CCOC ■ tf • ^" ''CC; JjGS,; -<:ige 105, bottom of table, read " Thompson's." For "Dauiells," page ltl6, 12th line from top of page, read "Daniell's." After "not," page 112, 3d line from bottom of page, read " quite." For "sewed," page 11(>, 3d line of description in table, read " served." For "sewed," page 116, 14th line of description in table, read "served." For " Sienu'us's," page 116, 2il line from bottom of page, read " .Siemens'." Insert reference letter (6) on center conductor of Fig. 46, page 121. Insert reference letter (a) on main conductor of Fig. 48, page 127. For " test," page 129, 14th line from top of page, read " best." For "coumponnd," jiage 139, 8th line from toj) of page, read " compound." For " tighly," page 13S», 14th line from bottom of page, read " tightly." For "Nicolls metallic oint," page 142, margin, read "Nicoll's metallic joint." For "insulaled," page 143, 1st line below Fig. 59, read " insulated." For " base," page 145, llth line from bottom of page, read " bare." For " ext emity," page 151, 9th line frotu bottom of page, read " extremity." For " turned out,'' page 155, 24th line from top of page, read " towed out." For "Siemens's," pages 166 and 167, read " Siemens'." For "No. 20," page 170, 2d line from bottom of page, read " Xo. 22." Strike out "page 160," page 171, 10th line from top of page. For "Markus's," page 172, 15th line from top of page, read " Marcus'." For "large," page 173, 1st line from top of page, read "larger." For " Wallaston's," page 177, margin, read " Wollaston's." For " is a," page 180, 8th line from top of page, read " in a." For "■Wallaston's," page 185, in table, read " Wollaston's." For "clianging,"' page 192, 20th line from bottom of page, read "charging." For "point," page Kl>, 8th line from bottom of page, read "front." For "(e)," pa-cl93, 4th line from bottom of page,' read "(/)." For " cliiinge," iiage 197, 13th line from bottom of |>age, read " charge." For "fuze and," page 20?., iiiargiii. read " fnze out." For "(e)" ]iagu yO:i, 17th line iVom bottom of page, read " (l)-" For " page l:i4," page 200, 17th line from top of page, read " page 147." For " page 134," paf;e 206, 11th line from bottom of page, read " page 147." For " blow in," page 2(J6, 10th line from bottom of page, read "b]o\y on." For " metalic," page 200, 3d line from bottom of page, read "metallic." For " moving," page 207," 5th line from bottom of page, read " mooring." For " fuze end," page 212, 7th line from bottom of page, re.id " far end." For ' For bury it," liage 217. 22d line from top of ])age, read " buoy it.' supports," page 219, lOtb line from bottom of ijage, read "outposts." For "(see page l-'O)," jiage 221, 5th Ime from top of page, read "(see page 199)." For " (g,) page 22:!. 3il line from bottom of page, read " (f/i)" For "(*, 22d line from top of page, read " passing tlirough the coils." For "deferential," page 242, 5th line from top of page, read "differential." For "batten," page 242, 9th line from bottom of page, read "battery." For " pages 94 to 90," page 243, 15th line from top of page, read " pages 104 to 106." For " reconnected," page 244, 11th liae from top of page, read " conni'cted." Page 244, at beginning of 8tli line from top of page, insert " to." For "Siemens's," page 250, 20th line from bottom of page, read "Siemens'." For " page 215," page 25^, 17tb line from bottom of page, read " jiage 210." Insert retereuce " (s)," page 2.59, on Fig. 107, to right of " c." For " Z," in equation (12), page 261, read " z." For "page 215," page 265, 21st line from bottom of page, read "page 216." For "page 88," page 267, 4th line from top of page, read " page 98." For " to all where," page 269, 4th line from top of page, read " to all station.s \v here." For "as far," page 272, 18tb line from bottom of page, read " so far." For "train mortars," page 273, in marginal note, read "twin mortars.'' For "sluices," page 291, 20th line from bottom of page, read " sluice." For " mnshroom anchor," page 303, margin, read " mushroom sinker.'' For " canvass," page 289, 7th line from bottom of page, read " canvas.'' For Fig. 9.3, page 224, substitute cut : Fig.Q2 CHAPTER I. INTRODUOTOEV. The term torpedo Las been hitherto applied, iu a vague kiud of way, to all the numerous contrivances which have, from time to time, been devised for producing submarine explosions calculated to act destructively against ships in their immediate vicinity. This term has been used whether these engines have been arranged defensively, the charge being ignited when a vessel is within range of their sphere of explosion, or whether offensively, that is, in a movable form for the attack of a vessel at anchor, or as a means of offense against a vessel in chase of a ship possessing the necessary apparatus, or under whatever circumstances they liave been employed. This term, "torpedo," does not seem applicable to defen- Definition of sive mines, or those which would be used to block up the ^'""'"'"'^ "'°^- channel of a river, or the approaches to a fortified sea-port, or in any other similar position; in fact, occupying a site analogous to that of a system of countermines in connection with a land fortress. In the following pages, therefore, I ])ropose to call all contrivances of the above nature, used for defensive purposes, "submarine mines," leaving the Defmition of term "torpedo" for all offensive combinations, to which it seems to be much more applicable. Under the comprehensive head of submarine mines is included a vast field for research, in which there is ample space for the development of inventive genius, in connection with the defense of fortified harbors, estuaries of rivers, and the coast generallj', a most important subject in a military point of view, and which, affecting as it does the attack of such places from the sea, renders it a consideration of the utmost gravity. The introduction of machines of this nature in war cannot be overlooked with impunity by a great maritime power like Great Britain, possessing, as she does, numerous colonies and an immense commercial navy which, in addition to her own coasts, must be defended in the event of war ; and as the employment of submarine mines seems to present such a considerable increase in defensive power, there is every reason to suppose that a judicious use of them would, on an emergency, prove of infinitely greater value to us than to a nation possessing less of the maritime element in its composition. Chinese subma- Subuiaiiue 0111168 liRve, from tiiiu' to time, been used in iiemues. ^'arfare. A very curious Chinese illustrated description of a system of tbis nature was broni;bt bonie very recently from that country. Tlie metliod of ignition of the charges in this Chinese system appears to have been exclusively R.is-ian fuima- arranged for mechanical action. iSimilar contrivances were also used by the Eussians in the defense of the Baltic dur- ing the Crimean war, without, however, any great amount of success. These seem also to have been designed for me- chanical action, as regards the ignition of the charge; but though several of them were fired by contact with the ves- sels of the blockading fleets, the damage done was insignifi- cant, the charges of powder used being comparatively small s ubmarincin aiuount. Again, iu the recent civil war in the United civil war in Amer° States of America, submarine mines were extensively used both by tlie Federals and confederates, especially by the latter, with veiy much more decisive results. Several of the Federal vessels were sunk, and many were so seriously damaged as, for the time, to be placed Aors de combat. Au excellent description of the means employed during this war has been given by Captain Harding Steward, Eoyal Engineers, iu his valuable pamphlet on submarine mines, which contains much information on the practical working of these machines and of the difficulties necessarily to be encountered therein. A very decided advance iu submarine mining is evinced in the arrangements made during this war; the machines used by the Eussians in the Baltic were simply allowed to drill, and were fired bj' mechanical means, thus rendering them equally dangerous to friend and foe, whereas here, we find the confederates mooring their charges in certain i^ositions and firing them, not only by mechanical but, toward the end of the war, by electrical agency — a very decided step in advance, as, in this way, they could at will be rendered perfectly harmless to a friendly vessel. while their chance of acting destructively against an enemy was vastly increased. Another iaii)roveiiieiit noticeable is the increase' in the amount of pow.ler employe 1 in each charge, regulated accdiding to certain rides derived from exi)eriment; the charges were, however, still insufficient. Ansirian sub.. The lesults arrived at during this war were so decided, that the investigation of the subject of submarine mines has since become almost general among civilized nations ; and we find them again used by the Austriaiis, for the defense of Venice, Pola, and the coasts of the Adriatic during their war against Prussia and Italy in 18G0. I am not aware that any opportunity occurred -of testing the efficiency of the inarine mines. system employed during this war, against an enemy's sbip, but the whole was exhibited at Paris in 1867. An exami- nation of this apparatus agaiu shows an advance in the science of submarine mining, for, wliereas in the confederate system, everytliing was to a certain extent tentative and hurriedly arranged, here we have worlcing patterns of all the materials and apparatus on a certain system, and capa- ble of being rendered available for any service required, by a simple reproduction of the number of articles necessary according to patterns which, after numerous experiments, had been decided on. The arrangement and construction of the equipment exliibited shows a considerable amount of ingenuity, and reflects much credit on the designer, Baron Von Ebner, of the Austrian Corps of Imperial Engineers. In this country a committee was appointed, in 1803, to pioatingob- investigate this subject, in combination witli that of passive tee appoiateci. obstrnctious, and their labors are now concluded. An im- mense namber of experiments have been made under their supervision, with a view to the detcruiination of the details of the apparatus, &c., best suited for the purpose; and many of tliese experiments have been carried on by the officers and men of the Royal Engineers, at Chatliam. Instruction in the theory and practice of electricity and com-so of in- its application to the ignition of gunpowder and other ex- Chatham.""' plosive agents, for mining purposes, both on shore, under water, and also as retjuired in connection with a system of submarine mine, has for some time been given in the School of Telegraphy, at Chatham. The subject is, however, of such vital importance that it 1ms become necessary to ex- tend the scale of instruction, from tlie small and make-shift way in which it has been taught, to sucli a system as would be required on actual service ; and for this pnr])ose a moving lighter and a certain luimber of boats, anchors of various kinds, cases to re[)resent submarine mines, chanis, cables, &(^, together with batteries, circuit-closers, and other elec- trical gear have been provided, and with these the instruction is now carried on. Submarine mines may be divided into two great classes, offsn-ive mmes otteusive and detensive. Ihe first, the ofiensive class, winch it is proposed to designate by the term " tor])edo," hitherto popularly applied to all, tails ii ore particularly tothepioviiice of the navy, though its use must not, on that accoinit, be neglected by the militar\ bianch of the service. It includes every class of device designed for the active attack of ves- sels, whether aiiauj-cd at the end of a spar or boom, in connection with a piojierly-titted torpedo-boat, to be used 10 ill ramiuiijg an cneuiy's ship or to be carried ou board skip and thrown out with a view of acting against a vessel in ehase, and exploded Ijy electricity or luechauicallj^, when in actual contact with her, or to be used for the attack of a vessel at anchor. To this class also belong drifting torpe- does, or those propelled by any mechanical arrangement through the water, and of such a form as would be applica- ble for the attack of floating or other obstructions, or of ponton-bridges, «S:;c. Instruction in such appliances is now regularly conducted on board Her Majesty's gunnery ships Excellent and Cambridge, and a very good practical book, in eoniK^ctiou with this course, has been drawn up by Lieu- tenant Fisher, E. N., who has charge of this duty on board the former vessel. The men ot theEoyal Engineers should be thoroughly practiced in the use and handling of such contrivances, especially with reference to the attack of pon- ton-bridges; and it is necessary that they should lie well practiced in the demolition, by torpeiloes, as well as in the construction of booms and other passive obstructions. As yet, however, but little has been done in this respect, our attention and time having been chiefly devoted to the de- velopment of a system of defensive mines. A torpedo-boat has, however, been designed and is constantly used during the course of instruction given ou board Her ^lajesty's ship Excellent. To the naval branch of the service would seem chiefly to appertain the designing and practical use of the apparatus adapted for searching for and carrying off an enemy's mines, and the defense of vessels against mines of every class, whether stationary or drifting. We now come to the second great class of these contri- vances, viz, the defensive or the submarine mine proper, which I propose so to designate, in contradistinction to the torpedo or attacking implement, and especially the mil- itary engine. Defensive Thcsc sfcm applicable to almost any circumstances, and mines, or subiiia- i i ■ i riue mines proper, may bc uscd With a Very great advantage to the defense, in innumerable instances, from that of a first-class sea-coast fortress against a tlrst-class fleet of iron-clads, to that of a fishing village against a small privateer. This assertion seems to be strongly borne out by the experience we have gained, from the perusal of the accounts of the naval opera- tions, during the late civil war iu the United States of America. During that war the iron-clad, and even wooden vessels of the Federal fleet, frequently silenced and ran past confederate shore batteries, the latter armed with numerous 11 and well-^seived pieces of heavy caliber, rifled as well as smooth-bore. For example, Forts Jacksoa and St. Philip, defending the entrance to New Orleans, and mounting about 100 heavy guns, with the advantages of numerous shoals and a swift current, failed to stop a squadron of wooden ships, which ran past them after a few days' bombardment from their mortar-vessels. Again at Vicksburgli, after a short bombardment, the Federal fleet rau past the batteries commanding the river, with the loss of only a few men, sub- sequently passing down again with a similar result. Ou this occasion there were about 30 guns in the shore batteries against 40 on board the ships ; some of the vessels were, however, iron-clads. Again, at Fort Fisher, at the mouth of Cape Fear liiver, leading to Wilmington, the confederate guns were on two occasions silenced by those of the Federal iron-clad fleet. These are only a few of the numerous instances in which similar results were obtained — in fact the obstructions and submarine mines of the confederates gave much more trouble, and caused much more delay and damage to the Federal fleets, thtin the batteries. Witness the notable example of Charleston, where, though the guns of Fort Sumter were silenced over and over again, the vessels were kept out for months by the obstructions and submarine mines, ^^dmiral opinion of Ad- J)avid 1). Porter, of the United States Xavy, in his vei-y Snitd 'sYatVs able report on the defensive powers of coast-batteries, states: ^"^^^ "The running jtast a battery is a very easy thing when there is a straight channel and sufficient depth of water; and there is no fort in any of the waters of the Iv'orth that cannot be safely passed, and (in military phrase) the posi- tion turned ; and no forts now built can keep out a lar,i;e fleet, unless the channel is obstructed." And again, '-Ob- structions and torpedoes are a better defense than our present forts." Such is tJje deliberate ojiinion of a very able naval officer, given after an experience of three or four years in the attack of water batteries of every variety; and what has been done once may, no doubt, be done again. Though it cannot be said that shore-batteries may not be very much improved, and their defensive powers against shi|)ping greatly increased, taking them gun for gun as against an attacking fleet, there seems to be sufficient data to show that the defensive power of the very best fort that can be built will be much incre;ised by a judicious arrangement of obstructions or submarine mines, or a comoination of both. If used in the defense of a first-class fortress, such as Ports- DefenKe of 8 mouth, for exam])le, they should be so arranged as to be arportTmouth"'' 12 covered by tlie .mius of the iiiits and tioating liattciies, so that wliik' acting- as oatwoiks of these latter, they would be protected by theiu from disturbance by tiie boats of a hostile fleet. De onse of a Auothcr casc, iu wliicli Submarine urines could be ettect- "aTiyerpoor "'' ively uscd, IS that of a great mercantile harbor defended by forts carrying a few heavy guns, as Liverpool, for example. Here we have a few guns in position, which might be silenced by a sufficiently powerful hostile fleet; but if a judicious arrangement of submarine mines were added to these, placed in such a position as to be covered by the guns, and by those of such vessels of war as might be at hand, and, at the same time, advanced sufficiently far to prevent the guns of an enemy's vessels from reaching the shijjping ill the port, the position as regards the defense would be immensely improved. In all cases, by a vei-y simple arrangement, to be hereafter describeil, the channel could be made iierfectly safe to friendly vessels, which could ruu in and out at pleasure, while it could at any moment be made instantly dangerous should an enemy attempt to follow, rspfni in an un- A third casc, iu which submarine mines could be used fffidfl'^t.'""'''"''' with advantage, is that of the estuary of a river leading to a mei'cantile harbor and not necessarily defended by forts of any sort, as for example Belfast. Tliis important pm-t is sit- uated a considerable distance up an arm of the sea, on a river, and is, or used to be, so nearly undefended by guns that, for the sake of exam])Ie, they need not be considered as an item in its defense. Under present circumstances Belfast would be open to the attack of a comparatively small fleet of hostile vessels, and its destruction would be a very serious blow in a commercial point of view. If a well-ar- ranged system of submarine mines, however, were placed iu the estuary of the river, with one or two gun-boats or a floating-battery, to prevent boats from searching for them, the place would be quite safe from any sudden attack, and would be capable of holding out against an eiiemVs srpiad- ron, with a fair luosiiect of success, till relieved. Here again the mines nmst be placed at such a distance as to keep hos- tile vessels wheie their fire would be ineftective against the shipping and towu. Should no gun-boats or floating-bat- teries be at hand, a few guns iu au earthwork, to cover the mines, would be advisable, but even without them a deiense on this system miglit still be cairied on, and it would only be tiecessary to jiut down a gi eater uumber ot mines, so that one might occasionally be fired at a boat engaged iu 13 grappling for them, as a cleterreut. As a rule they should not, however, be throwa away at small boats, bat reserved for more worthy objects. Another instance in which submarine mines might be. D''''^"^"''*'™"'" ^ harborri, ad Whit- advantageously employed, without any combination of pro-i'y- tecting guns, is that of a harbor close u[ion the sea, which could be easily reached by an enemy's guns ; such a place as Whitby, for example, which affords a port of considerable importance to the coasting and fishing trade. A few sub- marine mines laid 4,000 or 5,000 yards to seaward from this place would, by the fact of their existence, deter an enemy's vessels from approaching, as the advantage to be gained would not be worth the danger incurred, while a harbor of refuge would be secured to friendly ships. In such a posi- tion as this, it might not be practicable to use them at night or iu a fog, unless some means were adopted for signaling the approach of an enemy. Again, they might be used for the protection of such a Defense of town place as Brighton, where no harbor exists, but which is quite migbton. "'^^' open and assailable from the sea, and any attemiit to defend Avhich with guns could only end in its destruction by bom- bardment. In such a case a few submarine niiues, placed at a distance of a few thousand yards to seaward, would exercise a salutary deterrent effect. These mines should also be rendered inactive at night or in a fog, to prevent accidents, unless some means of signaling were adopted. Another case in which tliev might be usefullv emi)loyed, n-f-'n-^e of ? ■-' '^ J 1 J ! gpj.^ beacb. is that of a tiat open l)each, on which an invading force might be lauded with facility, as, lor example, Sandown ISay, in the Isle of "Wight. At this point a strong fort ha been built in connection with the defenses of Portsmouth? to prevent such a contingency. A few submarine mines judiciously placed in such a i^osition, and covered by the guns of the fort, M'ould, I imagine, vastly increase the chance of a successful defense, and act as a deterrent against any atten)i)t to laud; and probably in many similar positions a smaller fort, onlj^ carrying a sufflcient number of gnus to protect the submarine mines, would answer the purpose. One use to which submarine mines may be applied must Protection of ;iq not be forgotten; it is that by their means an inferior fleet'" has the jjower of placing an impassable barrier between itself and an enemy, reserving, however, the i^ower of jniss- ing out when required, and of retreating to a strong position at any moment, should it be unable to cope with its adver- saries. A fleet of merchant-vessels might also, so to s[)eak, be similarlv intrenched. 14 DeieDM^ by sub- The al)ore are a few of tlie cases in which it seems that sub- niariuo miii''^ 8pe- . . t ■ ■ i i ciaiiv applicable luanue uuiies Cdukl be used with (♦Hcct, atul there are, uo anri 'irdanrt and cloubt, iiiaiiy othei's wblch might be enumerated, and even a our coionit^s. .-, ,. ^,, - , ,. ». i- cnrsoiy consideration of the advantages to be derived gives an impression of tlieir importance, to a country with such a great length of coast as that of Great Britain, IrebT,nd, and our colonies to be defended. They seein especially adapted for the deleiise of colonial ports, many of which, under present circumstances, would be at the mercy of a comparatively small squadron of an enemy's vessels, or even a single iiou-ciad, which could probably ruu i^ast or silence the few guns defending them, and bombard or lay the port under contribution. The presence of a few well- placed submarine mines would, however, completely alter the state of affairs and render a different mode of attack necessarj-. There would then be no alternative but to begin the tedious and dangerous operation of clearing the chan- nel, or to land and attempt to capture the place without the aid of the ships, in which latter case the defenders would stand a fair chance of success in dealing with the attacking force, which would then probably be acting at a disadvan- tage, or, at best, on equal terms only. Another point gained would be, that each port so defended wbuld become a harbor of refuge into which a friendly vessel could pass freely, bnt which would be effectually barred against an enemy in pursuit. In case of war it would be no uncommon thing for a friendly vessel to be chased into one of our har- bors, as, for example, ilelbourne. In such a case a system of submarine mines would be invaluable. Finally, sub- marine mines may be used in combination with, or without, l>assive obstructions of every variety'. , Moral effect The experience of the late civil war in the United States cojhideruble. , p^ « teaches us that the moral effect or a system of defense by submarine mines would be very great, jleii will face a known danger readily, but it is not so with a hidden one. The result, therefore, would be a consideral.)le increase of cautiou in the mode of ap[)roach over places where subma- rine mines were supposed to be lodged, with a corresponding delay and loss of time in the attack, which, in many cases, would enable the defenders to hold out till relieved. Sup- pose, for example, such a place as Liverpool were attacked by an enemy's squadron, in its present state, protected as it is by a few moderately strong forts, past which iron-clad vessels might run without serious loss; it would be at the mercy of an enemy. If a judicious arrangement of subma- rine mines were, however, added to the present guns, the 15 same squadron could not get in in tliis off-band way, and would probably not think it worth while to incur any delay in attempting to force a passage, as, by the aid of the elec- tiic telegraph, it is more than probable that a strong re- lieving squadron would be off the port before many days had passed. There is one very important consideration with reference Co.t compara to this question, viz, that the cost of a system of defense, "" ^ ''"'^ ' by submarine mines, is comparatively trifling. A channel 1,000 yards wide might, in this way, be defended at an out- lay not exceeding that incurred in the purchase of half a dozen heavy rifled guns, to say nothing of the ammunition required for a modern artillery armament, the cost of which is considerable, or of the works in which the guns are placed. Again, the materials required in the construction of the Jiateiiai easily apparatus are all articles of commerce, easily procurable; the submarine cables, which would perhaps be the most difficult part of the equipment to obtain in out of the way places, may always be kept in store and laid down when required. And finally a system of defense, by submarine mines, can be worked by a comparatively small number of men. AW these are important points in connection with a subject which seems capable of such universal application, especially when viewed with reference to the defense of our numerous and distant colonial possessions. The advantage to be derived from the use of submarine Advantage; . . T „ . great increase in mines is a very considerable increase m defensive jiower. defensive power. One important point is that of setting free our fleet to act at sea against that of an enemy; as a very much smaller naval force would be required for harbor defease, and it might consequently be concentrated and used to greater advantage in active operations. Another is the addition, to a very considerable extent, of the defensive powers of our coast batteries and fortresses ; that addition being ob- tainable at a comparativelj^ small cost and with a compara- tively small number of specially trained men. A third is the acquisition of a power to defend places which have hitherto been deemed indefensible. A fourth is the power of converting every British harbor into a port of refuge, accessible at any moment to friendly vessels, but absolutely impassable to an enemy. CHAPTER II. CtEKJ'OKAL PEIXCIPLES. Nuiure of ml- AVe will HOW pi'oceecl to consider, in general terms, tlie marine mmes. „g^^^^j,g ^f submarine mines. Tliey may be briefly described as charges of gunpowder, gun-cotton, or other explosive agent, of'A'arious sizes op to 2,000 pounds of gunpowder, or its equivalent, inclosed in water-tight cases of iron or other material, and placed under water at such depths that, by their exjilosion, they may sink or seriously damage a vessel passing in their vicinity. They may be classed under two heads, viz: Mechanical, those which depend for the explo- sion of the charge on mechanical means, such as the simple percussion of a vessel coming in contact with them; and electrical, those which are fired by electrical agency, either by the vessel herself closing the circuit, or at will from the shore. The details of the arrangements in both these sys- tems shall be considered hereafter. Meciianicai The formcr class, or mechanical mines, are capable only Lubmmiie miu, s. ^^ ^^^^.^ limited usc. Whcu once placed in a channel it becomes equally impassable to friend and foe ; they are therefore only applicable to certain cases, as, for example, where it becomes necessary to block up a channel completely, that is. to say, to render it altogether impassable till the mines have been again removed ; for instance, to inclose an enemy's fleet and thus limit its sphere of action, or under any similar circumstances. They might be employed on a flat beach, dry at low water, to cover the flanks of electrical mines defending the navigable channel ; in such a case they could be placed in position or removed at low water in com- liarative security, and the number of electrical cables, &c., requiied might, by such an arrangement, be reduced. They «>isaa,ant;;seE. would not be applicable to the formation of harbors of ref- uge, as previously alluded to, where merchant-ships could run in to avoid an enemy. It would be absolutely necessary to make some arrange- ment so that they might be exploded at will, as the most eflectual way of getting rid of them when it became neces- sary to clear the channel, as the process of removal in the ordinary way, by boats, would be far too dangerous an operation to undertake; in fact, it would be difficult, nay, almost impossible, to get men to do it. 17 They possess the advantages of being capable of being Aear on the surface of the water. Under certain condi- tions it may be impracticable to conceal them altogether, as, for example, where there is a large fall of the tide; under such circumstances the smallest i)ossible indication of their position must be allowed. 8th. Where, from the depth of the water, the charges can- not be placed on the bottom, they should be so mooi'ed as to float from 15 to 40 feet below the surface. In places where there is a considerable rise and fall of the tide, special arrangements would be necessary. !)th. The place in which the voltaic batteries 'and instru- ments, connected with the ignition of electrical submarine mines, are arranged, should be in those portions of the de- fensive works which are likely to be held longest, so that a command may be kept over the mines to the latest possible moment in the defense. 10th. Great care should be taken to lay the electric cables in such positions as to render their discovery by an enemy as diflicult as possible. The confederates used many devices to conceal the conducting wires of their mines, and among others, that of carrying them in by circuitous routes and burying them under ground, to discover which, the 22 Federals dug treuclies across the courses which thej' would be most likely to take. 11th. The position of the mines should be well covered by the fire of the guns of the forts or floating batteries of the place to be defended, to prevent their disturbance by boats. 12th. Submarine mines should not be thrown away by (Iring at small boats, except under very exceptional circum- stances, but should be reserved for larger vessels. General princi- The oliject to bc attained, in arranging any system of .ichiumd.'""^ ° mines for the defense of a channel, is to x)lace them in such a position that a vessel in passing along that channel must, at some one moment, whatever course she may take, be in such a position as to come within the radius of destructive effect of one of the mines during her progress. In order to attain this end it would only seem necessary to place the mines so that the circles described by their radii of destruc- tive effect may at least touch each other. Theoretically this is no doubt the case, but practically such a system presents difficulties which would prevent its being worked out, and moreover has certain disadvantages inseparably connected with it. Among the practical difficulties is the danger of entanglement between the mooring cables of adjacent mines or their circuit-closers, especiallj' when there is any rise or fall of the tide ; when mines are very close to each other it is practically impossible to prevent entanglements of this nature, even with the most perfect mooring arrangements- Again, when mines are very close to each other, the explo- sion of one is very likely to injure its neighbors, or, where an electrical system of explosion is adopted, to disturb the circuit-closers, electrical cables, &c., connected with them. And the difficulty of paying out the electrical cables and arranging the gear in connection therewith, as well as the grappling for and raising a mine for examination, is much increased by this very close and precise formation. In fact, a certain amount of latitude, so to speak, is absolutely necessary in order to simplify the operation of mooring. n i andvantages Amoug the positivc disadvantages of such an arrangement nf a fciagle line, • 1 1 <-. i < i • /. i . IS the tact that it a breach were once made in such a line, that breach would, till repaired, afford a safe passage to an enemy's ship. Again, an enemy having once ascertained the position of such a line, could easily detine the limits of the area of danger, and take the necessary measures to avoid it. These disadvantages may be overcome by spread- ing the mines over a certain area, so that while reducing the difficulties of placing in position and preserving for the 23 defenders a certain formation, whicli secures to them the power of identification with the more precise information and delicate instruments within their reach, the difficulties to an enemy of obtaining a definite knowledge of the area defended may be proportionally increased. The simplest method in which a system of mines can be simple distribu- tion of mines for arranged for the defense of a channel, is shown in Fig. 1 aefenseofaciian- uel. which also illustrates the general principles on which they CL .. ■ 0'ixj0;i:ii©3XjXE)::;7'OIXi''0-'L' 'Q)'h (d\ 0: 0;\ 0L-' 0^ d f^ 0(r Fic,^ 1. 9 \ U Q •^j r?) '/fc should be arranged in all cases. In this figure a h repre- sents the theoretical line required to defend the channel) and it is only necessary to move every second mine back to the line c d, and every third to the line e /, to secure the objects required. A fourth line g h, or even a fifth .^ / J:, may be added with advantage, taking care that these last shall cover the intervals left between those in advance of them, in such a way that a vessel passing in obliquely 24 tlirongli the intervals of the first tliree lines, may come in contact with a mine in the fourth or fifth. An arrange- ment in lines is convenient, as giving- the greatest facil- ities for firing at will by the method of cross-bearingS) or for finding the position of a mine in the event of its becoming necessary to raise it for examination. If the lines are so placed as all to converge ou a single distant point, say half a mile or more distant, the combination is much simplified, while the actual position of each mine is thereby so little altered that it may without difficulty be made to fulfill all the necessary conditions. The rules regulating the intervals to be left between adjacent charges in a line of mines as well as between the lines themselves shall be dis- cussed hereafter. Let us now suppose a case in which it would, from the depth of water, strength of currents and other conditions, be practicable and desirable to institute a combined system of defense by passive obstructions and submarine mines, as, for example, an estuary of a river, such as that represented iu Fig. 2, defended by three batteries, x, y, and .