthouse Illumination.) Secondary Batteries.— Arrangements of voltaic cells that derive tlieir differences of electric potential from the action of an electric current sent through them from a sep- arate source, (See Storage of Electricity.) Secondary Clocks. — (See Clocks, Secondary.) Secondary Currents.— The currents induced in the secondary coil of an induction apparatus. (See Induction Coils.) In the United States this term is also applied to the cur- rents derived from secondary batteries. The word is generally employed m the former sense. Secondary Generators. —A term sometimes employed for transformers or converters. (See Transformers or Con- verters.) Seismograph, Electric An apparatus for electrically recording the direction and intensity of earth- quake shocks. Selenium.— A comparatively rare element generally found associated with sulphur. Selenium Cell- — A photo-electric couple consisting of selenium in combination with another metal usually copper, and capable of producing a current by the direct action of light. Selenium Cell, or Resistance.— A mass o' crystalline selenium, the resistance of which is reduced by placing it in leform of narrow strips between the edges of broad conduct- ing plates of brass. The selenium employed for this purpose is the vitreous variety, which has been fused and maintained for several WORDS, TERMS AND PHRASES. 543 hours at about 220° C. by means of which its resistance is reduced. By exposure to sun-light, the resistance of a selenium cell is decreased fully one-naif its resistance in the dark. The selenium cell is used in the Photophone. (See Photophone.) Selenium Eye. — An artificial eye in which a selenium resistance takes the place of the retina and two slides the place of the eyelids. The selenium resistance is placed in the circuit of a battery and a galvanometer. When the slides L,L, Fig. 345, are shut, the galvanometer deflection is less than when they are open. The opening of the aperture be- B tween the slides ^ Y ^ / ^ / \\L L, L, may be automati cally accomplished by the action of the light itself, by moving them by an electro - mag- Fig. Si5. net placed in the circuit of a local battery, and a selenium resistance so arranged that when light falls on the selenium resistance, the slides L, L, are moved together, and when the amount of such light is small, they are moved apart. In this way, there is obtained a device roughly resembling the dilata- tion or contraction of the pupil of the eye, from the action of light on the iris. — (See Photometer, Selenium.) Self-Iiiduetioii. — The induction of a current on itself, as distinguished from the induction it produces in neighboring conductors. (See Currents, Extra.) Self'-lndiietioii, Coefficient of A number representing the value of the induction produced by a circuit on itself, 544 A DICTIONARY OF ELECTRICAL The coefficient of self-induction varies with the shape of the circuit, and increases with the number of coils or turns in the circuit. The retardation in long telegraph lines, where num- erous coils of wire are used, or where there are long cables, is due to self-induction as well as to induction in neighboring conductors. According to Helmholtz, as phrased by Sylvanus Thomp- son, " The self induction in a circuit on making contact has the effect of diminishing the strength of the current by a quantity, the logarithm of whose reciprocal is inversely pro • portional to the coefficient of self-induction, and directly proportional to the resistance of the circuit, and to the time that has elapsed since making the circuit." Self-Recording magnetometer. — (See Magneto- graph.) Self- Winding Clocks.— (See Clocks, Self -Winding.) Semaphore. — A variety of signal apparatus employed in railroad block systems. The semaphore used on the Pennsylvania Railroad consists of a wooden post, in the neighborhood of twenty feet in height, on which a wooden arm or blade, six feet in length and a foot in width is displayed. When the block is clear, the arm is placed pointing downwards at an angle of 75* wrth the horizon- tal by day, or the semaphore displays a white light at night. When the block is not clear, the arm or blade is- placed in a horizontal position by day, or displays a red light at night. (See Block Signals.) Sender, Zinc (See Zinc Sender.) Sensibility of Galvanometer .—The readiness and ex- tent to which the needle of a galvanometer responds to the passage of an electric current through its coils. (See Galvan- ometers.) Separate Touch, Magnetization by (Sea Methods of Magnetization by Touch. Separate. ) WORDS, TERMS AND PHRASES. 545 Separately Excited Dynamo Electric Machine.— A dynamo electric machine, whose field coils are excited by means of a source external to the machine. (See Dynamo Electric Machine, Separately Excited.) Series Circuits. — (See Circuits, Varieties of.) Series Connections . — The connection of a number of separate electric sources, or electro-receptive devices, or cir- cuits so that the current passes successively from the first to the last in the circuit. (See Circuits, Varieties of.) Series-Multiple Circuit.— (See Circuits, Varieties of.) Series, Tlienno-Electric Series.) Shackle, Telegraphic - lation employed on a telegraph pole in order to confine to one point the strain caused by a wire leaving the insula- tor at a sharp angle. (See Poles, Tele- graphic.) Shadow, Elec- tric, or Molec- ular (See Thermo-Electric A special form of insu- re?. SU6. The comparatively dark space on those parts of the walls of Crookes' tubes, which have been protected from molecular bombardment by suitably placed screens. If a, in the Crookes' tube shown in Fig. 346, be connected with the negative pole of any electric source, and the cross shaped mass of aluminium at b, be connected with the posi- tive electrode, on the passage of a series of discharges, phos- phorescence is produced by the molecular bombardment from a, in all parts of the vessel opposite a, except those lying in 546 A DICTIONARY OF ELECTRICAL the projection of its geometrical shadow. (See Phosphores- cence, Electric.) Shadow Photometer. — (See Photometer, Shadow.) Sheet, Current The sheet into which a current spreads when the wires of any source are connected at any two points near the middle of a very large and thin conductor. A continuous electric current flows through the entire mass of a conductor, not in any single line of direction, but, if the terminals of any source are connected to neighboring parts of a greatly extended thin conductor, the current spreads out in a thin sheet known as a current sheet, and instead of flowing in a straight line between the points, spreads over the plate in curved lines of flow, which, so far as shape is concerned, are not unlike the lines of magnetic force. Shells, Magnetic (See Magnetic Shells.) Shellac. — A resinous substance possessing valuable insul- ating properties, which is exuded from the roots and branches of certain tropical plants. The specific inductive capacity of shellac as compared with air is 2.74. Shield, Magnetic for Watches.— A hollow case of iron, in which a watch is permanently kept, in order to seield it from the influence of external magnetic fields. (See Magnetic Screens or Shields.) Ships, Protection of from Lightning Strokes. — (See Lightning Rods for Ships.) Ship's Sheathing, Electric Protection of — (See Metals, Electric Protection of.) Shock, Electric A physiological effect produced on animals by the passage through them of an electric cur- rent, generally attended by a violent contraction of the muscular fibres. Short-Circuit . — A shunt, or by-pass, of comparatively small resistance, around the poles of an electric source, or WORDS, TERMS AND PHRASES. 54T around any portion of a circuit, by which so much of the cur- rent passes as virtually to cut out any other circuit connected therewith, and so prevent it from receiving an appreciable current. Short-Circuit Key.— (See Key, Short Circuit.) Shunt Circuits, Resistance of (See Cir- cuits, Shunt, Resistance of.) Shunt Circuits, Uses of (See Circuits, Shunt, Uses of.) Shunt Dynamo, — A dynamo electric machine the field magnet coils of which are in a shunt circuit around the ex- ternal circuit of the machine. (See Dynamo Electric Ma- chine, Shunt.) Shunt, *Electro-l?IagTietic In a system of tele- graphic communication an electro magnet whose coils are placed in a shunt circuit around the terminals of the receiving relay. The electro-magnetic shunt operates by its self induction. Its poles are permanently closed by a soft iron armature, so as to reduce the resistance of the magnetic circuit. (See Induction, Self.) On making the circuit in the coils of the receiving relay, a current is produced in the coils of the electro-magnetic shunt in the opposite direction to the relay current, and, on breaking the circuit in the relay, a current is produced in the coils of the electro-magnetic shunt in the same direction as the cur- rent in the receiving relay. The connection of the coils of the electro-magnetic shunt with those of the receiving relay, however, is such that on making the circuit in the relay the current in the shunt coils flows through the relay in the same direction, and on breaking the circuit it flows in the opposite direction. Therefore this shunt effects the following : (1) At the commencement of each signal in the receiving relay, it produces an induced current in the same direction which strengthens the current in the relay. 548 A DICTIONARY OF ELECTRICAL (2) At the ending- of each signal in the receiving relay, it produces a current in the opposite direction, which hastens the motion of the tongue of the polarized relay. (See Relay, Polarized.) Shunt for Galvanometer.— (See Galvanometer Shunt.) Shunt or Derived Circuit.— A branch or additional circuit provided at any part of a circuit, through which the current branches or divides, part flowing through the original circuit, and part through the new branch. In the case of branched circuits each of the circuits acts as a shunt to the others. Any number of additional or shunt circuits may be thus provided. (See Kirchhoff's Laws.) Shunt, Magnetic An additional path of mag- netic material provided in a magnetic circuit for the passage of the lines of force. Shunts, Multiplying Power of A quantity, by which the current flowing through a galvanometer pro- vided with a shunt, must be multiplied, in order to give the total current. The multiplying power of a shunt may be determined from the following formula, viz. : A = ( S ~^ g ) X C, in which S -+l = the Multiplying Power of a Shunt whose resistance is s ; g, is the galvanometer resist- ance ; C, the current through the galvanometer; and A, the total current passing ; s and g, are taken m ohms, and C and A, in amperes. Suppose, for example that but 1/10 the entire current is to flow through the galvanometer, then the resistance of the shunt must evidently be ^ g, for, s 1 1 s + g 1 + 9 10 or, 10 s = s-f g. 10 s — s=g •'• 9 s = g ; or s= ($) WORDS, TERMS AND PHRASES. 549 Sidero-Magnetic. — A term proposed by Sylvanus P. Thompson to replace the word ferro-magnetic. — (See Ferro- Magnetic.) Siemens and Halske Voltaic Cell.— (See Cell, Voltaic.) Signals, Electro Pneumatic Signals operated by the movements of diaphragms or pistons moved by com- pressed air, the escape of which is controlled electrically. Signaling, Velocity of Transmission of The speed or rate at which successive signals can be sent on any line without the retardation producing serious interference. (See Retardation of Signals.) Silurus electricns.— The electric eel. — (See Electric Eel. Silver Bath.— (See Baths, Silver, etc.) Simple Magnet. — (See Magnet, Simple.) Simple Voltaic Cell.— (See Cell, Voltaic.) Sine Galvanometer.— (See Galvanometer, Sine.) Single Fluid Cell. — A voltaic cell in which both elements of the couple are immersed in the same electrolyte. (See Cell, Voltaic Single Fluid.) Single Fluid Electrical Hypothesis. — A hypothesis framed to explain the phenomena of electricity on the as- sumption of a single electric fluid possessed by all matter. (See Electricity, Single Fluid Hypothesis of.) Single Touch. — A method of magnetization in which the magnetizing bar is merely drawn from one end to the other of the bar to be magnetized, and returned through the air for the next stroke. (See Magnetization, Methods of.) Sinistrorsal Solenoid. — (See Solenoid, Sinistrorsal.) Sinuous Currents. — (See Currents, Sinuous.) Siphon Recorder. — (See Recorder, Siphon.) Skin, Faradization of The therapeutic treat- ment of the skin by a faradic current. 550 A DICTIONARY OF ELECTRICAL For efficient faradization the skin should be thoroughly dried and a metallic brush or electrode employed. For very sensi- tive parts, as, for example, the face, the hand of the oper- ator, first thoroughly dried, is to be preferred as an electrode. Skin, Human, Electric Resistance of The electric resistance offered by the skin of the human body. The electric resistance of the skin is subject to marked dif- ferences in different parts of the body, where its thickness or continuity varies. It varies still more with variations in its condition of moisture. Even in the same individual the resistance varies materially under apparently similar con- ditions. Sled. — The sliding contacts drawn after a moving electric railway car through the slotted underground conduit con- taining the wires or conductors from which the driving cur- rent is taken. Slide Balance, Wheats tone's. —(See Balance, Wheat- stone's Electric.) Smee's Voltaic Cell.— (See Cell, Voltaic.) Socket, Electric Lamp A support for the re- ception of an incandescent electric lamp. Incandescent lamp sockets are generally made so that the mere insertion of the base of the lamp in the socket completes the connection of the lamp terminals with terminals of the socket connected with the leads that supply current to the lamp, and its removal from the socket, automatically breaks such circuit. The socket is generally provided with a key for turning the lamp on or off without removing it from the socket. Figs. 347 and 348, show forms of lamp sockets for incan- descent lamps and the details of the key for connecting or dis- connecting the lamp with the leads. Soldering, Electric The uniting of metals to one another, in which heat generaterd by the electric current is used to melt the solder in the place of ordinary heat. WORDS, TERMS AND PHRASES. 551 -(See Solenoid Prac- Solenoid, Dcxtrorsal tical.) Solenoid, Ideal A solenoid consisting of a cylinder built up of true circular currents, with all their faces of like polarity turned in the same direction and entirely in- dependent of one another. The practical solenoid differs from the ideal solenoid in that the successive circular circuits or currents are all connected with one another in series. Fig. 3U7. Fig. SIS. Solenoid or Helix. Electro-Magnetic Solenoid. — The name given to a cylindrical coil of wire, each of the convolutions of which is circular. A circuit bent in the form of a helix, supported at its two extremities, as shown in Fig. 349, and traversed by an elec- tric current, will move into the magnetic meridian of the place, and if free to move in a vertical plane, will come to rest in the line of the dip of the place. A solenoid traversed by an electric current acquires thereby all the properties of a magnet, and is attracted and repelled by other magnets. Its poles are situated at the ends of the cylinder on which the solenoid may be supposed to be wound. 552 A DICTIONARY OF ELECTRICAL The polarity of a solenoid depends on the direction of the current as regards the direction in which the solenoid is wound. This solenoid is sometimes called an electro-magnetic solenoid or helix, in order to distinguish it from a mag- netic solenoid or solenoidal magnet. (See Magnet, Sole- noidal.) A solenoid, if suspended so as to be free to move, will come to rest in the plane of the magnetic meridian. It will also be attracted or repelled by the approach of a dissimilar or similar magnet pole respectively, Fig. 351. Solenoid, Practical — The name applied to the ordinary solenoid in order to distinguish it from the ideal solenoid. (See Solenoid, Ideal. ) A practical solenoid consists, as shown in Fig. 350, of a spiral coil of wire wrapped in the manner shown in the figures at (1), (2) and (3.) The polarity of the solenoid depends on the direction of the current, and therefore on the direction of winding. In any solenoid, how- ever, the polarity may be reversed by revers- ing the direction of the current. (See Electro- Magnet.) A Right Handed, or Dextrorsal Solenoid, is one wound in the direction shown at (1). Fig. 850. WORDS, TERMS AND PHRASES. 553 A Left Handed, or Sinistrorsal Solenoid, is one wound in the direction shown at (2). The solenoid shown at (3) is wound so as to produce con- sequent poles. (See Consequent Poles, or Points.) -(See Solenoid, Prac- -A form of induction Solenoid, Sinistrorsal tical. ) Sonometer, Hughes' - balance for the purpose of examining the inten- sity of sounds, or the del- icacy of the ear in de- tecting or distinguishing sounds. (See Induction Balance, Hughes.) Sonoresce n c e A term proposed for the sounds produced when a piece of vulcanite or any other solid sub- stance is exposed to a rapid succession of flashes of light. See Photo- phone.) Sound (Subjectively) The effect pro- duced by a vibrating body. Sound (Objectively). Fig. 351. The waves in the air or other medium which produce sound. The word sound is therefore used in science in two distinct senses, viz. : (1.) Subjectively, as the sensation produced by the vibration of a sonorous body. 554 A DICTIONARY OF ELECTRICAL (2.) Objectively, as the waves or vibrations that are cap- able of producing- the sensation of sound. Sound is transmitted from the vibrating body to the ear of the hearer by means of alternate to-and-fro motions in the air, occurring in every direction around the vibrating body and forming spherical waves called waves of condensation and rarefaction. Unlike light and heat, these waves require a tangible medium such as air, to transmit them. Sound, therefore, is not propagated in a vacuum. The vibra- tions of sound are longitudinal, that is, the to-and-fro motions occur in the same direction as that in which the sound is traveling. The vibrations of light are transverse, that is, the to-and-fro motions are at right angles to the direction in which the light is traveling. Sound, Characteristics of (See Character- istics of Sound.) Sounder, Morse Telegraphic —An electro-magnet which produces audible sounds by the move- ments of a lever attached to the armature of the magnet. The Morse sounder has now almost entirely supplanted the paper recorder or register. On short lines it is placed directly in the telegraphic circuit. On long lines it is operated by a local battery, thrown into or out of action by the relay. (See Relay.) The Morse sounder, shown in Fig. 352, consists of an upright electro magnet M, whose soft iron armature A is rigidly at- tached to the striking lever B, working in adjustable screw pivots as shown. The free end of the lever is limited in its strokes by two set screws N, N. The lower of these screws is set so as to limit the approach of the armature A to the poles of the electro magnet ; the upper screw is set so as to give the end B, sufficient play to produce a loud sound. A retractile spring, attached to the striking lever near its pivoted end, and provided with regulating screw S S, pulls the lever back when the current ceases to flow through M. WJRDS, TERMS AND PiiKASUS. 