^. D c- f e n s e of a The most eligible points, which would be those where the channel by a com- - ' binationofsubma. chauncl is uarrowcst, or bends where facilities exist for eii- rine mines and .1. , , ti-i ti passive obstruc- filadmg the lines of obstructions by guns, and which would offer advantages for fixing th6 positions of the submerged mines very accurately by intersections, or cross-bearings as they are sometimes called, and other places offering local advantages, having been selected, grounded obstructions and booms might be formed, as in the positions a a, a-^ «i, in which openings are left in the ship-channel, to allow of free ingress and egress. Across these openings it would be necessary to place several lines of submarine mines, h h, &i hi arranged to be fired by electricity, extending so far on each side of the deep or ship channel as completely to cover it, and well protected by the fire of the forts x, y, 2, and a light boom, cZ f?, might be advantageously placed in advance, to cover the whole system from an attack by drifting torpedoes or boats. The spaces c c, Ci Ci are supposed to be covered by a few feet of water only, and it is assumed that they would be sufficiently protected by the flre of the forts, and by guard-boats provided with proper apparatus for day and night signaling ; no mines are therefore proposed iu connec- tion with them. The whole of the electrical cablesin connec- tion with the mines should be carried into the safest avail- able position, if possible into the fort z : but if this is not practicable, those of the outer group b h might be carried into either of the forts x or y, and those of the inner group hi hi into the fort z. The necessity for placing the electrical- 25 room, that into which the electrical cables of any system of submarine mines are carried, in a safe place is very great; on it depends the efBciency of the whole. It would not do to carry the electric cables of the group &i hi into either of the forts x or y, however conveniently they may be situated as regards the distance. They should be carried into the fort c, so that in the event of the forts x and y being lost, the space between them, covered by the group of mines, 26 would still remain as impassable as ever to the attacking ships. The electric cables in coimectiou with the advanced Hue of mines h b might perhaps be carried into the forts .v and y, if the distance were two great to admit of their being carried into the fort ~; but those of the group &i 61 should Di-iiDSL- of an most Certainly be carried into the fort z. Fig. 3 represents "vi'iho'ut^assive fiiiother case, as, for example, an open roadstead, protected obstrueiiona. ^^ forts iu wliich no passive obstructions of any sort could be used, but where the depth of water is not too great to admit of the eniploj'ment of buoyant submarine mines. More mines would be required uuder such conditions, and they might be arranged as shown in the sketch, the same general rules being observed as to the situation of the electrical-rooms from which the whole system is governed • that is to say, the cables in connection with the group 1) should be carried into either of the forts x or y, and those of the group bi into the fort z. 27 So much depends upon local circumstances, such as the nature of the channel or roadstead to be defended, the prob- able means of attack at the disposal of an enemy, the draught of water of the vessels of a hostile fleet, &c., that a great deal must be left to the discretion of the officer com- manding the defense, and the above must not be considered as stereotyped plans which should never be departed from. They are only intended to convey a general idea of the arrangements necessary to meet the objects in view, which would require much modification to suit the specialties of any particular case. a fronts. CHAPTER III. EXPLOSIVES. "We now come to the cousidoratioo of the nature of the explosive agent with which a submarine, mine can be most effectively charged. Explosive Several substances have been suggested for this purpose, including gunpowder, (of large and fine grain,) compressed gun-cotton, (fired with an ordinary and with a detouatiug fuse,) nitro-glycerine, dynamite and glyoxyline, (a new ex- l>losive material, a combination of gun-cotton and nitro- glycerine, recently invented by F. Abel, esq., F. E. S., war department chemist.) Gunpowder. Guupowdcr is probably the oldest and best known explo- sive agent that we possess. Its effects when fired in earth, rock, and masonry have been determined with great accu- racy, but we still have much to learn concerning it, when the surrounding substance is water. During the late civil war in America the confederates gave the preference to fine- grain or rifle-powder, under the supposition that it produced a better result for submarine purposes. An experiment, tried in a well in Pennsylvania, seems to bear out this idea. Ca])tain Harding Steward, in his notes on submarine mines, gives the following description of the result obtained on that occasion : " 50 pounds of rifle-powder sent up a column of water '-'>i) feet high, while, with the same charge of coarse- grain powder, a column of similar thickness was only driven 70 feet high, and the water was very much discolored, prov- ing the non-ignition of i:)art of the charge." The French seem to have got hold of the same idea, for, in some experiments recently carried on, they have been trying several varieties of gunx">owder, especially manufac- tured with a view to obtain more rapid ignition. The Austriaus have adopted fine-grain powder, in charges of IGS kilograms, or 3G9.G pounds, in some of their most im- proved forms of apparatus. A strong case It Is probablc, howevcr, that when gunpowder is used, gnnpowder is the Strength 01 case is ot more importance than the consid- eration as to whether coarse or fine-grain powder should be employed. A case of sufflcient strength to secure a proper development of the explosive force of the charge, would be likely to produce a greater increase in that force than would 29 result from a change in the form of powder of which the charge is composed. The experiments made by the float- ing-obstruction committee seem to prove this to be the fact. As regards compressed gun-cotton we are somewhat in compressed gun- the dark ; but a great number of experiments have been recently made with this substance, fired with an ordinary as well as with a detonating fuse, which throw much light on the subject, and from which its effects, as compared with those of proportionate charges of gunpowder, have been approximately determined. The results obtained from these seem to show a superior- ity, under certaiu conditions, for gun-cotton over gunpowder for submarine work; its ignition, at all times more rapid than that of gunpowder, is, when fired with a detonating fuse, immensely quickened, and the damaging effect of its explosion is much increased, both of which properties are in its favor.* It is to be remarked that the Austrians, who originally used gun-cotton in their submarine mines, appear to have given it up, in consequence of the difficulty they experienced in manufacturing it of uniform strength, and the danger of spontaneous explosion. Mr. Abel's process of making it in Abeis improve- a pulp seems to get over these difficulties. He has identi-™a°[u™'o/ gnS- fied himself with the advancement of the gun-cotton ques- """"• tion, and great credit is due to him for the light he has thrown upon that question by long and patient experimental research. Still greater credit is due to him for having dis- covered and perfected a metliod of treating gun-cotton, whereby it is rendered non-explosive when burned in the air, but in which the full energy is developed when fired in a close chamber, or with a detonating fuse. The method consists in reducing the gun-cotton fiber to a fine state of division or pulp, as in the process of paper-making, and in converting this pulp into solid masses, of any suitable form or density, under a j^ressure of 18 tons to the square inch. * Mr. Abel, who has investigated the action of detonating fuses in developing the explosive power of nitro-glycerine and gun-cotton, states that gunpowder, or any other exiilosive agent, may be made to exert its full explosive force when only confined in n, weak case, or bag, or even when exposed to the air, by being fired through the agency of a snddeu and sharp concussion, such as that produced by the explosion of a con- fined charge of fulminate of mercury. He states that the explosion of powder, by means of a detonating fuse, is decidedly sharper or more rapid than that produced by tiring it in a strong receptacle in the ordi. nary way. Some recent experiments have indicated that more work can be got out of a combined charge of powder by this means than by its explosion in the ordinary manner, under corresponding circumstances. 30 This method of manufacture is uow carried out by Messrs. Preiitice, at their works at Stowmarket. To the pulping is mainly due the safety attained, as it insures uniformity in washing, whereby the cotton is thoroughly freed from all acid, and thus every chance of spontaneous combustion is removed. The compression causes combustion to proceed slowly in the open air, owing to the condensed condition of the fibers, which, iu the loose state of cotton or rope, burn very rapidly. The gun-cotton is compressed into cylindrical or any other convenient forms, and a density equal to that of powder is given to it, whereby its portability and the explosive force of a given volume are greatly increased. The principle of thus combining safetj^ with force, in a highlj" condensed form, has produced very valuable resulfs. Before any definite opinion can, however, be pronounced on this substance as an explosive agent, it is necessary to try some further experiments with large charges. The effect of compressed gun-cotton, fired with a detonating fuse, is marvelous. The power possessed by a detonation of de- veloping suddenly the full explosive force of gun-cotton was discovered by Mr. Brown, of the chemical department, Woolwich ; and several forms of detonating fuses, to be fired either by electrical agency or by means of Bickford's fuse, have been coustructed by Messrs. Abel & Brown. The electric detonator is a modification of Abel's fuse, a charge of fulminate of mercury being substituted for the powder priming, and the. wooden fuse-case being strength- ened by an outer tin case, which assists in developing the ExpLMiments detonating power of the fulminator. The following sum- "id liyoxjdin™ mary o^" the result of some experiments carried on with it to'natiug'fuse. ' aud with glyoxylinc, under the auspices of the royal engineer committee, at Chatham, on the 6th August, 18GS, give an idea of the effect produced : Experiments were first made to show that neither of these substances, compressed gun-cotton and glyoxyline, will ex- plode when unconfined and merely fired with an ordinary fuse, either time or electric, but that they require a detona- ting fuse to explode them under such conditions. These experiments were most successful ; the gun-cotton when ignited with the ordinary fuse only burning, and the glyoxyline being simply blown about without ignition. When the detonating fuse was used, the charges being still unconfined, both substances exploded with great violence, disintegrating the pieces of wood on which they were placed. Five charges were fired successively against a stockade, formed of 1 foot 2 inches square timbers, placed close to- gether and firmly planted in the ground. The piles were chiefly of pine, except those specified to the contrary. The following is the result : 1st. Five pounds of glyoxyline hung in a bag about two feet from the ground. This blew in a hole about oue foot in diameter, resembling the effect that would have been produced if a round shot had passed through. Half the timber above the point of explosion was also carried away 2d. Ten pounds of glyoxyline hung in a bag about two feet above the ground. This produces just double the effect of five pounds, the whole of the timber above the point of suspension being carried away. 3d. Ten pounds of compressed gun-cotton laid along the foot of three piles. This cut a clean gap through two whole piles and half the third. 4th. Ten pounds of glyoxyline laid in a train against three timbers, two of oak and one of pine. This cut through all three. 5th. Five pounds ten ounces of glyoxyline and five pounds of comxiressed gun-cotton. Each charge laid along the ground against three and a half piles, and consequently covering a space of seven piles altogether. The piles were cut half through, with the exception of one which was split completely through, though not severed. The line cut was three or four inches wide. A plank being lowered over the counter-scarp of St. Mary's Experimeut front, to a depth of 10 feet, the total height being 18 feet, S™' ot'""'tint the following charges were placed on it : 20 pounds of gly- ^"'^ " '™°*' oxyline were laid along 3 feet of plank, and 20 pounds of gun-cotton along 3 feet more by its side. The explosion was extremely sharp, and a partial breach of the following dimensions was formed : 7 feet high, 11 feet wide, and 20 inches in depth. The brick- work was very much shaken for some feet on either side of breach, and pulverized for some inches more in depth. From these experiments it is probable that these sub- Result of exper stances may prove exceedingly valuable for making breaches '™™'"- in timber and masonry, when portability and rapiditj' of action is required, as, for example, to breach a stockade or form a lodgment in the revetment of a work. Tamxjing may be dispensed with, which is a great advantage ; but it must be borne in mind that, in order to produce a maximum of effect, absolute contact with the object to be destroyed is necessary, and for this purjiose it would be convenient to prepare the charges beforehand, by placing them in bags or tin cases of suitable form, generally cylindrical and very 32 long as compared to their diameter, so as to cover any space required. Some furtbor experiments were tried on the 5tli Sep- tember, 18G8, against the same stockade. The breaches formerly made had been repaired, bat certain alterations were introduced in its construction, viz, no earth was raised against the outside, the ground being level there ; this earth was moved inside, and, together with blocks of granite, iron guns, and railway iron, was used to strut up the timbers and strengthen the stockade in the interior. 1st. Five pounds of compressed gun-cotton in disks were laid on the ground outside, against one of the logs, (of fir,) forming the stockade. This log was 13 inches square, and was strengthened behind by a block of granite, weighing 9 cwt., and earth. It was also secured to the -adjoining logs by a ribbon with 7-inch nails. This charge, ilred with a detonating fuse, cut through three-fourths of the log at the foot and forced the block of granite behind 1 foot G inches to the rear. It was the opinion by those present that the riljbon alone prevented the log from falling. -!d. Seven and a half pounds of gun-coiton were now tried under similar circumstances, as in the first experiment, against a log of fir, 14 inches scjuare. This log was only strengthened behind with earth 3 feet 6 inches high by 1 feet at base. The log was cut tlirough and fell forward, the cut end being buried in the earth behind. 3d. Seven and a half pounds of gun-cotton were placed eciually on both sides of a corner log (of fir, 15 inches square) of the stockade. This log was powerfully supported on the other two sides by those adjacent to it, forming the stockade. It was cut clean through and the bottom driven out 3 feet, the log leaning in this position against the others. 1th. Seven and a half pounds of glyoxyline were placed loose on the ground against one log of fir 13 inches square, supported behind by small blocks of granite and earth 3 feet high by 4 feet at base. The log was cut comidetely through but remained standing, the top leaning forward about 2 feet beyond those adjacent to it. The efiects of this glyoxyline charge were not so local as those of gun-cotton. With gun- cotton the adjacent logs were not touched; with this charge of glyoxyline, however, the two adjoining logs were much splintered. This difference of etfect, between gun-cotton and glyxoxline, was probably due to the different manner in which the two materials were piled against the logs. The cotton, being in disks, was packed close up against the 33 logs. The glyoxyline, being in pellets, was piled loosely against the logs, and therefore the center of gravity was not so close to the logs as in the case of the gun-cotton. It also fell over a little againt the adjoining logs. .")th. A tin cylinder, 3.\ inches in diameter, and 3 feet 6 inches long, was loaded with 10 pounds of gun-cotton in disks, which, to lengthen the charge, we)'e separated by J- inch milled board. The cylinder was laid'against three fir- wood logs, 14 inches s((uare each, and which were supported l>ehind by two 18-pounder iron guns and two pieces of rail- way iron, besides being secui'ed to another by ribbons of wood and iron dogs. This charge was fired with a Bickford's fuse, at the end of which was a detonating arrangement. The explosion, which was very violent, over- threw the two left-hand logs, which fell forward, and very nearly severed the right one at the base, which, however^ remained standing, being prevented from falling by the ribbons and dogs securing it to the adjoining logs. This concluded the experiments against the stockade. nth. The gun-cotton disks were now tried against some palisades near the stockade. Four disks, weighing 4 ounces i each, were placed (ine under each of four adjacent palisades, their edges being 9J inches apart. One of the outer disks was then fired, in order to see whether the explosion would ignite those adjoining it. This did not occur ; only one was exploded, which cut the palisade against \\hich it was placed clean off level with the ground, but hardly even disturbed the adjoining disks. In order to test tlie effects of these explosives on beams Experimcrs on beara.s of timber ot timber, some experiments were made on a wooden sta- with Run-cotton ging in the ditch, to the west of St. Mary's horn-work. fuse. The timber was of fir, but very old and full of shakes. One of the beams, 10 inches square, composing the sta- ging, was bored with a Acrtical hole 1^ inches in diameter, into which 2 ounces of gun-cotton was put. This charge (iompletely severed the beam and split it, in several places, to a distance of 3 or 4 feet from the charge. One ounce of gun-cotton was now tried under similar circumstances. This shattered the beam considerably, and split it so that it could be seen through, but did not sever it. Large splinters of wood were thrown by these exijlosions to distances of as much as 20 yards. A single disk of gun-cotton, weighing 1 pound 2 ounces, Experiment on was now placed on the top of a block of granite 3 feetOwi'th gun-^cot'tou inches by 2 feet 9 inches and 2 feet deep. The block oftnJ. ^'^'""'^''"'^ granite had had several jumper-holes bored in it, which 34 luad, Lowever, beeu tamped up again, but must liave -weak eued it considerably. Tlie result of this explosion was that the block of granite was split vertically ail around at an average distance of 2 inches from the outer edges, besides having a hole 1^- inches deep scooped out iu the top of it at the seatof theoharge. It was also much shaken, and could easily have been picked to pieces. The result of the frac- ture around the stone was that, iu a few days, the part split scaled off and fell away from the block. The whole of these experiments would seem to prove that gun-cotton, prepared according to Mr. Abel's method and flred by a detonating fuse, is quite as powerful iu its action, if not more so, than the mixture of gun-cotton and nitro- glycerine, called glyoxyline. The average price of the two would be about equal, being (according to Mr. Abel) 20fZ. per pound weight, or 2^ times the price of blasting-powder ; but as the effects of one pound of gun-cotton for these purposes appear to be equal to those of 4 pounds of gunpowder, it would in reality be 3S per cent, cheaper to employ gun-cotton. The specific gravity of com- pressed gun-cotton is the same as that of gunpowder j that of glyoxyline one-third less. Gun-cotton is more liable to absorb moisture than glyox- yline, though it is not permanently injured thereby. The transportation of nitro-glycerine dissolved iu wood spirits, for the manufacture of the latter, is troublesome and expen- sive aud, unless carried about in this way, nitroglycerine is very dangerous to move, whereas gun-cotton is not so. For actual service, however, the glyoxyline would be man- ufactured beforehand, and the masses, (grains, disks, &c.,) would be coated with an impervious varnish, which would effectually inclose the nitro glj'cerine and protect the pre- I)aration from the atmosphere. Effect of com- The cffccts of thcsB explosives are so powerfully concen- ■ pressed gun -cotton fired.imrter water, trutcd and local, that it can hardly be doubled but that, if u'itli detooating ,.^ . , . , . i - , fuse. sunflcient quantities were used, iron plates of considerable thickness could be pierced by them, especially under water. A few charges of compressed gun-cotton have also been fired, with a detonating fuse, under water with the following result : 1st. A charge of SpoundsO^ounce was fired atourexperi- men tal target, (the squares of which are of fir, 1 i inches square and 1 inch thick,) at a distance of 20 feet from the target and with 7 feet six iuches immersion ; this broke 22 squares. 2d. Three pounds Of ounce, 30 feet distautfrom the taro-et, and with 7 feet 6 inches immersion broke 10 squares. Tn-enty pounds of powder, at a distance of 20 feet, pro- duced less result than this charge of gun-cotton at 30 feet. With both these experiments the shoclv experienced was most violent. The sprats and small whiting, for a consid- erable distance above the x)oint of the explosion, were killed and drifted past in great numbers. The above two experiments were made to test the com- parative strength of the explosion of gunpowder and its equivalent of gun-cotton. 3d. Charges of 1-5 pounds of powder and 3f of gun-cotton comparative ei- TT,7 -iir.-11'i 11 ^^^^ "*" powder were placed on the mud and nred at high water, at a depth and gun-cotton of 10 feet. The charges were fired together, and the coUmms ting in'^e, undrr of water were observed to be about equal, but more mud bottom™''™" '^ was intermixed into the column of water thrown up by the powder. The craters were examined at low water, when they were high and dry. Each crater was found to be 9 feet in diameter, the gun- cotton crater was 2 feet deep, and the gunpowder crater 4 feet deep. It would appear from this that the shock of the gun-cot- ton explosion onlj' compressed the mud in a downward direction, and the mud so compressed afterward recovered to a certain extent its original position. . In the gunpowder crater the mud was less violently but more thoroughly thrust aside, and thus a deeper hole v.-as made. The lateral effect, which was really what we wanted to arrive at, was about equal, the charges of powder and gun-cotton being as i to 1. Against an air-backing, which would be the condition presented by a ship's side, a decided superiority for the gun- cotton is shown in the first and second experiments. Before any definite conclusions can be arrived at, exper- iments on a larger scale must be undertaken. It may, however, be laid down as an established fact that the local action xiroduced by a charge of gun-cotton, ignited by a detonating fuse, is enormous ; that this effect is quite inde- pendent of tamping, except in loose or soft material, such as earth, and that the instantaneous explosion produced is in no way affected by a want of absolute contact or by a small interval between the disks, rings, or masses composing the charge, as shown by the fifth experiment of the 5th September, 1868 ; or, in other words, that no compression is required at the moment of ignition. This in submarine mining is a very great point gained, as it does away with the necessity for considering the strength of case, as far as tlic (levclopnieiit of the explosive force is concei'ued ; ;i tlioroughly water-ti,L;'lit emelope, of sufficient strength to resist the pi-essure of tlie water at the depth to which it is required to be snbiner,ij;ed, being alone re(|uired. The cer- tainty of immense local action being, as already stated, es- tablished, it only remains to be proved that the radius of destructive effect is at any rate cipial, with equal weights, to gunpowder, to relieve us i'rom many difficulties to which submarine explosions are at present liable, and it is to be hoped that this very desirable result may be arrived at. luiaiive- values In a very carefully written article which appears iu "Eu- snii-rattot^'andgineering ' of the iL'th February, 1SG9, tUe relative mechau- ex;nnimHrtiKw°t' ical foFCCs generated by the explosion of gunpowder, gmi- I-'iliy. '"" ' '""'" cotton, and nitro-gly<'erine have been determined theoretically and chemically, the pressure of the atmosphere being taken at 15 pounds ou the square inch, to be as follows: 1 grain of gunpowder, when fired, produces a pressure of 200 pounds on the s(jnare inch ; 1 grain of gun-cofctou i)ro- dnces a i)ressnre of 1,204 pounds on the square inch;* and 1 grain of nitro-glycerine i>roduces a pressure of 1,1G7 pounds on the square inch. It is probable that these values are not far from the truth, provided the explosion takes place under exceptionally favor- able circumstancesas to strength of case and completeness and rapidity of ignition, but such conditions would very I'arely occur in practice. A muxiniura of Pcrhaps the nearest approach to such perfection of igui- • "i.taiiiert 'i'y flting tion is obtained iu the case of gun-cotton or glj'oxyline, and rtI"on°ting fuse! '^ also witli guuijowdcr, flrcd with a detonating fuse; and if this theory is true, we may assume that the explosive effect of a charge of either of these substances, when fired with this particular form of fuse under favorable conditions, ap- lirtiaches very nearly to a maximum, or, in other words, to the elfect which would be produced by the same charge fired with an ordinary fuse, and contained in a case, the strength of which had been calculated to a nicety, so as just to exert the proper pressure to develop the maximum force at the moment of ignition, and yet not so strong as in the smallest degree to reduce that force by the pressure re- • quired to burst too strong a case. Gmicoitonnoii- Quc gTcat advantage of gun-cotton is that, if ignited iu exposue Miem^ ^.^,^^^^ ^^^^^^ sjiacc, it simply bnms without explosion, and that, in order to render it incombustible, it is only necessary * Thin result is based on data derived from tlic forius of guu-cotton origiually mauufactured as to density and conseiiueiit weight, viz, 11 l»i,iiid.s to tlie culjic foot. Compressed gun-cottou weiglis considerably mole; nearly as uuieli as gniipowder. 37 to wet it. This wettiug does not injure it in tlie least (le.uiee, and when dried again it is as good as ever. A drowned charge may consequently be restored to a perfectly ejficii'iit state. This property, together with the greater security for storage and manipulation consequent therou, gives it a great advantage over gunpowder. Toward the close of the late civil war in th*^ United States, a good deal of gun-cotton was sent out to the confederates, but it does not appear to have ever been used by them. The third explosive alluded to is uitroglyceriue. kSouie xitro-giyc._. exijerimeats, with a view to testing its capabilities for sub- mariue work, were made by the United States Government, but with what result I am unable to Siiy. Our experience of it, derived from experiments made at (Jluitham, is. ho v- ever, such as to lead us to discard it for the above ptiriiose. Its advantages are the very compact form in v.-hich charges might be arranged, its greater explosive effect, weight for weight, as compared with gunpowder, six of powder being about equivalent to one of uitro-glyt'crine, the peculiarly damaging effect of its explosion, and tliat leakage of water does not [>reveut its ignition; but it is extremely dangerous to store, and its effects ni)on those working with it seem prejudicial to health. Further, it seems to require much care in arranging the charge for ignition, and we found that, unless confined in a strong vessel, such as a shell, for instance, there was no certainty that it would be tired by an Abel's fuse, specially i^repared for the puri>ose ; it seems to require a large amount of compression, or to be submit- ted to concussion the moment of ignition. This latter fail- ing might possibly be got over, but its otiier disadvantages are quite sufficient to coudenin it as an explosive a,:^ent for submarine mines. Another substance which might be used for submarin(» Dyuamitt-. mining purposes is -'dynamite." This may lie described as a mixture of nitro-glycerine and silica, by which the for- mer is said to be made as safe to handle as ordinary gun- powder. Its discovery is due to Mr. Xobel, a German eii,i;i- ueer. The question of safety in carrying, storing, and manipulating this substance, requires further testing: if it is simply a painting over, as it were, of the ijarticles ol silica, it is possible that the shaking necessarily encountered in carriage, or even long storage, might have the effect of settling or runuiugthe nitro-glycerine together, under which circumstances it would become as dangerous as nitro-yly- cerine unmixed. The following experiments with submarine 38 mines flllcd with dynamite, made in September, ISCS, at Carlslvrona, Sweden, give some idea of its effects : Experimonts Tlie target was the hull of a (iO gnu frigate, which had rgl,?tVuii'"„t'al.een built in ISW; her timbers and planking were quite c^ilvoiT'' "' sound ; timbers of oak, about 13 inches square, 1 inch apart ; planking of Swedish pine, .IJ inches ; bottom strength- ened inside with wrought-irou diagonal bands, 6 inches by i;^ inches ; inside planking running half way up to the bat- tery deck of oak, inches thick. The hull had been ■raze ■1) down to the battery-deck, and the copper removed. The chief object was to ascertain the effect of dynamite, in a contact-mine, against a strong wooden vessel, as well as against a double-bottomed iron vessel ; and, with this object in view, a quadrangular opening had beeu effected on the port side and filled with a construction representing a strong double iron bottom, firmly fastened to an oaken frame that had been put on inside, on the four sides of the open- ing, and with through-going bolts, 1 inch in diameter, to the timbers. The mines were arranged as follows : Starboard side Ko. 1, about amidship, 7 feet below water- line, with the center of the mine 2 feet 2 inches from the bottom of the ship; charge, 13 pounds of dynamite in a thin iron case, (jJ^-inch plate.) The mines, although repre- senting contact-mines, were placed some little distance from the ship, on the supposition that they would or might be pushed to some distance away from the striking shix) before they exploded. ]N"o. 2. About 40 feet from stern, 7f feet below the water- line, center of mine, 3 feet from the bottom of the ship; charge, 16 pounds of dynamite in a glass vessel. Port side Xo. 1. About 30 feet from the stern, 5'^ feet below the water-line, 2 feet from the ship's bottom; charge 16 xiounds of dynamite in an iron case of -jL-inch plate. ' No. 2. About 10 feet from ISTo. 1, 6i feet below the water- line, 2 feet 2 inches from the ship's bottom; charge, 10 pounds of dynamite in a case as above. No. 3. 2 iet't 2 inches from the center of the iron bottom, 7 feet 1 inches below the water-line ; charge, 13 pounds of dyuamite in a case as above. These five mines were fired at the same moment, the hull was lifted about a foot, and sunk in IJ minutes. The wreck having beeu docked, the effect of the different mines were found to be as follows: Effect of the Starboard No. 1. Timbers broken and thrown inside, into the hold, on a space of about 15 feet by 8 feet, leaving a hole of those dimensions; three more timbers on one side of muifc'-. 39 the hole broten; inside oak planking rent off on a length of 14 feet; two iron bands torn up and bent, one of them broken in two places ; outside planking off on a space of about 21 feet by 12 feet ; several i^lanks, still higher up, broken. aSTo- 2. Timbers blown away on a space of about 8 feet square ; inside planking off on a length of 20 feet; two iron bands broken, and torn up and bent; outside planking off on a space of about 19 feet by 12 feet. Port side Xo. 1. Timbers blown away on a space 10 feet 6 inches by 12 feet at one end, and 6 feet at the other; inside planking off for a length of 14 feet ; one iron baud torn up, one broken ; outside planking off on a space of 18 feet by 25 feet and 15 feet. Zso. 2. Timbers blown away on a space 4 feet in length and 16 feet in height; on the sides of this hole, 10 timbers were broken ; two iron bands torn ui), one broken ; inside planking off for a length of about 20 feet ; outside planking off for a space of about 20 feet and 23 feet by 10 feet and 13 feet. Xo. 3. The gas sphere had hit the middle of the outside plates on one of the angle-iron ribs. This rib was torn from the timbers and bent up, nearly two feet in the middle, but not broken. There was an oval hole in the outside plates 4 feet by 3 feet between two ribs, which ribs, ■with the plates on edge riveted to them, were bulged out about o inches. The inner plate, one large piece, was blown up in a vertical position, after having cut all the bolts and rivets, GO of 1 inch, and 30 of f inch, save those that fastened the lower side to the oaken frame and timbers. On a length of about 30 feet and height of about 20 feet the bottom, on all sides of the iron construction, had been bent inwards ; the greatest bend "was about 3 inches; three deck-beams above had been broken. By the joint effect of all the mines, almost all the iron deck-beam knees had been rent from the side, and there • was an opening between deck and hull on both sides for a length of about lott feet. The last and newest explosive agent is glyoxyline, recently Giyoxyime. invented by Mr. Abel, chemist to the war department- This is a compound of gun-cotton and nitro glycerine, pre' pared by soaking the former, in a granulated state, or in the form of disks or pellets, in the latter, of which it will take up nearly its own weight; the masses are then coated with a varuish, which ijerfectly excludes air and incloses the nitroglycerine; when thus manufactured, it is said to be as safe to handle as ordinary gunpowder. Its explosive 40 effect, wlieu fireil with a tlctonatiii.L; fuse, is very similar to that ot .liun-edtton tired with the same fuse, and as the hitter is very miicli safer to handle, it is (toiiseiiueiitly greatly to he preferred, unless future experiments develop any pecu- liar advanta.L;es to l)e derived from the use of s'lyxoyliiie. It is of importance to keep in view the necessity of nsin^' an explosive substance for submarine, or indeed for any min- ing purjjoses, which, though powerlul in its eliects when reciuired to act, and of a nature suitable to the work to he done, may yet be safely stored and manipulated when ordi- nary care is used : and we may on this account at once put aside the many compounds which, though at first sight pre- senting advantages, are liable to explode unless handled with extreme care. Picrate of ])otassium is an example of this class, and the fearful explosion of this substance wbioli recently occurred in Paris, is enough to condemn it. Si?.- oi chargp. The next point to be considered is the amount of the charge, of powder or other explosive, to be e nj])!oyed in eacli mine. On this sid)ject we have still a good deal to learn, and, before we can bring the calculation of charges for sub- marine mines to the same degree of certainty which has been attained as regards those for ordinary earth, rock, or masonry, much remains to be done. The points to be determined are the depth at which a given (diarge is nu.ist efi'ective ; the lateral and vertical range at which a certain charge may be relied on to pro- duce a given result, and what that result would be on the bottom of a ves.-5el as strongly built as a modern ship of war. ExpBiieuce of The experience of thc Confederates Oil tliis i»oint isdcscribed ■ttntederateH on ^ .izeofci,aij;p. byCaiJtaiu Harding Steward, II. E., in his notes on sub- marine mines, as follows : " ATith submerged torpedoes, as employed by the confederates, the regulation of the charge depended on the depth of water, the nature of the bottoiiij and structure of the ships to be expected, except in the case of small torpedoes, moored a little below the surface and arranged for contact. ^Vith these the proximity of the charge to the object altered the conditions. The fol- lowing scale of charges, suitable to depths from two fathoms and upwards, was made for use in the James Eiver, Avhere the bottom is very solt. It is l)ased on data obtained from the destruction of wooden vessels of 800 tons, by the confederates; also from experiments, and is suitable to strongly built wooden vessels up to 1,0Q() tons: cii;n,« for a 3 fathoms 300 pounds of powder. ■^iilt iintfoiji for -LI oi'n.trn vessel. 3 fathoms 600 pounds of powder. 41 4 fathoms 900 pounds of powder. 5 fathoms 1, 200 pounds of j^iowder. 6 fathoms ,. . . 1, 500 pounds of powder. 7 fathoms 1, 800 pounds of powder. 8 fathoms 2, 400 pounds of xiowder. With hard bottoms the charges could be diminished, for smHiier uharges ^. , f -I ' j_ ^ T J.1 -£' T for a harrl bottom. the waste of powder is not so great. In the case oi a rocky bottom, as much as 2."j per cent, may be deducted, accord- ing to the American experiments, because the rebound of the portion of the gas that acts downward is almost coinci- dent with the upstroke of the rest. These charges, even considering the objects in view, appear excessive, but it must be remembered that the confederates used only one fuse for ignition. With a proper arrangement for igniting the charges at several points a reduction might have been made amounting to 40 per cent. As I have before men- tioned, the employment of large charges was made with a view of controlling a large area, and destroying the ves- sel through the commotion of the water, when beyond the direct action of the charge. This plan may be a good one with small vessels; but the worst feature of the system is the fact that, as in some cases, the result depends upon the lifting powers of the charge, the quantity of powder must necessarily be increased in proportion to the size of the vessels expected. A progressive increase of one third o barges in- of the amount given in the foregoing scale, for every extra vessels. thousand tons of measurement, was considered bj' the offl- cer superintending the mining oi^erations in the South as the least that could be done in the case of large vessels. This is no doubt true, but with vessels of 3,000 to 4,000 tons it brings the charges to quantities too large for proper arrangement." As regards this scale of charges recommended by the confederates, it seems to be somewhat fallacious to go on increasing the charges without limit, according to the depth, and we may therefore safely assume some point beyond which the charges should not be increased. Probably 2,000 pounds might for the present be assumed as a maximum, which ought to be sufficient to break the bottom of any vessel, however strongly she may be built, if fired in a proper position with reference to her. As the tonnage of a vessel increases, so generally does her strength ; but so also does her draught of water, and, consequent upon the latter fact? If the charges were always kept as deep as possible, a larger vessel would always find a larger charge in proportion to her size, in close proximity to her, wherever there was suffi- 4-2 cient water to allow her to pass. t>u the contrary the large charge would probably reach a smaller vessel, ami as etlect- ually damage her iiotwithstaiidiug the cushion of water iu- terveniug. Ill the sixteeuth volnme of the Professional Papers of the Corps of Eoyal Engineers, a description is given by Lieu- tenant vr. A. J. Wallace, E. E., of the means adopted for blowing up s(nne wrecks of vessels in tlie river Hoogly. Lieutenant Wallace's conclusions as to the size of the charges to be most advantageously employed, as derived from these experiments, are as follows : Size ot charges " Thc slzc of the chargcs when thev cannot be placed usi'd ill destruc- ..^ . -.,t.^ .. , tion of wrecks iniuside Or uudcr tlic wrcclc should, in uiy opinion, be regu- lated by the depth of the water. In from four to nine fathoms, 4:.")() and ."iOO pound charges were found to answer very well, but I think they might have been increased with advantage at the latter depth. '•Between three and four fathoms, 250 and 300 i^ound charges are generally the most economical ; a larger quan- tity simply throws the water to a greater height without Ijroducing a corresponding increase in destructive effect." It is to be remarked, however, that these charges were, in every case, arranged to be m actual contact with the vessel, and were intended simply to break np the wreck in such a way as to clear the channel, and, especiallj" at the greater depths, they would be found much too small for use as submarine mines. Ch!u-,a>m cou- The charges used by the confederates in their drifting to''rp''*e'^d ot?'to? torpedoes were usually about 100 pounds of powder, and "'"""■ were productive of comparaiively small results ; thisis in a great measure accounted for by the fact of their explosion occurring at, or very near, the surface of the water. The charges the.\' employed in the attack of vessels with their torpedo boats were 50 pounds of powder, which proved in- effective in many cases, and I think may be i)ronounced too small for the purpose required. Experiments A great numbcr of exiteriments have been made at made at Chatham for floatiug ob-Chathamfor the floating obstruction committee, with a view struction commit- tee, to determine the deiith at which a given t'harge is most effective, as well as the radius of explosive effect, or dis- tance from such charge at which a vessel would be destroyed. This series is not yet completed, as it will be necessary to fire some larger charges than those with which experiments have hitherto been made. The results as yet obtained give us the following information, which, though it can only be regarded as approximately true, must be our guide until the 43 subject is furtber inTestigated : first, tliat 100 pounds of powder is most efi'ective at a depth of 10 feet — that is to say, that as it approaches nearer to the surface much of its energy is lost by the escape of the gas toward the air, and the lateral effect is reduced proportionally. Actually on the surface the lateral force of explosion would be at a min- imum, which would in a great measure account for the small amount of damage caused by the confederate 100- pound charges in the mechanical contrivances already al- luded to. Again, if the charge be lowered the explosive effect seems to be smothered, so to speak, by the increased pressure of the water and the lateral effect consequently diminislied. When further experiments have been made the depth at which larger charges are most effective will be determined ; secondly, from the observation of the results Radius of . xpio- of certain experiments made with charges of known sizes, ' fired on the bottom with different superincumbent depths of water, it has been found that when a charge is immersed to that depth at which it is most effective the radius of explosive effect may be derived from the eciuation where R = radius of explosive effect in feet, and c the charge of gunpf)wder in pounds. "Where gun-cotton fired with an ordinary fuse is used, the value of c would have to be mul- tiplied by 1 and the equation would stand thus : sive effect. E = ^:JL' c, and so on for any other explosive substance used, the i)ro- portionate efi^^ct as compared with gunpowder having been obtained. The relations expressed in this equation are completely borne out l\y the result of an Austrian experi- ment on a large scale, in which precisely the same effect was obtained, in proportion to the size of the charge em- idoyed. When the results of the larger charges have been obtained, it is possible that the deductions arrived at may be some- what modified, but in the mean time they seem to be suffi- ciently near the mark to be adopted for any calculations we may have to make. In an experiment tried at Chatham on Her Majesty's ship Experiment on Teipsichore, a charge of 150 pounds of fine-grain rifle-pow- TerpskiiOTe."'^'^ der, placed in 22 feet of water, on the bottom of the river Medway, at a distance of 12 feet below the keel of the ves- sel and 2 feet horizontally clear of the side, made a hole at a distance of 19 feet, in a direct line, and nearly in a vertical direction, of such a size as to sink the ship in a few minutes. 44 ^Yl' learu from tho result of tbis exixn'iment that the ex- ph)sive force of a chari;e acts most strongly, whatever the depth may be at which it is sulimer.iied, in the direction of tlie line of least resistance, wliich in this case was through the bottom ot the vessel, precisely at the point where the charge broke through. Evpeiiments on In the spring of 18CC, a number of experiments were tried Ameik'i?''^ ■"' '''at Portsmouth, by firing several charges of various sizes, suspended at different horizontal distances frour the sides of Her Slajesty's shij) America, and at different depths of water. Xo very decisive results were obtained from these experiments, but the fact that the destructi\'e effect of cliarges, iu a horizontal direction, diminishes rapidly as the distance increases is to be remarked. Von sdieiiha's In liis Treatise ou Coast Defense, recently published, ' ■''''"""™ '■ Colonel Van Scheliha gives the result of several experiments which he made himself. Some of these results are very anomalous, and do not at all bear out preconceived notions. They, however, confirm the idea, of which there can be now no doubt, that the explosive effect of a charge acts most strongly in the direction of the surface, or line of least I'c- sistance, whatever may be the depth of the water. liciinauonciii- The destructive effect would appear to be limited to the ^lons ;is to tile ef- ^ ^ . ivct of a chaige area from which the gas ot tlie exploded charge drives away the water. The first effect of the explosion would be the formation of a globe of gas, exerting a pressure equal in all directions. Water being practically incompressible, the effect in the direction of the sides is a force which is instantly communicated horizontally through the water as a shock, for a considerable distance ; but iu consequence of the ready transmission of this shock, in all directions hori- zontallj', there is but little damaging effect. Tlie effect of the gas in a vertical direction, is no doubt much enhanced by its very low specific gravity as comjnired with water, but its expansion, originally due to the great heat which caused its production, is iiiime00 pounds of powder, which should be used in all cases up to a depth of 20 feet. As a limit in the other direction, we may assume 2,000 pounds of powder as a maximum charge to be adopted, to be used at a depth of not less than 40 feet of water. This latter size is not too large to handle with comparative ease. In considering the series of charges given by Captain Harding- Steward, as the result of the confederate experiments, we find that the square of the depth in feet gives very nearly the sizes of the charges of powder in pounds for depths between 20 and 40 feet, for mines laid on hard bottom, and charges. 46 if we add one-fonrtli to the sizes of cbari;o.s thus obtained, for soft muddy bottoms or buoyant mines held by moor- ings, we shall have a tolerably areurate means of approx- imately caleulatini;' the charges required between depths of I'O and U> feet. This relation of charges, as the squares of the depth, though not derived from any mathematical re- lationship between the forces existing, is a rule easily remembered, and which seems to give a. result sufficiently near the mark for practical purposes. Charges of the sizes above mentioned would seem to bo sufticient to sink any vessel passing fairly over them. The ships would draw more water in proportion to their size and strength, and, bearing in mind the rule that where practicable the mines should always be laid on the bottom, they would find in- creased charges opposed to them in proportion to their draught of water. The force required to break through the bottom of a vessel, so strongly built as a. modern man-of-war, has yet to be determined, and may lead to considerable modifica- tions in the strength of charges here suggested, propoitinu, as In the event of any other explosive than gunpowder eoniiiared with. * . . ,.,,.. giinpowiior, ofbemg used for snbmanne mines, as, tor example, if it is tobeusediiicuicu- found that guH-cotton, fired with a detonating fuse, pro- c .i„e.. j|^^^^^^ better results, it will only be necessary to discover the relative proportionate value due to the force generated thereby, as compiared with gunpowder, and apply it to the approximate rules given, in order to obtain similar informa- tion for the particular form of explosive used. There are again many places where gunpowder only may be obtain- able aud its use becomes a necessity, there being no choice in the matter. lutiTViii between Thc ucxt point to be considered is the interval to be allowed between two adjacent charges in the same line of submarine mines, so that the explosion of one shall not injure those next to it, or disturb the arrangement of their electrical cables, and yet that the chance of a vessel, run- ning between any two, aud thus esca[>ing injury, may be reduced to a minimum. This is a point on which nothing has yet been definitely determined, but is of so much importance that a series of experiments should be made as soon as possible, with a view thereto. The interval between any two mines, which would place one at such a distance from the other as to secure safety in the event of either being exploded, manifestly depends upon the size of the charges employed, or, in other words, the 47 distance at which auy given charge is calculated to act destructively. This may be approximately calculated, when gunpowder is used, from the equation B,= ^ Sc, (see page 33,) where R is the radius of destructive effect. If then we ijlace our mines in line at centi'al intervals of six times E, our j)resent experience goes to show that they will be safe from the explosion of those adjacent to them. To find the safe interval for gun-cotton, or any other ex- plosive used in a system of mines, it will only be necessary to multiply by the co-efficient, derived from actual compari- son of the effect with that of guupowder, to determine the value of E due thereto, and to arrange the mines in line at intervals of 6 R as before. This necessary interval be- tween the charges in line is one reason which renders the employment of two or more lines of mines essential to a proper maintenance of the defense. It also sufficiently ex- plains the objects to be attained, in placing them in such a way that the charges in the second line shall cover the intervals in the first, and that those in the third shall cover the intervals in the second, and so on. Again, with regard to the distance to be allowed between interval between , T £• • -i, • M 1 X* i Ti- each line of mines. any two lines ot mines, it is easily seen, by reference to Fig. 1, page 15, that just in proportion as we move our second and third lines back, we increase the chance for a vessel to pass safely through ; it is, therefore, desirable to keep these lines as close together as the other conditions of the case will admit. These other conditions are, first, the necessity for allowing a sufficient distance between the lines of mines, to enable the electric cables to be laid in a safe position midway between them, in carrying them to the electrical room from which the system is to be worked. Second, the necessity for placing the lines at such intervals that there shall be no ponfusion in determining the position of each mine, by intersection, after they have been submerged. This is absolutely necessary in case it is required to fire the mines by judgment, the position of a vessel being determined by intersection, or cross-bearings, as it is sometimes called. It is also necessary to facilitate the discovery of a mine, in Experiments re- case it is required at any time to take it up for inspection m"ine^*distancl"'[f And third, the average length of a large ship of war is an'"'*"^' item which must be taken into consideration in determining the distance above required. Keeping these conditions in view, the intervals between the lines may be approximately determined and, as a general rule, they should never be at 48 less tljiiii 100 yards or more than L'OO yards apart, niiless siicli an arran.i;'(.'iiu>nt is inconipatiblo with the peculiar cir- eiunstances of any pnrticuhir position to be dclen(h'd. It \voahl be very desirable to make a few experiments, with a view to the more definite determination ol'this ipies- tioii of distance, at ^\'hicll one charge would be sal'e from the effect of the explosion on another ; till this is done the- above general rules may be adopted. , .'•'■i'^' ''-'""•„,"' 111 the record of the destruction of wrecks iu the I'iver )ao', R. E., a-i 10 HoDoly, by Lituleiuuit Wallace, E. E., he mentions that one nistiiiice ot sntV'ty. ■ .- .- / / of t«(i charges of -l^O pounds each, placed 55 feet apart and at a depth of 4S feet of water, was cU'stroyed by the explo- sion of tlie other, probably stove in ; it is not said how dam- aged. This distance of 55 i'eet is manilestly I'ar too little I'or safety with a charge of tliat size; it is, however, men- tioned here as the only experiment which 1 have been able towder, or gnu-cotton fired with an ordi- nary fuse, is used, it must be sufficiently strong to hold the charge together, as it were, for an instant at the moment of ignition, so that its full effect may be obtained by as thorough a combustion as possible of the charge. When gun-cotton, fired with a detonating fuse, is used, our present experience seems to indicate that the case need only ttilflll the conditions, as regards strength, enumerated in paragraphs 1 and 2. 4th. In the case of a buoyant mine, it must be capable of being arranged with a large excess of flotation, so that when moored it may remain as stationary as i^ossible at the required point. 5th, It should be of such form as to be capable of being handled and moored conveniently. Cth. It should be of such a form as to secure a thorough, ignition of the charge with the smallest possible number of fuses. 7th. It should be of such form as to be easy of construction and not too costly. First, with reference to the form of case. Those hitherto ■ G«nerai form of ' case. used seem to have been either conical (see Fig. 4) or cylin- drical. The former appear to have been used by the con- federates as the general shape for their self-acting mechanical torpedoes. The apex (a) of the cone forms a convenient point to which the mooring-cable may be attached, while the base, terminated by a curved portion, (&,) serves as an air-chamber, conrcai form f,.r giving the necessary buoyancy to keep the mooring-cable taut, ^r.acting'^mlns'!'''' 50 and hold the mine iu a com- paratively stationary position in a current or tide-way. This seems a very sood form for self-acting mechanical mines, giving a good salient position on which to place the bosses to be strnck by a passing ves- sel, as at c, c, c. Cylindrical form The Cylindrical form appears best for cliEirpeB fired . electricity. '^' by to have been used by the con- federates, where they allowed their charges to rest on the bottom. The cylindrical shape admits of the charge being stowed in a very convenient form, and, for large charges, possesses advantages, as far as the igintion is concerned, as will be hereafter described. The Austrians have adopted a cylindrical shape for their buoyant charges, and those exhibited by them at Paris were of the forms shown in Figs. 5 and 6. These mines were Fig. 5. arranged I'O be fired by electricity, and, all things considered, the cylindrical form seems the best adapted for the size of charges recommended by them, viz, 370 pounds of powder, 51 whether arranged to be laid on the ground or to be floated from moorings at any required depth. It is imi)ossible at present to lay down any definite rule as to the form of case best suited for submarine mines ; be- fore this is done some experiments must be made with large charges of powder. All that has hitherto been done seems to point to the cylindrical as the best practical form, except for the case already mentioned, where comparatively small charges, to be fired by mechanical self-acting means, are to be used. A spherical form would, be theoretically the best, supposing a single point of ignition only to be used, because every part of the outside would be equidistant from that center of ignition ; but the construction of a case of this shape would be comparatively costly, and a cylinder, the height of which approaches nearly to its diameter, is suffi- ciently near in shape to a sphere for practical purposes. Xext, as regards the material of which the cases may be most advantageously constructed. Several substances have been suggested and tried for Jtateriais r,f this purpose, such as wood, iron, and vulcanized India rub- be composed. ber. The confederates appear to have used wooden barrels for their smaller charges, and cases of boiler-plate iron for their larger charges. The large charge of 1,7-jO pounds which destroyed the Commodore Jones in the James River, and that of similar size which so narrowly missed the Commodore Barney, were both in cases of boiler-plate iron ; these charges were both fired by electricity. A charge of 5,000 pounds of pow- der in an iron boiler, arranged to be fired by electricity, was Ijlaced at a distance of 1,jOO yards from Fort Sumter, at Charleston; at the critical moment, however, it failed to ignite from some unknown cause, which was probably either a defect in the iu.sulation of the electric cable, or a bad fuse. This charge had been four mouths under water before any attempt was made to fire it, and the art of test- ing fuses and insulation was not then known as it is now. The following is a description of the construction of the cases for submarine mines, exhibited by the Austrian war department, at Paris, in 1867. The form and arrangement of the charge of a gun-cotton Forms of cas..- mine in a wooden case is shown in the accompanying sketch, JriL,-. ' Fig. o, which gives an elevation and section. It consists of two strong wooden cases, one within the other; the inner one covered with zinc and the space between them filled in with tar. They are of the shape of a truncated cone, but the diameter of the bottom is very slightly greater than that of r,9 the tiip. The iuuer one has a mcau diameter of about 4 feet, and is about 4 feet iu height; it is calculated to con- tain 4 hundrodweiiiht of gun-cotton, made up iu coils and packed \Yith plenty of air space, as shown in section. Fig. 5 ; iu this section the air-space is shown dark. Abel's com- pressed gun-cotton affords great advantages over tlftit in coils, as applied bj the Austrians. The size of a given charge of, cotton is thereby reduced from three times that 01 powder to nearly an equal bulk, weight for weight. Figs. 6 shows an elevation and section of an iron case, cal- 4 ' Fig. 6. «- cuhited to contain about 3 hundredweight of gunpowder. It consists of an outer cylinder, (a,) at the top of which is a series of projecting buffers, held in position by strong springs, by the contact of which the circuit from the firing battery through the fuse is completed by a vessel passing over the torpedo. These buffers are shown in the sketch at the points &, h, b. Within the inner case a second iron cylinder (c) is placed to contain the charge of powder, a sufficient air-space, to give the requisite buoyancy, being allowed by the difference iu size of the cases. The outer case is about 4 feet in diameter and 4 feet in height. Ci^ptaiuHaiding Captain Harding Steward, K E., has suggested placing t'^OTsasto thf°usethe chargc iu an India-rubber bag, the bag being furnished of ^ inaiarubber ^j^^j au outcr covcriug of iron. This outer covering need not be necessarily water-tight,, and is only intended to protect the India rubber from injury by friction a.^aiust rocks, iSrc, and to give rigidity to the whole apparatus, so that it may be easily handled, jfnd, when required, moored by means of anchors in the usual way. In some experiments tried by the confederates it was found that a large charge of powder inclosed in an India-rubber bag did uot xjfoduce the same amount of explosive effect as the same charge in an iron or wooden case of considerable strength. It is probable that the envelope was burst by the first explosion and a portion of the charge wetted before the whole of the powder had beeu ignited, and in order to obviate this result, Captain Steward proposes to ignit€ the charges at a great manj" dilferent points, so that the whole may be fired as it were simultaneously, and the drowning effect thus partially obviated. This is done by a single fuse placed at theextremityof a metal tube, passing through the charge, and the tube being perforated at intervals, the flame and gas of a small priming charge is driven into the body of the main charge at a large number of points simul- taneously. A more minute description of this arrangement will be given in treating of the several modes of ignition applicable. It is to be remarked that the confederates only used one fuse in their charges, whatever their size might be, and this is ciuite sufficient to account for the non-ignition of the whole of the powder in a large charge when iuclosed in an India-rubber bag ouly. The advantages of Captain Stew- ard's system are the comparative cheapness of the case, and that it is not dependent on the iron outer covering for keep- ing the charge dry ; this covering may consequently be made by a comparatively inferior workman. In removing the wreck of the steamer Foyle, sunk in the india-rubber rr^i -r-.i--r-»-t-t-i - /. tiR^^ used in con- Thames at Barkmg Eeach, which service was performed by nection witii oper- the officers and men under instruction iu the School of Sub- Foyie. marine Mining, Chatham, the charges were all inclosed in vulcanized India-rubber bags, within an outer casing of half-inch boiler-plate iron. It was intended that the outer iron coverings should have been water-tight, but by some accident one of these cases leaked considerably ; the charge was, however, saved by the India-rubber bag, and ijerformed its work apparently as well as any of the others. This leak was attributed to the fact that the iron case had been left, for some time before it was filled with powder, in a hot sun; iu fact, the air inside felt very hot to the hand. When subsequently submerged, it was supposed that the cooling and con seijuent contraction of the air had caused a consider able increase of external pressure, and that tlie water had be loaded ia tlK' siui high lempcratui'e, ,r k.'iit ];.p>iit of 54: Ibrccd its way through some weak place. All the iron cases used ])ad been tested by liydraulic i)ressure, and were apparently sound before immersion, yet the fact of the -water having got into the case is indisputable. OAe lesson learned from this occurrence is, the advantage of using two water- tight cases for submarine mines, an inner one to hold the charge, and an outer one to withstand the pressure- of the water and to secure the neces.sarj' amount of flotation, not when the uiiue is required to be buoyant. Assuming that a the leak was occasioned by the cause above specified, it is necessary to keep iron cases out of the sun, and fill them with tlic air inside at a temperature somewhat similar to that of the water in which they are to be placed; and again, when it is necessary to store them, especially in po- sitions where they may be subjected to considerable changes of temperature, the screw-plug or man-hole should be left open to allow a free ingress and egress of air. As a matter of precaution, this should be made a general rule whenever it becomes necessary to store these cases ; this course is adopted with regard to large iron buoys. Lieu- The following report by Lieutenant Chadwick, E. E., on tenMut Chadwick, K. E , on boiler- the subjcct of boilcr-plate iron, as applicable for use in the plate iron for sub- , ,■ n ■, ■ ■ .,,,. marine mine cases, construction 01 Submarine mines, possesses considerable lu- Fig. 7. '^^ terest. Theresults of Lieutenant Chadwjck's investigations are, that envelopes for submarine mines should be double, an exterior wrought iron case, and an internal tin or India- rubber case, to contain the powder, leaving an air space of IJ inches to 2 inches between the two, and kept apart by wooden battens. The general form of case is shown in Fig. 7. This air-space is to prevent the interior case, con- 55 taiuiug the powder, being damaged by any sliglit leakage, or by the deijositioa of moisture produced by change of temperature. lu buoyant mines a considerable air-space is required to give the necessary flotation. Tor a buoyant mine it is recommended that the case should be of B B boiler-plate iron throughout, the sides J inch, and the ends f inch thick, fixed together by rivets, l)olts, and nuts of the same material and quality. The size for a buoyant mine t- > contain a charge of 1,000 pounds, jiiight be 10 feet long and 2 feet 9 inches in diameter. This gives an amount of buoyancy as determined by the follow- ing calculations : 1. To find the displacement : Displacement. Volume = length x area of base, (taking no account of the curved ends.) 101/ = 10' X 4^ X T. 16 X 4 = 10' X o'.939 = 59'.39 cubic feet. Displacement = volume in feet x weight of 1 cubic foot of water. = 59'.39 X 02. 42.J pounds = 3707.42 pounds in fresh water ; or 59'.39 x G4.05 = 3793.93 in salt water. 2. To find the weight of the mine : Area of skin = length x circumference. = 10' X ^^^- X 3.1416 = 10' X S.G39 = 86..39 square feet. ]^ow I" plate weighs 10 pound per square foot, (Eaukine;) therefore weight of skin = 8G.39 x 10 pounds = SG3.9 pounds. Weight of three joints each 3" wide : = 3 X circumference in feet x width x 10 = 3 X S'.Gl X i' X 10 = 64.8 pounds. Weight of 4 joints, (longitudinal,) = 4 x 2^ x^ X 10 = 22.-5 i)ounds. Weight of 2 circles of angle-iron, 3' in diameter at 4.2 pounds per foot, running : = 2 X % X 3.1416 X 4.2 4 = 59.38 pounds. Each end is a segment of a hollow sphere, the diameter of the base being 2 feet 9 inches, and the height 6 inches. The thickness of metal is f inch. "Weight. Flotation. (Jollapsing pres- sure. 56 Using the t'onmila for tlie snrfece of a segment of a sphere : B = r:.,l.h 11' \TC find the surface of the two ends = 2 x 3.1416 x -^ X ^ = S.Gl weight = S.-'JJ: X 15 [)onuds = lliO.G pounds. Summury of Weights. Pouuds. Skin • S03.90 3 joints ; - 01.80 1 joints, (loDgitndinal) i"-'. 51J 3 rings, (angle-iron) 59. 38 2 ends, (domed) 129. CO Charge 1, 000. 00 Case for do ' 150. 00 Total weight . ,. 3, iiOO. 18 3d. To find the flotation : Fesli ■\\'ater. jSalt water. Displacement 'S, 707. 42 3, 793. 93 AVeight 2, 290. 18 2,290. IS Flotaliou 1, 417. 24 lbs. 1, 503. 75 lbs. This may appear unnecessarily' large, but it is well to have an excess of flotation power, as it can easily be dimin- ished by using a slightly larger charge.