555 The dots and dashes of the Morse alphabet are reproduced by the sounder, as audible signals, that are distinguished by the operator by means of the different sounds produced by the up and down stroke of the lever as well as by the difference in the intervals of time between the successive signals. Sound*, Magnetic — (See Magnetic Sounds.) Source, Electric— Anything which produces a difference of potential or an electro-motive force. Spark Discharge.— (See Discharge, Disruptive.) Spark, Length of (See Length of Spark.) Fig. 352. Spark Tube.— A high vacuum tube, across which the spark from an induction coil will not pass, when the vacuum is sufficiently high. A spark tube, connected with incandescent lamps which are undergoing exhaustion, acts as a simple gauge to deter- mine the degree of exhaustion. When an induction coil dis- charge ceases to pass, or to freely pass, the vacuum is con- sidered as sufficient, according to circumstances. Sparking of Dynamo-Electric Machines.— An ir- regular and injurious action at the commutator of a dynamo- 556 A DICTIONARY OF ELECTRICAL electric machine, attended with spark at the collecting brushes. Sparking consists in the formation of small arcs under the collecting brushes. One cause of sparking is to be found in the brushes leaving one commutator strip before making con- nection with the next strip. Sparking causes a burning of the commutator strips, and an irregular consumption of the brushes, both of which produce further irregularities by wear or friction of the brushes against the commutator bars. Sparking from this cause may be avoided by so placing the brush as to cause it to bridge over the space between two consecutive bars, thus permitting it to touch one bar before leaving the other. Two brushes, electrically connected, are sometimes employed for this purpose, or the slots between contiguous bars are slightly inclined to the axis of rotation. At the moment the brush touches two contiguous commuta- tor bars, it short circuits the coil terminating at those bars. On the breaking of this closed circuit, a spark appears under the brushes. This spark is often considerable, since from the comparatively small resistance of the coil, it is apt, when short-circuited to produce a heavy current. Another cause of sparking is to be found in the self-induc- tion of the armature coils. The extra current on breaking forms an injurious spark under the brushes. This spark may be considerable since the current produced in the coil on mo- mentarily short-circuiting it by the brushes simultaneously touching the adjoining commutator segments may be large, Sparking occurs when the brushes are not set close to the neutral line. Since the principal cause for this change in the lead of the brushes is the magnetizing effect of the armature coils, it is preferable to make the number of windings of these as few as possible and to obtain the necessary differences of potential by increasing the speed of rotation and the strength of the magnetic field of the machine. Short armature coils also lessen the sparking due to self-induction. WORDS, TERMS AND PHRASES, 557 Sparking at the brushes is also caused by the jumping of improperly supported or constructed brushes. "When the brushes are not set close to the neutral point long flashing sparks are apt to occur. A lack of symmetry of winding of the armature coils will necessarily be attended by injurious flashing, from the impos- sibility of properly adjusting the brushes. Specific Heat.— (See Heat, Specific.) Specific Heat of Electricity.— A term proposed by Sir Wm. Thomson to indicate the analogies between the absorp- tion and emisssion of heat in purely thermal phenomena, and the absorption and emission of heat in thermo electric phe- nomena. As we have already seen heat is either given out or absorbed, when an electric current passes from one metal to another across a junction between them. (See Effect, Peltier.) Co, too, when electricity passes through an unequalh T heated wire the current tends to increase or decrease the differences of temperature, according to the direction in which it flows, and according to the character of the metal. (See Effect, Thomson.) "If electricity were a fluid," says Maxwell, "running through the conductor as water does through a tube, and always giving out or absorbing heat till its temperature is that of the conductor, then in passing from hot to cold it would give out heat, and in passing from cold to hot it would absorb heat, and the amount of this heat would depend on the spe- cific heat of the fluid." Specific Inductive Capacity.— (See Capacit y, Specific Inductive.) Specific Resi§tance. — (See Resistance, Specific.) Specific Resistance of Liquids.— (See Liquids, Spe- cific Resistance of.) Speecli, Articulate. (See Articulate Speech.) 558 A DICTIONARY OF ELECTRICAL Sphygmograph. — An electric apparatus for obtaining a record of the rate and strength of the pulse. Sphygmophone.— An applicatoin of the microphone to the medical examination of the pulse. (See Microphone.) Spiral, Roget's A suspended wire spiral convey- ing a strong electric current, and devised to show the attrac- tions produced by parallel currents flowing in the same direc- tion. The lower end of the wire spiral dips into a mercury cup. On the passage of the current, the attraction of the neighboring turns of the spiral for each other shortens the length of the spiral sufficiently to draw it out of the mercury and thus break the circuit. When this occurs the weight of the spiral causes it to fall and again re-establish the circuit. A rapid automatic make-and-break is thus established, accompanied by a bril- liant spark at the mercury surface due to the extra spark on breaking. Split Battery.— (See Battery, Split.) Spring- Jack. — A device for readily inserting a loop in a main electric circuit. (See Board, Multiple Switch.) Spring- Jack Cut-Out, — A device similar in general con- struction to a spring jack, but employed to cut out a circuit. An insulated plug is thrust between spring contacts, thus breaking the circuit by forcing them apart. Spurious Resistance. — A false resistance arising from the development of a counter electro-motive force. (See Counter Electro-Motive Force.) Standard Candle. — (See Candle, Standard.) Standard Carcel Gas Jet. — (See Car eel Standard Gas Jet.) Standard Cell. — A voltaic cell the electro-motive force of which is constant, and which, therefore, may be used in the measurement of an unknown electro-motive force. WORDS, TERMS AND PHRASES. 559 Absolute constancy is impossible to attain, but, if the current of the standard cell is closed but for a short time the electro- motive force may be regarded as invariable. Standard Cell, Clark's The form of standard cell shown in Fig-. 353. Latimer Clark's Standard Cell, assumes a variety of forms. The H-form is arranged as shown in Fig. 353. The vesse^ to the left contains at A an amalgam of pure zinc. The other vessel contains at M mercury covered with pure mer- curous sulphate. Both vessels are then filled above the level of the cross tube, with a saturated solution of zinc sul- phate Z, Z, to which a few crystals of the same are added. Tightly fitting corks C, C, prevent loss by evaporation. The value of this cell in legal volts is 1.438(1 — 0.00077 (t — 15° C.) (Ayrton.) The value t, is the temperature in degrees of the centigrade scale. Standard Cell, Fleming's Fig. 353. -The form of standard cell shown in Fie:. 354. The U tube, Fig. 354, is connected, as shown, by means of taps, with two vessels filled with chemically pure solutions of copper sulphate of Sp. Gr. 1.1 at 15° C, and zinc sulphate of Sp. Gr. 1.4 at 15° C. respectively. To use the cell the zinc rod Zn, connected with a wire passing through a rubber stopper is placed in the left hand branch. The tap A is opened and the entire U-tube is filled with the denser zinc sul- phate solution. The tap at C is then opened, and the liquid in the right hand branch above the tap is discharged into the lower vessel, but, from this part only. The •tap C is then closed, and the tap B opened, and the lighter copper sulphate allowed to fill the right hand branch above the tap C. The copper rod Cu, fitted to a rubber stopper and con- 560 A DICTIONARY OF ELECTRICAL nected with a conducting- wire, is then placed in the copper solution. Tubes are provided at L and M, for the reception of the zinc and copper tubes when not in use. The copper tube is prepared for use by freshly elec- tro-plating it with copper. The E. M. F. of this cell is 1.074 volts. If the line of demar- cation between the two liquids is not sharp, the arms of the vessels are emptied, and fresh liquid is run in. Standard Resistance Coil. — (See Resistance Coil, Standard.) State, inotropic — (See Allotropy.) State, Nascent (See Nascent State.) State, Passive of Iron. — (See Passive State.) State, Permanent Fig. 35U. State, Variable The condition of the charge of a telegraph wire when the current reaching the distant end has the same strength as at the sending end. -The condition of the charge of a telegraph wire while the strength of current is increasing up to the full strength in all parts. The duration of the variable state is directly as the length of the line and its total resistance. It is increased by leakage, and by the effect of the extra current. (See Currents, Ex- tra.) WORDS, TERMS AND PHRASES. 561 Static Charge.— (See Charge, Static.) Static Electricity. — A term formerly applied to electri- city produced by friction. (Now obsolete.) The term static electricity is properly employed in the sense of a static charge but not as static electricity, since that would indicate a particular kind of electricity, and, as is now gen- erally recognized, electricity, from no matter what source it is derived, is one and the same thing. Statics. — The science which treats of the relations that must exist between the points of application of forces and their direction and intensity, in order that equilibrium may result. Stay Rods, Telegraphic Metallic rods, attached to a telegraph pole, and securely fastened in the ground in order to counteract the effects of a pull or tension on the poles. (See Poles, Telegraphic.) Steel, Qualities of Requisite for Magnetiza- tion. — Qualities which must be possessed by steel in order to permit it to permanently retain a considerable magnetization. For the purposes of magnetization steel should possess the following qualities: It should be hard, and fine grained. Hard cast steel answers the purpose very well. Scoresby showed that an intimate relation exists between the quality of the iron from which the steel is made, and its ability to take and retain considerable magnetism. An admixture to steel of about .03 per cent, of tungsten is said to increase its magnetic powers. Cast steel is not generally employed for magnets, wrought steel being gen- erally preferred. St. Elmo's Fire. — Faintly luminous globes, due to elec- tric brush discharges, sometimes seen on the ends of a ship's masts, or other similar locations. 562 A DICTIONARY OF ELECTRICAL Step-oy-Step or Dial Telegraphy.— A system of telegraphy in which the signals are registered by the move- ments of a needle over a dial on which the letters of the alpha- bet, etc., are marked, Dial telegraphs are employed for communication by those who are unable to readily read the Morse characters. The annexed instrument, devised by Breguet, was formerly used on some of the railway systems of France. Fig. 355. Fig. 856. A needle advances over a dial in one direction only by a step- by-step movement. The alternate to-and-fro motions of the armature of an electro magnet are employed to impart a step- by-step motion to a peculiarly shaped toothed wheel T, T, Fig. 355, through the action of a horizontal arm c, attached there- to, and moving between the two prongs of a fork d, vibrating on a horizontal axis to which is attached a vertical pallet i. The receiving instrument is called the Indicator, and con- sists of a needle attached to the axis of this wheel. The needle moves over the face of the dial, shown in the Fig. 356, on which are marked the letters of the alohabet and the nu- merals. The sending instrument is called the Manipulator. It con- WORDS, TERMS AND PHRASES. 563 sists of a device for readily sending- over the line the number of successive impulses required to move the needle step-by- step from any letter on the indicator ,to which it may be point- ing, to the next it is desired to send. The dial, shown in Fig. 357. is marked on its face with the same characters as the in- dicator. The edge of the wheel is provided with twenty-six notches in which a pin attached to a movable arm engages. This arm is jointed so that it can be placed in any of the notches on the face ot the wheel. Fig. 357. Below the dial face, and attached to the same axis as the movable arm, is a wheel provided with undulations consisting of thirteen elevations and thirteen depressions. A lever T, pivoted at a, rests in these undulations at its upper end, and plays between two contact points at P and Q. If, now. the dials of the indicator and the manipulator both being at o, a movement is given to the arm by the handle M, 564 A DICTIONARY OF ELECTRICAL to any point on the manipulator, there are thus produced the required number of makes and breaks to move the needle of the indicator to the corresponding 1 letter or character. Step-toy-Step Telegraphy.— (See Telegraphy, Step-by- Step.) Stool, Insulating. — A stool, provided with insulating supports of vulcanite or other insulator, employed to afford a ready insulating stand or support. (See Insulating Stool.) Storage Cell§, or Accumulators. — Two inert plates of metal, or of metallic oxides, immersed in an electrolyte in- capable of acting on them until after an electric current has been passed through the liquid from one plate to the other. On the passage of an electric current through the electro- lyte, its decomposition is effected and the electro positive and electro negative radicals are deposited on the plates, or unite with them, so that on the cessation of the charging current, there remains a voltaic cell capable of generating an electric current. A storage cell is charged by the passage through the liquid from one plate to the other of an electric current, derived from any external source. The charging current produces an electrolytic decomposition of the inert liquid between the plates, depositing the electro positive radicals, or kathions, on the plate connected with the negative terminal of the source, and the electro negative radicals, or anions, on the plate con- nected with the positive terminal. On tbe cessation of the charging current, and the connec- tion of the charged plates by a conductor outside the liquid a current is produced, which flows through the liquid from the plate covered with the electro positive radical, to that covered with the electro negative radical, or in the opposite direction to that of the charging current. The simplest storage cell is Plante's cell, which, as origin- ally constructed, consists of two plates of lead immersed in dilute sulphuric acid, Hg S0 4 . On the passage of the charg- WORDS, TERMS AND PHRASES. 565 ing current, the plates A and B, Fig. 358, dipped in H 2 S0 4 , are covered respectively with lead peroxide Pb 2 , and finely divided, spongy lead The peroxide is formed on the positive plate, and the metallic lead on the negative plate. When the charging current ceases to pass, the cell dis- charges m the opposite direction, viz., from B' to A', that is, from the spongy lead plate to the peroxide plate, as shown in Fig. 359. \ ' descent lighting in order ffEjjgi aration of the circuit from ^^^^^^B^^S||HBil : S w i I v h, Rever§iii£ ■"•""" | * m> ~ 1 ~mb... | J T ■■ j=g=g=rte^ 7 reversing the direction of ^T ZJ" -1 — ^'! '_ ': " ' '- lk ^^^^^P^" the battery current Fig. 361. through a galvanometer. A simple reversing switch consists of four insulated brass segments mounted on a plate of ebonite and furnished with openings between them for plug connections. The battery terminals are connected to two diagonally opposite segments asB and D, Fig. 361, and the leading wires of the galvanometer, or other instrument, to the other segments as C and A. If now the plugs are placed between B and C, and A and D, the battery current flows in one direction. If, however, the plugs are placed between A and B, and C and D, the battery cur- rent will flow m the opposite direction. The battery current is cut off if one plug is removed. In practice, however, it is perferable to remove both plugs, so as to avoid any current from want of sufficienc insulation. WORDS, TERMS AND PHRASES. 573 Sympathetic Vibrations. — Vibrations set up in bodies by sound waves of exactly the same wave length as those produced by the vibrating- body. The pitch or tone of the note produced by the body set into sympathetic vibration, is exactly the same as the pitch or tone of the exciting waves or vibrations. Synchronism. — The simultaneous occurrence of any wo events. A rotating cylinder, or the movement of one index or trail- ing arm, is brought into synchronism with another rotating cylinder or another index or trailing arm, not only when the two are moving with merely the same speed, but when in addition they are simultaneously moving over similar portions of their respective paths. In the Breguet Step-by-Step or Dial Telegraph (See Step-by- Step or Dial Telegraph), the movements of the needle on the Indicator, are synchronized with the movements of the needle on the Manipulator. In systems of Fac-Simile Telegraphy, the movements of the transmitting apparatus are synchronized with that of the receiving apparatus. In Delany's Synchro- nous Multiplex Telegraph System, the trailing-arm that moves over a circular table of contacts at the transmitting end, is accurately synchronized with a similar trailing-arm moving over a similar table at the receiving end. Delany, who was the first to obtain rigorous synchronism at the two ends of a telegraphic line hundreds of miles in length, accomplises this by the use of La Cour's phonic wheel, through the agency of correcting electric impulses, automat- ically sent in either direction over the main line, when one trailing arm gets a short distance in advance or back of the other. Synchronous Multiplex Telegraphy. — (See Tele- graphy, Synchronous Multiplex.) System, Astatic (See Astatic System.) 574 A DICTIONARY OF ELECTRICAL System, Block of Railway Telegraphy.— (See Block System for Railways.) System, Centimetre-Gramme-Second of Measurement. — (See Centimetre- Gramme-Second System of Measurement.) Systems of Distribution by Alternating Currents. — System of electric distribution by the use of alternating currents. Such a system embraces, (1) An Alternating-Current Dynamo-Electric Machine. (2) A Conductor or Line Wire having a metallic circuit. (3) A number of Converters whose primary coils are placed in the circuit of the line wire. (4) A number of Electro Receptive Devices placed in the cir- cuit of the secondary coil of the converter. — (See Converter or Transformer.) Systems of Distribution by Constant Currents.