* The dimensions given above are suflieient to resist any tendency to collapse from external in'essure. Let / = length in inches. d = diameter. t =: thicliuess. g = collapsing pressure per square inch. Then q = 9G72000 --~ uearly; (see Eankine's Applied Me- chanics, page 307.) Therefore, in the present case, n = 'j(>720(i0 - y-^ ' ■ ' ' ^ 120 X 33 = 152. C lbs. per square inch, which represents a pressure of about 350 feet depth of water. This calculation is made without regard to the covering plates over the joints, which would probably quadruple the strength, •The amount of flotation nt.'ces.saiy depends on tlio strength of the current in which a buoj-ant submarine mine is moored, as \Yin bo ex- phiined hcreat'tei. 57 as three such joints would exist, the case being conveniently formed of four plates, and consequently I, the length for calculation, would become 30 instead of 120. The strength to resist internal bursting iiressure is given by the equation *=^4 (Eankiue.) Where t = thickness. }- = radius. T , . Bursting pres- p = bursting pressure. sm-e. / = tenacity, which may here be taken as 34:,000 pounds per square inch. (Eankine.) Then * — ^^ ^^''° lO - 34000 or, p = 515 pounds per square inch. Therefore bursting pressure is nearly 520 pounds per square inch. To develop the whole force of the powder, when fired in the ordinary manner, a much greater strength would probably be necessary ; but to obtain it, the thickness of the case would have to be increased to so great an extent as to render it unmanageable. It would appear, therefore, that to produce a given effect it would be better to employ an excess of powder, ignited bj" several fuses, than to at- tempt to produce a maximum effect from the charge by increasing the thickness of the case. It might be well to try, on a considerable scale, the effect of iuclosiiig the pow- der in a loosely-"woven bag of gun-cotton, with the object of igniting the charge from the exterior, by which the disper- sion and loss of part of the charge might be prevented. There is no doubt that, under oriliiuiiy circumstances, we should use a cylindrical case, more apprc/aching in form to that adopted by the Austriaus, and shown in Figure 6, than to that given by Lieutenant Chadwick, shown in Figure 7; this latter Mas designed to be moored foie and aft, as would be necessary in a very strong current. Our present experi- ence goes to show that, in a three or four linot current, a single mooriag-hawser will answer every purpose, pro- vided plenty of bftoyancy is given to the mine. We have as yet no sealed iiattern of an approved form of case for submarine mines, and till one is determined on, it is only iiossible to deal in general terms with the subject. A good many experiments have been tried by the float- Result of ex- ing obstruction committeee, to ascertain the requisite strength of \ase" strength of case to fulfill the necessary conditions already btmctim'cfmt^u- enumerated, and the following appears to be the result of "' their investigations, so far as carried out : 58 '•These experiments lead to the g-eneml conclusion th;it llie clTcct of a chnrge of gunpowder exphided nuder wutei' is enhanced in a very great degree by the strength of thv case in which it is inch>sed, seeing that even with so small a charge as i pounds the maximnm effect of the force is not attained until a case is provided of i-inch iron, and which will stand a gradual pressure from within of 330 pounds per square inch. " It may therefore be assumed that the manageability of a charge vrill alone determine the maximum weight or strength to be given to a torpedo, and that all the strength which it may be found necessary to give to tlie case, in order to resist the pressure of the column of water under whicb it is submerged, will tend to increase the effective- ness of the charge, there being no risk that such extra stren;^th of case will involve an expenditure of force, in its rupture, at all approaching in cx'tent to tire advantage gained by its resistance, and the consequent increase of time afforded for the development of the explosive force of tbe charge."' A corroboration of this o})inion appears in the account of the experiments on board the Excellent, where the effect of 5-5 pounds of powder in a shell approximated to that of 25 pounds in a barricoe. Expeiim e 11 1 B It only now remains to continue the series of experiments rlquir^X" '"°'"' With large charges, of such size as would be used on actual service, to enable a definite conclusion as to the form and strength of case best suited for the purpose, to be arrived at. The charges hitherto used in the experiments carried out have been small, as the apparatus would not admit of large charges being fired in connection with it. A continu- ation of this series of experiments, in connection with an apparatus of similar form, but on a larger scale, under the' directioii of the royal engineer committee, is now being carried on, from which more definite results will no doubt be obtained. These experiments are not, however, sufii- cientlj' advanced to warrant any decided conclusioa upon the results obtained from them. Cylindrical form As far as wc yet know, I think we may say that a cylin- mennTd." "™"' dcr of a morc or less elongated form seems to fulfill the re- quired conditions best, but whether it should be of India rubber, protected as described, of boiler-plate iron, or of any other material, has still to be determined. Should, however, boiler-plate iron be decided on, I think we may safely assume that a thickness of J inch of metal (the burst- ing pressure for which, on an elongated case, of the dimen- 69 sions shown ia Eig. 7, calculated to contain 1,000 pounds of powder, would be 515 pounds ou the square inch) will give a sufficient resistance to the bursting effect of the ex- plosion for the size of charge recommended. In all eases, the most approved form of envelope to con- Bamin maybe tain a charge of powder for submarine mining purposes, abm. may not always be at hand, and it may be necessary to use ordinary barrels, or any other available articles. Bar- rels are very readily obtained anywhere, and, whenproperlj' strengthened, are a tolerable substitute for the more ap- proved form of case; they are, moreover, made of sul^cient size to contain a considerable charge of powder. In blowing up wrecks in the river Hoogly, as reported by Lieutenant Wallace, E. B., in Volume XYI of the Pro- fessional Papers of the Eoyal Engineers, page 116, barrels were used. These were of different sizes, viz, hogsheads, half-barrels, and kilderkins, holding respectively 500, 300, and 15(1 pounds of powder. Lieutenant Wallace tried sev- eral methods for strengthening the two larger sizes, which he found necessary, and that employed by Sir Charlfes Pas- ley, in his operations upon the wreck of the Eoyal George, and shown in the annexed Fir,. 8. Fig. 8, was found to be the most effectual. It consists in strengthening the ends of the barrels with wood. The project- ing tops of the staves of the orig- inal barrel were half cut away? and the strengthening of wood arranged to break joint with them, while at the same time fill- ing up the spaces cut away. This done, the whole barrel was well payed over with pitch and tar, and, when required to re- main a considerable time under water, the whole was sewn up in a stout canvas covering, also well saturated with the same composi- tion of pitch and tar. Lieuten- ant Wallace found that, in a strong tide-way, a charge of 500 liounds of powder required a weight of 400 pounds to sink it, whereas in slack water, less than half that weight was sufficient. 60 All cases must As in submaviiie mines the charges must generally remain tt'ht^"'^ water. ^^ (jQyg||-^gj,^^^jg ^-j^^^, imder crater before explosion, it is most necessary to make the case, whatever it may be, xQvy water- tight, and with this view the inside of a barrel might be lined M'ith a coating of marine glue or cement. In the experiments carried ou by the iioating obstruction committee, the latter was found to give a perceptible increase of exphisivc efi'ect, when used as an external coating to X X tin cas(_\s for small Au internal tin chargcs, by glviug au increase of time for ignition. An inter- ber bng recom- ual Case ot X X tiu would also, i imagme, prove a very eneet- t'lircharge^ir "' '' i vc mcaus of keeping the charge dry. In using it care should be taken to fix it firmly inside the barrel, as any independent motion might disturb the connections of the electrical con- ducting wire or destroy its insulation. An internal India-rub- ber bag, as recommended by Captain Harding Steward, placed inside a barrel would also afford a ready means of preser^-ing the charge in a dry state. If greater flotation than that afforded by the barrel, when loaded, is required, in order to fit it for a buoyaiit mine, it must be given by buoys or corks attached to it. A atcam-bniior Another make-shift which may be used for submarine miii- .igoodmake-siiitt. .^^ purposcs is a stcam boiler, and any otlier envelope presenting the necessary requisites of strength, to resist the external and bursting pressure at the moment of ignition, in a sufficient degree to insure a good explosive effect, and also possessing the property of being very water-tight, would answer the purpose. In all cases it would be necessary to use the same precautions in the preparations of these arti- cles as recommended for the barrels, and which indeed are the essential points to be attained in any envelope for sub- marine mining purposes, whether of a make-shiit character or constructed especially for the purpose. A strong caso Thcsc remarks, with reference to the strength of case gunpowder ^"'o r ncccssary to develop the explosive effect of any given charge, witii'' M^ordinary liavc reference especially to guni^owder ; and as circam- cottOT^fired w»h' stances may occur in which gunpowder alone is obtainable, it [s'^nor™ Issen" they must not be omitted in considering the organization of *'"'• any system of submarine mines. If any oth _n' explosive be used, the necessity for employin g a case of sufficient strength, with reference to the peculiarities of that explosive, must " still be kept in view. Compressed gun-cotton fired with an ordinary or with a detonating fuse is the most lik'ely agent to be employed. If fired with the ordinary fuse it would still be necessary to take the strength of case, to develop the full explosive eifect of the charge, into consideration, and the conditions would be verv similar to those of gnu- 61 powder, bearing in raiud that, where an equivalent only is used, a case of proportionately smaller size ^rill be suiEcient. If fired with a detonating fuse, we may probably omit the consideration of the strength of the case as far as the development of the explosive effect of thechargeis concerned. The other conditions to be fulfilled, viz, capacity to keep out water, sufQcieut strength to bear handling without danger of fracture, &c., enumerated in the beginning of this chap- ter, must, however, be kept in view. It is impossible as yet absolutely to say that gun-cotton, fired with a detonating fuse, is our best explosive for sub- marine mines ; but it possesses many advautages, not the least of which is this ability to dispense with all considera- tion of the strength of case necessary to the development of the maximum explosive effect. CHAPTEK y. 3IOOEING-. The next point to be considered is the mode of mooring a submarine mine when it is to be flouted up from the bottom and not actually laid on it. The question of mooriug seems at first sight a very sim- ple matier; practically, however, it has been found to be one of the most difficult problems to be solved in conuectiou with a system of submarine mines. In order to possess a maximum of efflcieucy, no indication of the position of a mine should appear on the surf;ice of the water,* and y(jt the spot to within a few feet where it is deposited must be known to the defenders of the position in which it is used. It has been found tliat the least current, or even a moderate breeze,, renders the placing of even a single mine in a defi- nite position a matter of very considerable difficulty. When a series of mines are to be inoorcd in proper relative posi- tion, this difficulty is much increased, and it is agniu con- siderably augmented in projtortion to the depth of water. Under certain conditions, therefore, special means, to be . herealte.- described, must be employed. (jirj.Lisio b, Kt- The objects to be attained in mooriug are as follows : 1st. That the charge should be kept as nearly as possible stationary atthe point where it is required to act. This is particularly necessary Avhere there is a tide Vi'hich, flowing first in one direction and then in another, tends to cause the mine to shift its position, and is indispensable in the case of mines to be fired by judgment. L'tl. The mooring should be so arranged that there shall be as little twistiug as passible, which might break or injure the insulation of the electrical cable. 3d. The anchors or heavy weights used should be suited to the nature of the holding ground or bottom. 4th. Mooring-cables should be so arranged that they may not be likely to become twisted togetJier or entangled. Buo\-ant submarine mines may be, moored by one or more cables, according to the different circumstances of the case, * In certain cases it is impoK.siljlc tciliilly to (•Duceal tlio position of a system of mines, as, for examjile, wlien tliore is a considerable rise and fall of the tide. When sucli is tlie case the very smallest indication pos- sible should be allowed to appear on the surface of the water. ■a. 63 and several modes of mooring have been suggested and adopted. The following is a description of that used bv the Aus- Austrian mode , ''of mooring. trians during the war in 1866, and exhibited by them at Paris in 1867 : In the Adriatic, where there is almost no tide or current to disturb submarine mines or cause them to revolve and twist up their mooring-chains, a verj- simple arrangement for keeping them in their required positions has been found effectual. This is shown in sketch Fig. 9, which gives the Fig. 10. form employed with the original gun-cotton charges which were arranged to be iired at will. It consists of a simple wo'oden platform of triangular form, on which heavy weights, marked (Ic) in sketch, are placed at intervals; this platform is attached to the submarine mine by three wire ropes, in connection with its angles, which are fastened to three chains holding the charge at any depth below the surface of the water required, by means of arrangement shown in sk.-cch Fig. 10. This consists of a pulley (l) attached to the ex- tremity of the wire-rope of platform, through which the moorin'g-chain of the charge is passed and fastened by a key or catch marked (m) at the required length by means of a self-acting arrangement shown in Fig. 11. This key is of considerable weight, and consequently slips down as the charge is hauled into its place, but the moment the chain is slackened the two arms {«, a) shown in dots which are made to allow the latter to pass through in one direction only, catch into a link of the chain and hold the charge firmly into its place. The ap- Austrian catch. 64 pni-atns is so coiisituctcil as to allow the eUaiu to be passed freely through it, and is provided with uuts to admit of its Fi3. n. Allfctrian musi room auch'oi". Block and jjul ley. which t'lectriCLil actiou occurs not ^\'ater, to be pkiced contact in Kea- ci' M'otcr beiug separated, in order to disconnect it from the chain when required. In our mooring experiments an apparatus of this nature, weighing 60^ pounds, has been used in cou- neetion with a halt-inch chain with good results. ' In connection with the self acting submarine mines more recently adopted, a mushroom anchor has been used. This mode of mo(;ring is said to have been quite effectual in the still water of the harbors of the Adriatic. The details of the block and pirlley used in connection with this key are shown in Pig. 12. The sheave (a) is made of cast iron galvanized, and the remainder of wrought iron. The sheave (a) and axle (&) were, in the first instance, made of gun-metal, but the electric actiou, set uj) between this and the iron of which the remainder was constructed, had the effect of decomposing the latter very rapidly, and the api)aratus in consequence soon became useless. Experience teaches us that no two metals between which electrical n action is likely to occur should be placed in contact in sea- as the latter is quite sufficient to induce voltaic ction, to the detriment of one of the component parts, and destroy the apparatus. An ordinary sha<;lde is attached to the block to enable it to be fastened into a link of a 65 cliain or thimble when required ; when convenient it may be fastened directly into the eye of the mushroom anchor, Fig. 12. which, under certain conditions, would simx^lify the arrange- ments very much. The dimensions shown are adapted for a J-iuch chain. TVlien new it works very well, but rust soon renders it stiff. Fig. 1.3 shows another description of catch by which a Fig. 13. i/^-i; cliar.uc, which has been hauled down, may be held in its place. It consists of a simple pair of barbs, {h h.) working on an axle and held open bj' an India-rubber spring, [a a,) capable nf being compressed; if pushed away from the India ruljber they simply press against each other, shoul- deis being provided on each, close to the axle, to sustain any iiressure exerted against them. To use this apparatus it is only necessary, alter measuring the depth of water at the point where the mine is to be submerged, to insert the catch at the required distance in the mooring-cable below the charge, and haul down through a thimble or eye on the mushroom anchor or moorings, when the mine will be re- tained at the required depth below the surface. It possesses the advantage over the Austrian arrangement. Fig. 11, that it can be used ia connection with a hemp or wire cable, whereas the Austrian can only be used with a chain. Barbed ciitcb. 6G Catcbes of this kiud Lave been used in onr mooring prac- tice with A'ery good results wben new. \Mien tliey have been some time siibuierged tlie rust malies tlie Joints very stiff. And tbey tlien become bard to pull tbrongb the I'ing or thimble in connection witli them. The Austraiu catch possesses the same delect, becoming very stiff' trom rust; in fact, any iron apparatus must necessarily be injured in this ■way, and, for the reasons already specified gun metal is in- admissible in close proximity to iron. Tlie rusting is not perhaiis of any very great importance, as, wben once down into position, a mine would seldom be required to be moved. A series of experiments in mooring were carried on at Chatham during the autumn of 18G7, and the following ex- tracts from the reports of Lieutenant O. Ohadwick, E. E., who had immediate charge of these experiments, throw some light on the difficulties to be encountered in sub- merging charges. Bxperimenis ia u ^yjien the dei)th of water is so great that a submarine moonug in Med- ^ ^ way, near upuor mine, if phiccd ou the bottom, would require for efficiency an excessively large charge, it must be floated up from the mooring to which it is attached. This introduces great com- plication in the arrangements and also increased chance of derangement, either by accident or by the operations of the enemy. For still, tfdeless waters, the Austrian method would no doubt answer. In any current, however, the case would be liable to spin round and entangle the conducting wire with the moorings and produce kinks in these, unless indeed the size of the triangle were inconveniently large. It is also easily grappled and taken up ; indeed one placed in the Medway at Upnor was, after a few hours, hooked by an anchor of a barge or steamer and carried away." mMit^'o'f moorur While OU the subject of methods of mooring when there is '-■■■'Mff. any current, the following must be avoided : Fig. 14 shows an ordinary cask with two mooring cables {a a) underneatli. The object of using two cables is to keep the mine in a per- fectly stationary position, but our experience, derived from experiments carried on in the Medway, is, that unless the attachments of these cables to tliat mine are kept well apart they are certain to become twisti'd round each other when there is a current, and especially in a tide- way where it runs tirst in one direction ami then in another. It is clear, too, that if, in the process of lowering or by any other chance, the mooring cables get a single turn around each other, the effect of their having been originally arranged apart is completely lost, and they become as free lo revolve as if botli cables have been attached to the same point. Practi- 67 cally it was found that with a current of about three knots an hour, as in the Medway, barrels arranged as in Fig. 14 Fig. 14. invariably became twisted up in such a way that an electric conducting wire, connected with the mines to which tbey were attached, would inevitably have been much kinked and probably injured. To obviate such a result Lieutenant Chadwick proposes, smaii charge ^ ^ ' moored on a spar. with small charges and at moderate depths of water, to lash the mine on a spar on which a rough frame-work to fit the form of the barrel had been arranged, and attach the moor- ing-cables to the extremities of that spar as shown in Fig. 15, thus securing the necessary distance between the points P'ig. 15. I" of attachment to prevent the chance of entanglement. In '' order still further to secure this, the anchors to which the ' cables are attached should be placed weU apart, and plenty of 68 Ladder moor- buo.vauc.v allowcd to keep the cables tijilit. In certain '«'■ positions it may be inconveuient to place tlie anchors far ai)art, and when this is the case, a ladder arrangement may be effectively used. Fig. 16. Layr yra^terLme- Circuit Close J^^ine Fig. 16 shows a combination of this sort, somewhat similar to that tried in connection with experiments on board Her Majesty's ship Cambridge. The following report by Mr. Charles Cockran, gunner, Eoyal iv^avy, extracted from the report of tlie committee on active obstructions, published in ISGS, gives the results ob- tained : ".i buoyant torpedo, consisting of a 27-gallon iron oil- cask, containing 15 gallons of water, and a strongly l)uoyant nun-buoy to represent the circuit-closer, were fitted with two mooring-ropes from the circuit-closer to the torpedo and thence to the mooring-ballast, the ropes being sex)arated by Avooden rounds or spreaders, one to three feet long, to resist the tendency to twist. This arrangement, with two insulated wires connecting it with. the electric battery, was placed iu position on the 18th of April, 1868, in 10 fathon:s water in a part of the Hamoaze liable to strong eddy tides; and at the end of 21 days it was removed. While it was in position the arrangement was twice examined by di^'ers, who reported theniooring-roiiesand conducting-wires to be clear of turns; 69 and tliat. wlien taken up. a round turn was found in the mooriiig-iopes close to the ballast, but the whole of the upjier portion of the ropes and the insulated wires were clear. Thi-; means of emploviiic;' hemp-rope, in the absence of wire- rope, in a manner calculated to resist the revolving tendency of the circuit-closer, appears to have proved successful. It is. however, to be observed that the rounds or spreaders are liable to lodgments of sea weeds or other objects, which might sink the circuit closer ; and that the plan does not therefore recommend itself for adoption, except when wire- rope is not procurable. "The liuoy-rope. which had been attached to the ballast for recovery after exijeriment, repeatedly took several turns around tlie mooring-ropes, though cleared by the divers at each examination." In Fig. 10 rather more spread is shown than was used in the Hamoaze experiment. This would no doubt decrease the tendency to twist, but the broader spreaders would af- ford a greater space for the deposit of sea-weed, &c. In deciding, therefore, on the particular dimensions to be em- ployed, local circumstances, such as the cxuantity of sea- weed or other floating matter, the strength and direction of currents, their steadiness or eddying qualities, and all simi- lar difflcnlties. sliould be carefully considered so as to injure, as far as practicable, a minimum of evil in the form adopted. In a tide-way where there is a current of more than live Mooring fore and .■^.It, knots an hour, twti anchors may be advantageously useil, placed up auddowii stream at a considerable ilistauce apart, depending on the force of the current and the height from the bottom at which the mine is to float. At first, considerable difficulty was experienced in i)laciiig the anchors at a correct distance apart, but by the following method small charges have been laid down successfully and have maintained their positions when so placed. The following arrangement, desig-ned by Lieutenant Chad- wick, E. E.. was tried in the river 3Iedway during the autumn of ISO', aud moorings with a charge attached were thereby successfully lowered into position without much difiiculty. A derrick. Fig. 17, was rigged at each end of a boat, the distance betweeu the ends being that which the moorings were to have when on the bottom. To these the mooring- anchors were suspended, being attached to the ropes by nippers which released them when on the bottom. The charge itself was made to sink by means of a heavy saddle. Fig'. IS. placed over it, and thus its upward tendency did 70 Bot draw the moorings togotlier; (a) sIjows the mine, (h) the weighted saddle. j-^ ^ The length of the mooring-cables having been i»reviously adjusted according to the depth of water, when the moorings were placed on the bottom the saddle was drawn up, and the charge rose into its proper position. Fiff. 18. Small charges, of the size of IS to 36-gallon casks, were successfully placed in this manner with a 30-foot gig, ponton- baulks being used to form the derricks. The larger kind of ship's boats, such as a 4l2-foot launch, are provided with a Avindlass placed across the boat, in the center of its length. Under this are two hollow trunks fixed water-tight over holes in the bottom ; througli these ropes may be passed to the windlass, and in this manner a heavy object may be carried under the bottom of the boat. A load 71 of from two to three tons may be safely carried in this man- ner. In ordtr to place a large buoyant charge, of 1,000 pounds to 2,000 pounds, for example, three of these larger boats would be required to carry it and its anchors, one fur each anchor or mooring-block, and one for the charge itself. They would be connected by a rope, which, if kept stretched, would insure the anchors being placed at the proper dis- tance apart. In some cases ponton-rafts, with triangle guys erected on them, might be used, but they would be difficult to manage in a current. Some further experiments were subsequently made in the Mooring ex- ^ A i- periment off Medwav opiiosite Chatham dock-vard, where there was no Chatham dock- " ' yard. chance of the apparatus being carried away by passing ves- sels, as was supposed to have been the case with those placed in the river opposite Upuor Castle. The following is the result of these experiments as reported by Lieutenant O. Chadwick, E. E. : "Two large casks (36 gallon) were moored in the river Mooring by a with mushroom anchors of 10 cwt. each. Their total buoy- ancy was about 10 cwt., and each contained a weight of .5 cwt., representing the charge, so that there was an upward straiu on the mooring-rope of 5 cwt. The length of the rope was !•") feet, so that the toii of the barrel was about 20 feet from the bottom of the river. "The depth of water at low water was, in one case, 20 feet and in the other S feet. "A clip-hook was tirst used to release the mooring from the tackle by which it was lowered ; but this was found not to answer, from the twistiug of the rope when lowering, which caused the tripping line, in connection with the arrangement, to wind round the parts of the tackle. " The next plan used was a double rope, passing through a double block on the sheers erected on the raft and through the eye ou the mushroom anchor. This arrangement also gave great trouble, from the twisting of the ropes together, and it was found impossible to clear the rope from the moorings when a single mooring cable was used.'' Lieutenant Chadwick, in conclusion, recommends the fol- lowing mode of lowering mines into their places to be adopted : '■ The mines, with their moorings attached, should be car- ried to the place where they are to be submerged, in a barge or lighter, provided with a derrick or crane, for taking them in and out. 7-2 .siiip's launch "For loweriiiti' them into position a ship's launch might be p;n^oI"r"™™'us,.,h provided with the irttiugs sliowu i.i Fig. 19. In the center, or perhaps rather more forward, ;i crab-capstan, a, miglit be placed. Over the stern are two davits, {b b) with F{g. 19. sheaves, their outer ends being about leet ajiait. Between theui is an inclined plane (c) on which the case (d) containing the charge is placed. " The mushroom anchor (e) is lowered by means of two ropes, attached to two eyes in its sides, as shown in Fig. '20. Fig. 20. Each of these ropes leach through the sheaves in the end of a da\it, and thence to the crab-capstan. IJy thus separating the ropes it is hoped that twisting may be avoided. " The mine should be placed on the inclined plane, and the mushroom anchor between the davits, by means of the crane in the shore lighter. This done, the boat is ready to be towed to the destiued position of the mine. The anchor should then be lowered gradually down, and the miuelauuched over the stern. To detach the ropes by which an anchor has been lowered, common marliiie-s[iikcs, ivell greased, and which are arranged to hold these r()[)es by being passed through a double heart-knot, may be used. These niarline- spilves haviu g been withdrawn by means of lines, (//) attached for the purpose, the anchor is thus released." A o2-foot pinnace is sufficient to lower an anchor or mooring-lump weighing 20 cwt. ; but for larger weights a larger boat would be required. Ecbuits of ex- A 32-foot pinnace having been fitted up as recommended periments iu moor- . ing with pinnace by Lieutonant (Jhadwick, a series ot experiments were nni "ciiadwick'B made with her during the summer of 18G8. The result of ''^"' these experiments showed that, though this system an- swered remarkably well for lowering a mushroom anchor or 73 moorinsf-lump into position, and there was no twisting or difficulty in detaching the ropes by which it was so lowered, there was still an itmnense amonnt of care required in handling the charge and circuit-cl(jser in connection with it, in order to prevent damage to the electric cable and disarrangement of the mooring-gear, and tliat even with a depth of only six or seven fathoms, at which the experiments were tried, and a three or four knot current, such as that of the Medway, it was so difficult to get a mine into any required definite i^osition as to be practically impossible. The conclusion consequently arrived at has been that in most cases, and especially in deep water and with lar^e charges, it will be necessary to lower the moorings first into the required position and haul the charges down to them, in order to insure that accuracy of position which is essen- tial when a mine is to be fired by judgment; and in order to obviate, as far as possible, the great strain on the anchor, which necessarily occurs during the j)rocess of hauling down, the mine should be weighted, the weights being sub- sequently removed when the operation of submerging is complete. The bottom at the point where the apparatus soft muddy bnt- tom very l.'vora- was iilaced was soft mud, and consenuentlv very favorable we for muBhroom ' ^ ■ ^ anchor. to the mushroom form of anchor. The current runs about three knots an hour at the point where the exi)eriment was tried ; the top of one barrel was just awash, while the moor- ingcable of the other allowed several feet of slack, at dead low tide. The mooringcable used was a 3 inch wire cable composed of a strand of No. 20 galvanized iron wires, and manufactured by Messrs. Xewall & Co. The result of this mode of mooring was most satisfactory ; there was no twist- ing of the barrels and consequent torsion of the mooring- cable ; that barrel which was moved so as to be just awash at low water, seemed simply to turn a little, as indicated by a vane arranged to show above the water, Imt never to make even a single whole revolution, and almost immediately turned back again. The position of the bairel altered but little, whether the tide was running in or out, probably not more than two feet either way from a central point. There was, of coarse, more motion with the other barrel which had a considerable amount of slack cable at low water. The wire cable was a great improvement on the ordinary hemp cable, with which the barrels, in the first experiments, were moored, and the mushroom anchor did its work remarkably well. The conclusions arrived at from these experiments seem conciunon. ar- te be as follows: that a single cable should be used when-from above^T"'' ever possible, and that a wire rope is superior to a hemp ""™"'- 74 one, beiug less likely to twist, kinlc, or wear from friction; tliat a musbroom aoehor is the best form for a soft uiuddy bottom. On a bard rocky bottom, the dead weight of the moorings must be depended on to keei^ a mine stationary, and, if a very heavy mushroom anelior is used, its edges should be furnished with toes or points, as shown in Fig. 20, to eatch in the crevices of the rocks. Plenty of buoyancy should be given to the case to keep the charge stationary ; buoyancy about equal to the weight of the charge will suffice in a current of four knots an hour, but it might be increased with advantage on a stronger current. "With a current up to four knots an hour a single iron wire cable, with an anchor which holds sufficiently, will answer every purpose; but where the current is very strong, with a rise and fall of tide, it will probably be necessary to moor with two cables, one from each end of the case, and two ordinary anchors. Wheu two cables are iised, they should be placed as far apart as possible, and the anchors well spread out, and the buoyancy should be suflicient to keep the cables very taut. From the experiments made at Chat- ham, it has been found that, two cables attached to a case close to each other, twist together immediately, and the case is by this means soon drawn down out of position. When anchors arc not obtainable, heavy blocks of stone or pigs of iron ballast, or any heavy weight, may be used to replace them for moorings. The following suggestion bj' Lieutenant Jekyll, E. E., is worthy of consideration, and would no doubt be found practicable in many cases, if not with very large, certainly with charges of moderate size : Mooring to a " Submarine mines used defensively will generally, if not heavy chain sug- ' gested by Lirii- always, be moored in straight lines. E. ' ' "In x^ractiee, the greatest difficultj" is experienced in mooring any object in a yiarticular spot, especially Avhentwo mooring-chains are required, as will sometimes be the case, to prevent twisting. I suggest that, instead of anchors, a heavy chain cable be employed to moor the mines. "A section of the channel to be defended having been made, the line assumed by a chain could be laid down to scale. The positions of the mines and their distances apart, depth from the surface, &c., having been arrived at by cal- culation, could also be laid down on the section. The points where the small mooring-chains of eacb mine meet the large chain would appear on the drawing, and the dis- tance of each point from either extremity having been measured off the scale, could be marked on the chaiu. 75 "Before sinkiug the heavy chain, the small mooring- chaius should be rove through the links at the places marked, and the ends Ijuoyed, sufficient length being allowed for the buoys to reach the surface. "The conducting-wires could next be laid, and the ends attached to the same buoys which support the mooring- chains. In this way everything could be prepared, the cables tested, &c.. before the mines were required at all ; in- deed, if the operation offixing the same were practiced before- hand, it could be left out until there was considerable prob- ability of the mines being required for use. By keeping the mines ready loaded in suitable magazines, and having the cables frequently tested, the probability of injury would be greatly diminished. "The great advantage of using a heavy chain would be the absolute certainty of having all the mines in their pro- per places; it would also simplify the moorings by doing away with a multiplicity of anchors and anchor-buoys. "A 2i-inch chain cable weighs 400 pounds per fathom. The mines would probably never be nearer than 70 or SO feet apart, so it is evident that the chain would be quite heavy enough to counteract any flotation which would in practice be given to the mines." In a current of any strength, it would be necessary to use two parallel cliains across the current, to prevent the mines swin;;iug with the change of tide, but the same ad- vantages would hold good. This idea is quite compatible with the system of hauling down the mines to previously placed moorings, as it would only be necessary to sup])ly a pulley, of the form already described, shackled on to the chain cable at proper inter- vals, and witli the necessary tackle rove through them. A modification, sugg(-sted Ijy Lieutenant Bucknill, E. E., on Placing moor- Lieutenant JekylTs plan, has been tried in the Medway, in 7 with a directing fathoms of water, and been found to answer very well. ThebyLieiuenant arrangement used was as follows: A strong hem])en cable was ' ■ ■ ■ laid out across the river, from the mooring-lighter at Catness, the outer extremity being anchored. Previous to immersion, this cable was markeil at intervals, at the points where it was intended subsequentlj' to lay down the line of mines in con- nection with it. In this state it might have remained at the bottom of the river for a considerable time without injury, the slack having been taken up in order to keep it in a fair and even line, and prevent unnecessary movement. To place the moorings in ])(isition the following course was adopted : A mushroom anchor, with gear attached, having 76 been attached to one ot the riavits of the iiinnance, the direct- iug-hawser was shicked off sufScently to admit of its being nndeiTun, and was passeil o\'er the bow of the boat at the fore row-locks ; she was warped along to the position re- quired, as indicated by the mark previously made in the hawser. One end of a branch hawser was n_^ow bent on at this point, and the other extremity made last to one of the eyes on the mushroom anchor, the necessary amount of slack being left to allow the anchor to be passed into its proper iiosition. For small charges up to 100 pounds of powder, a distance of MO feet, or a little more, from the directing-hawser would probably be suflioieut, and, when no greater distance than this is required, it only remains to cut away the spun-yarn lashings securing the cable which retains the mooring at the extremity of the davit, and, thus set free, the anchor falls into its required place. On actual service, however, much larger charges than 100 pounds would be used, and it would be iieeessary to 2>lace the moor- ings at a greater distance than 30 feet from the directing- cable; to do so, it is only necessary to veer out the branch cable, thus letting the boat drop down to the position re- quired, and cut away the lashings as before. The anchor having thus been got into position, any further arrangement for attaching the charge, electric cable, and circuit-closer, may be carried on without difficulty. Favorable Favorablc weather, a.nd a proper direction of current, weather necessary -..-,_, \vhiie piac in g especially m a ti.dal channel, are very essential to success mooriuga iu posi- - '' , !• , - - • ... (ion. when the operation ot getting moorings into position is undertaken, the difficulties being much increased by a fresh breeze and rough water. It must be borne iu mind that, in order to insure a maximum of efficiency, the ](i)sitioii of the moorings must be detined within very narrow limits. ~iW3— Maxfi' HcU'i/aer. Fig. 2] o o One or two lines of mines may be laid on this ]irinciple in connection with a single heavy hawser or mooring-chaiii. 77 The general iirran;;-e:rient of a single liue so constituted is ^ho\vu in Fig. '21, and that of a double line in Fig. i'2. o Moirser. Fig. 22. 6 This plan aHijrdseonsiderablefacilitiesfor tlieexamination Exammation of of cliarges aftiT they Lave been submerged. In order to charg " "' ^ "^ reach any particular charge it would only be necessary to uridcrruii the main hawser till the required Ijranch was readied, by it to raise tlie inooring-anchor, and with it tlie mine to be exauniied. In the event of the main hawser beini;' broken, it would not be a very difficult operation to grapple it and Xn'ws. it to the surface for repair. When the main hawser is not in use for any of the purposes above mentioned, all slack should betaken in to prevent unneces- sary motion. This system appears to answer very well up to a de])tli of seven fathuiiis, and it would be very desirable to try it in \'ery much deejier wati/r. The fact that the exact position of a mine, within a yard, must be known to the defenders, must be always kept in view; and in order to simplifj' identification as mui;h as possible, an arrangement in lines, directed on some given point, will .i;enei'aliy lie best. This would seem to be an additional leasun foi' placing the moorings first in correct position, and after waid hauling the mines down to them, and would seem t(.) be the easiest and most practical course whether a sin.^ie mooring cable is used or whether a mine is moored fore-and-aft to resist an extraordinary current, as, for instani/e, an unusual rise and fall of tide. In abroad channel and with deep water, as, for example, at Spithead^ the difficulties of arr.ingement in lines would Ije increased, and lirobably in sii(;Ii a case it would be necessary to anchor a couple of large vessels fore-and-aft, and, after hauling them 78 into the exact line, to conuect them by a hawser, by which latter the boats eagaged ia lowering the mooriugs would be guided. It would, iu many cases, be not only desirable but neces- sary to place the uiooriugs in position at leisure in time of pca'ce, and thus the most difficult and tedious part of the operation being done, a channel could, on a threatening of hostilities, be very rapidly put in a state of defense. Power of woric Whcu au auchor has been placed in position it is neces- g?ar'of J,7haui:saryto retain the power of working the running-gear, m iog-down arrange- .- .j^]^ ^]jg hauliug-dowu arrangement, in a prac- inout rauat be re- ^^'-'^^'^'-'^ ^ -, . taincd. ^■^^..^l foriji^ and for this purpose the arrangement shown m Fig. :-••';! is suggested. In this arrangement a buoy («.) is placed in connection with one end of the cable, rove through the pulley (?>) shackled on to the eye of the mushroom anchor, while at the other end an ordinary anchor (c) is attached. This latter is cast at such a distance from {a) that there is no chance of entanglement between the cable attached to the latter and that in connection with the anchor-buoy, (b.) By this arrangement it is manifest that, by weighing the anchor, (c,) both ends of the line rove through the pulley or loop (b) may be obtained at any moment with facility, and there is no chance of the two parts of the mooring-cable becoming twisted round each other, however long they may have remained submerged. It is essential to efhciency that there should be no such winding round each other of the Fiff. 23. Waisr Lvu,. cu h two parts of the cable, as even a single turn would destroy the action of the running-gear through the pulley. If the buoy id) cannot be conveniently used, the anchor (c) may be deposited in position without it, and, should it be 79 necessary to weigliit, the line (b c) could be easily grappled and brought to the surface, sufficient slack being allowed for this i^urpose. xVu ordinary weight of any sort, sufficiently heavy to counteract the upward pull of the buoy, (a,) might be used instead of the anchor, (c.) The buoy (a) should be kept some distance below the surface, as well to prevent injury to it by vessels striking it, as to keep its position, which would indicate that of a future submarine mine secret. A modification of this plan, shown in Fig. 24, li?rS been Arrangement of suggested by Quartermaster-Sergeant J. Mathieson, E. gest°'a'^by'"Qua?- T-, Tj_ ■ j_ • - -I • , -I 1 t e r m a 6 1 er-Ser- iLi. It consists m simply arranging two buoys, one atgeant Matweson, each end of the ruuning-gear, passing through the pulley 'Viq. 24. Water Line-. c. a/ or loop (c) in such a way that the buoyancy of one of them, as (&,) shall considerablj' exceed that of the otlier, («,) and the latter, having been hauled down close to the moorings, would be held there till required to be moved. In such an arrangement care must be taken to make the buoy («) sufficiently strong to resist the continuous pressure of the water at the depth at which it is required to remain. It possesses the advantage over the system first described of greater simplicity, but is more easily disarranged, for if the buoy (a) rose slightly, from any depression of the buoy (&,) there would be a certain amount of slack in the cable, and a consequent capability of entanglement by twisting around that part of it attached to (&,) which would at once destroy the efficiency of the combination. It has, however, been tried practically in the Medway, in five or. six fathoms of water, with considerable success. Whichever of these plans is adopted, the utmost care is required in keeping the cables and buoy-lines clear during the process of lowering the moorings, as well as iu subse- 80 queut maiiipalatiou, as any entaiigU'iiieut would be fatal to success, aiul more care is necessary with (lie second metliod tliaii with the first. Wl)eu laid down, too, tliey should be examined at intervals tcr see that the running gear is iu worlving order. A mine on the Whcrc a chargc is to be laid on the bottom, it should be bottom must be , , . ., ^ • j. i_' BO heavy as tore- ol sullieieut weij;lit to uisure its remaining stationary. m.-,iu stationary, lj^.^^^^.^j,,,,- AVallace, iu hls accouut of tlie demolition of wrecks iu the Hoogly, gives his experience as follows: "Sometimes, in a. stroug tide-way, a charge of 500 pomuls of powder recpiired a weight of about 400 pounds to sink it; whereas in slack-water less than half that amount was suf- ficient."' These weights, of course, refer to charges arranged in barrels, as used by him, and iu all cases the weight of any particular form of case must be taken into account. Mode of tiincing The ucxt polut to be cousidcrcd is the best mode of low- si charge in posi- . . . , , • i i j.i tion. ering a hea^•.^' charge into its position at the required deptu below the surface, and, when lowered, of attaching it to the auclior. Two modes have been desciibed by which this may be effected; either by first measuring tlie depth of water by sounding, then attaching the anchor, with the uecessary amount of cable, aud lowering both together, or by lowering the anchor first and drawing the charge down to it, and, when it has reached the required depth, there fastening it securely. The first plan is so simple that it requires no explanation. Our exiteriments have, however, x^roved that when it is re- quired to jdace a mine in position, the limits of which are defined, it is practically impossible of execution, except with small charges, veiy moderate depths of water, antl favorable circumstances of weatlier and current. By the second method a mine may be jilaced much more accurately in position, and it is ]»ractical!y much more easy of execution. Barge used by The Austriiins ein[)loyed a larg(> boat or barge, on which Austrians for-.-. .1^ i-i4-i i mooring subma- ^ dcmck wiis ercctcd, iiy whi(;h tlie aneh(.)r or mooring ar- rangement was first lowered into its place. To this anchor was iittached a. certain amount of wire cable, to the upper extremity of which was fixed a pulley, Fig. 10, already de- sciibed. Before the anchor was lowered into the water, an iron chain attatdied to the case was passetl through the pulley, and by it the charge was drawn down to any re- quired depth and there held by the self-iicting arrangement previously alluded to, Pig. 11. 'When the heavily-weighted wooden ]datform, also used occasionally by the Anstriiins for mooring purposes, was employed, the charge was held down to the required depth niie mmee. 81 i>y three niooriug cables, oue attacbed to each aii;;le of the platform, and the only difference was that three pulleys and keying arrangements were required instead of one. as used with the anchor. The Austrians, however, carried on their operations where there was no tideway, but it is probable that • a charge, moored by three cables in this way, might twist and be drawn down if acted on by a current, unless the three points to which the cables were attached were placed very far apart. We have now had some experience in placing charges in position, by the method of hauling down to an anchor already laid, and keying by the Austrian and other catch described. and it is certainly not only quite practicable, but in many cases preferable to any other plan that we have tried. In our experiments at Ciiatliam the apparatus at first Pumon raft , . . . . Used for mooriug used lor placing the charges in position was composed of purpose?. any materials that could be obtained on the sjiot; and we have since gone into the question of the special apparatus and arrangements best suited for the purpose. Sonic of the charges moored in the earlier stage by a single mush- room anchor Avere lowered from a ponton-raft by means of a derrick erected thereon. A raft of tlii^ nature forms a tolerably good platform Irom which to carry on sucb an operation in smooth water. It possessed fjiie serious disad- vantage, liowevci-. namely, that there being no gunwale, small stores were frequently pushed overboard and lost. If, thercfiire. a ponton-raft is ever used as a make-shift for such ti purpose, it would be desirable to add a temporary gunwale to it. Our ex]ierieiice in mooring suljmarine mines Experience de- may be summed up as follows: When possible, place the ments at "chat. moorings in position at leisure, and be ^ery careful to get them into the exact sites previously decided on for the mines. Arrange the running-gear in the simplest form, and try it at intervals to see that it keeps in good order. When a channel is to be i)ut in a state of defense, bring the charges to the required point, and haul them down into position. With a current up to four knots an hour, a mine may be efficiently moored with a single wire-cable, provided plenty buoyancy is given. With a current of five knots an hour or more, charges, to be held in a defined i)Osition, should be moored i'ore and aft. For this purpose a double line of moorings is required, and in hauling down it is necessary to take care that the top is horizontal when the mine is in position. G 82 Mod.' nf morning Tbci'O is oiio probloiii, with referein'C to snbuiarine mines, with a conhiiii-ra- i-tt . ^^^ , t t i t ^^ j. c MeiwiiiHiii,iioi\vliicU has still to be solved, namely, that or moormg lu a spot where there is a considerable rise and fall of tide, so as to show III) indieation, or at least a minimum of indieatiou, on the siirfaee as the depth of water deereases. Many sug- gestions have been made with a view to the solution of this (juestion, but none can be said to be completely successful. jiode of ii.oor- (.hiarteruiaster-Seryennt J. ^lathiesou, R. E., has suggested ing Miggesiril by ' ' yuart.-nnaster. the usc ■■ ot a cable connected therewith made fast at one extremity and passing through a fixed pulley to a windlass at the other. The tixed extremity of this regulating cable and the pulley, through which it passes to the windlass, must both be below the lowest le\-el to which it is necessary to haul down the mines, and consequently below the surface of the water. In order to raise or lower the mines thus arranged it would only be necessary to slack out or haul in the cable, by means of the windlass as required, and it is easily seen 83 that a comparatively small amount of cable takea ia or let out would effect the necessary diff'erence of level in the mines. In such a conihinatioD the mines should have plenty of buoyancy. In this system it is to l:>e feared that the friction, insepar- able from the use of pulleys submerged for any length of time, would act prejudiciallj'. This combination has still to he tested ; it seems, however, worth trying, and if success- ful might probably be used in certain positions with advan- tage, especially if the number of mines attached to each cable is not very great. In the absence of anv reliable svstem of moorini;'. to ful- staijonary ar- raDgement o f fill the necessary requireruerits with a considerable rise and moorings for a channel with con- fall of the tide, and for the present we cannot lav aown anv fsaerabie rise and -,.. . , ,. .. Ill ^ , ^ ^-ili of Tide. definite rules on this point, it would be necessary to arrange the mines to float at such permanent levels as to be suffi- ciently near the surface at high water to act effectually, and yet not so near as to be visible at low water. By the use of large charges, with a proportionately large radius of explosive effect, this might jjrobably be doue except in extreme cases : and where it would be impossible to keep when neces- f, ■ t ^ - T--^i sarilv viiible cir- them absolutely out of sight, the miues and circuit-closers cuit-iiosers, tc. might be covered with sea-weed, or disguised in any suit- ' "s^'-"- able way, in order to conceal to the utmost their real nature. In all cases, and in this especiallv, dummies should be pf "^ finm- freely used to perplex an enemy and conceal the position of the real miues. These dumuiies should bear a close resem- blance to the real article, should only be sufficiently conspic- uous to attract attention, without revealing their real char- acter, and might l>e ptlaced in any convenient position, or even occasionally shifted at night, so as to increase the delusion and perplexity. A mu.shroom anchor is in most cases, and especially on a Extemporized soft muddy bottom, the form which seems best adapted for mooring submarine mines. Such articles may not, however, always be at hand, and it may become necessary to use some extemporized arrangement. That shown in Fig. 23, and consisting of a strong heavy wooden shaft with a number of wooden arms or flukes was, after experiment, con- sidered a very good form by the authorities of the United States of America. This might easily be made wherever hard- wood timber is avail- able. Again, the wooden weighted plat- form of the Austrians is one that b4 uii.ulit be easily constructed in many cases. It seems par- ticularly applicable where a charge is to be mo\ed over a rocljy bottom or bad holdiug-ground, where it must be kept lu positiou by the dead-\vei!;ht of the arrangement. The wooden platform affords a broad space on which any num- ber of heavy weights can be conveniently placed and the materials of which it is formed, viz, wood and iron, are pro- curable everywhere. The system of mooring l)y these cables seems objectionable, as. with a current, they would be very likely to become twisted together ; but there is no rea.son why a single cable from the center should not be adopted if proper precautious to strengthen the connection of the central point, to which the cable would be attached with the outside by means of iron stays, or in some other manner, vrere used, ordinarv It is unnecessary t" descrilie how ordinary anchors may be anchors. t ^ . "^ , used for mooring submarine mines. Large »t.iue^, Large stoucs, pigs of ballast, or any heavy weights may pigs of ballast, ' ■ , ,'^ £■' &c., for mootiDgbe Used whtTe the more appropriate tonus ot apparatus can. purpobes. ^^^^ ^^ obtained. These must necessarily be sutiiciently heavy to hold a mine in position by their simple dead-weight- Weight of moor ^^ very important point for consideration, is the v.'eight of the anchor or mooring apparatus necessary to hold any given size of charge in jiosition. This will depend on its buoyancy, and the strength of the current in which it is to be moored, and also on the nature of the bcttom or holding- ground. The Austrians recommend ^ery heavy mourings — as much as seven times the weight of the charge of powder in cer- tain cases. This was necessary, because the Austrians always hauled a buoyant charge down to its proper position after its moor- ings had been placed. The large excess of weight acted against the strain in hauliug-throngh the block, which was, of course, equal to that of the buoyancy on each por- tion of the ro]>e, or double on the whole. Without a con- siderable excess of weight, we have found that, during the process of hauling down, the moorings are very liable to be drawn out of position. Calculation of \^,^_ however, the tendencv to move depends on the amount weight of moor- ' "^ ^ iDge- of buoyancy, the pressure exerted l>y the current, and the tenacity or otherwise of the holding-ground, the weight of anchor or mooring apparatus uecessaiy to overcome that tendency to move may be calculated as follows : Let B be of the buoyancy, or excess of ih.itation over weight of a charge of a given submiirine mine: let T be tln' j)res^!ire exerted bv 85 any given current on the same mine when moored to the bot- tom a.ud floating freely tbereiu, it is evident that tlie result- ant of these two forces, or -/ B- + P-, gives the force tend- ing to move the mine ont of its position. Xow, sujipose a case where tlie water is absolutely still, P becomes nothing, and the force tending to move the mine would l)e simply equal to li, the buoyancy, and that force would be exerted iu a vertical direction. To balance this we should require an effectis-e weight exactly equal thereto, and taking into consideration the necessity of providing an excess in order to keep tiie mine stationary, it would be necessary to at least double sucli weight in practice. In calculating the weight to be opposed to the flotation in order to keep a given mine Irom drifting out of position in c(nisequenceof the action of a current, the effective value of the anchor or moorings must be taken as its weight, minus the weight of water dis- placed by it. The loss of weight by immersion would, of course, depend on the bulk of the mooring apparatus towhicli the mine is attaclied, and, when this bulk is considerable, it becomes a. most iuijjortant consideration in the calculation ; when a simple iron mushroom anchor is used, it is i>robable that its weight, if double the buoyancy, would be amply sufficient in perfectly still water. Again, let W be the weight of mooring required; if the Ibrcgoing conclusions are cciri'ect, we should then have \Y=-2 V n- + i'^ 111 still water, where r=0, W would be equal to -B. or double tlie buoyancy as already assumed to be suffii_:ient. Where it is intended to haul a mine uoyancy necessary to be gi\'en to a buoyant mine, and here again we must start from some kind of assumed basis, and, from tlie experience we have had in mooring Oi)erations in the Medway, it would seem that, even in still water, the buoyancy sliould not be less than the weight of the charge; and where a current exists it should not only not be less thauthe weight of the charge, but should be not less than three times the force exerted in the form of lateral pressure by that current. For example, if it were required to move a. 500-pound charge in still water, it ought to have a buoy- ancy of .">00 pounds as a ininimuin. Xow, suppose it to be subjected to a lateral pressure due to a current of four knots an hour, which, on a cylindrical curved surface, may be put down roughly at 300 pounds for the size of case which would be re(|uired for a oOO-pound cliar.uc it should then 8(5 have a Hotation of iiot less than !»0() pounds. In calculat- iug tlie piTssuru exerted. iiy a. cnrrent on a, cylinder, assum- ing the curved surface to be presented to it, half tlie pres- sure wliicli -would be exerted on a flat surface cqnal to its greatest sectional area may be taken; tbis will be near enough for the puipo.se. We have assumed the buoyancy, in the case Avhere a current exists, a.s equal to tln'ce times the pressure exerted by tliat current, in order that the mine luayuot be moved far out of a central position, vertically over its moorings, such motion being limited by the direc- tion of the resultant of the two forces acting on it: wheu the mooring-cable is very short, however, this buoyancy may he considerably reduced. In any case when a buoyant mine is to be retained within certain limits, vs'hen moored with a given length of cable and acted on by a known cur- rent, it is a very easy matter to calculate the buoyancy necessary to produce the required result. Excess over c^a- ^\^i^ cxccss of buovaiicv ovcr the calculated amount is culated buoyancy ncccs.saiy. " ' alwavs neccssary to ob\-iate the ill-effects of .slight leakage or any other disturbing cause which might tend to reduce efficiency. It is probable that an addition of one-fourth would be sufficient in cases where the conditions arc favor- able, but more may be added 'wheie imperfect or make- shift arrangements are employed. Muddy boitoHi The deductions to be derived from the above statement favorable for t i i i ■ i -it mooring opera- ar(_' applicable oulv to cases in which the bottom is hard, and the mine must be held in position by the simple dead- weight of the anchor or mooring apparatus to which it is attached. Wlien the bottom is soft this weight may be considerably reduced, and in an extremely soft muddy bot- tom like the iledway, it is probable that threivfourths of the weights, calculated as abo\e, would be sufficient, especially where an anchor of the mushroom form is used, this form lieing very api^licable to sucli situations. A 10-cwt. mushroom anchor, left for three or four weeks at the bottom of the ^JTedway, was found to have sunk com- pletely into the mud, and it re(juired very strong tackle and a mooring-lighter to weigh it. To facilitate search by a diver for an anchor at the bottom of a river, it has been found a good plan to paint it white. Calculation of Jn Older to calculate the lateral iiressure exerted on any lateral pl^•N^u^e. mine by a ;.;iven cnrrent, the following formula may be used: P = J.OS.j X V- where \'=- velocity of the current in miles i)er hour. From this eijaation P will be found in terms of pressure in pounds per .squaie foot of flat surface, which is, as already stated, nearly doable that on the curved surface of a cylinder. CHAPTER VI. MODE 01'' KrXITION'. Having deternuned ou tlie form of case, size of charge, and mode of placing submaTine mines in position, it next becomes necessary to decide Low they shall be ignited so as to do as much damage as possible to an attacking ship. This may be done either mechanically or by electricity. First with regard to the mechanical mode of ignition. ML-chanicaUgui- ° '^ lion Several arrangements have been tried, with more orless suc- cess, by which charges of powder may be ignited by mechan- ical action. In several of the confederate torpedoes, which were raised from the bottom of the James Eiver at Kich- mond, and the drawings, and some of the originals of which I had an opportunity of seeing, through the kindness of Brigadier-General IMicbler, of the United States Engineers, a simple gnn-lock and xiercussiou-cap were used. Tliese may simpie gim-iock. be considered as among the most piimitive contrivances of this nature, and, from various circumstances, such as oxida- tion or incrustation in the metal in the more delicate parts, perhaps the least likely to act at the I'ight inoment. An improvement in this was the simple percussion system, by which a charge was ignited by the vessel herself striking directly on a cap containing a detonating mixture; the most delicate of these, mentioned by Captain Harding Steward in his notes on submarine mines, appears to be Brook's fuse. Brooks fuse. which was arranged in the form of a nipple projecting from the case containing the charge, formed of copper of differ- ent thicknesses, according to the amount of sensitiveness to be given, and primed with fulminate of silver. The de- tails of this fuse are given in Captain Harding Steward's paper already referred to, and need not therefore be repeated here. Several other forms of detonating fuse were also tried by the confederates, both for land and submarine service. An account of several ideas for mechanical ignition, devised from time to time, may also be found in the report of the com- mittee ou active obstructions. Another mode of mechanical ignition used by the con- Sulphuric acid federates, and previously by the Kussans in the defense of the ports in the Baltic, is the Avell-known sulphuric-acid fuse, formed on the principal of ignition by sulphuric acid dropped upon a mixture of equal parts of chlorate of potash and loaf sugar. The sulphuric acid was placed in a small ;i] fnsp. 88 .i;]:iss nlolmlc, wliicli was so arranged as to In; hnikfii by a blow whicli would be, given (Ui toucbing tlie side of a ves- sel, and the aeid set live, falling on tbe mixtnre ol' ciilorate lit potash and Idaf-sngar, prodnced the reipiired ignition. Captain Earxling Steward gives an Jierount oftlie attack ottbeT7nited (States frigiite .Alinnesota by the confederate toriiedo-ltoat Sqnib, in wliieh (Japtaiu Davidson, Avho was in charge of the latter, attributes the partial failure of his attack to the slow ignition iiroilueed by the chemical fuse (sulphuric acid, chlorate of ]>otasli, and loaf-sugar) ns(_-d; he supposes that, in eiinse(|nence of this comp;ii';iti\'eiy sjovr ignition, the torped(i-1ir)at had i-ecoiled '■'> or f feet be fort' tbe actual explosion took place. improv.acii.-mi- Thcrc is no doubt that ignition by the sulplmric-aeid iiisc is coQjparatively slow — that is to say, slow as coiDjiared with that of guni)Owder; but it may be very much iiii])roved by the addition of a small quantity of ferio-cyanide of potassium or sulphuret of antimony. J-'i'om experiments made in the chemical laboratory at the Hchoijl of Military iMigineering. (Jhatham, it has been found that an addition of one-tJjirdof ferro-cyaidde of potassium to tiie mixture of eqiial ]iarts fif chlorate of potash and loaf-sugar, produces an ignition as rapid as that of gunpowder. Sodium 01 ),ohi-.: Another very simph.' mode of producing ignition lias beeu suggested by Captain Campbell Hardy, of the Itoyal Artil- lery ; it is simply caused liy dropping water upon the metal sodium, when ignition takes place. I'otassium v.ould aKo answerthepurpose, but isinferior to sodium, thelatterhaving a greater afiirjity for oxygen. Captain Haidx mad.e several experiments with this substance at Halifax, Zsova Scotia, with good results : the only fault he found with it was its comparatively slow ignition, wiiich, however, lie thinks juight be in)[)ioved by j»iei-cing the body of the sodium with small holes. It v\(.)uld be well worth while iiia.l-;ing a few experiments with this substance, for e\en if the results ob- tained from it areuotso ^oodas those of the more ap])ro\x'd form of chemical fuses, it is so safe to handle that it jiresents many advantages which might be brought into use where other forms are not obtainable. The metal sodium can now be procured almost (/\ery wliere, in the form of a paste, which is easily cut and manipulated. It must, however, ite pre served in naphtha or sonn.' sul)stance conraining no oxygen, or it would soon absorb oxygen from the air and beeome useless as an explosive agent. The following deseijption of an adaptation of tlie ^ul- phuiicacid fuse, arranged by F. ^^bel, cmj., ]•" ];. s., cljem- Bium fuse. Ab' 1 « t.-i'lie.lo- pririK'/. Fig. 26. 89 ist to tlie war clepartiueut, has been approved by the floatiug obstruction committee, ar.d is extracted from their report : "In Fig. _;(), [a) shows the socket U> receive the primer, which is arranged to be fixed firmly on to the case contain- ing the charge, as sho\Yn in Fig. "21 ; {h) is the powder-cham- 1)er to hold the priming charge ; (e) is a screw-nut closing the powder-chamber ; ((Z,) Fig. 27, a flexible India-rubber tube ; (e, e) are screw-bauds ; (/) a lead tube containing the explosive mixture; {[/) a glass tube containing oil of vitriol; {/() eye to receive the firing line; (/, () guard in segments ; (./) guard ring , (/i) a screw pin." •'Before the charge is placed in position, a cord or wire is attached to the eye of the guard-ring (j), and the screw-pin (Jc) in the side of the guard-ring is removed. When the primer is to be rendered active, after it has been i^laced in position, the guard-ring {j) is removed by pulling the cord attached to it. A\'hen this has been accom^dished tlie guard (/, i) will fall away from the primer, leaving it active. The safety-guard of the primer is on no account to be re- moved until the mine has been placed in the position assigned to it. When a sufficient strain is put upon the eye (/() the lead tube (/) bends and the fraction of the glass tube (r/) is thus determined, whereui)on the primer is fired."' Tlie socket (a), Fig. 20, which is to receive the primer, Piimer-socket. a.nd which accompanies it in the packing-case, is fixed by means of screws or rivets into the opening of the vessel which is to be converted into a submarine mine. The usual precautions are to be taken to make thejunction bet\\'een the soclcet and the case water-tight. A piece of iron-idil. about F.iiriead. twelve inches long, is bent at tlie end into the form (if an eye ; the other end is then screwed or driven into the case, in such a position that the rod is parallel to the primer when the latter is inserted in the s-eocks the moment it came to the sur- face. This arraugement for shutting off, as it were, tlie fuse from the charge of powder, is applicable to almost auy form of mechanical ignition that maj- be devised. Passing from the mechanical we now come to the elec- . Eiecsricai trical mode of ignition, in which a very important matter for discussion is the fuse. Several forms of electrical fuses have been devis(Ml and used for the ignition of gunpowder, gun cotton, &c. The , ?'"'' confederates used the platinnm-wire fuse and Grove's or Bunsen's battery in many of their mines, which were ar- ranged to be tired by electricity. This form of fuse, in con- uection with the first-named battery, has for a long time formed a part of the engineer equipment of the British army for land-mining operations, and the result of some experiments with it, in connection with submarine mines, have been so successful that it is to be hoped that it will satisfactorily fulfill the necessary conditions for the latter purpose. There are numerous advantages to be derived from the Advaiit:igea ot ^ tliL- X'latiQUiu-wirt; use of the platinum-wire fuse, of which the following are the principal : 1st. Great facilities are alfordedfor testing the circuits. I'd. It does not deteriorate by climate, iV'c, and can be stored for any length of time without damage. 3d. It can be very easily' improvised, and the materiids of which it is composed are simple. -Ith. It does not require the very high insulation in the conducting cable which is necessarv Avhen a fuse, tired by a current of high tension, is used ; and it may be fired through a cable in which a comparatively large fault exists. 5th. There is no danger of an accident during the pro- cess of testing, for which purpose more powerful batteries may consequently be safelj^ used. Considerable care is ne- cessary in testing Abel's fuses, for example, as more than one of the most sensitive form has been fired by eight small Daniells cells. It has been ascertained by experiments carried on in the river Medway, opposite Gillingham, that in sea-water a re- turn-wire is not necessary, and that even earth-x^lates of any considerable size are not essential when using this fuse in connection with Grove's battery; fuses having been suc- cessfully fired with earth connectionsformed of a few inches only of bare wire, with the addition of u compariitively fuse. 94 MUiill luiiiibi'V of battery cells over the miinber necessary with a return-wire or ordinary eartU-plates. Exp^riin.Mits rjjjg followin"'is a sbort account of tbe experiments tried: ^vlthpI;ltml^n nine "^ i.iia Grovo's i..,i- ^v pLatiuum fuse, represented by j% incii of pbatinum wire, in a tberiuogalvauometer, was pbxced in circuit witli half a mile of a cable, composed of Hooper's core, with a conductor consisting of a strand of 7 Xo. i'l! 13. ^V. G. copper wires, and without a retum-Afire. One pole of t!ie battery was connected by a short length of Xo. VJ B. "\V. (}. copper wire, with the copper sheathing of the mooring hghier, the outer extremity of the cable being soldered to a tin case :.' feet (> inches high, and - feet inches in diam- eter, to form the other earth connection, this tiu being about 100 yards from the lighter. With this combination j'j inch of i>latinum wire, weighing l.G grains to tbe yard, were fused with six cells of Cirovc's battery of the ordinary military pattern. A second half mile of a similar cable luiving been ai.lded to the conductor, -f^ inch of platinum wire were fused with eight cells ; on a third half mih' of cable, making in all li miles of conductor, being added, the platinum vrire fused with l^j cells. In order to ascertain whether an increase of distance he- tweeu the earth-plates in any wa>' altered the conditions of DL-taiicebetwi-en the casc, the tiu Can, forming the outer earth-plate, was eai'th-pIatf?,s,iasL'a- ' ' wat.r, 110 objec- moved to a distance of rather more than .500 yards from the tlon, lighter, and connected with 11 miles of conductor as before, the electric cable being moved out for this purpose; ATitli this combination -^^ inch of platinum wire were fused with lli cells, and in a second trial with 13 cells of the battery, thus proving that there was no additional resistance inter- posed liy the iucreaseil intervening mass of water, or, iu other words, that the water resistance was practically )u/. i;xperijoerits to Purthcr exi^erimeuts have been tried with ( rrove's battery, aelermine the luia- imumofeartticon- and the platiuum fuse, to determine the minimum of earth nectionwith Grovi-s battery connection, retjuisite eiiectually to fuse the platinum wire, witliout inordinately increasing the number of battery cells. With a conductor, consisting of half a mile of cable, (Hoopers core, similar to that used iu former experiments,) and j\ inch of platinum wire in a thermogalvanometer to represent the fuse, the following results were obtained: Xuniber of ei-lls to proiliiec I'usiou. Extent of eat-tb in iiiebcs of bare wire. 21 7 15 S » 3i 10 3 95 One pole of the battery was on this, as on the former oc- casion, attaehed to the copper of the vessel as an earth- plate. With on mile of conJucting cable in ciiciiit and similar arranf;enieiits to the above, the ffillowing results were ob- tained : NtiinlM'r of cells to ]iio(lurc tiision, K\'t<.