— Systems for the distribution of electricity by means of constant currents. Distribution by means of constant currents may be effected in a number of ways ; the most important are : (1) Distribution with Constant Current or Series Distribu- tion. (2) Distribution with Constant Potential or Multiple Distri- bution. In a System of Series Distribution, the electro receptive de- vices are placed in the main line in series, so that the electric current passes successively through each of them. In such a system each device added increases the total resistance of the circuit. In order therefore to maintain the current strength constant, independent of the number of devices added, the electro- motive force of the source must increase with each electro- receptive device added, and decrease with each electro- recep- WORDS, TERMS AND PHRASES. 575 tive device taken out. If the number of electro-receptive de- vices be great, such a circuit is necessarily characterized by a comparatively high electro-motive force. Since the current passes successively through all the electro- receptive devices, an automatic safety device is necessary in order to automatically provide a short circuit of comparatively low resistance past the faulty device, and thus prevent a singie faulty device from invalidating the action of ail other devices in the circuit. Arc lamps are usually connected to the line circuit in series. In a System of Multiple Distribution, the electro-receptive de- vices are connected with the main line or leads in multiple-arc, or parallel, so that each device added decreases the resistance of the circuit. In order, therefore, to maintain a proper current through the electro-receptive devices, the mains must be kept at a nearly constant difference of potential. The electro-receptive devices employed in such a system of dis- tribution are generally of high electric resistance, so that the introduction or removal of a few of the electro-receptive devices will not materially alter the resistance of the whole circuit, and will not, therefore, materially affect the remaining lights. In this system automatic safety devices, operating by the fusion of a readily melted alloy or metal, are provided for the purpose of preventing too powerful currents from passing through any branch connected with the main conductors or leads. — (See Plug, Fusible.) Incandescent lamps are generally connected with the main conductors or leads in parallel or multiple-arc. Distribution of incandescent lamps by series connections is sometimes employed. Such lamps are usually of compara- tively low resistance, and are provided each with an auto- matic cut-out, which establishes a short circuit past the lamp on its failure to properly operate. During the passage of an electric current through any series distribution circuit, energy is expended in different portions of 576 A DICTIONARY OF ELECTRICAL the circuit, in the proportion of the resistance of these parts. In any system, economy or distribution necessitates that the energy expended in the electro-receptive devices must bear as large a proportion as practicable to the energy expended in the source and leads. In series distribution, this can readily be accomplished even if the resistance of the leads is com- paratively high since the total resistance of the circuit in- creases with every electro-receptive device added, Compara- tively thin wires can therefore be employed, for a very con- siderable extent of territory covered, without considerable 'oss. In systems of multiple distribution, however, this is impos- sible ; for, since every electro-receptive device added de. creases the total resistance of the circuit, unless the resistance of the leads is correspondingly decreased the economy be- comes smaller, unless the resistance of the leads was orig mally so low as to be inappreciable as compared with the change of resistance. In systems of distribution by alternating currents, this is avoided by passing a current of but small strength and con- siderable difference of potential over a line connecting distant stations, and converting this current into a current of large strength and small difference of potential where it is required for use. Tachograph. — An apparatus for recording the number of revolutions of a shaft or machine per minute. Tachometer, or Speed Indicator.— An apparatus for determining the number of revolutions of a shaft or ma- chine per minute. Various forms of apparatus are employed for this purpose. Tachyphore. — A term proposed by Wurtz for a system of electric transportation, in which a carriage of magnetic material is propelled by the sucking action of solenoids placed along the track and energized in succession during the passage of the car. WORDS, TERMS AND PHRASES. 577 Tangent. — One of the trigonometrical functions. (See ( Trigonometry. ) Tangent Galvanometer. — A galvanometer in which the current strength passing through the deflecting coil is pro- portional to the tangent of the angle of deflection it produces in the needle. (See Galvanometer, Tangent.) Tangent Scale. — A scale designed for use with a galvano- meter, on which the values of the tangents are marked, in- stead of equal degrees as ordinarily, thus avoiding the neces- sity of finding from tables the tangents corresponding to the degrees. Such a scale may be constructed as follows: Draw the tangent B T, to the circle, Fig. 362, and lay off on it any num- ber of equal divisions or parts as, for example, the thirty shown in the annexed figure. Connect these parts with the centre C, of the circle. The arc of the circle will thus be Fig. 362. divided into parts proportional to the value of the tangents of the angles. These parts are more nearly equal the nearer they are to B, and grow smaller and smaller the further they are from B. In tangent galvanometers, it is therefore very difficult to accurately determine the current strength when the deflections of the needle are very large. Tape, Insulating A ribbon of flexible material impregnated with kerite, okonite, rubber, or suitable insulat- ing material employed for insulating wires or electric con- ductors at joints, or other exposed places, 578 A DICTIONARY OP ELECTRICAL Sometimes the tape is formed entirely of the above named insulating materials. Tapper, Double Key.— The key used in systems of needle telegraphy to send electric impulses through the line in alternately opposite directions as desired. (See Telegraphy, Single Needle.) Target, Electric A target in which the point struck by the ball is automatically registered by electric devices. A variety of targets have been devised ; generally, how- ever, the target is divided into a number of separate sections, provided with circuits of wires on the making or breaking of any of which, by the impact of the ball, the section struck is automatically indicated on an electric annunciator. Teazer, Electric Current A name employed by Brush for a field magnet shunt circuit around the external circuit of his dynamo-electric plating machine. (See Dynamo- Electric Machine, Shunt.) Tel- Autograph. — A telegraphic system for the fac-simile reproduction of handwriting. Tele-Barometer, Electric An electric record- ing barometer for indicating and recording barometric or other pressure at a distance. Telegraph, Electric ■ — An apparatus for the electric transmission of signals between stations connected by electric conductors. Various systems of telegraphy are in common use, all of which, however, consist of various forms of the following apparatus, viz. : (1) Transmitting Apparatus, by means of which electrical impulses are sent into the line. (2) Receiving Apparatus, by means of which the electric impulses are caused to produce visible or audible signals, which may, or may not, be permanently recorded. (3) A Conducting or Line Wire connecting the two stations. WORDS, TERMS AND PHRASES. 579 (4) Main and Local Batteries for producing the currents employed in the transmission and reception of the signals. (5) Various Relays and Repeaters, employed on long lines, in order to permit additional local batteries to be used to carry the electric impulses over longer lines than could otherwise be employed. Telegraphic Code.— (See Alphabet, Telegraphic.) Telegraphic Embosser. — (See Embosser, Telegraphic./ Telegraphic Joints. — (See Joints, Telegraphic.) Telegraphic Xeedle.— (See Needle, Telegraphic ) Telegraphic Switch Board. — A device employed at a telegraph station by means of which any one of a number of telegraph instruments, in use at that station, may be placed in, or removed from, any line connected with the station. In the switch board shown in Fig. 363, the upper left hand binding post is connected to earth ; the four re- maining binding posts are connected to two separate instruments. The sec- ond and third from the top, to one instrument, and the fourth and fifth, to another instrument. The four posts tg ' at the top of the figure are connected to two lines running east and west. Various connections are made by the insertion of plug keys in the various openings. Telegraphy, American or Morse System of — In the Morse system, as now generally employed in America, the transmitting apparatus consists essentially of a telegraphic key, by means of which the main line circuit can be readily made or broken in accordance with tbe dots and dashes of the Morse Alphabet. (See Alphabet, Morse.) 580 A DICTIONARY OF ELECTRICAL A metallic lever A, Fig. 364, is supported on a pivot at G, between two set screws D, D, so as to have a slight move- ment in a vertical plane. This motion is limited in one direc- tion by a stop at C, called the anvil or front contact, and in the other direction by a set screw F, which constitutes its back stop. The front stop C, is provided with a platinum contact or stud, which may be brought into contact with, or separated from, a similar stud placed directly opposite it. These contacts are connected to the ends of the circuit, so that Fig. 36U. on the movements of the key, by the hand of the operator placed on the insulated head B, the line is closed and broken in accordance with the dots and dashes of the Morse alphabet. A spring, the pressure of which is regulated by the screw F', is provided for the upward movement of the key. A switch H, is provided for closing the line when the key is not in use, since the system as generally used in the United States the line is operated on closed circuit. In the Morse system each station is provided with a key, relay, sounder or register, and a local battery. The closed circuit, connecting one station with another, being broken by the opening of the switch H, on the working of the key, so as WORDS, TERMS AND PHRASES. 581 to open and close its contacts, the armature of the relay opens or closes the circuit of the local battery and operates the sounder or registering apparatus connected therewith. (See Sounder, Telegraphic. Registering Apparatus, Telegraphic.) Telegraphy, Automatic Apparatus by means of which a telegraphic message is automatically trans- mitted by the motion of a previously perforated fillet of paper containing perforations of the shape and order required to form the message to be transmitted. The paper passes between two terminals of the main line, the circuit of which is completed when the terminals come into contact at the perforated parts, and is broken when sepa- rated by the paper. The advantages of the automatic telegraph arise from the fact that since the paper fillets can be prepared beforehand, great speed is attained by their aid. In the automatic tele- graph some form of registering apparatus is employed. Type-printing telegraphs are often used for registering apparatus, in which case the impulses required for the trans- mission of the different letters are automatically sent into the line by the depression of corresponding keys on a suitably arranged key -board. Telegraphy, Chemieal — (See Recorder, Bain's Chemical.) Telegraphy, Dial (See Telegraph, Step-by- Step.) Telegraphy, Double Needle A system of needle telegraphy in which two separate and independently operated needles are employed. This system differs from the single needle system only in the fact that two needles, entirely independent of each other are mounted side by side, on the same dial, so as to permit their simultaneous operation by the right and left hand of the operator. Each needle has therefore a separate wire. The 582 A DICTIONARY OF ELECTRICAL increase in speed of signaling thus obtained is not, however, sufficiently great to balance the increased expense of con- struction. Single needle instruments, therefore, are preferred to those with two needles. Telegraphy, Diplex A method of simul- taneously sending two messages in the same direction over a single wire. Telegraphy, Duplex Devices whereby two telegraphic messages can be simultaneously transmitted over a single wire in opposite directions. Various duplex telegraphs have been devised. The Bridge Duplex is shown in Fig. 365. The receiving re- lay is placed in the cross wire of a Wheatstone's balance. (See Balance, Wheastone's Electric.) Fig. 365. When the ends of this cross wire are at the same potential, which will occur when the resistances in the four arms are proportionally equal, no current passes. The battery is connected through the transmitter K, which is arranged so that the battery contact is made before the connection of the line to earth is broken, to H, where the circuits branch to form the arms of the bridge. Adjustable re- sistances A, B, are placed in the two arms of the bridge. The line wire L, connected as shown, forms the third arm and a Words, terms and phrases. 583 rheostat or other adjustable resistance R, connected to a con- denser C, as shown, forms the fourth arm. (See Rheostat.) The relay M, is placed in the cross wire of the bridge thus formed. Small resistances V and W, are placed in the circuit of the battery to prevent injurious short-circuiting-. A similar disposition of apparatus is provided at the other end of the line. If, now, the four resistances at one end are suitably adjusted, the relay will not respond to the outgoing current ; but, since an earth circuit is employed, it will re- spond to the incoming current. The relay at either end, there- fore, will only respond to signals from the other end. The operator may thus signal the distant station while, at the same time, his relay, not being affected by his sending, is in readiness to receive signals from the other end. Fig. 366. , Fac-Simile, or Autographic or Telegraphy Pantelegraphy. — Apparatus whereby a facsimile or copy of a chart, diagram, or signature is telegraphically transmitted from one station to another. Bakewell's Fac-Simile Telegraph, which was one of the first devised, consists of two similar metal cylinders c, c', arranged at the two ends of a telegraph line L, at M and M', as shown in Fig. 366. These cylinders are synchronously rotated and 584 A DICTIONARY OF ELECTRICAL provided with metallic arms or tracers r, r', placed on a horizontal screw in the line circuit and moved laterally, over the surface of the cylinder on its rotation At the transmitting station the chart, writing, or other design is traced with varnish, or other non-conducting liquid, on the surface of the metallic cylinder, as at M, and a sheet of chemically prepared paper, similar to that employed in the Bain Chemical System is placed on the surface of the receiv- ing cylinder at M'. (See Recorder, Bain's Chemical.) The two cylinders being synchronously rotated, the metallic tracer breaks the circuit in which it is placed when it moves over the non-conducting lines on the cylinder, and thus causes corresponding breaks in the otherwise continuous blue spiral line traced on the paper-covered surface of M'. The telegraph keys at R, R', are used for the purposes of ordinary telegraphic communication before or after the record is transmitted. Caselli's Pan-Telegraph is an improvement on Bakewell's Copying Telegraph. Better methods are employed for main- taining the synchronism between the transmitting and re- ceiving instruments, for which purpose a pendulum, vibrating between two electro magnets, is employed. Telegraphy, Fire Alarm A system of tele- graphy by means of which alarms can be sent to a central station, or to the fire engine houses in the district, from call boxes placed in the line. The alarms are generally sounded by an apparatus similar to a district call, so that the pulling back of a lever rotates a wheel, by means of which a series of makes and breaks are produced, the number and sequence of which, enable the receiving stations to locate the particular box from which the signal is sent. In the case of some buildings, the alarms are automatic, and either call for help from the central office, or for the watchman in the building, or else turn on a series of water WORDS, TERMS AND PHRASES. 585 faucets or jets, in order to extinguish the fire. In these cases thermostats are used. (See Thermostats.) Telegraphy, Gray's Harmonic Multiple A system for the simultaneous transmission of a number of separate and distinct musical notes, over a single wire, which separate tones are utilized for the simultaneous transmission of an equal number of tele- graphic messages. The separate tones are thrown into the lines by means of tuning forks automatically vibrated by electro-magnets. These forks interrupt the circuit of batteries connected with the main line at the transmitting end of the line. The com- posite tone thus formed, is separated into its component tones by receiving electro-magnets called Harmonic Receivers, the arm- ature of each of which consist of a steel ribbon or plate tuned to one of the separate notes sent into the line. As the com- plex or undulatory current passes through the coils of each harmonic receiver, that note only affects the particular arma- ture that vibrates in unison with its ribbon or reed. The op- erator, therefore, at this receiver is in communication only with the operator at the key of the circuit that is sending this particular note into the line. The same is true of the other receivers. The Morse alphabet is used in this system, the dots and dashes being received as musical tones. In practice it was found that there was no difficulty in each operator recognizing the particular sound of his own instrument in receiving, although many instruments were in the same room. Telegraphy, Induction A system for telegraphing by induction between moving trains and fixed stations on a railroad, by means of impulses transmitted by induction between the car and a wire parallel with the track. In such a system, conducting wires directly connecting the stations and the moving trains are thus dispensed with, and 586 A DICTIONARY OF ELECTRICAL the signals are received by means of induction effects pro- duced between the moving- train and the fixed station. Two systems of inductive telegraphy are in actual use, viz. : (1) The Static Induction System of W. W. Smith and Edison, and (2) The Current or Dynamic Induction System of Wil- loughby Smith and Lucius J. Phelps. In the System of Static Induction, one of the condensing surfaces which receives or produces the charge, consists oi a wire placed on the road so as to come as near the top of the cars of the moving train as possible. The other condensing surface is composed of the metal roofs of the moving cars. Each condensing surface is connected to suitable instruments and batteries, and to the earth ; the line wire at the fixed station being connected to earth through- a ground plate, and the metal roof of the cars to earth through the wheels and track. Under these circumstances variations in the charge of either of the condensing surfaces produce inductive impulses that are received by the other surface as telegraphic signals. The Morse alphabet is employed, but in place of the or- dinary receiver or sounder, a telephone is used. In the System of Current Induction, the line wire is placed near the track, so as to be parallel with a coil of insulated wire placed on the side of the car and which receives the in- ductive impulses. The coil of wire on the train is connected with instruments and batteries, and forms a metallic circuit. The line wire is also connected with suitable batteries and receiving and transmitting instruments. An induction coil is generally employed since the greater and more rapidly varying difference of potential of its second- ary wire renders it better suited for producing effects of induc- tion. A telephone is employed as a receiver, as in the system of static induction. The metallic car roof and the lower truss rods have been successfully used as the primary and secondary conductors of the induction coil. WORDS, TERMS AND PHRASES. 