-iit nf eartli in inclit.s of ban- wiro. ■2(\ • a liO i Tlie latter failed to fuse, but heated tlie platinum wire to redness. Tlie result of these experiments show tli^t earth-plates of the ordinary size will answer e\ery puiposi', when used in coiint'Cti(.)n with drove's battery and the platinum fuse for submarine miniii!;' purposes. ^Ir. Brown, of the chemical department. r(jval ar.--rnal. incrta„ofiusiii- H'ives tlie followii)/4' information, as the result of some ex- '^y "le Kudden re- permiiients made by him with Grove's battery and the pla- ofabatt-iy. tinum fuse. He finds that the best results were obtained by suddenly reversinji' the poles of the battery: that is to say, that a fuse which will not fire with a given number of cells of a battery may be successfully tired )iy simply revers- ing' the poles of the same battery. The reason of this is that, by keeping one ])ole of a battery coiistanrly on. eopper earth-coniieciioiis, which are the best for general purposes, l>ecoine coated either with sub-chloride of coiiper or with ' bubbles of hydrogen, both of which jiartially insulate. A sudden re\eisal of the poles of the battery dissiiiates these (■(jmbinations for a time, that is to say, till they again fornr by changing phices. as it were, on the opposite earth-plates, to those on which each was originally deposited. A similar effect is produced whatevei- may fie the metal of which earth- plates are composed ; that is to say, a filirr of hydrogen bub- bles will be deposited on the earth-plate attached to the negative, or zinc, pole of the battery and a film of sirb- chloride of the metal on that connected with the positive or platinum pole, both the result of the decomposition of sea-water by the electrical current. A platiuum-wire fuse has been designed for submarine Form of piau- num fuse for sub- miuing inirposes, which, as far as it has been at present marine mining . , , imrpo-e.= . tried, seems to answer satistactonly. It consists ot a couple of copper wires of No. IG B. W. G., fixed into an ebonite core (rt), as shown in Fig. 3.3, and the opening through flhich they are introduced made thoroughly water-tight by filling it with waterproof composition. It was found im- possible to cast the efionite directly on to the bare wire, 96 which wonhl have been a niiicli more satisfactory ariaiige- ment, because the sulphur of the ebonite acted power- fully on the copper conductor and destroyed it. This core is provided with a shoulder {(1) to enable it to be fitted into the case in such a manner as to pre- vent leakage of water. The extremities (c c) of the copper wires are /q inch apart, and so arranged that a thin x)la- tinuni wire may l)e easily soldered on to connect them and form the bridge of the fuse. A cap {d) screws on to hold the priming charge and protect theln'idge (c c) of the fuse; and in this cap is a loading-hole (e) to introduce the prim- ing. The priming may be either ordinary gunpowder, gun- cotton, or, when the fuse is to be made detonating, in order to produce the effect due to this mode of ignition, fulmi- nate of mercury, which latter must be inclosed m a strong case in order to produce detonation at tlie moment of igni- tion. For this puritose the. whole ca]) (il) may be made strong. The outer terminals (//) of the copper wires are iusulated, and arranged for attachment to the electric cable and to earth; a circular opening, (c/ //,) fbnr inches in diameter, is 97 left in the i:ast' (/' /) of tbi; siiiin?, for the paipo.-ie of iutro- (liicin;; the eharge. The opening' is made four inches in diameter to allow gun-cotton, in the forni of disks, to be introduced, if it is desired to use this explosive. This open- ing is provided ^yith shoulders at (g) and (/(). on which the corresponding shoulder (7^) of the fuse fits, and the latter is forced down, by means of a circular s'^'vew, (t,) fitting into a corresponding screw in the opening of the case, {i.) This forces the shoulder of the fuse down upon a ring of India- rubber packing. (I,} shown iu black in the section, and makes all water-tight. Gun-cotton priming has the efl'ect of rendering the fuse (inneott on priming forms a more sensitive than gunpowder, as it ignites at a much lower v <> r >• ►■^■nsitiv. temperature, as may be seen from the following experiments tried by Lieutenant Bucknill, E. E. With a conductor of one and one-half miles of cable, (Hooper's core, as previously described,) and ordinary platinum fuse, as made in the school for laud inining, primed with gunpowder, fired with 12 cells of Grove's battery, and the platinum wire fused with 13 cells. The fuse. Fig. o3, designed Ity Lieutenant Buck- nill, was next tried. With the same cable, (one and one-half milesj — Gun-cotton priming fired with G cells. Mealed powder fired with 11 cells. Cotton and powder mixed fired with 7 cells. With one-half a mile of conductor, the following results were obtained : Gun-cotton priming tired with 2 cells. ^lealed powder fired with i cells. Cotton and powder mixed fired with 2 cells. With the same cable (one-half mile) and a leak of one foot of bare wire in the conductor — Gun-cotton priming fired with 4 cells. Mealed iiowder fired with 7 cells. With the same cable (one-half mile) and a leak of 2 feet of bai e wire — Gun-cotton jiriming fired with .3 cells. Mealed jiowder fired with 8 cells. ■\Vith a conductor of one mile of cable and a leak of 2 feet of bare wire — Gun-cotton priming fired with 9 cells. .Alealed powder fired with l'> cells. In one case of mixed powder and cotton the powder did not surround the cotton, and the latter ignited without firing the former. It is therefcra necessary to imbed the 7 Orove's battery. OS cotton well in tlie primiiig-powdei', aud no failure lias ever (iccnrred when this \vas properly done. Kh.jtii<- butt.r.v In order to fire a eliar.i^c by means of tlie i)latiuuni-wire lor use ^vith pljili- ' ' numfusc. fuse, a battery producing' a current ol large quantity must be employed, ignition being produced by beatiug the piece of fine platiimiu wire in the circuit to fusion, by tbe pas- sage of the electric; circuit Grove's, Bunsen's, Walker's, or Smee's batteries are among tbose suitable for this purpose. oroviMiatirir. Tbc cxpcrimeuts rccorded were carried ou witb Grove's battery, of tbe form adopted for miuiug in the British serv- ice. .V. detailed account of this battery may be found iii Schiiio's " Xotes on Electricity,"' aud the reasons for its adop- tion are recorded in an article by Captain (now Colonel) Ward, 11. E., in the fourth volume of the new series of corps papeis. Defects uf Grove's battery ]H»ssesses the defect of inconstancy ; that is to say that, after having been in action, or even mounted and ready for use, for a comparatively short time, the active force of the current is considerably diminished, and in time it would no longer possess the power to fire a platinum fuse. From experiments tried at Chatham it has been ascer- tained that when used under similar conditions to those for which it would be employed as an agent for submarine mines, L'i hours is about the limit up to Avhich it will per- form its work with certainty. If adopted for this purpose, therefore, it would be necessary to take it to pieces, clean, and remount it every 24 hours. When this battery remains in a passive state — that is to say, not actually in action — it does not deteriorate so rapidly as when in constant use ; and, as in working a system of submarine mines, it \\ould only be in action at long inter- vals, each of comparatively short duration, it would not be so unsuited for the purpose as might, at first sight, appear. In conse(|uence, however, of this defect, it would be desir- able to obtain, if possible, a constant battery for the pur- pose recjuired, and with this view experiments have been instituted with other forms of batteries. Platinum wire may be fused by means of Walkers zinc carbon battery, which has the advantage over Grove's bat- tery of being more constant. It may be allowed to remain mounted for weeks together, without any considerable re- duction in the strength of the working current, aud in this respect would be preferable for a permanent station. Mr. Walker states that he has fused -,?„ inch of jilatinum wire of 1.95 grains to the yard, with cells of a battery of this form, composed of plates2 inches wide and ."! inches immersed 99 ia dilute sulphuric acid, (lof acid to 8 of water.j \Vitli Tor 8 cells the wire isfused better, and with 9 it worlis very well. The plates of the battery used by Mr. "Walker are comparatively small, and consefxuently a large number of cells of this size is required to produce the same result which would be ob- tained from tAYO cells of the service pattern, portable form of Grove. In order to test the efficiency of this battery, therefore, an experiment vras tried in the telegraph-school at this station, (Chatham,) by combining together a num- ber of plates of "Walker's battery so as to form two large cells. By arranging in this way so as to obtain an immersed surface of 140 square inclies of zinc, we were just able, with two cells, to fuse j^ inch of platinum wire of l.'.»5 grains to the yard. This surface of 1-10 square inches might easily l)e obtained, in a compact form, by giving the plates a cylindrical, or, perhaps better, for the more easj- manipulation of the car- bon, a iiolygoual form, uuder which they might be combined in a diameter of IJ inches, and height of 8 inches, extreme outside measurement, for each element of the battery. A few large cells of this form of battery have accordingly been procured for experimental purposes, and the results ob- tained with them have proved so promising that further investigations are about to be made. The platinum-wire fuse is itself verv simple and ver\" Electric fuse for ., - . , . ^ .ise with current easily made at any tune; but in consequence of the defects "f iiigii tension. as regards the battery for use with it, and the apparent dif- ficulties ill overcoming these defects, eftbrts have been made to produce electrical fuses capable of being fired by a current of high tension, in contradistinction to one of large quantity, which latter, as produced by Grove's and other batteries, is necessary for use with the platinum-wire fuse; also keeping iu view the necessity of using a constant bat- tery. One of these, invented by Mr. Beardslee, of Xew York, n Jiiiieesfuee. consists of a cylindrical piece of soft wood, about three- quarters of an inch in length and about three-quarters of an inch in diameter, shown at («) Fig. .34, through which two copper nails (b h) are driven home in a slanting direction, so that while the two heads come as close together as possible without absolutely toiiching, the pointed ends are at some distance apart from each other, and project below the wooden cylinder. To these ends are soldered the bare terminals of two insulated copper wires, (c c;) and a piece of soft wax, («7, '; of the same size as the wooden cylinder, is pressed around the points of junction. A groove is made with a file across the heads of the copper nails, into which is rulibed a little 100 black-lead from a peucil.* Kouiid tbe wooden eyliuder are now wrapped s(>veral folds of paper, formiug a cylinder %, 34. about i!.^, inches in leu,i;tli, one end being tightly fastened with a string ronud the insulated wire at (e.) This paper cylinder is then filled with a mixture of very fine grain and mealed powde r, (/,) and the end (r/) is choked with twine- The entire fuse is afterward coated with black varnish. Another fo ini of electrical fuse is the Austrian, invented by Baron A'on Ebuer, of the Austrian Fig. 35. engineers, which is shown in Fig. It consists of an outer cylinder of gutta-percha, covering an inner core (le. a uniform ek^etrical resistance in each fuse. A very similar fuse to this, in fact alimist identical, and ciiily differing in form, is used by the Prussians for mining Fig. CG. purposes : this is shown in Fig. .jC : {(jj is a small cylin- der of hard wood, through which a conducting wire is drawn to the hollow s^iace ( // ) in the center. Similar precautions to those adopt- ed in the Austrian fuse are taken in making and gauging tlje break in the conducting wire, and in filling in the couiposition. which is the same as that used by Baron Von Ebner. Tlie opening is st(_i])ped with a cork, shown at (() in sketch. Of tlicse two last forms the Austrian seems to be the nt.'>t. being less likely to b<^' damaged by a sudden strain or tug. which might easily alter the interxal between the points of the conducting wires in contact with the fuse coinpo~.ition in the Piussian iiise. .Vuother similar form of fuse is tliat invented by Mr. Abel, chemist to the war department. This fuse was devised and experimented with exteusively in 1S.")S ; and thi- abo%'e 'nor(.' icccntly designed fuses (viz, IJeardslee's, the Austrian. and Prussian) are based upon the principles first applied in that fuse. It has been modified since its first invention in a few details. Fig. 37 shows its most n-cent form. The prim- ing of the original fuses consisted of 10 parts of subphcis- phide of coiijier. prepared by a special method, i,') parts of subsulidiide of copper, and lo parts (if chkirate of potassa : tliese jiroportions of the ingredi(.'nts are. however, now varied. s(j as to furnish fuses (if different degrees of conductivity and sensitiveness to suit different i^urposes. Tiu^ ingre- dients are n-duced to a very fine state of division, and are thorouglily incorporated in a mortar, with the addition iif a little alcohol : the mixture is then dried at a low tempera- ture, and preser\-eil in tightly-stiijipered bottles till rerpiired for use. This coin[)ositiou is very sensitive as an electric priming material, and is ])erfeetly stable so lorjg as it iv 10: livcseiTed from access; of moist ure. This couditioii, essen- tial to the penuaueut etfieieiiey of the fiisi>, is secured Fig. 57. C'011Stl'LK't,i ft^^c■, by thi- present form of eonstructiou, and the precautious adopted iu packing such vrarlilie stores as frictiou-tubes. time-fuses. iS:c., saflice to insure the preservation of these fuses. In applying tlie electric s[)ark to the explosion of fuses, the distance from each other of the metallic points, between -which the spark passes, must be adjusted with great nicety; and it is also important, when a number of charges are t(i be exploded in divided circuit by means of a magneto- electric machine, that no residue should be left between the poles after the ex^dosion of the fuse, which would still serve to conduct the spark across the interval. The composition discovered l)y ]\Ir. Abel completely fulfills the latter condi- tion, and the former is ingeniously secured by the form of fuse adopted, and hereafter described, which is now an article of store olitainable at the royal arsenal, AYoolwich. ' Eeferring to Fig. 37, (& li) is a body of beech-wood, hol- lowed for half its length for the reception of the bursting- charge, and perforated by three holes, one vertical, for the reception of the capsule of sensitive mixture, and two hor- izontal, to receive the conducting-wires: {u a) are two insu- lated copper wires introduced into the vertical perforation in the body, and resting on the sensitive mixture ; {d) is a small charge of mealed powder contained iu the cavity of the fuse, and fired by the ignition of the sensitive mixture. 103 The insulated wires are prepared for these fuses iu cou- siderable lengths. They consist of copper wires of 24 gauge, (= 0.022 inch diameter,) inclosed in a coating of gutta-percha 0.1.3 inch iu diameter, and seiiarated about O.OC inch from each other. A x^iece of the double-covered wire, about two inches long, is employed iu the construction of the fuse. The gutta-purcha is perfectly removed from about 1.23 inches of each wire at one end, and the other extremities of the wires are furnished with clear sectional surfaces by care- fully cutting the double-covered wire across with sharj) scissors, care being taken that the ends of the wires are not pressed into actual contact by this operation. A small quautity of the i)riming composition is put into a small cylindrical paper-cap, (c, c.) made to fit the double- covered wire. Tlie prepared i>iece of the latter is then in- serted into this cap, and the exposed sectional surfaces of th(^ wires are liruily pressed down upon the composition, so that the latter becomes compressed jiuto close contact with them. The cap is afterward coated Avith strong shellac varnisli. The actual (use is thus completed, but it has still TO be fitted in such a manner as to permit of its ready em- ployment, and to protect it thoroughly from damp. With this view the capi)ed end of the double-covered wire is inserted into tlie perforation (/) in the head of the wooden cylinder, so as to ])roject about 0.15 inch into the caA'ity (<■/) of the cylinder. The bare ends of the wires are l)resseil into small grooves iu the head of the cylinder, (e e,) and each extremity is bent into one of the small channels or eyes {cF d') with whicli tlie cylinder is provided, and wliich are at right angles to the central perforation. They are then wedged tightly into position in these channels by inserting into the latter two small copper tubes, (shown in outline (V d',) whicli fit closely into the holes, aud are driveu in over the wire ends, being afterward filed down Hush with the surface of the cylinder. The cavity of the latter is then filled with meal-powder, which is tightly rammed down, so that the fuse itself be- comes firmly imbedded in it. The opening of the cavity is afterward closed by pressing into it a plug, of softened gutta-purcha. and, finally, the complete fuse is coated witli black varnish. In order to counect this fuse with the electric exploding apjiaratus, it is only necessary to insert the bared extremity of each conducting wire into one of the small copper tubes or eyes {d' d') in the head of the fuse, and to fix it there by 104 licudin.i; the wire round on to the wood, as shown at e' . Ei- .nidity is impartod to tho connection by twisting or tnrnin.u the wires together over the top of the fuse, as at (/). I'er- feet contact should be secured by a copper tack used as a wedge. liefore inserting the wires, with tlie fuse fixed upon them, into a charge of gunpowder or other explosive, it is advisa- ble to cover the connections of the wires and fuse, either by trapping a pit.'ce of gut-skin, oiled canvas, or other water- ])roof material round the head of the fuse. The powder for ordinary fuses is contained iu the cavity of the wooden body, and the fulminate for detonating fuses in a cylinder of sheet tin, tightly fitting on the fuse-head. AbtiM 1 u -ii! This fuse is adapted to the electricity obtained bv friction, i-eatsof i.i-h HH- ,,!■ to the momentary induced currents derived Irom perma- nent or electro-magnets, or an induction-coil. It can also be ignited by the direct voltaic current; about 60 cells of Dauiells's or 30 cells of Grove's batteiy being necessary to overcome the resistance with certainty, although very deli- cate fuses may be tired by ]- cells of Daniells's battery, or eveu less. ,., , Abel's fuses can be tested by passing a weak cun'eut of three or four Bauiells's cells through them, with au astatic galvanometer. Each fuse should be thus tested before it is placed in a charge. lilt The difference between the detonating fuse (required for gun-cotton) and the service elect™.' fuse, consists in the substitution of fnlminate of mercury for the priming charge of gunpowder, and iu addition of an external tiu casing for the bottom of the fuse; the ser\-ice electric fuse is painted black, while the head of the detonating fuse is painted red. rftv.t uf i.-t Uaving heard considerable donbts expressed as to the (uses. durability ot the composition in this fuse, when subjected to the x^assage of test currents, some experiments were made at Chatham w ith a number of them, taken at random from our stoclc, with the result shown in the following table. (See page 105.) These fuses were of the old form, possess- ing a very high electrical resistance. From these experiments it appears that the electrical re- sistance of the fuses were not mateiially altered by the pas- sage of a test-current through them, under any of the difter- ent circumstances in which it was applied; they all fired at the end of the experiments without any failare, and there seems to be no danger of ignition w^hen using a test-current, provided that current is properly adapted for the purpose. A large number of these fnses are used iu the course of in- Testhi lUSf. Abel in,5- fus( 105 J- X X X -»- X X X :( Tt ri CI ~i z'. ■;( X X X X X X X X X ■^ "; y. '^- '/I '^^ y^ y: Y- y. 106 stnictiou yiveii in the electrical school at Ghatliain, and the percentage defective is so extremely small that it may be safely asserted that Abel's fuse is remarkably well suited for the purpose for which it was designed. It possesses the essential quality of certainty of ignition, and is further of such construction that its electrical condition can be easily and safely ascertained at any time, both before and after it is placed iu the charge, by means of a test-batteiy and deli- cate galvanometer. Precautious Some of the fuses most recentlvma.de by Mr. Abel are necessary in Ti^^t- ingAbeisiu-r.ntextremelv sensitive, and have been hred by the passage of neTiest form. . ^ ' p-.t-.-ii h ' i-- i a continuous current, oi iJaniells cells or the ordmary form, in from -4 to C hours and upward. These very sensi- tive fuses are no doubt preferable for simple mining pur- poses, but it must be borne in mind that they are unsuitable, and even absolutely very dangerous, when placed in a circuit in which they are subjected to the continuous passage of even a very feeble current of electricity, for a compara-' tively short time. When such a combination is required, the less sensitive form of Abel's fuse, that with which our experiments Avere made, must be used, and in fact may be used with perfect safety. It must not, however, be supposed that these very delicate fuses, above referred to, cannot be tested; this maybe done with perfect safety, provided a suitable battery and galvanometer is used. It would not do, bowever, to put them in the hands of every one, and they should only )jc intrusted, vrhen used for submarine mining purposes, to a most careful workman, who must also be an experienced electrician. In using Abel's, or indeed any fuses, each should be carefully tested and marked previous to being placed iuthe charge, to avoid the smallest chance of ignition in the latter position while testing. Extcmpori i e a lu ccrtaiu cases when Abel's or any other manufactured fuses may not be attainable, it may become necessary to make extemporary fu.ses for use on the spot. This may be done in several Avays, which ba^e in'oved more or less suc- cessful. For example, a fuse, (capable of being used with a constant battery of a large number of cells, may be extemporized on the principle of Beardslee's, as described in the report of the committee on active obstructions, as follows : "A small cylinder, Tig. ;!8, of hard wood or cork, about f inch in diameter and {} incli thick, is provided Avith a groove («) round its <-ircumference, and two i)erf orations, {h i,) about -j- inch apart, of a suitable size to receive two moderately thin pieces of copper Avire, (about IS V>. W. .'uye: Fig. 38. 107 gauge being a i-onveuieut size.) Oae extremity of both of tliese wires is sliarx>ened with a file and then converted into a hook, the head of which is afterward flattened, as shown in Fig. 3!J. ••The straight ends of the wires are then passed through the holes in the cylinder and the flattened heads are fixed in the wood, by driving the pointed extremities into the latter. In this way the broad, thin metal surfaces which form the poles of the fuse are fixed in a I)arallel position on the surface of the wood or cork, and should be as close together as possible without actually touching. This arrangement is shown in Fig. 40. Before, however, the wires are thus placed in po- sition, the surface of the -^^."^ ^S- cylinder, upon which the *'• -'^ - ""^"-'^^^^s^ess^s^sz^s^ poles are to be fixed, is brushed over lightly with a feather-tip or hair-pencil, which has been dii)ped into a solution of ordinary pliotographic collodion. When the poles have been fixed into the cylinder thus prepared, the small surface of wood which inter- venes between them is coated with graphite by drawing a pointed black-lead pencil across it two or three times. A cap of thin paper is then tied round the cylinder (a,) Fig. 41, so as to inclose the poles of the fuse ; this cylinder is filled compactly with fine-gr;iin guujiowder, and the open end is then choked, as shown at {/',) Fig 41. "The protruding wires of tlic fuse (r c,) I'ig. 41, which si'r\e to connect it with the conductini; wires, are coated iJ Fig. 40. Fig. 4,1. to within a short distance of their extremities by molding ordinary bc(_s-wax round them with the fingers, and then tightly wrapping the wax over with thin strips of tape or lag of any kind, which is secured at the ends with thread. 1U8 The entire fuse, exee[it the hare ends of tlie wires, may tben be brushed ovei- with Brnuswick black, or any other description of varnish or laeiiner which may be at liaiid. "The only material nut universally obtainable, which is required iu the prodnctioa of these fuses, is collodion, which is, however, now so very extensively nsed, that it will generally be. readily procurable. A small bottle, corked or stoppered, containing one or two ounces of collo- dion, will snftice ffir the i)reparation of a very large uumbev of fnses."" This fuse may be iired liy means of a constant battery of sufficient power, or by ^Vlleatstone■s magnetic exploder, the former of which generates a continuous current, and the latter a rapid sueeession of short currents. It would rarely be fired by means of a frictional or otlier macbine capable of producing a single discharge only, because, iu order to produce the necessary heatiug-power, a continuous passage of the current through the plumbago-bridge is essential. In using this fuse it frequently happens that a short interval elapses between the closing of the electrical circuit and ignition, this time being required to produce the necessar,v amount of heat alluded to. Lieimuat Pi^h- Another form of fnse. designed by Lieutenant Fisher, i-i's exfempnri/.od i"-'- E. X., is similar in general construction to the above, but differs in the composition of tlie bridge, b^or plumbago Lieutenant Fisher substitutes a mixture of powdered char- coal and resin : this, he states, produces a fuse which tests sufficiently well, and is very certain of ignition. The mate- rials of which it is composed are so simple and easily pro cured that it bids fair to make a very useful fuse, easily made wliere a supply of the more i>erfect Abel's fuses may not be at baud. As, however, the efficiency of a mine de- l^euds very considerably on the quality of the fuse, extem- porary fuses should never be used when the more perfect Ibriiis are attainable. i'ov,'.ion I..; in>e Xcxt, as regards the position iu wliii.-h a fuse may be in R charge. iij_ iini, , -ij. most advantageously placed, and the number leqmred to tire any given charge. It has been already stated that, in order to develop the full esjdosive effect of t-ven a small charge of powder, when fired underwater, a very strong case is required; in fact, that the maximum etfect of a i-pound chai'ge was not at- tained until a case of J th-iueh iron, cafjjible of standing a grad- ual pressure from within of 330 pounds per square inch, was used. For large charges, of 500 pounds and upward, it is therefore evident that it would be (juite impossible to malce 109 ca.ses pioportiouatel^' .strcmg to seeuie a .similar de\-elopiiieiit of explosive ctt'ect. liL^eause tliey would become enormouslr heavy. We iJiay, ]io«ever, to a certain extent obviate this eftect of loss of power, as it were, by igniting the charges when of large .size, at several points, xirovidiug, in fact, several centers of ignitiou. and thus burning as much as possible of the charge and converting it into gas. before the (envelope is broken and the water admitted. Let us first consider what would be tin- maximum charge Ji^ixi-niimchargf which it would be desirable to fire vrith a single fuse, suppos- sinriL- in-'-. ing that in other resi>ects it is fa voraljly circumstanced; that is tosay, the case being- of the best form andofas great strength as circumstanci's will admit, i.K:c. The radius of ignition due to a .single luse. when fired under the <.'!reiimstaiices above described, has not yet been ascertained, but it is supposed to be about 1 foot, and, starting with this 1 iasi.->. our maximum charge, to be fired from a single center of ignition, is at once detcriiiine poumN of powder, adding a fresli fuse, suitably placed, for each additional 2.j0 pounds, or fraction of 2.j0 pounds, in the clnirge to be fired. This has reference to gnnpowdi_-r fired with au ordinary fuse. ^Yhen gun-cotton and a detonating fuse are used, a raui;h greater bulk may he exploded from a single ccJiter of ignition. The distribution and holding in proper relati\ e position outribmion or of a number of fuses in a large charge' of pov.der is a matter uirKi'.ciiargc.' '" '' of some little nicety, and in addition wa have the increased diflicnlty ol' testing the fuses after being xilaced in the charge, and the increasi^d chance of failure and trouble in replai-ing a defecti\e fuse, or adjusting any accidental de- rangement of tlie conducting'-wires .should a defect occur in the heart of the charge it.self, which would render the emptying out of the case necessary. In ordei' to obviate these defects, the following aciv ingenious arraugi.'ment has been suggested by Captain Harding Steward. E. E. The description is extracted from his rei]((rt : " The charge of powder should )je packed in an India-rub. c,.^tuiu st. w- l)er bag, about 12 inclus in diaim-ti'i-. (internal.) and of a""'""'*"'- length sutficientto contain it; (a bag 12 inches long will take a chaige of loO poixnds. ) "For the firing ariangcmcnt a brass tube and a fuse primed with powder are refiuisite. Tlie brass tube should be no suflicieutly loug to run the wlmle length of the bay when filled and tied at the end, and should have an internal diam- eter of one inch. To tit the tube for its object, it is neces- sary to cut slits i inch wide and 11 inches loug at central intervals of three iuches, and following a spiral line round the tube. (See Fig. 42.) These slits should be covered with brass wire-gauze, of a mesh sufficiently small to exclude powder, and one end of the tube should be closed and tlie other provided with short lugs. •■ A fuse primed with 2 drams of powder, placed iu the • ■ud cif the tube and "well secured to the lugs, also tigbtlv Q 1 &. •covered, so that ouly the wires protrude, completes the ar- rangement. It is theu put altogether in the central line of the charge and secured, so that it shall not vary its position. Ill '■ On applying electricity of a kind suited to the fuse em- ployed, jets of gas are driven from all tlie openings in the tabe. Tbesi' jets, accompanied by flame or without it, fire the powder Avithin their reach, and the result is the complete ignition of the outlying portions even before the gas evolved by the grains first ignited ba.s time to rupture the case or bag and let in the water. " The experiments made with this mode of i,i;nition have, owing to circumstances, been confined to lighting several trains and heaps of iiowder arranged about the lube, at inter- vals sufficiently large to prevent them communicating on one being fired. The );j;iiition was in all cases attended with perfect success. " Thefu.ses employed were of my own making, and suited for the electricity of a magnetic exploder. Equally good results can be obtained by priming Abel's mining-fuse, or his experimental fuse, with two drams of powder, pro. vided that the fuse, wlieu packed, fits the tube tolerably well. Two drams of powder only are proposed, as with three and with four drams it was found that the blast not only (in the above experiments; drove away the powder, but prevented the emission of gas from the two or three holes nearest to the fuse. It is, however, possible tbat with a confined charge an increase of the priming might not be attended witU the above results. If it is thought desirable to employ two fuses, so that in the event of one of them proving to be bad ignition may be secured through the other, the same can be done by arranging two tubes three inches apart, connecting their ends in order to keep them in their relative positions. " The mode of ignition proposed will be found so complete that metal cases for torpedoes can be dispensed with, and barrels used instead, for a water-tight covering is all that is required for the charge. " The proposed plan is also likely to prove useful iu all cases iu which ignition by means of chemical fuses, or by detonation, is used ; for the powder, according to existing plans, is only ignited at a single point, and that oneis close to the exterior of the mass of the charge, consequently the combustion of the charge would take place under unfavor- able circumstances. " In the event of the proposed mode of ignition being em- ployed for land-mines, it will certainly economize powder, but its utility will not be so apparent, for the surrounding earth cannot spoil a portion of the charge, as water does ; also, that detective ignition can always be compensated for by an 112 iucroasc of tlie cliar,;;!'