587 The automatic make and break used for operating- the in- duction coil, causes the Morse characters employed in this system to be received in the receiving telephone as shrill buz- zing sounds. The receiving telephones used on the trains have a resist- ance of about 1,000 ohms. Fig. 367. Telegraphy, Multiplex A system of tele- graphy for the simultaneous transmission of more than four separate messages over a single wire. (See Telegraph, Syn- chronous, Multiplex.) Telegraphy, Printing A system of tel- egraphy in which the messages received are printed on a paper fillet. In Callahan's Printing Telegraph, two type wheels are 588 A DICTIONARY OF ELECTRICAL employed, one of which carries letter type and the other numerals on its circumference. These printing wheels are placed alongside of each other, as shown in Fig. 367, but on separate and independent axes. The type wheels are moved by a step-by-step device. When the proper letter or numeral is reached at the receiving end, the printing wheel is stopped, and a paper fillet is pressed against its surface. The printing wheel is kept covered with ink by means of an inked roller. Fig. 368. The transmitting instrument is similar in its operation to the Breguet Manipulator. Separate transmitters are used for each of the wires. (See Telegraphy, Step-by-Step.) Telegraphy, <£uadriiplex — - — — A. system for the simultaneous telegraphic transmission of four messages over a single wire. WORDS, TERMS AND PHRASES. 589 There are various systems of quadruplex telegraphy. For the details of their operation the student is referred to stand- ard books on telegraphy. Telegraphy, Single Needle ■ —A system of telegraphy by means of which the signals transmitted are re- ceived by observing the movements of a vertical needle over a dial. Movements of the top of the needle to the right of the observer represent the dashes, and movements to the left, -the dots of the Morse alphabet. Fig. 370. Fi &- 37L The single needle apparatus of Wheatstone and Cooke's svstem is shown in Figs. 368 and 369. Fig. 368, shows the external appearance, and Fig. 369, the internal arrangements as seen from the back. An astatic needle is placed inside two coils of insulated wire C C. Only one of these needles N, is visible on the face of the receiving instrument. The current from the line enters at L, passes through the coil C C, and leaves at N. 590 A DICTIONARY OF ELECTRICAL The movements of the needle to the right or the left are ob- tained by changing the direction of the current in the coils C C. This is effected by working the handle when send- ing, and thus moving the commutator at S, S, and bringing the contact springs resting thereon into different contacts. In the more modern form of Single Needle Instrument, shown in Fig. 370, a single magnetic needle N S, Fig. 371, only is placed in the coil. This needle is rigidly attached to a light needle a, b, used only as a pointer, and is alone visible in the front of the figure on the left. The relative disposition of these needles is shown in the drawing on the right. The reversals of the current, required to deflect the needle to the right or left, are ob- tained by means of a double key or tapper, shown in Fig. 372. 1~] The levers L and E, are connected respect- wCm!X^2 ively to line and earth, and, when not in use, I , rest against C, connected with the positive ■ ]|| r 1 I side of the battery ; but when depressed con- 's nect with Z, attached to the negative side of Fiq 872 * ne Dat tery. The depression of L, therefore, sends a negative current into the line and deflects the needle, say, to the left, while the depression of E sends a positive current into the line and deflects the needle to the right. The terms positive and negative currents are used in telegraphy to indicate currents whose direction is positive or negative. Telegraphy, Speaking A system for the telegraphic transmission of articulate speech. (See Tele- phones.) Telegraphy, Step-foy-Step A system of telegraphy in which the needle of a dial, or the type wheel of a printing telegraph, is moved step-by-step by electric impulses sent over the line. (See Telegraphy, Needle or Dial.) WORDS, TERMS AND PHRASES. 591 Telegraphy, Sub-Marine A system of telegraphy in which the line wire consists of a sub-marine cable. In long sub-marine cables, in order to avoid retardation from the self-induction of the current, and the static charge arising from the cable acting as a condenser, very small currents are used. To detect these a very sensitive receiv- ing instrument, such as the mirror galvanometer, or the siphon recorder, is employed. (See Galvanometer, Mirror. Recorder, Siphon.) According to Culley, the retardation in the case of one of the sub-marine cables between Newfoundland and Ireland, amounts to two-tenths of a second before a signal sent from one end produces any appreciable effect at the other end, while three seconds are required for the current through the cable to gain its full strength. Telegraphy, Synchronous-Multiplex, Delany's System. — A system devised by Delany for the simultaneous telegraphic transmission of a number of messages either all in the same direction, or part in one direction and the remainder in the opposite direction. The Delany System embraces the following parts : (1) A circular table of alternately insulated and grounded contacts at either end of a telegraphic line. (2) A synchronized rotating arm or trailing contact, at each end of the line, driven by a phonic wheel, and maintained in synchronous rotation by means of electric impulses automatic- ally sent out over the main line in either direction, on the failure of the wheel at either end to rotate synchronously with that at the other end. (3) Transmitting and receiving instruments connecting similar contacts at each end of the main line, and forming prac- tically separate and independent lines for the simultaneous transmission of dispatches over the main line in either direc- tion. 592 A DICTIONARY OF ELECTRICAL The main line is simultaneously connected at both of its ends to corresponding operating instruments, and transferred from one set of instruments to another so rapidly that the operators, either sending or receiving, cannot realize that the line has been disconnected from their instruments and given to others, because each of them will always have the line ready for use, even at the highest rate of manipulation, and will, therefore, to all practical intents and purposes, have at his disposal a private wire between himself and the operator with whom he is in communication. Therefore, although more than one operator may be spoken of as simultaneously using the line at any given time, yet in point of fact no two operators are in reality absolutely using it at the same time ; but they follow one another at such short intervals, and the line is taken from one operator and transferred to another so rapidly that none of them can at any time tell but that he has the line alone, and that there- fore it is practically open for the use of every operator just as if he alone had control of it. There will, therefore, be established, by the use of a single line, as many private and separate lines as there are trans- ferences of the line from the time it is taken from the first operator, and again given back to him. This system has been extended to as many as seventy-two distinct and separate printing circuits, maintained and operated on a single connecting line wire. Fig. 373, shows the apparatus at each end of the line, at the stations X and Y. The apparatus at each end is substantially identical. A steel fork a, at each station, is automatically and continuously vibrated by the action of the local battery L B, and the electro-magnet A, called the vibrator magnet. Platinum contacts x, xf 1 , placed on the inner faces of the tines of the fork, make and break contact with delicate con- tact springs y, y 1 . The fork being mechanically started into a vibratory mo- WORDS, TEEMS AND PHRASES. 593 tion, will automatically make and break its local circuit, and thus send impulses into the fork-magnet A, that will continu- ously maintain the vibrations of the fork, m a well-known manner. The making and breaking of the contacts x and y, conse- quent on the fork's vibration, opens and closes a circuit of an- other local battery called the motor circuit, m which is placed an electro-magnet D. the function of which is to maintain the continuous rotation of the transmission apparatus C, ^ sk ^n vrn w^ Fig. 373. The continuous vibration of the fork makes and breaks the contacts at x and y, and thereby makes and breaks the motor circuit. The alternate magnetizations and demagnetizations of the cores of the motor-magnet D cause the rotation of the transmission apparatus C. The motor-magnet and transmission wheel or disc C, pro- vided with projections c, c, is the invention of Paul La Cour, and is styled by him a ' Phonic Wheel," 594 A DICTIONARY OF ELECTRICAL The transmission apparatus is illustrated in detail in Figs. 374 and 375, and is an exact counterpart of the receiving appar- tus at the other end of the line. A base plate E, provided with Fig. 37k. binding posts, carries a vertical rotary shaft F. A circular table F 1 , is provided with a series of insulated contacts ar- ranged symmetrically around the axis of rotation of the shaft. Fig. 375. A radial arm F 2 , connected with the shaft F, carries at its outer extremity a trailing contact finger /. As the disc C is rotated by the electro-magnet D, the trailing contact f, WORDS, TERMS AND PHRASES. 595 sweeps around the circular table F 1 , and is brought success- ively into contact with the insulated contact-pieces placed on the upper face of the table F 1 . The main line Q. Q, has one of its ends connected with the trailing' finger/. As the shaft F, rotates, the line is therefore brought into successive electrical connection with the series of insulated contacts in the upper face of the table F 1 . Any suitable number of insulated contacts may be placed on the circular table F 1 ; sixty are shown in Fig. 376 In practice these contacts are connected in accordance with the number of circuits which it is desired to simultaneously maintain on the same wire. In the special case shown in the figure referred to above, it is arranged so that four separate circuits shall be established on the same line wire. The sixty contacts are placed in six independent series, numbered from 1 to 10, consecutively. In the arrangement here shown two of the contact pieces in each series of ten are connected tn the same circuit, and as there are six series, each of the circuits so connected will have twelve contacts for each rotation of the disc, and twelve electrical impulses, as will be afterwards described The detailed mechanism by means of which the separate and independent circuits so obtained are utilized for the trans- mission and reception of messages is shown in Fig. 376. R, R 1 , R 2 and R 3 are polarized relays; S, S 1 , S 2 and S 3 are ordi- nary Morse sounders, although in the practice of this inven- tion some improvement has been introduced in connection with the receiving instruments. The connections with the main and the local batteries M B and L B, are clearly shown in the figure. It will be noticed that the relay R is connected with the wire r, and with the contacts 1 and 5 ; R 1 , is connected by r 1 , with the contacts 2 and 6 ; R 2 , by the wire r 2 , with the contacts 3 and 7; and R 3 , by the wire r 3 , with the contacts 4 and 8 Sim- ilar instruments and circuits are placed at each end of the line. 596 A DICTIONARY OF ELECTRICAL Without further describing the operation of the instruments shown in the figure, it need only now be borne in mind that the corresponding relays at the distant stations are connected with the correspondingly numbered contacts When, there - fore, the trailing contact finger at each station simultaneously touches the contacts bearing the same number, the corre- Fig. 876 sponding instruments connected with these contacts at each station will be placed in communication over the main line, the trailing contact finger /, completing the connection of the mam line with the contact arm in the manner already de- scribed. Telegraphy, Time graphic transmission of time. -A system for the tele- WORDS, TERMS AND PHRASES. 597 A system of time-telegraphy includes a master clock, the movements of whose pendulum automatically transmit a number of electric impulses to a number of secondary docks and thus moves them ; or self winding clocks are employed, which are corrected daily by an impulse sent over the line from a master clock. — (See Clocks, Electric.) A o-auo-e for elec Tele-Manometer, Electric trically indicating and recording pressure at a distance. Fig. 381. The tele-manometer includes a pressure gauge furnished with electric contacts operated by the movements of the needle of the steam gauge for instance, and indicating and recording apparatus. An alarm bell is provided to call attention to any rise of the pressure above, or its fall below the given or pre- determined limits for which the hands have been set. 598 A DICTIONARY OP ELECTRICAL Telemeter. — An apparatus for electrically indicating and recording at a distance, the pressure on a gauge, the reading of a thermometer, or the indications of similar instruments. (See Tele-Barometer. Tele-Manometer. Tele-Thermometer.) Teleplierage. — A system (Fleeming Jenkin) for the con- veyance of carriages suspended from electric conductors, and driven by means of electric motors, that take directly from the conductors the current required to energize them. Two lines are provided, an up and a down line, that cross each other at regular intervals. Each line is in segments, and the alternate segments are insulated from each other, but are connected electrically by cross pieces on the supporting posts. In this way the line shown in Fig. 382, is obtained. @ - °» f *H5) U* I ' ■*" *• Fig. 882. The two lines are maintained at a difference of potential by a dynamo-electric machine at D, Fig. 382. As the train at L T, or L' T', is of such a length as to come into contact with two different segments at the same time, it receives a current sufficient to run the motor connected with it, the current being received through a conductor joining a pair of wheels that are insulated from the truck. The general arrangement of the line is shown in the an- nexed Fig. 381. Telephone. — An apparatus for the electric transmission of articulate speech. The articulating telephone, though first brought into public use by Bell, was invented by Reis, in Germany, in 1861. In America, after very protracted litigation, Bell has been decided WORDS, TERMS AND PHRASES. 599 legally to be the first inventor, but scientific men very gener- ally recognize the principles of the invention to be fully an- ticipated by the earlier instruments of Eeis. Bell, however, is justly entitled to credit for his improvements in the Eeis apparatus. In Bell's Magneto-Electric Telephone, the transmitting and receiving instruments are identical. A coil C, of insulated wire connected with the line, is placed on a core of magnetized steel, mounted opposite the centre of a circular diaphragm of thin sheet iron, rigidly supported at its edges. In transmitting, the message is spoken into the mouth-piece at one end, as at D, in Fig. 378, and the to-and-f ro motions thus imparted to the metallic diaphragm at- tached to the mouth-piece P, produce in- duction currents in the coil C, on the magnet M. (See Induction, Electro Mag- netic.) These impulses, passing over the main line E L, produce similar movements in the diaphragm P', of the receiving in- strument, at D', and thus causes it to repro- duce the message, in articulate sounds, to one listening at the receiving instrument. A ground circuit is shown in the figure, as usually employed in practice. A magneto - telephone constitutes in reality a magneto- electric ma- chine, driven or propelled by the voice of the speak- er, in which the currents so produced instead of being commuted are employed uncom- muted to reproduce the uttered speech. In actual practice this instrument is replaced by the electro- magnetic telephone, in which the to-and-fro motions of the Fig. 378. 600 A DICTIONARY OF ELECTRICAL transmitting diaphragm are caused to vary the resistance of a button qf carbon, or a variable contact-transmitter similar to that employed by Reis in some of his instruments. The variable resistance is placed in the circuit of a battery, so that on speaking into the transmitter, electric impulses are sent over the line and are received by a telephone with a magnet core provided with a coil in the main line circuit. The telephone is arranged for actual commercial use in the United States in the manner shown in Fig. 379. Telephone, Electro-Capillary A telephone in which the movements of the transmitting diaphragm produce currents by means of variations in the electro-motive forces of the contact surfaces of liquids in capillary tubes. (See Electro Capillary Phe- nomena.) In Breguet's telephone both the trans- mitting and the receiving instruments are similar in construction and operate by means of electro-capillary phenomena. A vertical capillary tube communicates at its upper end with an air space below a diaphragm, and at its lower end with a mercury surface on which rests a layer of acidulated water. A line wire connects Fig. 379. ^he mercury reservoirs of the transmit- ting and receiving instruments, the remainder of the circuit being formed by another wire connecting the mercury near the upper parts of the two vertical tubes. The alterations in the contact surfaces at the transmitting end produced by the movements of the diaphragm, cause electric impulses that produce similar movements of the dia- phragm at the receiving end. Telephone, Electro-Motographic or Edi- son's Electro-Chemical Telephone.— A telephone in WORDS, TERMS AND PHRASES. 601 which the receiver consists of a diaphragm of mica or other elastic material operated on the principle of the electro-moto- graph. A straight lever, which forms part of the line circuit is rigidly attached at one end to the centre of the receiving diaphragm and rests near its other end on the moistened sur- face of a chalk cylinder, maintained in rotation by suitable mechanical means. Electric impulses being sent into the line by the voice of a speaker talking at a transmitter of ordinary construction, produce slipping movements of the cylinder that reproduce in the receiving diaphragm articulate speech. Telephonic Exchange. — (See Exchange, Telephonic.) Telephonic Joints of Wire.— (See Joints, Tele- graphic.) Telephote or Pherope.— An apparatus for the tele- graphic transmission of pictures through the action of light on selenium. (See Telephotography.) Telephotography. — A system for facsimile transmis- sion by means of dots and lines transmitted by means of a continuous current whose intensity is varied by a transmitting instrument, containing a selenium resistance. (See Tele- graph, Fac-Simile. S elenium Resistance.) The transmitter consists of a dark box, mounted on an axis, so as to be capable of a sidewise motion. The picture to be transmitted is thrown continuously on the face of the box by any lantern projection apparatus, and a small opening con- taining a selenium resistance receives the alternations of light and shade, and transmits the same as variations in the strength of the otherwise continuous current in the circuit of which the selenium resistance is placed. The picture is re- ceived at the other end on a sheet of chemically prepared paper moved synchronously with the transmitting box. Telescope, Reading A telescope employed in electric measurements, for reading the deflections of the galvanometer. 602 A DICTIONARY OP ELECTRICAL A mirror, suspended above the needle on the same fibre that holds the needle, reflects a spot of light on a scale by which the amount of deflection is indicated. (See Galvanometer, Mirror.) A form of reading telescope is shown in Fig-. 380. An illumined scale M, receives the spot of light reflected from the mirror attached to the galvanometer suspension, and the deflection is observed in the mirror by the telescope F. Teleseme.— A self-registering hotel annunciator, by means of which a dial operated in a room, indicates on the an- nunciator the article or service required. Tele-Thermometer, Elec- tric An electric record- ing thermometer for indicating and recording temperature at a distance. Temperature Alarm.— (See Alarm, Fire, etc.) Temperature, Effects of on Electric Resistance. — (See Resistance, Effects of Tem- perature on.) Tension, Electric A term often loosely applied to signify electro-motive force, dielectric stress, difference of potential. This term is now very generally abandoned. Terrestrial Magnetism. — (See Magnetism Terrestrial.) Testing, Methods of (See Measurements, Elec- tric.) Therm. — A heat-unit recently proposed by the British As- sociation. A therm is the amount of heat required to raise the temper- Fig. 380. WORDS, TERMS AND PHRASES. 60S ature of one gramme of pure water at the temperature of its maximum density one degree centigrade. (See Calorie.) Tliermo-EIectric Battery. — (See Battery, Thermo- Electric.) Tliermo-EIectric Couple. — Two dissimilar metals joined so as to produce thermo-electric currents through dif- ferences of temperature. Tliermo-EIectric Diagram. — (See Diagram, Thermo- Electric.) Tliermo-EIectric Inversion. — An inversion of the thermo-electric power of a couple at certain temperatures (See Diagram, Thermo-Electric.) Tliermo-Electricity. — Electricity produced by differ- ences of temperature at the junctions of dissimilar metals. If a bar of anti- mony is soldered to a bar of bismuth, e====J ^ and their free ends connected by means of a galvan- ometer, the appli- cation of heat to ~ Fig. 381. the junction, so as to raise its temperature above the rest of the circuit, will produce a current across the junction from the bismuth to the antimony, (against the alphabet, or from B to A). If, the junction be cooled below the rest of the circuit, a current is produced across the junction from the antimony to the bismuth, (with the alphabet, or from A to B). These cur- rents are called thermo-electric currents, and are proportional to the differences of temperature. Even the same metal, in different physical states or condi- tions, such as a wire, part of which is straight and the remain- der bent into a spiral as at H C, Fig. 381, if heated at F by the flame of a lamp will show o> current developed in it. A DICTIONARY OF ELECTRICAL The same thing may also be shown by placing a cylinder of bismuth J, Fig. 382, in a gap in a hollow rectangle of copper A B, inside of which a magnetic needle M is supported. A The rectangle of copper being placed in the magnetic me- ridian, on heating the junction by the flame of a lamp F the needle will be deflected by a current produced by the differ- ence of temperature. Thermo-Eleetrie Pile, differential (See Differential Thermo-Electric Pile.) a + Fig. 383. Fig. 38k. Thermo-Electric Pile or Battery.— A number of separate thermo-electric couples, united in series, so as to form a single thermo-electric source. WORDS, TERMS AND PHRASES. 605 Figs. 383, and 384, show Nobili's Thermo-Pile, in which a number of bismuth-antimony thermo-electric couples are con- nected in a continuous series, as shown in Fig. 386, and insu- lated from one another, except at their junctions, and packed in a metallic box, and supported as shown in Fig. 385. The free terminals of the series are connected to binding posts. Differences of temperature between the two faces of the pile, where the junctions are exposed, result in a current whose difference of potential is equal to the sum of the differ- ences of potential of all the thermo-electric couples. A careful inspection of the drawing will show that the junc- tions are formed successively at opposite faces of the pile, so that if the junctions be numbered successively, the even junc- tions will come at one face, and the odd junctions at the other. This is necessary in order to permit all the thermo- electric couples to add their differences of potential ; for, if, Fig. 385. as in Fig. 385, a thermo-electric chain be formed, no currents will result from equally heating any two consecutive junc- tions J J, of the metals A and B, since the electro-motive forces so produced oppose each other. Thermo piles have been constructed by Clamond of couples of iron and an alloy of zinc and antimony, of sufficient power to produce a voltaic arc whose illuminating power equalled 40 carcel burners. Many practical difficulties exist which will have to be surmounted before such piles can be employed as commercial electric sources, - 606 A DICTIONARY OF ELECTRICAL Tiiermo-EIectric Power.— (See Power, Thermo-Elec- tric. ) Thermo-Electric Series.— A list of metals so arranged, according- to their thermo-electric powers, that each metal in the series is electro-positive to any metal lower in the list. Thermo - Electro - Motive Force. — Electro - motive force, or difference of potential, produced at thermo-electric junctions by differences of temperature. Thermometer, Electric or Tliermo- Electroineter. — A device for determining the effects of an electric discharge by the movements of a liquid column on the expansion of a confined mass of air through which the discharge is passed. Thermometer Scale, Centigrade (See Cen- tigrade Scale.) Thermometer Scale, Fahrenheit (See Fah- renheit Scale.) Thermophone. — Any instrument by means of which sounds are produced by the absorption of radiant energy. (See Photophon A telephone has been constructed in which the motions of the receiving diaphragm are effected by the expansions and contractions of a thin metallic wire connected to its centre and placed in the circuit of the main line. Thermostat. — An instrument for automatically indicat- ing the existence of a given tem- perature by the closing of an electric circuit through the ex- pansion of a solid or liquid. Thermostats are used in sys- tems of automatic fire tele- graphy, and in systems of auto- es'- s86 ' matic temperature regulation. Three- Wire System.— A system of electric distribution, invented by Edison, in which three wires are employed, WORDS, TERMS AND PHRASES. 607 In this system three conductors are connected to a source of electric energy, Fig. 886, and the difference of potential between the central and the two outer conductors is always maintained the same. The lamps or other electro-receptive devices are placed in multiple arc between either branch, and so distributed that the current in each branch is the same. When such a balance is established no current flows through the central or neutral conductor. But when that balance is disturbed the surplus current in one branch is taken up by the central conductor. This system effects considerable economy in the weight of wire required. Thunder. — A loud noise accompanying a lightning dis- charge. Thunder is due to the sudden rush of the surrounding air to fill the vacuous space accompanying the disruptive discharge of a cloud. This space is caused by the condensation of the vapor formed on the passage of the discharge through drops of rain or moisture in the air, as well as by the expansion of the air itself. ' Thunder-Storms, Geographical Distribution of (See Storms, Thunder, Geographical Distribution of .) Tick, Magnetic. A faint metallic click heard on the magnetization and demagnetization of a magnetizable substance. (See Magnetic Tick.)* % Time Ball, Electric A ball, supported in a prominent position on a tall pole, and caused to fall at the exact hour of noon, or at any other predetermined time, for the purpose of thus giving the exact time to an entire neigh- borhood. The release of the ball is effected by the closing of an elec- tric circuit, either automatically, or through the agency of an observer. Time Cut-Outs, Automatic. Automatic cut-outs arranged on storage batteries to cut them in or out of the circuit of the charging source, at predetermined times, 608 A DICTIONARY OF ELECTRICAL Time Telegraphy.— (See Telegraphy, Time. Clocks, Electric.) Tongs, Discharging (See Discharging Rods.) Top, Induction (See Induction, Top.) Torpedo, Electric (See Ray, Electric.) Torsion Balance.— (See Balance, Torsion.) Torsion Galvanometer.— (See Galvanometer, Torsion.) Total or Dead Earth.— (See Earths.) Touch, Single, Separate or Double Methods of Magnetization by.— (See Magnetization, Methods of.) Tourmaline. — A mineral consisting of natural silicates and borates of alumina, lime, iron, etc., possessing- pyro- electric properties. (See Pyro-Electricity.) Tower, Electric. A high tower provided for the support of a number of electric arc lamps, employed in systems of general illumination. Tower, System of Electric Lighting,— The lighting of extended areas by means of arc lights placed on the top of tall towers. The tower-systenl of electric illumination is only applicable to wide, open spaces, since otherwise objectionable shadows are apt to be formed. Train Signaling. — (See Telegraphy, Inductive.) Transmission of Energy. — (See Energy, Transmis- sion of.) Transmitters, Electric Various electric ap- paratus employed in transmitting or sending the electric im- pulses over a telegraph line. In most telegraphic systems, the transmitting apparatus consists of various forms of keys for interrupting or varying the current. In the telephone the transmitter consists of a diaphragm operated by the voice of the speaker. (See Tele- graph. Telephone.) WORDS, TERMS AND PHRASES. 609 Tran§former or Converter. Transformer.) Treatment, Hydro-Carbon — (See Converter or of Carbons.- (See Flashing Carbons, Process for.) Trigonometry. — That branch of mathematical science which treats of the methods of determining' the values of the angles or sides of a triangle. There are in every triangle three sides and three angles. If any three of these parts are given, except the three angles, the values of the remaining parts can be determined by means of trigonometry, by what is called the solution of the triangle. Trigonometrical Functions.— Certain quantities, the values of which are dependent on the length of the arcs sub- tended by angles, which are taken for the measures of the arcs instead of the arcs themselves. The trigonometrical functions are the sine, the co-sine, the tangent, the co-tangent, the secant, and the co- secant. These are generally abreviat- ed, thus, viz. : sin, cos, tan, cot, sec, and co-sec. The Sine of an angle, or arc, is the perpendicular distance from one ex- tremity of the arc to the diameter pass- ing through the other extremity. Thus in Fig. 387, B D, is the sine of the angle B O A, or of the arc, B A. The Cosine of an angle, or arc, is that part of the diameter which lies between the foot of the sine and the centre. Thus D O, is the cosine of the angle B O A, or of the arc B A. The cosine of an arc is equal to the sine of its complement. Thus E O B or B E, the complement of B A, has for its sine I B, which is equaL to O D. (See Complement of Angle.) than a right angle, or 90°, such, for 610 A DICTIONARY OF ELECTRICAL instance, as the angle TOG, or the arc B E F G, B D is its sine. This is also the sine of BOA, or of B A, which is the supple- ment of TOG, or B E F G. Hence the sine of an arc is equal to the sine of its supplement. The same is true of the cosine. The Tangent of an angle, or arc, is a straight line touching the arc at one extremity, drawn perpendicular to the diameter at one end of the arc, and limited by a straight line connect- ing the centre of the circle and the other end of the arc. Thus C A is the tangent of the angle B O A, or the arc B A. The Co-tangent of an angle, or arc, is equal to the tangent of its complement, thus E T, is the co-tangent of the angle, B O A, or the arc B A. The tangent of an angle, or arc, is equal to the tangent of its supplement. Thus A C, is the tangent of the angle BOA, or the arc B A. It is also equal to the tangent of the angle BOG, or the arc B E F G, the corresponding supplement of the angle BOA, or of the arc B A. The Secant of an angle, or arc, is the straight line drawn from the centre of the circle through one extremity of the arc and limited by the tangent passing through the other ex- tremity. Thus O C is the secant of the angle B O A, or of the arc B A. The secant of an arc is equal to the secant of its supple- ment. The Co-seeant of an angle, or arc, is equal to the secant of its complement. Thus E T is the co-secant of the angle BOA, or of the arc B A. It will be observed that the co-sine, the co-tangent and the co-secant are respectively the sine, tangent, and secant of the complement of the arc, or in other words, the complement-sine, the complement-tangent, and the complement-secant. Trolleys. — Rolling contacts that move over the overhead lines provided for a line of electric railway cars, and carry off WORDS, TERMS AND PHRASES. 611 the current required to drive the motor car. (See Sled Plow.) Tubes, Geissler (See Geissler Tubes.) Tubes of Force.— (See Force, Tubes of.) Tubes of Induction.— See Force, Tubes of.) Tubes, Mercury Vacuous glass tubes in which a flash of light is produced by the fall of a small quan- tity of mercury placed inside it. The light is caused by the electricity produced by the friction of the mercury in falling against the sides of a spiral glass tube placed inside the vacuous tube. Tubes, Plucker (See PlilckerTubes.) Tubes, Stratification — (See Stratification Tubes.) Type-Printing Telegraph.— (See Telegraph Print- ing.) Type writer, Electric A type- writing machine in which the keys are intended to make the contacts only of the circuits of electro magnets, by the attractions of the armatures of which the movements of the type levers required for the work of printing are effected. Electric typewriters secure a uniformity of impression that is impossible to obtain with hand worked machines; they also greatly lessen the mechanical labor of writing. — (See Dynamo- graph.) Ultra Gaseous Matter.— A term sometimes applied to radiant matter. — (See Matter, Radiant.) Underground Conductors. — Electric conductors placed underground by actual burial, or by passing them through underground conduits or subways. Underground conductors, though less unsightly than the ordinary aerial conductors, require to be laid with unusual care to render them equally safe, since, when contacts do occur, all 612 A DICTIONARY OF ELECTRICAL the wires in the same conduit are apt to be simultaneously affected, thus spreading- the danger in many different direc- tions. They are, however, less liable to danger arising from accidental crosses or contacts. Undulatory Currents. — (See Currents, Undulatory.) filiform Magnetic Field.— A field traversed by the same number of lines of magnetic force per unit of area of cross section of the field. — (See Fields, Magnetic.) Uniform Potential. — A potential that does not vary. An electric source is said to generate a uniform potential when it maintains a constant difference of potential at the terminals. Unipolar Induction. — A term sometimes applied to the induction that occurs when a conductor is so moved through a magnetic field as to continuously cut its lines of force. If the conducting wire ABC, Fig. 388, be rotated (in a direc- tion towards the ob- server) around the pole N of a magnet, it will continuously cut its lines of mag- netic force and will therefore produce continuous cur in the direction of the arrows. The end A is supported in a recess in N, while the end near C slides on a projection on the middle of the magnet. Unipolar dynamos operate on the continuous cutting of lines of magnetic force. Strictly speaking there is no such thing as a unipolar dyn- amo, or unipolar induction, since a single magnetic pole can- WORDS, TERMS AND PHRASES. 613 not exist by itself. Continuous cutting- of lines of magnetic force, however, can exist and produces, unlike the ordinary bi-polar induction, a continuous current. Unit Angle. — (See Angular Velocity.) Unit, B. A. The British Association unit of resist- ance or ohm. — (See Ohm.) Unit of Acceleration. — (See Acceleration, Unit of.) Unit of Activity. — (See Activity, Unit of.) Unit Diflernce of Potential or Electro-Motive Force. — Such a difference of potential between two points that requires the expenditure of one erg of work to bring* a unit of positive electricity from one of these points to the other, against the electric force. (See Erg.) Unit Jar. — (See Jar, Unit.) Unit of Current, Jacobi's A current which passed through a voltameter will liberate in one minute a cubic centimetre of oxygen and hydrogen at 0° C. and 760 m. m. barometric pressure. 1 One Jacobi's Unit of Current equals Weber per second. (Obsolete.) 10 ' 82 Unit of Heat, New.— (See Therm.) Unit of Hass.— (See Mass, Unit of.) Unit of Power.— (See Power, Unit of.) Unit of Pressure, New (See Barad.) Unit of Resistance, Jacobi's — The electric re- sistance of 25 feet of a certain copper wire weighing 345 grains. Another unit of electric resistance proposed by Jacobi was the resistance of a copper wire one metre in length and one millimetre in diameter. Unit of Resistance, Matthiessen's The resist- ance of one statute mile of pure annealed copper wire \ of an inch in diameter at 15.6° C. 014 A DICTIONARY OF ELECTRICAL Unit of Resistance, Varley's —The resistance of one statute mile of a special copper wire T X g of an inch in diameter. Varley's unit was afterwards adjusted by him to equal 25 Siemens mercury units. Unit of Resistance. — Such a resistance that unit dif- ference of potential is required to cause a current of unit strength to pass. Unit Quantity of Electricity.— The quantity of elec- tricity conveyed by unit current per second. Unit of Supply, Electrical A unit-pro visionally adopted in England by the Board of Trade, equal to 1,000 amperes flowing for one hour under an electro-motive force of one volt. This would, of course, equal 1,000 watt hours, and would be the same as 100 amperes flowing for ten hours under one volt. One unit of electrical supply is equal to 1.34 actual horse power expended for one hour, and will feed 13.4 Swan lamps of 21 candle power for one hour. It is equal in illuminating power in Swan lamps, to the light produced by 100 cubic feet of gas consumed in twenty 14-candle burners in one hour. Unit Strength of Current.