. The plan, however, pennits of the series of fuses beiiij>- dispensed with, Avhich is, however, a mode of ignitiou little used in field-iniiiiug- ojterations. "With very large eliarges, (say from 300 to SOOpoiiuds,) the following- out of the eylindncal form, wilh a diameter not exeeeding 11' inches, as recommeuded, woidd involve incou- veuiently long powder-cases. It is therefore necessary to subdivide the mass of powder, and to employ branches ■with the tube. This can be best ettected by treating a, mass of powder as made up of a series of cylindeis 12 inches in diameter, and providing a tube for each, one ease alone being- provided for the whole." Tube, M ith Such a tubc, -with branches radiating from a single poiut, ranches, -- c? i 7 has been devised by Captain Steward. In the head of each branch he places a small priming charge, and the gas pro- duced by its ignition would no doubt act in a similar way, down each branch, to that of the fuse with the single tube. The advantages of a singU' fuse, or center of ignition, iii each charge are very great. It is extremely difficult to test a number of fuses of high electrical resistance in a single circuit without a very delicate galvanometer, or such au increase of power in the testing-battery as to run the chance of firing one of the fuses, and thus causing a premature ex- lilosion. Again, one bad fuse, among a number combined for the ignition of a large charge, might destroy the effi- ciency ofthe whole arrangement, or cause difficulties in igni- tion. And finally, should the tests indicate something- wrong, it would be a comx^aratively easy matter to replace a single defective fuse at one center of ignition; whereas the ri'- adjustmeut of a number would involve considerable difficul- ty, and probably necessitate the emi)rying out of the entire case. A few experiments on a very small scale, with charges o^ G pounds of powder, were tried by the floating obstruction committee to ascertain the value of the tube, but no definite results were obtained, nor is it likely that they would be with such small charges, supposing that the theory that a charge of 250 pounds of powder may be fired with a single center of ignition is correct. In order to settle this cpiestion it would be necessary to try comparative experiments with charges of not less than 500 pounds of ]iowder, the com- parative eii'ects with and -without the tube being carefully jneasured by any suitable means. Though, for the present, we are not prepared to concur in Captain Steward's ideas, that India-rubber bags, combined -witli tubes, but without a mt'tal co\ criug of such strength 113 as to develop the explosive force, are sufficient practically to secure complete igaition of a charge ; or that a considera- bly elongated cylinder is the best form of case ; still the tube arrangement is extremely ingenious, and would proba- bly render the use of a large number of fuses in a charge of powder of considerable bulk unnecessary. Several other methods have been suggested for producing Austrian plan of this very desirable result of a thorough ignition of the charge ; ^'* gnn-cotton. for instance, the Austrians place a pound or two of gun-cot- ton in actual contact with the fuse, and this substance be- ing much quicker of ignition than gunpowder, the gas and tlame produced is supposed to permeate the interstices be- tween the grains of the latter and thus secure a thorough combustion of the charge. Lieutenant Chadwick, E. E., has suggested enveloping Gun-cotton bag ' ' ^^ *■ ^ snggegted br Lieu- the charge of powder in a bag of gun-cotton, under the sup- tenant ciiadwick, position that by su rrounding it, as it were, by an enveloije of flame, which would be produced by the more rapid igni- tion of the giui-cotton, the combustion would be continued inward and that none of the powder could escape uu burnt. The effect of such an arrangement would be well worth try- ing. In order to prevent any chance of a miss fire, the Aus- each Vent°er''o°ri^- trians recommend the use of two fuses at each center of ig-""''™- nition, so that if one fails there is a chance for the other to produce the required result, and there is no doubt that in all cases, especially where there is any question as to the good quality of the fuses, this is a very necrssary precau- tion, especially when there is only one center of ignition in a charge. It must not, however, be confounded with the use of two fuses, one at each of two distinct centers of igni- tion, in a charge; it is simply the arrangement of two fuses at a single ijoint where one, if good, would do the work, and is only a matter of precaution. When no arrangement, such as Steward's rube, is used, Piling f^ « in ^ ' ' ' position. and we wish to distribute a number of fuses aiiout in the mass of any given charge, a very good means of keeping tliem in their proper position is to lash them to uieces of wood which, being rigid, may be arranged so as tx) remain stationary. This should be done before the charge of pow- der or other explosive is put in the case. With reference to the above remarks on the subject of a strong case re- 1 ^ n ■ ' 1 -w • qtitred for gui- the number of fuses required and their distribution m a powder iired w^h given charge of large size, it must always be borne in mind""^ '"^"^^ '"""^ that when gunpowder or gun-cotton fired with an ordinary fuse is used, a case of sufficient strength to develop the 8 114 force of the cbaroe is always necessary, whatever number of points of ignition may he employed. In fact, it cannot be too strongly impressed that the provision of a strong case (except where gun-cotton, fired with a detonating fuse, or some compound similar in the character of its ignition, is used) is a matter of vital importance. When gun-cotton fired with a detonating fuse is used, the strength of the case, as regards the development of the explosive force of the charge, seems to be a matter of no importance ; it is to be hoped, therefore, that we may be able to adopt this ma- terial and mode of ignition, which would eliminate one con- siderable source of difliculty. CHAPTER VII. ELECTEIC CABLES. The next point to be con.siderert is the most suitable form of insulated conducting-wire or cable for employment with electrical suljmarine mines. The qualifications required in such a conductor are ^^ ^iS.^^Tcm™^ "' follows : 1. Capacity to bear a certain amo^int of strain without breaking. 2. Good insulation, composed of such a substance that it may be readily stored and kept for a considerable time with- out being injured. This is an essential, as the lines will only be submerged while actually in use in time of war, for which purpose they must consequently be kept in store, and always ready in sufiicient quantities. ■J. For situations where there is a rocky or shingly bot- tom they must be provided with an external covering capa- ble of protecting the insulation from destruction. Special precautions must, of course, be taken to secure the cables at points where they may be necessarily exposed to a con- siderable wash of the sea, such as the places, where they may be led into a fort, &c. ; but as there are others where no such special precautions can be applied, we must provide for the contingency by an external protecting covering over the insulation. 4. Pliability, so that it may be wound on or paid out from a moderately-sized drum without injury. Several forms of cable have been devised to meet the above conditions. That used by the Austrians was manu-miiies. factured by Messrs. Siemens Brothers, of Charlton, and con- sists of a metallic conducting-wire, insulated with gutta- percha, and protected externally by hemp and by several plies of copper tape, wound on in a peculiar manner, so that each strip overlaps the preceding one, as shown in Fig. 43; this is a patent of the above-mentioned firm. One defect of gutta-percha insulation is its liability to become hard and brittle when exposed to dry heat, and the consequent necessity of keeping it stored under water. In order to obviate this defect, Messrs. Siemens have recently rejilaced the gutta-percha by vulcanized India-rubber in some of their cables. Austrian cables for submarine 116 Tlie following list gives the dimensions and compositiou of some of the forms of cable inauufactured by them for luiU- tary purposes : 3020 3030 3031 5014 501.". £ s.d. 83 81 81 70 03 63 ewt. 6 Description. A conductor, cnnsistinf^: of a strand ol' tlii-no soft iron wires, cacli of 0.05 inch diametoi, insulated "with two layers of gutl.a-percha and compound to ().'23(i inch, sewed with best Italian hemp strings, and covered with one coutiu- rious copper .sliintiiin;;- to a total diameter of 0.39 inch. A conductiij-, .strand of three soft irou wires, each 0.03 inch, covered with three layers of vulcanized India rubber to 0.364 inch, a layer of hemp, shealhed with copper sheet, and covered with tape i^aintod ^\-liitc. Same as last, but covered with phnted hemp instead of painted tape. Same as 30-:;i1, but no outer covering of tape or hemp on the copper. Sanu- conductor as 3029, sewed with hemp, and covered with tape painli_'d white, with no copper sheathing. Same as last, but covered with plaited hemp instead of painted tape. ^ Advantages and ^^'e luive occasJonallT foiiud the copper-ta lie covering ou detects of ^:ableb ' l l l o protected withtbese cablcs to act preiudiciallv under certain circnmstauces, copper tape. as, for example, if by any chance a kiuk occurs in paying out the line, and a sharp strain is suddenly applied, the cop- per tape is at that point drawn in such a way astocutthrougli and destroy the iusulatiou. In handling these cables, there- fore, it is necessary to be extremely careful. Wlieu once laid down this outer covering of copper tape appears to be a very efficient protection, and it is, of course, less affected by the sea-water than iron. lu using it, however, it is iieces- saiy to take certain precautious to obviate the electrical action which would ensue were the copper covering to be brought into contact with irou in salt-water. Under sucU conditions the iron would inevitably corrode very rapidly. The rapidity with which this electrical action destroys iron under the above circumstances is almost inconceivable, and much trouble on this account has been es;perienced in cur- rying on some of our experiments. An elevation and section, showing the general constrac- tion of Messrs. Siemens's cables in full size, are given in Fig. 43 ; (a) is the conductor; (/j) the insulation of gutta-percha or li: Indian rubter : ^c^and !cl) two coverings of hemp : and le) the cater protecting coijfier sheathing, laid on in a peculiar way. Another form of electric cable, suitable for submarine min- ing purposes, is manufactured by Mr. Hooper, of the Tele- graph Work.s, Mitcham, (now Hooper's Cable Comijauy. limited,) and possesses many qualities which render it espe. cially applicable for this service. It may be described as follows : A metal conducting-wire. generally of copper, covered with an alloy to protect it from chemical action : over this is a thin coating of raw India rub- ber, then a thin coating called the sep- aration- of India rubber, mixed with oxide of zinc; over this is a thickness of vulcanized India rubber, more or less, according to the amount of insula- tion and protecting covering required, and the outside protected by tarred hemp and iron wire, or, where the cable is not to be subjected to such usage as to render an outer wire covering neces- sary, by a simple layer of India-rubber felt. In the process of manufacture, the India-rubber, after being laid on, is subjected to a very high temperature, under a pressure of steam at SOOdegTces Falirenheit. which fuses it into a solid mass: and while thus improving the insulation, renders it indestructible by heat of any degree likely to occur even in a tropical climate. The object of the separator is to pre- vent the sulphur of the 6uter or main insulator penetrating to, and attacking, the inetal conductor. The high deuree of insulation attained is due to the use of India rubber, which is an excellent dielectric, and its capabilities in resisting high temperatures have been very severelj- tested in the existing lines in Ceylon, India, and the Persian Gulf, most favorable reports of which have been received. The advantages claimed for this cable by Mr. Hooper are summed up briefly as follows : high insula- tion, flexibility, and capability of with.standing dry atmo- spheric heat, which would destroy gutta-percha. Hoop':r'= cable. 118 Defect of In dia rubber iusu lation. A full-size elevation and section showing tlie general con- struction of Hooper's cables are given in Fig. 44: ; (a) is the conductor ; (h) the India-rubber insula- tion ; (c) the covering of tarred hemp ; and (d) an outer covering of iron wires ; Xo. 11, B. W. G., each separately cov- ered with tarred hemp, wound on spi- rally. •The table in page 120 gives in a com- j)rehensive form the different cables of Hooper's form, suitable for subma- rine mining purposes. Those with a stand conductor of three or four small wires only, viz: Xos. 323 A, 321 A, 37G and 323, do not ])ossess a very large amount of tensile strength, which, being necessary for submarine mining pur- poses, must be supplied by the addition of an outer covering as already de- scribed. India rubber insulation possesses one defect as compared with gutta-percha, viz, that it does not cling, as it were, to the metallic conductor; and that, consequently, if the India rubber is once cut through, any strain in the cable has a tendency to 'pull the conductor away and increase the fault. The conductor cannot be thus pulled away from the insulation, when the latter is formed of gutta-perch, which seems to cling to it Advantages of and prcvcut such a result. As far as we vet know, how- India rubber m- ^ . ' suiatiou. ever, India rubber is not so easily ailected by dry heat as gutta-percha, and is therefore preferable for storage ; tlie latter cracks and perishes unless considerable care is exer- cised in iireserviug it, which is best done by keeping it under water. India rubber ijossesses higher dielectric pre perties than gutta-i)ercha. Gray's cable. A cablc, vciy siuiilaT in appearance to Hooper's, is man- ufactured by the India rubber. Gutta-percha, and Telegrapli- works Company, of Silvertown, Xorth Woolwich. The chief difference in this cable, as compared with Hooper's, appears to be the absence of the separator, on the use of which, however, Mr. Hooper lays peculiar stress. The form of insulation adopted by the Silvertown Company is called (rray's patent. 119 A cable of this form was used in the operations against cabie u-i.i m - demo ition of tn ■ the HTeck of the Golden Fleece at Cardiff in December, ^eck 'Goideii Fleece." l'?69. and January. 1610. It consists of a strand of 3 So. 20, B. TT. G. copper wiies. insulated with India rubber (Gray's patent) to a diameter of y-^ inch, and protected externally with two servings of tarred hemp, wound spirally in opposite directions. This cable possesses considerable tensile strength : when one end of a short length was made fast to a rigid point, it resisted two men pulling at it with their full strength without injury. It remained perfect during the whole of the operations against the wreck of the Golden Fleece, which extended over a period of two months of very rough usai;e. and turned out to' be admirably suited for the purpose to which it was applied. Its cost is about £33 per mile. For rocky bottoms or situations where the cable is sub- jected to risk of mechanical injury, a further external pro- tection of iron wires and tarred hemp must be used. This would of course increase the cost. A full-size elevation and section of this cable, which give a very good general idea of the forms manirfactured by the Sih ertown Company, are shown in Fig. io ; (a) is the Fig. 45, metallic conductor; (b) the insulating material, (Gray's patent;) (c) and ('?j two servings of tarred hemp, wound spirally in o[)posite directions. A multiple cable may in many cases be found convenient where it is required to carry a large number of wires in a compact form into a fort. The following description of cable has been designed for this purpose, and seems to meet the necessities of the case : It is composed of seven distinct cores, each of which consist> of a strand of 3 Xo. i'-. B. W. G. copper wires insulated with India rubber (Gray's patent) to a diameter of -f^ incli. The interstices between the cables are filled with hemp libers disposed longitudinally, to afford as much tensile strength as possible, and the whole is protected with a double serving I it' tarred hemp. The cost of this cable wiU be about £220 per mile. For a rocky bottom, a situation where the cable Multiple cubl 120 ■;onyi lod ^qSioAV luiox uojorainp opiSiiiQ I -g, a: § t- c c o X' — X E-I ~ 5 XT ~ " ^ o" !^ Ij-f x" f-~ t- ' -r" S^ '-^ le agents of electrical ignition, while at the same time rendering it very evident that the utmost care is indispensable in testing and using them. The inductive efi'ect with a multiple cable would mani- festly be very much increased in consequence of the prox- imitj' of the adjacent conductors. Frictional electricity mu.st not. therefore, be used to fire charges in connection with a multiple cable, or even when separate cables lie parallel to each other for a short distance, in connection with any system of submarine mines. Induction does not occur to such an extent as to fire an Abel's fuse, when a constant battery is employed. Such a battery may therefore be used with perfect safety to fire any particular mine of a system attached to a multiple cable without endangering the others. With the platinum fuse there is no danger whatever of ignition by induction. 124 Testing-box for j^ order to facilitate the couueotions of the several sepa- connectiou of Imoa to multiple cable, rate liiios, diverging froiu the extremity of a multiple cable, a testiug-box has been designed. Into one side of this box the multiple cable is introduced through a water-tight joint, while the separate cables make their exit on the other side, through similar joints, and pass thence to the several mines of the system. Within the box is provided an additional separate water-tight joint for each cable, so arranged, on a principle designed by Quartermaster-Sergeant J. Mathiesou, E. E., that each cable may be rapidly connected or discon- nected to give facilities for examination and testing. In order to bring this box to the surface for the latter purposes it is only necessary to provide a buoy and a line of snfficient strength to enable it to be weighed. The buoy -line must be strong enough, not only to carry the weight of the testing- box, but also that of a short length of the cables connected with it, sufficient to reach to the surface. This testing-box must be placed in such a situation as to be easily attainable, even in presence of an enemy's blockading squadron, and the buoy attached to it must not be conspicuous. It i^ essential that it should be in a safe and well-guarded position, as any injury to it, or to the multiple cable, would be fatal to every mine connected with it. The necessity for safety would also regulate the length of the multiple cable and the point at which the separate cables should diverge; this must always be dependent on local circumstances. A detailed description of this testing-box shall be given hereafter. Cables with Another form of cable has been suggested by Quarter- bianches designed master-Scrgeant J. jNIathieson, E. E., in connection with a by Quarterraas- ^ ' ' ter-sergeant Ma- gystcm of clectrical sclf-acting miucs, arranged to be fired on thieson. '' 070 the circuit being closed by the contact of a ship, the igniting agents being a quantity battery and platinum fuse. The following is a description of his proposal: From his firing station he carries a multiple cable, («,) Fig. 47, to a test-box, (6,) from this test-box, which is arranged in a precisely similar manner to that already described; single conducting cables (c, c, c,) (insulated at their outer extremities,) with branches, (fZ, f7, f?,) are carried to the positions in which it is required to place the mines ; finally, to the branches are connected the several mines with their respective circuit- . closers, and when any one of these latter is struck by a vessel, the circuit of a battery, in connection through the multiple cable («) with the particular line (c) to which it is attached, is closed and the mine fired. After any particular mine has thus been fired it becomes necessary to cut it out of the circuit, otherwise the current passing away through 125 tlie bare extremity of the fractured wire, to which it had been attached, would cause such a loss of battery power as Xjrobably 1o prevent any fuse in connection with the same cable being fiied, even if its circuit-closer were struck by a Fig. 47. vessel. Furthermore, it is necessary to eliminate this ex- pended line from the system without going near it. In order to do this (Quartermaster Sergeant Mathieson projioses to use a quantity battery, (Grove's or Walker's,) and to place a short length of thin platinum wire at a point (e) in the branch {dj between the main cable (c) and the platinum fuse (/', ) which latter fires the charge. The platinum wire at (e) is so arranged, within a Mathieson's connector or other suitable insulated covering, that on its being fused the extremitj- of the cable at (e) is at once insulated, under which circumstances the loss of current, through the fractured extremity of the cable of an exploded mine, would be stopped and the full force of the battery be preserved to fire any mine attached to the same cable, (j ously by Captain David, E. M. L. I., while the latter was •=''^''"'- under instruction in the electrical school at Chatham, is to cover it with rope, to place it in the core, as it were, of a hempen cable. Two short lengths of Hooper's core have been covered in this manner, in the rope in;uiufactory at Chatham dock-yard, for trial. The insulated wire was held steady in the center, and the rope was made upon it in the 128 usual way, so that ia outward a))pearauce it differed in no rospeut from an ordiuary hempeu cable. It has been sug- gc^sted by the floating obstruction committee as a cheap and ready means of covering an electrical cable, and so pro- tecting it from external injury, and from experiments tried with the lengths in our possession, it promises to be very useful iu certain positions, and might no doubt be used with advantage when the more approved form of cable is not obtainable, and when the bottom on which it is laid is not too shingly or rocky and likely to cut through the external hempen coverings. In forming the rope upon it, considerable care is necessary to prevent any great amount of tension or torsion coming on the insulated wire, as either one or the other is likely to injure it. It was suggested by Captain David, in connection with an idea he had for exploding charges in combination with a floating boom, or to indicate that a boom was broken. Captain David's His idea was to lay one or more of such rope protected an electric cable clectric cablcs aloiig the whole length of the boom, carefully attaching them thereto. With such an arrangement any attempt to break the boom must be accompanied by a frac- ture of one of these cables ; and the bare extremity of the conducting wire, falling into the water as soon as the cable ^vas cut through, would be sufiicient to complete the circuit of a battery, one pole of which \\as attached to the cable with the other to earth. It is easily seen how a charge pre- viously placed in such a circuit would thus be fired, and would destroy any vessel or boat in its vicinity. It would only be necessary to insulate the extremity of the cable beyond the charge, as regards the firing battery, to render the system inactive till the cable was cut. It is, no doubt, probable that this cable, resembling iu outward appearance an ordinary rope, would not excite suspicion and would be likely to be cut, but any mine iu connection with it, near enough to injure a vessel or boat, would also generally be near enough to damage the boom itself, a result which would not be at all desirable. Some experiments were tried by Captain David which demonstrated the practicability of the idea, as far as the firing of a charge is concerned. Such a combi- As an indicator of the continuity or otherwise of a boom kniicator.l " "* "" at night or in a fog, it would probably be useful. The ar- rangement of an insulated cable for such a purpose would be the same as that for firing a mine, but instead of a charge of j)Owder or gun-cotton, a galvanometer would be introduced into the circuit, and a fracture of the conductor indicating the breakage of the boom by storm or an enemy's operatious, 129 woald at once be indicated by a deflection of that galvan- ometer, consequent upon the current from the battery, the circuit of which would be completed through the severed cable as before. In this manner a most effective watch from the interior of a fort could be kept over obstructions in a channel, even though such obstructions were perfectly invisible from any cause whatever. The electrical conducting cable is perhaps the most im- improTiseaeiec- ])ortant item in any system of electrical submarine mines ;'™°^ "^"^ an accident to it would nearly always render a mine inef- fective ; it is therefore a difficult matter to treat of, in refer- ence to any improvised arrangements that may be practica- ble. As a general rule, in the event of the more approved forms of cable not being obtainable, the test condncting- wire and insulator at hand should be used ; and, bearing in mind the conditions to be fulfilled, already enumerated, it should be most carefully tested under a considerable press- ure of water before being employed. Any of the ordinary forms of conducting-wire insulated with gutta-]}ercha, might, with the addition of some external protecting covering, be made available, or even a wire insulated with a thick cover- ing of well-tarred canvass might answer for a short distance. In forming an imi)romptu cable, a large conducting- wire of small electrical resistance should be selected. The reason of such a selection is manifest, with reference to the well- known law of division of electrical currents. CHAPTER VIII. WATEK-TIGHT AND INSULATED .TOINT.S AND Ci iXNEOTIONS. Tlic next point to be considered is tlie mode of eniryiug the coudnc'ting-wiies and :ittaelied fuse into tlie cliarye, so as to insure a- water-tight joint, and keej) the arrangement in proper ennditiou for ignition at any niomeut required. Tlie great object is to exclude the water ; tliis was eil'ected in the Austrian apparatus by means of a stnflinglxix. M;itiaioaou's The followiug suggestion of Quartermaster -iSei'geaut J. discing fuse'"iDtoMathieson, i*. E., is perhaps tlie best that has yet been de- "^ ''"®^'' vised for attaining the above very desirable object, and it not only possesses the advantage of being extreuxdy water-tight, but is also capable of being opened at any time, with the greatest facility , for the examination of the fuse. The mode in -which this may be done may be easily understood from the following descriptions : Objects to be at- He has designed sexeral arrangements ro meet the objects tained. o o j to be attained, which may be enumerated as follows, viz, that the opening, through which the eouducting-wires of the fuse are introduced, may be water-tight, and that the apparatus may be easily unscrewed and the fuse taken out for examinat ion , or for tlie introduction of a new one, in the event of a defect being discovered. Apparatus foi- a One of tliesc is shown iu section in Fig. 49; (« «) are two ■^ '''^''' cylinders of ebonite, through which a pair of holes are bored for the reception of the wires attached to the terminals of an Abel's fuse, and with shoulders {b h) on each, the lower one arranged to fit on a llauge, attached to the metal case, to contain the charge, and the upper to receive a metal screw (c (.;) which, when screwed home, would exercise a pressure tending to force the two ebonite cylinders into close contat^t, as well as to fix them firmly into the ease for the charge. Within the holes for the reception of the insulated conducting-wires (//) are a pair of ebonite tubes fitting over the latter, and their extremities beveled into a wedge form. Four cylinders of vulcanized India rubber, {fjg,g(J,) each perforated to enable them to pass over the insu- lated wires, (/ /,) are placed just over the wedge-formed extremities of two ebonite tubes (e e.) A ring or washer (/f)ofvulcauized India rubber is placed between the shoulders of the lower ebonite cylinder and the flange of the metal case ou which it rests. A metal shoulder, ((,) formed with a 131 female screw to correspond with the screw (c e,; receives the latter, anrt it is easily seen how, when (c c) it is screwed home, the several parts of the apparatus are forced closely together, and pressure is brought to bear upon the India- rubber cylinders (g (/, g g) and the Imlia rubber ring or waslier (ft.) These are thereby forced into all the interstices in their vicinity, and everything becomes perfectly water- tight. The shoulder (i i) should be cast or welded on to the case to contain the charge, so as to form one solid piece with it. When the metal, of which the case for the charge is comi)osed, is iron, the screw (c c) must also be of iron: if any other metal, brass for example, were used in contact with iron in sea-water, an electrical action would be imme- diately set up, and the iron would be Tcry rapidly decom- 132 posed. This is au important point to remember in constrnction of apparatus of this nature. the Apparatus for Another similar form of apparatus has been designed by ii -I- with a barrel ^"^ -,x-,^ oj Quartermaster-Sergeant Mathieson, K. E., for carrying the conducting-wires into a charge placed in an ordinary wooden barrel; this is shovrn in section in Fig. 50, and is precisely similar in principle to that for the metal case, Fig. 49. There being no iron here to decompose, the metal screws, &c., may be formed of brass, which is an advantage, as this latter metal is more easily worked in the form required ; (« a) are the two ebonite cylinders; (&) the brass coupling-screw; (c) a brass socket, in connection with another brass screw (d) within the barrel ; (e e) are the ebonite tubes as before ; (//') 133 ludia-rubber washers, and {g g) the insulated conductiug- wires to connect the fuse. The screw ((/) is furnished with spikes, which grip the inside of the barrel and secure rigid- ity. Another form of apparatus, somewhat similar to that Apparatus for described in page 96, but an improvement thereon, has been wire?a-e^ " "''" designed for use with a platinum-wire fuse and a metal ease for the charge ; this is shown in section, Fig. 51 ; (a a) is a shoulder of i>ecidiar form, cast or welded on, and form- ing one solid piece with the metal of the case, in which a circular opeuiTig. i inches in diameter, is left for the intro- duction of the charge of gun-cotton disks ; [h b) is a socket with shoulder, made to fit over (a a ;) {v c) is a metal coup- ling screw; (f?) is the platinum- wire fuse, formed on precisely similar principles to that described in page 96, but in this case made to screw into the socket (& b) so that it may be taken out for examination without disturbing the main arrangements by which the loading-hole is secured; (e e) 134 ;ue vulcauized India-rubber rings or wasbers, by wbicli the whole is made water-tight, in piecisely a similar manner to that already described; (//) are the fuse terminals ; these are insulated with vulcanite, which has been made to adhere to the ebonite frame (ercha cable remove about li inches of the insulation at the ta-pereha joint, ^^^^^^^_ ^,j.^^,^, warffliug gcutly it is easily pulled off with the fingers, (this is much safer than cutting ;) clean the two ends with emery-cloth, and file a. .Vinch scarf on them, (see Pig. 5(J.) The wires are then caught with the scarfs together in two Fig. 56. small A'iscs, fixed on a bench, one working on a slide, so that they can be set at any reiiuired distance apart, and soldered. After soldering, clean the scarf off with a small file. Theu bind it round with four strands of fine copper wire, laid side by side; loop one end on the left-hand vise, and wind from left to right, taking care that the wires are evenly laid on and do not ride over each other; the length of the binding should be about 1 j inches ; the ends of the binding wires are now snapped off by a shai'p tug with the pincers. This binding is then soldered at the center and at the ends, leaving two i)arts of the binding unsoldered, so that if the scarf be drawn asunder the four-strand wire shall still connect the two ends and form a metallic circuit. The joint is then well washed to remove all acid from the coppei; Tosearf a strand J^^ Scarfing a straud conductor, the two ends are first sol- condnotor. dcrcd, making them solid. If the diameter of the conductor exceed Xo. 14 gauge, two courses of binding are used, the first soldered all over, the second in the center and' ends only. This is the mode adopted for snbmarine-telegrapb cables, but for the comparatively short lengths used for sub- marine mining purposes, an efficient metallic connection may be made, in the case of a strand conductor, by simply twisting the wires of the two portions to be joined tightly together ; after cleaning them and soldering, care must he taken to prevent any projecting ends of wire remaining at the junction. 139 To complete the insulation, clean the joint all over with to complete in- a little spirit of naphtha on a rug, and give it a' thin layer of Chatterton's compound ; warm the joint in the flame of a spirit-lamp, and taper the gutta-percha by drawing it gently with the Augers until it ue irly reaches the center ; then with a hot tool, designed for the purpose, work the two portions together to form a solid mass ; then apply a thin layer of coumpound, followed by a strip of sheet gutta-percha ^ inch tliick and large enough to cover the whole, warmed together with the joint, and lapped round it, taking care that llie under part and ends shall adhere first ; warm the whole gently again, and close it from the bottom upward taking care to expel the air in front. When the two edges meet, cut them off as close as possible with a pair of scissors and work them into one another with the tool, doing the same at the ends; then gently warm the whole, and burnish it off with the wet hand. In this way the insulation is completed to the same diameter as the original. In joining gutta-percha the great point to guard against is not to give it too much heat ; if it is a litte too hot it be- comes oily and will not adhere. The insulation having licen thus completed, any outer protecting co\'ering of wire, hemp, »&c., should be laid on and secured which completes the operation. Intliecaseof an India-rubber cable thefollowing method is recoinmen(l dry at tlie moineut wlieu the joint is made. nr-.ii » uKtaiiic A very ingeiuons mode of making tlie wire jjortion of the joint has been iuveuted by Donald Nieoll, esq., of Kilburn, His idea su.i^gested itsidf in connection with his own sys- tem of nndergTonnd telegraph-wires, but is e(iually appli- cable to the formation of joints of the nature re(iuired for submarine work and is very simple. He first prepares the extremity of one of the conducting- wires by tbrming it by means of a very neat and ingenious little instrument into a sjiiral twist, (see Fig. r»S,) and the corresponding extremity Fig. 58. oi the cable to be connected being left sti'aight, it is sli]>pecl in, the whole x^laced on a small anvil, and, !)