— Such a strength of current that when passed through a circuit one centimetre in length, arranged in an arc of one centimetre radius, will exert a force of one dyne on a unit magnet pole placed at the centre. Unit of Velocity, tfew The Kine— (See Kine.) Units C. O. S. The centimetre-gramme-second units. — (See Units, Fundamental.) Units, Derived Various units obtained or derived from the fundamental units of Length, L, Mass, M, and Time,T. The derived units and their dimensions are as follows : Words, terms and phrases. 615 Area, L 8 . — The Square Centimetre. Volume, L 3 . — The Cubic Centimetre. Velocity, V. — Unit Distance traversed in Unit Time, or L V=- • (1) T Acceleration, A. — The rate of change which will produce a change of velocity of one centimetre per second. V A = — • (2) T Substituting in equation (2) the value of V in equation (1), we have, L T L A = - = - • (3) Force, F. — The Dyne, or the force required to act on unit mass in order to impart to it unit velocity. F = MxA • (4) Substituting the value of A derived from equation (2), we have, V F = Mx- • T Substituting the value of V derived from equation (1), we have, M L ML F=-x-= • (5) T T T 2 Work or Energy, W. — The Erg, or the work done in over- coming unit force through unit distance. ML ML 2 W = FxL = xL = • 616 A DICTIONARY OF ELECTRICAL Power, P.— The Unit Rate of Doing Work. ML 2 W T 3 ML 8 P = - = = • (6) T T T s Units, Electro-Magnetic A system of units derived from the C. G. S. units, employed in electro-magnetic measurements. Units, Electro-Magnetic, Dimensions of f ML Current strength = Intensity of Field x Length = T Quantity = Current x Time = |/M x L . Potential. Dif. of Pot. ) Work ^MxL* Electro-motive force f Quantity T8 Electro-motive force L Resistance = = — • Current T Quantity T 2 Capacity = = — • Potential L Units, Electrostatic Units based on the force exerted between two equal quantities of electricity. Two systems of electric units are derived from the C. G. S. system, viz., the Electrostatic and the Electromagnetic. These units are based respectively on the force exerted between two quantities of electricity, and between two magnet poles. The electrostatic units embrace the units of Quantity, Potential, and Capacity. No particular names have as yet been adopted for these units. Unit of Quantity. — That quantity of electricity which will repel an equal quantity of the same kind of electricity placed WORDS, TERMS AND PHRASES. 617 at a distance of one centimetre from it with the force of one dyne. Electrostatic potential, or power of doing electrostatic work, is measured in units of work, or ergs. Unit Difference of Potential. — Such a difference of poten- tial between two points as requires the expenditure of one erg of work to bring up a unit of positive electricity from one point to the other against the electric force. Unit of Capacity — Such a capacity of a conductor as re- quires a charge of one unit of electricity to raise it to unit potential. Specific Inductive Capacity. — The ratio between the induc- tive capacity of a substance and that of air, measured under precisely similar conditions. The specific inductive capacity is obtained by comparing the capacity of a condenser filled Avith the particular substance, and the capacity of the same condenser when filled with air. The specific inductive capacity of air is taken as unity. Units, Electrostatic, Dimensions of.— Quantity : = |/ force x Quantity Time Work (distance) 2 , 3 V Y F x L 2 : 4/MxL T M^ L 2 Current = MxL 3 T 2 Potential = Resistance Capacity = IxL Quantity Potential T = L _1 T = = L . T L T Current Quantity Potential 618 A DICTIONARY OF ELECTRICAL One Quantity Specific Inductive Capacity = = A simple Another Quantity ratio or number. Force , , Electro-motive Intensity = — IVP L* T- 1 = Quantity |/MxL T The fractional and negative exponents used above are merely convenient methods of expressing the contraction of roots, and division by the quantity represented by the nega- tive exponent. Units, Fundamental The units of length, time, and mass, to which all other quantities can be referred. The unit of length is now generally taken as the Centimetre ; the unit of time as the Second ; and the unit of mass as the Gramme. These form a system of measurement known as the centimetre-gramme-second system, or the C. G. S. system, or absolute system. The dimensions of the fundamental units, are designated thus : Length = L. Mass = M. Time = T. Units of Heat. — (See Heat, Units.) Units, Magnetic. — Units based on the force exerted be- tween two magnet poles. Unit Strength of Magnetic Pole. — Such magnetic strength of pole that repels another magnetic pole of equal strength placed at unit distance with unit force, or one dyne. Magnetic Potential. — Power of doing work possessed by a magnet pole. Magnetic Potential is measured, like electrostatic potential, in units of work, or in ergs. WORDS, TERMS AND PHRASES. 619 Magnetic Potential, Unit Difference of. — Such a difference of magnetic potential between two points that requires the expenditure of one erg of work to bring up a magnetic pole of unit strength towards a like pole. Unit Intensity of Magnetic Field. — Such an intensity of magnetic field as acts on a north-seeking pole of unit strength with the force of one dyne. Units, Magnetic, Dimensions of i/ML 8 Strength of Pole, or ) = , (Distance) 2 = Quantity of Magnetism ) T Work |/MxL Magnetic Potential = = • Intensity of field = Strength of pole T Force |/~M~ Strength of pole L 8 xT Units, Practical — Multiples or fractions of the absolute or centimetre-gramme-secohd units. The practical units have been introduced because the abso- lute units are either too small or too large for actual use. Electro-motive Force.— The Volt = 100,000,000 C. G. S. or absolute units, that is, 10 8 absolute units of resistance. (See Volt) Resistance. — The Ohm = 1,000,000,000 absolute units of re- sistance, or 10 9 absolute units. (See Ohm.) Current. — The Ampere = -^ Absolute Unit of Current. (See Ampere.) Quantity. — The Coulomb = -^ Absolute Unit of Quantity, of the electro magnetic system. — (See Coulomb.) 1 Capacity. — The Farad = Absolute Unit of Cap- 1,000,000,000 acity, or 10 9 units of capacity. (See Farad.) Universal Discharger. — (See Discharger, Universal.) 620 A DICTIONARY OF ELECTRICAL Vacuum, Absolute A space from which all traces of residual gas have been removed. A term sometimes loosely applied to a high vacuum. It is doubtful whether an absolute vacuum is attainable by any physical means. Vacuum, High Such a vacuum that the length of the mean free path of the molecules of the residual atmos- phere ]s equal to, or exceeds, the dimensions of the containing vessel. (See Layer, Crookes'.) Vacuum, Low or Partial Such a vacuum that the mean free path of the molecules of the residual gas is small, as compared with the dimensions of the containing vessel. (See Tubes, Geissler.) In a high vacuum, groups of molecules can move across the containing vessel without meeting other groups of molecules. In a low vacuum, such a group of molecules would be broken up by collision against other groups before reaching the other side of the vessel. Vacuum Pumps.— (See Pumps.) Vacuum Tubes. — (See Tubes, Vacuum.) Valency. — The worth or value of the chemical atoms as regards their power of displacing other atoms in chemical compounds. (See Atomicity.) The worth, or valency, of oxygen is twice as great as that of hydrogen, since one atom of oxygen is able to replace two hydrogen atoms in chemical combinations. Valve-Burner, Electric Argand (See Ar- gand Valve-Burner, Electric.) Valve, Electric An electrically controlled or operated valve. In systems of electro-pneumatic signals, gaseous or liquid pressure controlled by electrically operated valves, is em- ployed to move signals, ring bells, control water and air valves, or to perform other similar work. WORDS, TERMS AND PHRASES. 621 Vapor Globe of Incandescent Lamp.-A glass globe surrounding the chamber of an incandescent electric lamp, for the purpose of enabling the lamp to be safely used in explosive atmospheres, or to permit the lamp to be exposed in places where water is liable to fall on it. Such a vapor globe is shown in Fig. 389. Variable State of Charge of Telegraph Line. — (See State, Variable.) Variation, Annual, Diurn- al, Irregular, Secular. — (See Declination, Magnetic, Va- rieties of.) Variation Chart. — (See Chart, Variation.) Variation Compass.— (See Compass, Variation.) Variation Needle. — (See Needle, Declination.) Variations, Magnetic — (See Magnetic Variations.) Varnish, Electric or Insulating Varnish. — A varn- Fig. 389. ish formed of any good insulating material. Shellac dissolved in alcohol, applied to a thoroughly dried surface and afterwards hardened by baking, forms an excel- lent varnish. Vegetation, Effects of Electricity on Most vegetable fibres contract on the passage of an electric cur- rent through them when in the living plant. 622 A DICTIONARY OF ELECTRICAL Velocity, Angular (See Angular Velocity.) Velocity of Discharge.— The time required for the pass- age of a discharge through a conductor, as compared with its length. By means of a rapidly revolving mirror Wheatstone meas- ured the velocity at which the discharge of aLeyden jar passed through half a mile of copper wire as 288,000 miles per second. The velocity of discharge through long conductors or cables is much lessened by the capacity of the cable and the effects of induction, etc. (See Retardation.) Velocity Ratio. — A remarkable ratio, in the nature of a velocity, that exists between the ratio of the electro-static and the electro-magnetic values of the electric units. This ratio will be understood from the comparison of the following units : Mi li T- 1 L Quantity = j j — = — = V • M* L^ T Here the value of the ratio, viz. , the length divided by the L time, is clearly in the nature of a velocity, for V = — • T Mi ii T-i T 1 Potential = — ^ - = — = — • M? jj t-2 L V L L 2 Capacity = = — =■ = V* • L-i ts t 2 L _i t T 2 1 Resistance = = — = — • L T- 1 L 2 V 2 A remarkable similarity exists between the value of the velocity expressed in C. G. S. units, and the velocity of light, which is of great significance in the electro-magnetic theory of light. (See Light, Electro-Magnetic Theory of.) The velocity of light is, say, 2.9992 X 10 10 centim. per second. The velocity ratio, v, is 2.9800 X 10 10 centimetres per second. WORDS, TERMS AND PHRASES. 623 Ventilation of Armature. — Devices for the free pass- age of air or other fluid through the armature of a dynamo- electric machine in order to prevent its over-heating. (See Dynamo-Electric Machine, Armature, Ventilation of.) Vernier. — A device for the approximately accurate measurement of smaller differences of length than can be readily detected by the eye. There are a variety of vernier scales in use. Vernier Wire Gauge. (See Wire Gauge, Vernier.) Vibration. — A to-and-fro motion of the particles of an elastic medium. (See Waves.) Vibrations, Sympathetic (See Sympathetic Vibrations.) Vis-Viva. — The energy stored in a moving body. Hence, the measure of the amount of work that must be performed in order to bring a moving body to rest. M V The vis-viva = • 2 This term is gradually becoming obsolete. Vitreous Electricity. — A term formerly employed to indicate positive electricity. It was formerly believed that the friction of glass with other bodies always produced positive electricity. The term is now replaced by positive electricity. (See Resinous Electricity.) Volcanic Lightning. (See Lightning, Volcanic.) Volt. — The practical unit of electro-motive force. Such an electro-motive as is induced in a conductor which cuts lines of magnetic force at the rate of 100,000,000 per sec. Such an electro-motive force as would cause a current of one ampere to flow against the resistance of one ohm. Such an electro-motive force as would charge a condenser of the capacity of one farad with a quantity of electricity equal to one coulomb. 624 A DICTIONARY OF ELECTRICAL Volt- Ampere. — The watt or unit of electric power. (See Power, Electric.) Volt-Meter Oalvanometer.— (See Galvanometer, Volt- Meter.) Voltaic Alternatives.— (See Alternatives, Voltaic.) Voltaic Arc. — (See Arc, Voltaic.) Voltaic Battery. — (See Battery, Voltaic.) Voltaic Cell. — An electric source consisting of a voltaic couple and one or two electrolytes. (See Cell, Voltaic.) Voltaic Couple. — Two dissimilar metals, or a metal and a metalloid, capable of acting as an electric source, when dipped in an electrolyte, or capable of producing a difference of electric potential by mere contact. (See Couple, Voltaic.) Liquids and gases are capable of acting as voltaic couples. Voltaic Element. — One of the two substances that form a voltaic couple. (See Couple, Voltaic.) Voltaic Electricity.— Electricity produced by the agency of a voltaic cell or battery. Electricity is the same thing, or phase of energy, by what- ever source it is produced. Voltaic or Current Induction. — A variety of electro- dynamic induction produced by circuits on themselves, or in neighboring circuits. (See Induction, Electro-Dynamic.) Voltameter. — An electrolytic cell employed for measuring the strength of the current passing through it by the amount of chemical decomposition effected in a given time. Various electrolytes are employed in voltameters, such as aqueous solutions of sulphuric acid, copper sulphate, or other metallic salts. In the water voltameter shown in Fig. 390, the battery terminals are connected with platinum electrodes immersed in water slightly acidulated with sulphuric acid, and placed WORDS, TERMS AND PHRASES. 635 inside glass tubes, also filled with acidulated water. On the passage of the current, hydrogen appears at the kathode, and oxygen at the anode, in nearly the proportion of two volumes to one. (See Ozone.) Fig. 390. In the case of sulphuric acid {hydrogen sulphate) the decom- position would appear to be as follows : H 2 S0 4 =H 2 + S0 4 . The hydrogen appears at the electro negative terminal, or kathode. The S0 4 appears at the electro positive terminal or anode, but, combines with one molecule of water, thus, S0 4 -|- H 2 O = H 2 S0 4 -f- O, gaseous oxygen being given off at the anode. measurement of electric currents, because a certain electro- motive force must be reached before electrolysis is effected. The voltameter in reality measures the coulombs, and, therefore, is valuable as a current measurer only when the current is constant. Coulomb-meter would, therefor, be the preferable term. Then, again, time is required to produce the results, and considerable difficulty is experienced in maintaining the cur- 626 A DICTIONARY OF ELECTRICAL rent strength constant, either on account of variations in the electro-motive force of the source, or of variations in the resistance of the voltameter. Voltameter, Siemens' Differential — A form of voltameter employed by Sir Wm. Siemens for de- termining the resistance of the platinum spiral m his electric pyrometer. (See Pyrometer, Electric.) Two separate voltameter tubes provided with platinum electrodes and filled with dilute sulphuric acid, are provided with carefully graduated tubes to determine the volume of the decomposed gases. (See Voltameter.) A current from a battery is divided by a suitable commu- tator into two circuits connected respectively with the two voltameter tubes. In one of these circuits a known resistance is placed, in the other the resistance to be measured, i. e., the platinum coil used in the electric pyrometer. Edison's electric meter consists of a Voltameter. (See Meter, Electric.) Volt-ammeter. — A variety of galvanometer capable of di- rectly measuring both the difference of potential and the am- peres. Volt-Coulomb. — The unit of electric work. The Joule. (See Joule.) Voltmeter. — A galvanometer for measuring the electro- motive force, or difference of potential, between any two points in a circuit. (See Galvanometer.) Vulcanized Fibre. — A variety of insulating material suitable for purposes not requiring the highest insulation. Vulcanized fibre is, however, seriously affected by long ex • posure to moisture. Vulcanite or Ebonite, — A variety of vulcanized rubber extensively used in the construction of electric apparatus. Though an excellent insulator, vulcanite will lose its insu- lating properties by condensing a film of moisture on its sur- WORDS, TERMS AND PHRASES. 627 face. This can be best removed by the careful application of heat. The surface is very liable to become covered by a film of sulphuric acid due to the gradual oxidation of the sulphur. Mere friction will not remove this film, but it may be removed by washing with distilled water. A thick coating of varnish will obviate this last defect. Watchman's Electric Register. — A device for per- manently recording the time of a watchman's visit to each locality he is required to visit at stated intervals. These registers are of a variety of forms. They consist, how- ever, in general, of a drum or disc of paper driven by clockwork, on which a mark is made by a stylus or pencil, operated by the closing of a circuit by a push button pressed or key turned by the watchman at each station. Water Battery.— (See Battery, Water.) Water Dropping Accumulator.— (See Accumulator, Water Dropping.) Water, Electrolysis of ■ — The decomposition of water by the passage through it of an electric current. When pure, water does not appear to conduct electricity ; it is therefore not quite certain that pure water can be elec- trolytically decomposed. The addition of a small quantity of sulphuric acid, or of a metallic salt, however, renders its elec- trolysis readily accomplished. Water-Eevel Alarm. — (See Alarm, Liquid Level.) Water Pyrometer.— (See Pyrometer, Water.) Watches, Demagnetization of Pro- csesses for readily removing magnetism from watches. The demagnetization of watches can be readily effected by a method proposed by J. J. Wright. The watch is held by its chain and slowly lowered to the bottom of a hollow conical coil of wire, and then slowly withdrawn from the coil. 628 A DICTIONARY OF ELECTRICAL The wire is wound on the coil, as shown in Fig. 391, in the shape of a cone, viz., with a single turn at the top, and gradually increasing in number of turns towards the bottom. The conical coil is con- nected with a source of rapidly alternating cur- rents. As the watch is low- ered in the coil, it be- comes gradually mag- netized more and more powerfully with oppo- site polarities, thus com- pletely reversing* and removing any polarity it previously possessed. As it is now slowly raised from out the hollow cone, this magnetization be- comes less and less, until, Ftg ' 39L if removed from the coni- cal coil while high above its apex, all sensible traces of mag- netism will have disappeared. Watt.— The volt-ampere, or unit of electric work. (See Work, Electric, Unit of .) Watt-Hour, Watt-Minute, Watt-Second.— Units of work. Terms employed to indicate the expenditure of an electrical power of one watt, for an hour, minute, or second. Watt-Meter.— A galvanometer by means of which the simultaneous measurement of the difference of potential and the current passing is rendered possible. The Watt-Meter consists of two coils of insulated wire, one coarse and the other fine, placed at right angles to each other WORDS, TERMS AND PHRASES. 629 as in the ohm-meter, only instead of the currents acting on a suspended magnetic needle, they act on each other, as in the electro-dynamometer. Waves, Amplitude of —(See Amplitude of Waves.) Waves, Eleetric (See Oscillations, Electric.) Fig. 392. Waves of Condensation and Rarefaction.— The alternate spheres of condensed and rarefied air by means of which sound is transmitted. (See Sound Waves.) Weber. — A term formerly employed for the unit of elec- tric current, and replaced by ampere. (See Ampere.) 630 A DICTIONARY OF ELECTRICAL Weber. — A term proposed by Clausius and Siemens for a magnetic pole of unit strength but not adopted. This same term was also employed to designate the unit strength of current. Now replaced by the term ampere. Weight, Atomic (See Atomic Weight.) Weight, Breaking of Telegraph Wires.— (See Breaking Weight of Telegraph Wires.) Welding, Electric Effecting- the welding- union of metals by heat of an electric origin. In the process of Elihu Thomson, the metals are heated to electric incandescence by currents obtained from inverted induction coils, and are subsequently pressed or hammered together. Fig. 392, shows the Thomson apparatus for the Direct System of Electric Welding. The dynamo is combined with the weld- ing apparatus. The armature contains two separate wind- ings ; one of fine wire, in series with the field magnet coils, and another of very low resistance, being formed of a U-shaped bars of copper. No commutation is used, the alter- nating currents being- well adapted for heating* purposes. The terminals of these poles are, therefore, directly connected to the clamps that hold the bar to the welder. Fig. 393, shows the apparatus for the Thomson Indirect System of Electric Welding. This system is applicable to heavy work, and cases where more than one welding- ma- chine is operated by the current from a single dynamo. In this case a high tension current is converted into the large welding- current employed by means of a suitably proportioned transformer. The welding process is the same in either system, and con- sists essentially in leading the welding current into the pieces to be united near their points of junction when brought into firm end contact. As the current is lead across the junction the temperature rises sufficiently to soften the metal, when WORDS, TERMS AND PHRASES. 631 the pieces are firmly pressed together by the motion, of the clamps or holders. In the process of Benardos and Olzewski, the heat of the vol- taic arc is employed for a somewhat similar process. Wheatstone's Balance. — (See Balance, Wheatstone 1 s.) Wheel, Barlow'§ or Sturgeon's (See Disc, Faraday's.) Fig. 393. Wheel, Phonic See Phonic Wheel.) Wheel, Reaction (See Reaction Wheel.) Whirl, Electric A term employed to indicate the circular direction of the lines of magnetic force surround- ing a conductor conveying an electric current. See Field Electro Magnetic,) 632 A DICTIONARY OF ELFCTRICAL Whistle, Automatic Electric Steam steam whistle, employed on foggy days in some systems of rail- way signals, when the visual signals can not be seen, in which the passage of the steam through the whistle is automatically obtained by the closing of an electric contact, or the passage of the locomotive over a certain part of the track. Wimsliurst Electrical Machine.— A form of convec- tion electric machine invented by Wimsliurst. Like the Holtz ma- chine, the Wimshurst machine is a convection induction machine. It is, however, more effi- cient in action, and will probably soon super- sede the former ma- chine. The Wimshurst machine consists of two shellac-varnished glass plates, that are rapidly rotated in opposite di- rections. Thin metal- lic strips are placed on the outside of each of the plates, in the radial positions shown m Fig, 394. These metal strips act both as inductors and carriers; the carrier of one plate acting as an inductor to the other plate. Two curved brass rods, terminating in fine wire brushes that touch the plates, are placed as shown, one at the front of the plate, and one at the back, at right angles to each other. Pairs of conductors, connected together, provided with collect- ing points, are placed diametrically opposite each other, as shown. Sliding conductors, terminated with metallic balls, are provided for discharging the conductors. Leyden jars Fig. SOU. WORDS, TERMS AND PHRASES. 633 the inner coatings of which are connected with the two dis- charging rods, and the outer coatings together may be em- ployed in this as in the Holtz machine. The exact action of this machine is not thoroughly under- stood. Wind, Electric The convection stream of air particles produced at the extremities of points attached to the surface of charged, insulated conductors. (See Convection, Electric. Flier, Electric.) Fig 305. Windage of Dynamo. — A term proposed for the air gap between the armature and the pole pieces of a dynamo. Winding, Compound (See Compound Wound DynaniO-Electric Machine.) Winding*. Ampere — (See Turns, Am- pere.) 634 A DICTIONARY OF ELECTRICAL of Coils.— (See Bi-Filar for accurately measuring the B C Hi r&\ . D Windings, Bi-Filar — Windings of Coils.) Wire Gauge. — A device diameter of a wire. The round wire gauge, shown in Fig. 395, is very generally used for telegraph lines. Notches of varying widths, cut in the edges of a circular plate of tempered steel, serve to ap- proximately measure the diameter of a wire, the side of the wire being passed through the slots. Numbers, indicating the different sizes of the wire, are affixed to each of the openings. Wire Gauge, Vernier or Micro meter A gauge employed for accurately measuring the diameter of a wire in thousandths of an inch, based on the principle of the vernier or micrometer. See Fig. 396. The wire to be measured is placed between a fixed support B, and the end C, of a long mov- able screw, which accurately fits a threaded tube a. A thimble D, provided with a milled head fits over the screw C, and is attached to the upper part. The lower civ- Fig. 396. cumference of D, is divided into a scale of 20 equal parts. The tube a, is graduated into divisions equal to the pitch of the screw. Every fifth of these divisions is marked as a larger division. The principle of the operation of the gauge is as follows : Suppose the screw has 50 threads to the inch, the pitch of the screw, or the distance between two contiguous threads, is, therefore, ■£$, or .02 of an inch. One complete turn of the screw will therefore advance the sleeve D, over the scale a, the .02 inch. If the screw is only moved through one of the 20 parts marked on the end of the thimble or sleeve parts, or the ^ of a complete turn, the end *"• £', tw or -001 inch. w words, terms and phrases. 635 Suppose, now, a wire is placed between B and C, and the screw advanced until it fairly fills the space between them, and the reading shows two of the larger divisions on the scale a, three of the smaller ones, and three on the end of the sleeve D. Then 2 larger divisions of scale a = 0.2 inch 3 smaller divisions of scale a = .06 3 divisions on circular scale on D = .006 Diameter of wire = 0.266 Serious inconvenience has arisen in practice from the numerous arbitrary numbers or sizes of wires employed by different manufacturers. These differences are gradually leading to the abandonment of arbitrary sizes for wires, and employing in place thereof, the diameters directly in inches or thousands of an inch. Wire, Grounded (See Ground or Earth.) Wire, Insulated Wire covered with any insu- lating material. Cotton and silk are generally employed for insulating pur- poses, either alone, or in connection with various gums, resins, oi* other materials, which are plastic when heated, but which solidify on cooling. India rubber, caoutchouc, and various mixtures and compounds are also employed for the same purpose. For most of the purposes of line wires, high insulating powers, combined with a low specific inductive capacity, is required in the insulating materials. For overhead wires a waterproof covering is necessary. In the neighborhood of combustible materials, some fireproof covering is desirable. Wires, Conduictibility and Sizes of . The following tables give the resistance, size, weight per foot, etc., of wire according to some of the principal wire gauges. 636 A DICTIONARY OF ELECTRICAL Number, Diameter, Weight, Length, and Resistance of Pure Copper Wire. AMERICAN GAUGE. Weight Resistance of Pure Copper Diara. Sp. Gr. -8.889. Length. at 70° Fahrenheit. Grs. per Ft. Lbs. Ohms Feet No. Inches. per 1000 Ft. per per 1000 per Ohms per feet. Lb. Ft. Ohm. Lb. 0000 .460 4475.33 639.33 1.56 .051 19605.69 .0000798 000 .40964 3549.07 507.01 1.97 .064 15547.87 .000127 00 .36480 2814.62 402.09 2.49 .081 12330.36 .000202 .32495 2233.28 319.04 3.13 .102 9783.63 .000320 1 .28930 1770.13 252.88 3.95 .129 7754.66 .00051 2 .25763 140379 200.54 4.99 .163 6149.78 .000811 3 .22942 1113.20 159.03 6.29 .205 4S76.73 .001289 4 .20431 882.85 126.12 7.93 .259 3867.62 .00205 5 .18194 700.10 100.01 10.00 .326 3067.06 .00326 6 .16202 555.20 79.32 12.61 .411 2432.22 .00518 7 .14428 440.27 62 90 15.90 .519 1928.75 .00824 8 .12849 349.18 49.88 20.05 .654 1529.69 .01311 9 .11443 276.94 3956 25.28 .824 1213.22 .02083 10 .10189 219.57 31.37 31.88 1.040 961.91 .03314 11 .09074 174.15 24.88 40.20 1.311 762.93 .05269 12 .08081 138.11 19.73 50.69 1.653 605.03 .08377 13 .07196 109.52 15.65 63.91 2.084 479.80 .13321 14 .06408 86.86 12.41 80.5!) 2.628 380.51 .2118 15 .05706 68.88 9.84 101.63 3.314 301.75 .3368 16 .05082 54.63 7.81 128.14 4.179 239.32 .5355 17 .04525 43.32 6.19 161.59 5.269 189.78 .8515 18 .04040 34.35 4.91 203.76 6.645 150.50 1.3539 19 .03589 26.49 3.78 264.26 8.617 116.05 2.2772 20 .03196 21.61 3.09 324.00 10.566 94.65 3.423 21 .02840 17.13 2.45 408.56 13.323 75.06 5.443 22 .025347 13.59 1.94 515.15 16.799 59.53 8.654 23 .022571 10.77 1.54 649.66 21.185 47.20 13.763 24 .0201 8.54 1.22 819.21 26.713 37.43 21.885 25 .0179 6.78 .97 1032.96 33.684 29.69 34.795 26 .01594 5.37 .77 1302.61 42.477 23.54 55.331 27 .014195 4.26 .61 1642.55 53.563 18.68 87.979 28 .012641 3.38 .48 2071.22 67.542 14.81 139.893 29 .011257 2.68 .38 2611.82 85.170 11.74 222.449 30 .010025 2.13 .30 3293.97 107.391 9.31 353.742 31 .008928 1.69 .24 4152.22 135.402 7.39 562.221 32 .00795 1.34 .19 5236.66 170.765 5.86 894.242 33 .00708 1.06 .15 6602.71 215.312 4.64 1421.646 34 .0063 .84 .12 8328.30 271.583 3.68 2261.82 35 .00561 .67 .10 10501.35 342.413 2.92 3596.104 36 .005 .53 .08 13238.83 431.712 2.32 5715.36 37 .00445 .42 .06 16691.06 544.287 1.84 9084.71 38 .003965 .34 .05 20854.65 686.511 1.46 14320.26 39 .003531 .27 .04 26302.23 865 0(6 1.16 22752.6 40 .003144 .21 .03 33175.94 109-865 .92 36223.58 WORDS, TERMS AND PHRASES. 637 Table Showing the Difference between Wire Gauges. London. Stubs. Brown & Sharpe's , .454 .460 .425 .425 .40964 .380 .380 .36480 .340 .340 .32495 .300 .300 .28930 .284 .284 .25763 .259 .259 .22942 .238 .238 .20431 .220 .220 .18194 .203 .203 .16202 .180 .180 .14428 .165 .165 .12849 .148 .148 .11443 .134 .134 .10189 .120 .120 .09074 .109 .109 .08081 .095 .095 .07196 .083 .083 .06408 .072 .072 .05706 .065 .065 .05082 .058 .058 .04525 .049 .049 .04030 .040 .042 .03589 .035 .035 .03196 .0315 .032 .02846 .0295 .028 .025347 .027 .025 .022571 .025 .022 .0201 .023 .020 .0179 .0205 .018 .01594 .01875 .016 .014195 .0165 .014 .012641 .0155 .013 .011257 .01375 .012 .010025 .01225 .010 .008928 .01125 .009 .00795 .01025 .008 .00708 .0095 .007 .0063 .009 .005 .00561 .0075 =004 .005 .0065 .00445 .00575 .003965 .005 .003531 .0045 .003144 638 A DICTIONARY OF ELECTRICAL New Legal Standard Wire Gauge (English). Tables of Sizes, Weights, Lengths and Breaking Strains of Iron Wire. Size on Diameter. Section- al area Weight of Length of Cwt. Breaking strains Size on Wire Gauge. Inch. Mi lie- metres. in sq. inches. 100 yards Mile. Lbs. Anneal- ed. Bright. Wire Gauge Lbs. Yards. Lbs. Lbs. 7/0 .500 12.7 .1963 193.4 3404 58 10470 15700 7/0 6/0 .464 11.8 .1691 166.5 2930 67 9017 13525 6/0 5/0 .432 11. .1466 144.4 2541 78 7814 11725 5/0 4/0 .400 10.2 .1257 123.8 2179 91 6702 10052 4/0 3/0 .372 9.4 .1087 107.1 1885 105 5796 8694 3/0 2/0 .348 8.8 .0951 93.7 1649 120 5072 7608 2/0 1/0 .324 8.2 .0824 81.2 1429 138 4397 6595 1/0 1 .300 7.6 .0707 69.9 1225 161 3770 5655 1 2 .276 7. .0598 58.9 1037 190 3190 4785 2 3 .252 6.4 .0499 49.1 864 228 2660 3990 3 4 .232 5.9 .0423 41.6 732 269 2254 3381 4 5 .212 5.4 .0353 34.8 612 322 1883 2824 5 6 .192 4.9 .0290 28.0 502 393 1544 2316 6 7 .176 4.5 .0243 24. 422 467 1298 1946 7 8 .160 4.1 .0201 19.8 348 566 1072 1608 8 9 .144 3.7 .0163 16. 282 700 869 1303 9 10 .128 3.3 .0129 12.7 223 882 687 1030 10 11 .116 3. .0106 10.4 183 1077 564 845 11 12 .104 2.6 .0085 8.4 148 1333 454 680 12 13 .092 2.3 .0066 6.5 114 1723 355 532 13 14 .080 2. .0050 5. 88 2240 268 402 14 15 .072 1.8 .0041 4. 70 2800 218 326 15 16 .064 1.6 .0032 3.2 56 3500 172 257 16 17 .056 1.4 .0025 2.4 42 4667 131 197 17 18 .048 1.2 .0018 1.8 32 6222 97 145 18 19 .040 1. .0013 1.2 21 9333 67 100 19 20 .036 .9 .0010 1. 18 11200 55 82 20 (Issued by the Iron and Steel Wire Mfrs. Association.) Wires, Cross (See Cross, Electric.) Wires, Crossing. (See Crossing Wires. WORDS, TERMS AND PHRASES. 639 Wood's Button Repeater.— (See Repeater, Tele- graphic.) Work, Electric.— The Joule. (See Joule.) Work, Electric, Unit of The volt-coulomb or joule. (See Volt- Coulomb. Joule.) Work, Unit of The erg. (See Erg.) Yokes of Electro Magnet. — The solid cross pieces of iron that join the ends of the field magnet coils of dynamo elec- tric machines, or of electro magnets generally. Zero Methods.— (See Null Methods.) Zero Potential. — The potential that would exist at an infinite distance from any electrified body. In practice, the potential of the earth is regarded as the zero potential. (See Potential, Zero.) Zig-zag Lightning. — Forked lightning, (See Lightning, Zig-zag.) Zinc, Amalgamation of The covering or amal- gamation of zinc with a layer of mercury. To amalgamate a plate of zinc, its surface is first thoroughly cleaned by immersing the plate in dilute sulphuric acid of about one part of acid to ten or twelve parts of water, A few drops of mercury are then rubbed over its surface, thus coat- ing it with a bright metallic film of zinc amalgam. Care must be taken not to use too much mercury, since the zinc plate will thus be rendered brittle. The necessity for amalgamating the zinc arises from the loss of energy through local action, on ordinary plates. The action of the amalgam appears to be to cover the sur- face of the zinc plate with a layer of chemically pure zinc. On the polarization of the battery on closing its circuit the zinc ends of the zinc-amalgam are turned towards the negative plate, thus in effect producing a plate of chemically pure zinc. 640 A DICTIONARY OF ELECTRICAL, ETC. Zincode of Voltaic Cell. — A term formerly employed to indicate the zinc terminal or electrode of a voltaic cell. The negative electrode or kathode, are preferable terms. Zone, Polar A term proposed by De Watteville for the zone or region surrounding the therapeutic electrode applied to the human body for electric treatment. Zone, Peripolar A term proposed by De Watte- ville for the zone or region surrounding the polar zone on the body of a patient under electro therapeutic treatment. Zinc Sender. — A device employed in telegraphic cir- cuits, in which, in order to counteract the retardation pro- duced by the charge given to the line, a momentary reverse current is sent into the line after each signal. A zinc sender generally consists of a low resistance Siemens relay introduced between the line and the front contact of the signaling key. THE END. APPENDIX Balance or Neutral-Wire Ampere Meter.— An ampere meter placed in the circuit of the neutral wire, in a three-wire system of electric distribution, for the purpose of showing tie excess of current passing over one side of the system as compared with the other side, when the central wire is no longer neutral. Balanced metallic Circuit. — A metallic circuit, the two sides of which have similar electrical properties. Banked Battery.— (See Battery, Banked.) Battery, Banked. — A term sometimes applied to a bat- tery from which a number of separate circuits are supplied with current. The term, banked battery, is sometimes applied to a multi- ple-arc connected battery. Bed* Piece of Dynamo Electric Machine. — The frame on which a dynamo is supported. The bed-piece is sometimes called the dynamo frame. Bell, Night. (See Night Bell) Board, Cro§§-Connecting. (See Cross Con- necting Board.) Box, Cable. (See Cable Box.) Box, Junction. (See Junction Box.) Branch. — A term applied to any principal distributing conductor from which outlets are taken, or taps made. Break-Down Switch. — A special switch, employed in small three-wire systems, for connecting the positive and nega- tive bus-wires in such a manner as to permit the system to be supplied with current from the dynamo in use on one side of the system only. a APPENDIX. Bridges. — Heavy copper wires suitably shaped for connect- ing the dynamo electric machines in a station to the bus-rods or wires. Bug'. — A term originally limited to quadruplex telegraphy to designate any fault in the operation of the apparatus. This term is now employed, to a limited extent, for faults in the operation of electric apparatus in general. Bug-Trap. — Any device employed to overcome the "bug" in quadruplex telegraphy. Bu§-Rod§ or Wires. — Heavy copper rods employed in a station, to which all the generating dynamos are connected and from which the current passes to the different points of the distribution system over the feeders. Cable Box. — A receptacle provided for holding and secur- ing the terminals of a cable, or underground conductor. Cable Laid-Up in Layers. — A term applied to a cable, all the wires of which are in layers. Cable Laid-Up in Reversed Layers.— A term ap- plied to a cable in which the conductors, in alternate layers, are twisted in opposite directions. Cable Laid-Up in Twisted Pairs. — A term applied to a cable in which every pair of wires is twisted together. Calling-Drop. — An annunciator drop employed to indi- cate to the operator in a telegraphic or telephonic system that one subscriber wishes to be connected with another. Calling- Wire. — A wire employed in a telegraphic or telephonic system, by means of which a subscriber communi- cates with the central office, or one central office communi- cates with another. Cam, Listening. (See Listening Cam.) Capacity of a Cable.— The electrostatic capacity of one conductor of a cable as compared with the capacity of the remainder of the conductors grounded. APPENDIX. 3 Centre of Distribution.— In a system of multiple-distri- bution, a place where branch cut-outs and switches are placed in order to control communication therewith. Climbers and Straps.— Devices employed by linemen for climbing wooden telegraph poles. Colombin. — A name applied to the insulator between the parallel carbons of the Jablochkoff candle, consisting of a mixture of sulphate of barytes and sulphate of lime. Commutating Transformers, Distribution by (See System of Electrical Distribution by Commu- tating Transformers.) Condensers, System of Alternate Current Distri- bution by IHeans of (See System of Alternate Current Distribution by Means of Condensers.) Condensers, System of Continuous Current Dis- tribution by Means of (See System of Continu- ous Current Distribution by Means of Condensers.) Contraplcx Telegraphy.— A name given to a special system of duplex telegraphy. Cross Arm. — A horizontal beam attached to a pole for the support of telegraph, electric light and other electric wires. Cross Connecting Board.— In a system of telegraphic or telephonic communication, a board to which the line ter- minals are run before entering the switchboard, so as to readily place any subscriber on any desired section of the switchboard, Cross Connection, Telephonic A device em- ployed in systems of telephonic communication for the pur- pose of lessening the bad effects of induction, in which equal lengths of adjacent parallel wires are alternately crossed so as to alternately occupy the opposite sides of the circuit. Cross-Talk.. — In telephony an indistinctness in the speech transmitted over any circuit due to this circuit receiving, * APPENDIX. either by accidental contacts or by induction, the speech transmitted over neighboring circuits. Curb, Double (See Double Curb.) Curb Signaling.— In cable telegraphy a system for avoid- ing the effects of retardation by rapidly discharging the cable before another electric impulse is sent into it, not by connect- ing it to earth, but by reversing the battery and then connect- ing to earth before beginning the next signal. Curb Signaling, Double Curb In curb signal- ing, a method by which the cable, after connection with the battery for sending a signal, is subjected to a reverse battery, but instead of being put to earth after this connection as in single curb signaling, the battery is again reversed and con- nected to earth. The time during which the cable is connected to the re- versed battery before being put to earth, that is, the time during which it receives the positive and negative currents may be made of any suitable duration. Curb Signaling, Single Curb In curb signaling, a method by which the cable after connection with the battery for sending a signal, is subjected to a reverse battery current and then put to earth before again being connected to the battery for sending the next signal. Cut-out, Duplex (See Duplex Cut-out.) Decalescence. — A term proposed by Prof. Elihu Thom- son for the absorption of sensible heat which occurs at a cer- tain point during the heating of a bar of steel. Decalescence will thus be observed to be the reverse of recalescence, which is the phenomenon of the emission of sensible heat at a certain point during the cooling of a heated bar of steel. (See Recalescence.) Distribution of Continuous Currents by Means of Condensers. — (See System of Continuous Current Distribution by Means of Condensers.) APPENDIX. 5 Double Curb. — An instrument invented by Sir William Thomson, employed in curb signaling-, by means of which the signals are made and the curb, either single or double, in any required proportion, is applied automatically. Double Curb Signaling. — (See Curb Signaling, Double Curb.) Double Plug. — A plug so constructed that when in- serted in a spring-jack it makes two connections, one at its point and one at its shank. (See Spring Jack.) Double Trolley System of Electric Railroad*.— A system of electric railroad propulsion, in which a double trolley is employed to take the the driving current from the overhead wires. The double trolley system differs from the single trolley system in that it employs no earth return. The parallel wires also avoid the effects of injurious induction in neighbor- ing telegraph or telephone wires. Duplex Cut-out. — A cut-out so arranged that when one box is fused or melted by an abnormal current, another can be immediately substituted for it. Electric Thermo Call.— An instrument for sounding an alarm when the temperature rises above, or falls below, a fixed point. In one form of this instrument a needle is moved over a dial by a simple thermic device and rings a bell when the tempera- ture for which it has been set is attained. The thermo-call is applicable to the regulation of the temperature of dwell- ings, incubators, hot houses, breweries, drying rooms, etc. Feeder. — One of the conducting wires or channels through which the current is distributed to the main con- ductors. Feeder-Switch. — The switch employed for connecting or disconnecting each conductor of a feeder from the bus-bars in a central station. b APPENDIX. Feeder-Equalizer,— An adjustable resistance placed in the circuit of a feeder for the purpose of regulating the difference of potential at the junction box. Fire Balls. — A term sometimes applied to globular light- ning. (See Lightning, Globular.) Force de Cheval.— The French term for horse power. The force de cheval is equal to 32,560 foot pounds per minute. Frame of Dynamo Electric Machine.— The bed piece that supports a dynamo electric machine. The frame is sometimes called the dynamo bed piece. Graduators. — Devices, generally electro magnets, in- serted in a circuit so as to obtain the makes and breaks, required in a system of telegraphy, so gradually that they fail to influence the diaphragm of a telephone placed in the same circuit, and thus to permit a simultaneous telegraphic and telephonic transmission over the same wire. Ground Detector. — In a system of incandescent lamp distribution, a device, placed in the central station, for show- ing by the candle power of a lamp, the proximate location of a ground on the system. Horse Power of Water.— The Indian Government's term for horse power developed by falling water. The estimate is made by the following simple rule : 15 cubic feet of water falling per second through one foot equals 1 horse power. House Main. — A term employed in a system of multiple incandescent lamp distribution for the conductor connecting the house service conductors with a centre of distribution. House-Service Conductor. — A term employed in a system of multiple incandescent lamp distribution for that portion of the circuit which is included between the service cut-out and the centre or centres of distribution, or between this cut-out and one or more points on house mains. APPENDIX. 7 Hysteresis. — Molecular friction to magnetic change of stress. That property of a medium in virtue of which work is done in changing the direction or intensity of magnetic force among its parts. Intercrossing. — In a system of telephonic communica- tion, a device for avoiding the disturbing effects of induction by alternately crossing equal sections of the line. (See Cross- Connections, Telephonic.) Joint, Sleeve. (See Sleeve Joint.) Junction Box. — A moisture-proof box provided in a system of underground conductors to receive the terminals of the feeders, and in which connection is made between the feeders and the mains from which the current is distributed to the individual consumer. Kinetic Theory of Matter. — A theory which assumes that the molecules of matter are in a constant state of motion or vibration towards, or from, one another. Applying the kinetic theory of matter to gases, the mole- cules of which have great freedom of motion, the mole- cules are so far removed from one another as to be but little, if any, influenced by their mutual attractions. They are therefore assumed to move in straight lines with very great velocity until they collide against one another, or against the sides of the containing vessel, when they are reflected and again run in straight lines in a new path. Leg. — In a system of telephonic exchange, a single wire, where a ground system is used, or two wires where a metallic circuit is employed, for connecting a subscriber with the main switchboard, by means of which the subscriber may be legged or placed directly in circuit with two or more parties. Legging Key-Board. — A key-board employed for the purpose of legging an operator into the circuit connecting two or more subscribers. 8 APPENDIX. Lines, Overhead. (See Overhead Lines.) Listening Cam. — In a telephonic exchange system a metallic cam by means of which the operator is placed in cir- cuit with a subscriber. Main Feeder. — (See Standard or Main Feeder.) Main, House (See House Main.) Mains, Street (See Street Mains.) Matter, Kinetic Theory of (See Kinetic Theory of Matter.) Motor-Generators. — Dynamo-electric generators in which the power required to drive the dynamo is obtained from an electric current. Motor generators are used in systems of electrical distribu- tion for the purpose of changing the potential of the current. They consist of dynamos, the armatures of which are furnished with two separate windings, of fine and of coarse wire respect- ively. One of these, generally the fine wire, receives the driving or motor current, usually of high potential, and the other, the coarse wire, furnishes the current used, usually of low potential. Motor-Generators, System of Electric Distribu- tion by (See System of Electric Distribution by Motor- Generators.) Neutral Relay Armature. — A term applied in contra- distinction to a polarized relay armature, in which the relay armature, consisting of a piece of soft iron wire, closes a local circuit whenever its electro-magnet receives an impulse over the main line. (See Polarized Armature.) Neutral Wire. — The middle wire of a three-wire system of electric distribution. Night Bell. — In a telephone exchange, a bell switched into connection with the shunted circuit of an annunciator APPRNDIX. 9 case, and provided for calling the attention of the night operator by its constant ringing to the falling of a drop. Outlet. — In a system of incandescent lamp distribution the point of attachment for a socket in a fixture. Overhead Line. — A term applied to telegraph, tele- phone, and electric light or power lines that run overhead, in contradistinction to similar lines placed underground. Phantom Wires. — A term applied to the additional cir- cuits or wires obtained in any single wire or conductor by the use of some multiplex telegraphic system. (See Telegraphy, Multiplex. Synchronous Multiplex System of Telegraphy.) Plionopli'x Telegraphy. — A system of telegraphic transmission in which pulsatory currents, superposed on the ordinary Morse currents, actuate a modified telephonic re- ceiver, and thus permit the simultaneous transmission of several separate messages over a single wire without inter- ference. Platy meter. — An instrument invented by Sir William Thomson for comparing the capacities of two condensers. Plug's. — Metallic connections in the shape of plugs for making or breaking circuits by placing them in, or removing them from, metallic sockets connected with the circuits to be made or broken. Plugging. — Completing a circuit by means of plugs. Recalescence. — The property, first pointed out by Bar- rett, possessed by steel when cooling after being heated to in- candescence, of again becoming incandescent after a certain degree of cooling has been effected. A steel wire heated at the middle or near one end to a bright red, and allowed to cool in a dim light, will be ob- served to cool until a low red heat is reached, when it will be observed to reheat at some point in the originally heated por- tion. This re-heating is manifested by a brighter red spot 10 APPENDIX. which moves along the portion originally heated. This reheat- ing is called recalescence, and is due to latent heat (potential energy) which, disappearing when the bar was heated, again becomes sensible^kinetic energy) on cooling. The temperature at which recalescence takes place is sensibly the temperature at which heated steel regains its magnetizability. Relay Armature, Neutral (See Neutral Relay Armature.) Service Conductor, House (See House Service Conductor.) Service, Street (See Street Service.) Single Curb Signaling.— (See Curb Signaling, Single Curb.) Sleeve Joint. — A method of joining conducting wires by passing them through tubes and then twisting and soldering. Stackling a Wire. — Placing an insulator between the two ends of a cut wire. Standard or Main Feeder. — The main feeder to which the standard pressure indicator is connected, and whose pres- sure controls the pressure at the ends of all the other feeders. The term pressure in the above definition is used in the sense of electro-motive force or difference of potential. Street Main§. — In a system of incandescent lamp distri- bution the conductors through which the current is distri- buted from the feeder ends, through cut-outs, to the district to be lighted, and from which service wires are taken. Street Service. — In a system of incandescent lamp distri- bution that portion of the circuit which is included between the main and the service cut-out. Switch, Break Down —(See Break Down Switch.) APPENDIX. 11 System of Alternate Current Distribution by Means of Condensers. — A system of alternate current distribution in which condensers are employed to transform current charges of high potential received from an alternat- ing current dynamo, to charges of low potential which are fed to the lamps or other electro-receptive devices. In the system of McElroy the conversion from high to low potential is obtained by making the plates of the condensers charged by the dynamo, or primary plates, smaller than the secondary plates, the ratio of the area of the primary plates to that of the secondary plates being made in accordance with the ratio of conversion desired. System of Coi tin nous Current Distribution by Heans of Condensers. — A system of distribution devised by Doubrava in which a continuous current is conducted to certain points in the line where a device called a " disjunctor " is employed to reverse it periodically and the reversed currents so obtained directly used to charge condensers in the circuit of which induction coils are placed. The condensers are used to feed incandescent lamps or other electro-receptive devices. System of Electrical Distribution by Commuta- ting Transformers. — A system of electrical distribution in which motor-generators are used, but neither the armature nor the field magnets are revolved, a special commutator being employed to change the polarity of the magnetic circuits. System of Electric Distribution by Motor- Generators. — A system of electric distribution in which a continuous current of high potential, distributed over a main line, is employed at the points where its electric energy is to be utilized for driving a motor, which in turn drives a dynamo, the current of which is used to energize the electro-receptive devices. 12 APPENDIX. In another system of motor-generators the motor and dynamo are combined in one machine with a double wound armature, the fine wire coils in which receives the high potential driving current and the coarse wire coils furnish the low potential current used in the distribution circuits. System of Simultaneous Telegraphy and Tele- phony over a Single Wire.— A system for the simul- taneous transmission of telegraphic and telephonic messages over a single wire. These systems are based, in general, on the fact that a gradual make and break in a telephone circuit fails to appreci- ably affect a telephone diaphragm. By the use of graduators the makes and breaks required for the transmission of the tele- graphic dispatch are effected so gradually that they fail to appreciably influence the telephone diaphragm and thus per- mit simultaneous telegraphic and telephonic transmission over a single wire. (See Graduators.) Tailings. — False markings received in systems of auto- matic telegraphy, due to retardation. Telegraphy, Contraplex (See Contraplex Telegraphy.) Telegraphy, Phonoplex —(See Phonoplex Telegraphy.) Thermo Call, Electric (See Electric Thermo Call.) Thermolysis. — A term applied to the chemical decom- position of a substance by heat. Thermolysis, or dissociation, is an effect produced by the action of heat somewhat similiar to the effect of electrolysis, or chemical decomposition produced by the passage of an electric current. When a chemical substance is heated, the vibration of its molecules is attended by an inter-atomic vibration of its constituent atoms so that a decomposition ensues. If the temperature is not excessive these liberated APPENDIX. 13 atoms recombine with others which they meet, but at higher temperatures such recombination is impossible and a perma- nent decomposition ensues, called thermolysis or dissociation. Torque. — The stress on a shaft due to electro-magnetic action, that is, the turning effort exerted by the armature of a motor, for instance, under the influence of the current. The torque is usually measured in pounds of pull at the end of a radius or arm 1 foot in length. Transposing. — In a system of telephonic communication a device for avoiding the bad effects of induction by alter- nately crossing equal consecutive sections of the line. (See Cross- Connection, Telephonic.) Trolley System, Double for Electric Rail- roads. — (See Double Trolley System of Electric Railroads. Trunk Lines. — In a system of telephonic communica- tion lines connecting distant stations and used by a number of subscribers at each end for purposes of intercommunication. Triiiiking Switchboard.— A switchboard in which a few subscribers only are connected with the operator, thus enabling him to obtain any other subscriber by means of trunk wires extending to the other sections. Units and Terms, Proposed Wew The fol- lowing units and terms have recently been proposed by Oliver Heaviside, but have not been generally accepted or adopted. These definitions are given in Mr. Heaviside's language. " Conductance. — Capacity for conducting electricity. "Numerically, the ratio, in absolute measure, of the current strength to the total electro-motive force in a circuit of uni- form flow. A quantity with the nature of a slowness or re- ciprocal to a velocity. The practical unit is called the mho." "Conductivity. — Conductance per unit volume." (i Elastance. — Capacity of a dielectric for opposing electric charge or displacement. 14 APPENDIX. "Numerically, the ratio, in absolute measure, of the differ- ence of potential in an electrostatic circuit to the total charge or displacement therein produced. The reciprocal of per- mittance and a quantity of the inverse nature of a length." "Elastivity. — Elastance per unit volume of dielectric." "Impedance. — Capacity for opposing the variable flow of electricity. " Numerically, in the absolute measure, the ratio of the total electro-motive force to the current strength at any instant in a circuit of variable flow. A quantity with the nature of a velocity and in any circuit always greater than the resistance." "Inductance. — Capacity for magnetic induction. " Numerically, in absolute measure, the number of unit lines of magnetic force linked with a circuit traversed by the unit current strength. Sometimes alluded to as the coefficient of self induction. A quantity of the nature of a length." "Inductivity. — Specific capacity for magnetic induction. " The numerical ratio of the induction in a medium to the induction producing it." "Permittance. — Electrostatic capacity. Capacity of a dielec- tric for assisting charge or displacement. "Numerically, the ratio, in absolute measure, of the total charge or displacement in an electrostatic circuit, to the dif- ference of potential producing it. A quantity with the nature of a length." "Permittivity. — The numerical ratio of the permittance of a dielectric to that of air. "Also known as specific inductive capacity." "Reluctance. — Capacity for opposing magnetic induction. "Numerically, the ratio, in absolute measure, of the magneto- motive force in a magnetic circuit to the total induction therein produced. A quantity with the nature of the reciprocal of a length. Sometimes described as magnetic resistance." APPENDIX. 15 "Reluctancy or Reluctivity. — Reluctance per unit volume. 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