>■ a single blow of a hammer, pressed so closely together that soldering is almost unnecessary, v\'hile the joint is rendered capable of standing a considerable tensile strain. Advantages and The great advantage of a joint insulated with this India- in'dfr?u'bbe°ri'"lj''t'i' tubiug is the facility with which it can be made at tubo.iomt. j^jj^. ■(;j^J^ jj^^i under any circumstances; it is also very economical. The chief danger to it is the chance of a pro- jecting end of a wire perforating the India rubber and causing a leak, through which a loss of current would take place; care must therefore be talcen to prevent such aii accident. One mode in which the chance of such a contingency may be reduced, is by lashing pieces of wood on over the joint, outside the India-rubber tubing, to prevent any bending at that particular point. Under j\rr. Xicoll's system, no pro- jecting eiids are left in making the joint, and the chance of a perforation is thus reduced to a minimum. Dent's ijottic Auotlier very good joint, in nmuy respects superior to the India-rubber tube, is that invented b.\' Mr. Dent, of the chemical department, royal arsenal, Woolwich. It con- sists of two parts, viz, a cylinder or plug of vulcanized India rubber, about linch in length, and the same in diameter, through which three holes of sufticieut size to admit the two insulated wires, [b h,) Pig. ,59, and a tapering cylinder of wood, have been bored by means of a red-hot wire ; and a lomt 143 stout glass tube(cc)about 1 iucli in diameter and If inolies in length, sealed at one end. Fig. 59. This joint is employed as follows: Each insnlaled wire is I'iissed through one of the holes in the vulf-anized rnblier cyliiidcr. and the clean bare ends of tlie metal wire are then twisted together and cut oif short. If tape-covered wire is used the tape must be previously removed from about three inches of each wire. Into the third hole of the cylinder is loosely inserted a tapering plug of hard wood, [d) about finch ill diameter at the larger end, and 2 inches in length. The cylinder, with the wires and plug, is then firmly presseil into t'le glass tube, and the wooden plug is afterward forced into the hole as tightly as possible, as shown in Fig. .39, which has the effect of forcing the India rubber against the sides of the glass cylinder and around the insulated wires. It is important that the India-rubber cylinder should fit tightly into the glass tube, and that the perforations made to receive the wire be not larger than absolutely necessary. A very small quantity of grease applied to the surfaces of the insulation of the wires, the plug, and the cylinder will greatly facilitate the fitting up of the joint and improve its efficiency . This joint is extremely simple and economical, and is easily Advantages and made. A joint made on this principle was severely tried Dents bottle joint 144 by being kept under a pressure of 18 feet of water, aucl tested at intervals with a. retleeting galvanometer, under which treatment no appreciable loss of insulation was indi- cated during a period of teu days. At the end of this time Fig. 60, „ the glass cup was found broken, as if forced outward by pressure from the swelling of the plug or wedge, while it 145 remained submerged. It proved itself, however, an excel- lent joint as regards insulation. One of its defects is its inability to stand a tensile strain, in order to defrease the ' chance of which, as much as possible, the. insulated-wire connections are tied together, as shown in Fig. 59. Another is the chance of the breakage of the glass by a blow, to ob- viate which the glass cup is covered with an India-rubber cap; it is, however, easy to arrange it in such a manner that it may not be subjecteil to either of these contingencies. Another defect, above referred to. is the danger of break- ing the glass, by pressure exerted from the inside, in con- sequence of the swelling of the wooden plug after immersion in water. In order to obviate it, the ping should be made of box or some other very close grained Vood. Another, and much more elaborate, joint is that invented oiovsr sjoim. by Corporal Glover, R. E. It consists of an ebonite cylinder (a,) Fig. 60, fitted with two grooves to receive the uprights [h h) of a brass disk (c) which forms one end of the appa- ratus. This ebonite cylinder is bored through the center to admit the wires to be joined with theiriiisulation, and the diameter of the bore is expanded, at each extremity, into a conical hollow to receive two similarly shaped plugs (rZ d) of vulcanite, which latter pass over the insulation of the wires and fit accurately into the cavities left for them : (7i) shows a horizontal and («) a vertical section through the ebonite cylinder. A brass disk (f.) --imilar to (c) >)ut with holes to receive the brass nj^rights of the latter, is placed over the top of the ebonite cylinder, and is held firmly on by screws (//) passing on to the uprights. A small pro- jecting ring {g) on the lower disk (c) and a .similar arrange- ment on the u[)per one {e) keei^ the vulcanite plugs from being forced out laterally when pressure is applied. A me- tallic connection having been established by twisting the conducting-wires together, the outer protecting covering having, as before, been carefully removed, the base wire is drawn into the center of the ebonite cylinder, the screws (//) are tightened, and the vulcanic plugs are driven for- cibly into their respective cavities, making the whole water- tight. A little grease carefully applied to the insulating- material at the points of pressure will in this, as in other similar cases, improve the insulation of the joint. The defects of this joint are its high cost and the uneven Defect of bearing given by the two screws used in tightening up; this '^'"^"■'^J'''"'- latter might, however, be obviated by the employment of three screws, in a triangle, instead of two, by which all side 10 146 B e iH I- 11 s t e 1 joint. motion, after tlie process of tishteuing up, would be obvi- ated. 1 Another joint is that said to have been invented by Mr. Beardslee, of Xcmy Yorlv, but bearing the name of Goodyear's patent on a specimen left at Cliatham by him. It consists of an ebonite cylinder, [a.) Fig. 61, with closed ends, one a fixture and the other fitting the cylinder with a screw (6.) Fig. 61 Each end has a perforation of sufficient size to admit the insulated wires (c c) which are to be connected. The bare extremities of the wire having been cleaned to the extent of aboutf inch, each one is passed through one of the perforations in the joint, as well as through a disk of Aulcanized rubber (d (1) of -§- inch thick, and one of metal (e e) ^ inch thick. The bare extremities of each conductor are secured bj- spreading them out upon the metal disks, and these are then brought into close contact in the interior of the ebonite cylinder by screwing up the movable end thereof as tightly as possible. Specially appii- Thisjoiut Is sijcclallj' applicable to a strand conductor, cable to a strand t /. i n n • . • i i ■ j conductor. composed oi a number ot fine wires, which may be separated and spread over tUe metal disks so as to insure good con- tact. The usual precautions, as to the removal of any outer protecting covering and greasing the insulation, must be borne in mind in forming this joint. It is particularly necessary, in employing this joint, to guard against direct strain being thrown upon the wire 147 extremities which are inclosed, as they would be even more liable to be drawn out of the cylinder, in which they are rigidly fixed, than in the case of other joints : the electrical connection, in this case, being formed by the simple contact of the two metal disks and not by twisting the wires together. The wires should therefore be firmly braced together at a short distance from the point of juncture, as shown in Figs. ol and 59. The defects of this joint are its inability to stand a ten- Defects of sile strain, which would tend to draw out the wires, or so """^ " '"" ■""°'' far separate the metal disks on which the wires are spread out as to break the metallic contact, and thus interrupt the current, and that the wires to be connected cannot be sol- dered. Another joint is that invented by Quartermaster-Sergeant . m a t h i e « o n 's Mathieson, It. E. It consists of two ebonite cylinders, (« «.) Fig. (J-, perforated to receive the cables to be couuected, the opening at the outer extremities being just large enough to admit the insulation of the wire to pass freely, while the inside is larger, thus forming shouklers against which thick perforated vulcanite rings (b b,) encircling the insulation, are placed. Within tliese cylinders is an ebonite tube with wedge-formed ends in contact with the vulcanite rin;;s, within which the wire connection should be placed. The center of tube (c) is of square section, and fits into a hollow of similar form in the cylinder (a a ;) the ends of the tulje are. of circular section ; the object of the square center is to prevent the wires to be connected being twisted round and round during the process of tighteninj; np, as any torsion of this nature would be liable to diMiirauge the metallic connection within or to injure the insulation. A coupling- screw, ((/,) with a shoulder to catch a corresponding shoulder on one of the ebonite cylinders, and a corresponding screw on the other, completes the arrangement. Portions of the coupling-screw, and one of the ebonite cylinders, are made of hexagonal form, to fit a couple of spanners to be used in tightening up the apparatus when greater force than that which can be applied witii the hands is necessary. It is easily seen how, by tightening np the coupling-screw, the two ebonite cylinders maj- be drawn together and the internal tube forced upon the vulcanite disks, making the whole water-tight. To make an insulated joint with this apparatus, the coup- To make a joint. ling ((/) is unscrewed as far as possible without separating the two parts, (a fl,)andalittle grease is applied to the threads of the screw ; the whole apparatus is then slipped bodily 148 on to one of the insulated cables to be coiniected ; tlie insu- lation of each cable, ba\'iiig been previously rubbed with a little grease, is then carefully tapered off to a blunt point Fig. 62. and rubbed with a little grease, taking care that this grease does not extend to the metallic conductor. The extremi- ties of the metallic conductors, having been carefully cleaned, are next twisted together so as to leave as short a length of naked wire as possible, care being taken that the diameter of the two wires, when twisted together, does not exceed that of the insulation. The exposed metallic joint is next drawn back into the center of the connector, which is then sciewed tightly up with a spanner and the India- rubber packing so firmly wedged round the insulation 149 as to exclnde damp most effectually from the bare con- ducting-wire in its center. If the connector be unscrewed and the ends of the wire ^^,^„f^;;^;'* "pp^^' carefully drawn out, the same apparatus may be used any """^ """■ """"• number of times, provided it has not been injured by the explosion of a mine. If the inside be wetted it mu>t not be nsedagain till thoroughly dried ; especial care is neces- sary if it has been accidentally wetted with sea-water, the latter being a better conductor of electricity than fresh water. When the caWe is covered with an outer protection of tape, hemp, or any similar substance, it is necessary to remove this carefully from the vicinity of the joint, as the damp would penetrate through the fibers were it allowed to remain. In order to test the efficiency of this apparatus, a piece ot'j^^^p™°«°' ^" cable, which had previously been tested for insulation and tound good, was cut into nine pieces and joints made at the cuts with Mathieson's joint, thus forming eUihi points through which the current might leak. This was sunk to the bot- tom of the river 3Iedway, a depth of 36 feet, and tested from day to day -for a period of more than two months, with 48 Daniell's cells, and an astatic galvanometer, without show- ing any indication of leakage of current. Tiiis joint ])0ssesses considerable tensile strength, but were it likely to be submitted to any considerable strain, it is nevertheless a good precaution to form a loop in the cable, as recommended for those previously described aud shown in Figs. 57 and .59. When an insulated cable has an outer protecting covering Mathiesou-- joint of wire, a modification of 3Iathieson's joint must be used, wire ^TMictmn This is shown in section. Fig. 6.3; a simple addition in the '^°''^"°^' shape of two ebonite tubes (« a) made to pass easily over the outer protecting covering, with India-rubber cylinders (6 h) also fitting over the same, in addition to those in contact with the ebonite tube covering the metallic joint of the conducting-wires, is all that is necessary. It is easily seen how, by simply drawing the parts of the apparatus together by means of the coupling-screw, everything may be made water-tight and consequently insulated as before. In making a joint on a cable with an outer protecting covei ing of wire, this latter must necessarily be removed, and a weak place, at which the cable would bend easily, would be formed. The joint described, by gripping the outer covering beyond the actual point of connection, prevents any such bending 150 with tlie danger inseparable from it of piercing the insula- tion by a projecting wire. Fig. 63. These joints mast be made to fit the insulation of the cables they are intended to connect with a certain amount of accuracy. They must be sufficiently loose to slip easily over it, before being screwed up, and the limit, within which a joint made for one size of cable may be used for "Si smaller one, is dependant iipon the extent to which the India- rubber cylinders may be com- pressed, so as to fill up the vacant space and make the joint water-tight. When there is no iron in contact to be damaged by the electrical action set up by the ' sea-water, the coupling-screw and outer portions of this joint may be made of gun-metal, which gives greater strength than ebonite. Matliieson s is decidedly the , Adyautugea ofi^egt, pf' jjll the temporary Mathieyon a joint. ^ ^'" joints described, possessing, as it does, excellent insulatiug qualities, great facilities for making or detaching a con- nection between two cables in a short space of time, and being capable of standing a considerable tensile straiu. In many situations it may conveniently be used to supply the Ijlace of a permanent insulated joint, to which, as far as insulating qualities are concerned, it is quite equal, and to which, where facilities for examination are required, it is superior. EKperiments to All the temporary joints, above described, were tested teat temporary • ■ -i ' i t-^ in joints. for insulation, suuilarly to Dent s, (see page 14J:,) and au stood the test, which was a very severe one, remarkably well. ]\Iathieson's was again more severely tested, as already described, with very satisfactory results. CHAPTER IX. s^"lB^IEEGI^'G jitxes, etc. We now come to the mode of laying down the mines in snch a position that they shall be most effective, and at the same time so disposed that the explosion of one shall not injure the caljles, circuit-closers, &c.. in its vicinity. The position of the mines having been first determined, .. MaAing posi- ^ 07 tion of mines, should be marked off by means of buoys, arranged to corre- spond with the charges to be subsequently placed in position, and points on shore to guide the vessels employed in laying them. The moorings may either be first placed in position, and the mines and circuit-clo.sers hauled down to them, or the whole (moorings, mines, and circuit-closers) may be launched (Tverboard, attached together in proper relative position, at the same time. In deep water it would probably be found preferable to adopt a system of hauling down to moorings previously placed, while in shallow water it would, under certain circumstances, be found quicker and more convenient to adopt the latter mode of proceeding. The cases ready charged, and with the electrical cables, &c., attached, having been lowered into position at such intervals as may be' required, according to the size of charge to be used, and eacli carefully buoyed with a numbered buoy, the paying out PayiDgom eiec- of the cables may be proceeded with. The electrical cable attached to each, having been previously arranged on a drum, should be placed on board a pinnace or launch, which should prueeed directly to pay it out in a line as nearly as possible perpendicular to the line of mines. Each boat should be provided with a small testing-battery and astatic galvanometer, by which the insulation and electrical resist- ance of the .system should be tested at intervals, from the moment of submerging the mine till the other extemity of the cable is safely lodged in the testing-room. Any defect likely to cause a failure in firing at the proper moment would, in this way, be immediately discovered during the operation of submergence. As the boat, in paying out the cable, passes the position marked out for the second or covering line of mines, care should be taken to have it, as nearly as possible, midway between two adjacent mines in this Hue, to prevent the cable being damaged by the explo- 152 sion of tlie mines iu tliis lino; tlie mines of, this second line would, as stated in page 23, be so placed as to cover the intervals of tlie iirst. In passing this line the position of the electric cables should be marked off by buoys as a guide to those layiui^ down the second line of mines, which, as soou as the work of the first has proceeded so far, may at once be commenced. In order to distiuguisli between the buoys markingthe positions of the mines from those indicating the directions of the cables, different colors might be used ; as, for example, those attached to the mines might be pointed red, and those in connection with the cables black. As tlie third line of mines would be placed to cover the intervals of the second, it would be uecessary, after proceeding in a direct line fur about 100 yards in rear of the second line of mines, to change the direction in which the cable is to be laid by carrying it i^erpendicular to the direction hitherto followed, till a point directly in rear of one of the mines of the second line is reached, when it should again be turned inward, and would be in a position to pass safely through the center of an interval between two mines of the third line, as it had previously passed through those of the second, so as not to be injured iu the event of their explosion. In passing this third line of mines it should be again buoyed for guidance in laying the mines belonging thereto, and so on till the extremity of the cable was connected to its corresponding •wire, if a multiple cable were used for any portion of the distance, or if each were to be taken iu singly, till safely landed in the fort in which the operating-room is placed, when it should be attached to its proper binding-screw, and its insulation and resistance carefully tested and registered. Lines of cables '^^^ samc proccss would be goue through with every 'i'wefrcimcharges '-'^''"'8'^'? *^® utuiost carc beiugtakeu so to lay the cables that they shall be as far as possible away from the mines in the \icinity of which they may be required to pass, so as to give the least chance of injury from the explosion of the latter. By the arrangement above described they would also be in a favorable position for underruuning and pick- siack to be ai-i"8' "-iP? should sucli au Operation become necessary. A cer- '""-'' tain amount of slack should be allowed in laying the cables to facditate picking them up for examination and repair. This amount of slack will depend ou the depth at which a cable is submerged. Positions of Tl'« position of each charge should be identified by means Med by^Bli-tags of bearings taken by two theodolites, from points well sit- ami^ marked on a ^^,^1-^ J fQj. the purposc, aud marked in position on a plan, with the number of each mine, as a guide to facilitate its 153 discovery at any future time. This done, and the whole system having been proved to be electrically coireet. all the suriaee-buoys should be removed, to prevent any indication of their position Vjeiug given to an enemy. Dummies to deceive an enemy may be judiciously arranged in a manner not too ostentatious, but they should never be placed in .such a position as miglit, in ever so remote a manner, lead to the di^Loveiy of a real mine. Fig. 04 gives a grneral idea of the position of the cables if laid down on the prin- ciple described : the cables are indicated by the dotted lines (e c c, &c..j the mines of the system are shown at (m III m, &Q.) Fig. 64, m rru rw TTV mi O O O o o I c fr. O 1 '-' c ■7- 1 nv \ Q 1 nv 9 i ? i |c 1 \c 1 i ^ ' TTh G tw nv \ G r-^' They should be laid, as far as possible, parallel, and never be allowed to cross directly over each other, otherwise the operation of underruuning will be much complicated. 154 Electric cables Tlio arrangement of the cables above described is that in flank of mines, whlch the shortcst possible length would be consumed, and would, perhaps, be the safest from discovery by an enemy's boats. In certain cases, however, it might be convenient to carry them by a detour to the fort, as for example round the flank of the second and third line of mines, and there wonld be no difficulty in this, always bearing in mind that they should, in the first instance, be carried directly back for about 100 yards, so as to be safe from injury due to the explosion of their own line of mines, and that their subse- quent course should be so arranged as to keep them safe from damage from the explosion of any other mine in the system, cabiestobepro- lu Selecting auy line to bc taken, placcs where the cables Jf sen. would be subjected to a wash of the sea should be, as much as possible, avoided, and when it becomes necessary to place them in positions where they are necessarily subjected to the friction and rubbing consequent npou the motion of the water, special precautions must be employed for their protection. Position of eieo- The Confederates used all sorts of devices to conceal their c'oDce'^aied.* ° " elcctrical cables, such as laying dummies, making consid- erable detours inland, &c., and such precautions must always be taken when required by peculiar circumstances. It is impossible, however, to lay down any rule for such cases, which must be left to the ingenuity of those in charge of the mines, who will be best able to judge of the capabilities of any particular position. The only general rule which can be laid down for guidance in such circumstances is to place the cables where they can be subjected to the greatest amount of supervision, and where they can be most easily defended from injury by an enemy. Mode of placing The following proposcd mode of placing submarine mines mines in position, <^ l x i- o propo.sed by Lieu- in ail V glvcu positiou, and of dealing with the cables in con- tenant Anderson, ' E. E. uection with the different charges, has been drawn up by Lieutenant Anderson, E. E., and is applicable where the land or river banks are conveniently situated for erecting the poles. The direction of a line of mines, to be placed, across a channel, may be determined by two poles previously erected on the shore, as shown at (a and &,) Fig. 65. The arrange- ment to give the intersections on the above-mentioned alignment, where each mine is to be placed, is shown by the jjoles marked (v, and 1, 2, 3, 4, 5, 6) to correspond with the numbeis of the mines. \2 6 / 5/ 4 ^ ^ ^ 155 The proposed mode of placing the charges in position is as follows : Soundings are first taken at the required points, and the length of mooring-line for each charge determined accord- ingly. The anchor is to be suspended from the davit of the working pinnace,, and everything made ready to let it go with a run. The electric cable to be stoiipered to the moor- iugline between the charge and the anchor, and a strong mooring-chain or wire rope to be provided to connect the charge to the circuit-closer, so that, by this chain, both the charge and anchor may be raised if required. The electric cable, between the circuit-closer and charge, should be stop- pered to the chain or wire rope in the same manner as from the charge to the anchor. The length of the electric cables, from the anchors of the different charges to the point {d) on which they converge, would vary according to the posi- tion of the charges with regard to the center line of the channel. Each electrical cable to be coiled on a small i^ort- able drum, so that it may be easily moved in and out of the working i^innace. To place the first charge the pinnace (with the anchor to puc^ the , , first mine. connected with the charge and circuit-closer by moorings of proper length, as above described, and suspended by the davits at the stern) would be turned out into the exact alignment given by theline(a &,)proct'ediugonlyfastenough to obtain steerage-way; as soon as the stern of the pinnace arrived at the intersection given by the alignment (e 6,) the order would be given "let go,"' and immediately anchor, charge, and circuit-closer would be drawn down into position. The electric cable would then be payed out, at first directly away from the charge, and finally taken to the boat ((?,) which had been previously anchored in a position 100 yards or more in rear of the center of the part of the channel to be defended. When many charges are to be placed in the same line, it is recommended, in order to avoid the use of long cables and consequently unwieldy drums, that the cable from the charge 6 should only be long enough to reach to the boat (c/,) in which the end of this cable is for the time being secured. The next charge, with all its attachments complete, having been arranged as before, the pinnace would again slowly cross the channel along the alignment {ab,) till her stem arrived at the intersection 5 with the pole (c,) when the anchor would be let go, and the cable of this charge carried in the same manner to the boat (d.) Thus all the charges up to 'So. 1 would be siniihirly deposited into position, and their cables carried as far as the boat {d.) 156 Tests to bemade Tcsts for Continuity and insulation slioiilcl be made as soou -^"iicp."^ "" ™""' as each electric cable arrives at the boat (rf.) M^hen a multiple cable is to be employed for the main conductor, (and if battery power were always used for firing there would be no objection to the use of such a cable,) it would now be a simple matter, by means of insulating ebonite joints, to con- nect each cable to its corresponding main conductor; or, if cir- cumstances permitted, it would be advantageous to establish at this [)()iiit of the electrical circuit a test-box, into which all the cables from the charges might be carried, and in which the connections with the main conductor might be made. This test-box, which should be of iron, and supplied with a lid screwed firmly down to the body of the box by means of nuts and screws aud a substantial washer, sljould be suffi- ciently heavy to insure its not being disturbed at the bottom of the channel by the force of the tide or current. A test- box would facilitate examination for the discovery of any leak or fault that might occur in the circuit. This could be done without disconnecting the other wires in the test-box; and in the event of any one charge being exploded or car- ried away, it would only be necessary to renew the cable from the test-box to that particular charge. Where the use of a multiple cable is impracticable, each must be car- ried separately into the fort from which the system is to be controlled. It would, probably, be most convenient to have the drum of the multiple cable or the separate drums of the single cables in the fort, and lay the cable or cables there- from to the anchored boat {(1.) Tliis 0]ieration might thus be carried on simultaneously with that of mooring the charges. The objection to it in the case of cables carried in singly would be the joint to be made in the boat, ('>, or two buoys, wheK:' poles could not be used, would be found convenient. For short dis- tances, across the ^ledway, for example, the arrangement with a directing hawser w(jrks with snfllcieut accuracy. The next point to be considered is the best mode of intro- ^J^^j';:^^"^';,';;^",^"^' ducing the cables into a fort or sea-battery. In doing so ^'°''* they should be i»rotected to the utnit^st, not only from injury by an enemy, but from the friction and rubbing necessarily caused by the wash of the sea. Bearing these objects in view, advantage must be taken of local circumstances w hich will present an endless variety of conditions, which must be met by expedients suited to the nature of each particu- lar case. A great deal mast therefore be left to the discre- tion of the ofdcer in immediate charge, and very few gene- ral rules can be laid down. As already stated, it is, however, necessary to carry them into such forts and defensive posi- tions as are likely to hold out longest in any system of defense, and not, as a matter of course, into those nearest to them. They must be covered to the utmost from an enemy's fire, and, as far as possible, be protected from his interference in any way, as his great object would be to break and destroy the electrical circuit; when exposed to rubbing and motion from the wash of the sea, they should be provided with an outer protecting covering of iron wires, copper tape, or something similar, as already described in treating of the description of electrical cables best suited for the purpose, and should be further, as far as possible, covered and placed in sheltered situations. It is a great matter in such situations to weight a cable well, and a good 158 expodieut would be to attacli it to a lieavy chain. This wouhl he a good plau to adopt iu carrying it over shallows not only near its entrance into a fort, hut wherever they may occur along its line. iiu.iiiicntion of Tlie following design for introducing the cables into a antw. G. Nichoi. fort, is a uiodliication of one proposed by Lieutenant W. G. Fig. 66. e Nicholson, E. B. ; it is applicable to the particular section shown, and serves to give some idea of the essential points to be kept in view, while the details of each particular case 159 must, as already stated, be modified according to local cir- cumstances. A plan of the proposed mode of introducing the wires is Testing - room, shown in Fig, 66, and a section in Fig. 67 ; (a) is a testing- agTand hooa."'* room, into which all the cables must be brought, and where the apparatus, by which the whole system is controlled, is arranged; (&) is a store adjoining; (c) is a shaft 2 by 4 feet, by which access is gained to the gallery [d] cut through the outer masonry of the fort ; the shaft (c) is provided with a ladder ; (e) is an iron-plated h'ood carried down to the level of thebottomofthesea; theiron plating is carried sufficiently far below low- water mark to secure the hood from the enemy's shot; (/)isagun-metal diaphragm, through which each cable passes by means of an apparatus precisely similar to Jlathieson's joint; this diaphragm need not be water-tight, and is only intended to prevent the wash of the sea rushing violently into the passage {d) and thence in the testing-room, as would be the case without it in stormy weather. A man-hole {g) gives access to the hood and permits the sea, rushing in through the hood and checked by the diaphragm, (/,) to escape without bursting in the latter. The cables, on arrival at the foot of the hood, are carried Frame? to carry in on a system of frames, as shown in section. Fig. 68. "^^ These are placed at intervals along the hood and gallery, and are provided with four shelves or compartments, each carrying 20 cables, laid in a separate groove and numbered, making a total of 80 for the whole. These frames should be of gun-metal ; iron is too apt to oxidize, and wood, which would be alternately in water and air with every rise and fall of the tide, would be liable to rot and render constant repairs necessary. The frame-work occupies half the breadth of the gallery, leaving the other half for access and exami- nation of the cables. On arrival at the shaft (c,) each twenty cables are collected together and carried up along the sides of the shaft to the testing-room. Should it be necessai\y to carry more than 80 cables into the fort, it would only b6 necessary to arrange a series of hooks, on the far sides of the frames, on which several additional lines could be sup- ported. The flooF of the testing-room should, if possible, not be Levei.of floor of less than three feet above high-water spring tides, other- H^lfZll *""' wise, it would be very liable to be flooded by the wash of the sea in rough weather, for even with the diaphragm, (/,) there would still be a certain amount of motion in the water. Where possible, the outside of the hood should not be less than 10 feet below low-water spring tides, because at such 160 ft dei)tli, except on extraordinary occasions, tliere would be comparatively little motion from the wasli of the sea. Fig. 68. To make con iicction with '*x t'TJor. '(Section of gallery showing 1 frame. Number of cables, i?0.) The man-hole ((7) gives access to the hood; for the manip- ulation of the cables, it would only be necessary to go in at low water and establish a communication with the exterior by pushing- a buoy beyond the outside of the hood by means of a pole of sufBcient length ; the buoy, on floating to the surface, would carry a line with it, which would be all that is necessary, and bj' it a cable might be hauled in or out as required. This would, in a great many cases, do away with the necessity of employing a diver, though it would, neveX' theless, be necessary that a diver be at hand where any very extensive system of submarine mines may be used for de tensive purposes. i.ientiiy of eiich In passlug from the outside to the testing-room, the iden- fuiiy" preserver" tlty of cach Cable must be carefully preserved throughout by means of a number, and each would be finally attached to a binding screw or connection similarly uumbered, so that any particular one might be easily picked out if required. 161 Much care would be necessary to prevent confusion in carry- ing in the electric cables, iu the first instance. The arrangement of a system of submarine mines in lines Disadvant a g e T . T . • , 1 , of an arrangement possesses one serious disadvantage, viz, that an enemy, of mines mime. having once ascertained the i)osition of one mine of a line, either by its explosion, or by any other accidental circum- stance, would know within limits where the others were to be looked for. In order to obviate this disadvantage, it Mode ofobviat- 1 T T 1 ,, . . ing thin disadvan- would always be necessary to scatter a lew mines at irregu-tage by advanced lar intervals in front of the advanced line — to put them, so i"t??™is.""^ '"^ to speak, in the position of skirmisliers, retaining the line- formation for the main defense. These advanced mines might either be simply electro-self-acting, or arranged for "ignition on the same principle as those of the main system, as circumstances required. The first object of an enemy would be to clear a passage Defense of . mines from drift- of suflacient width through the system to enable him to passers. freely in, and for this purpose he would probably employ drifters, with or without dragging-grapnels, for the purpose of either firing some of the charges by striking the circuit- closers, or grappling and destroying the electrical cables , and other gear. These drifters might be boats allowed to float in with the tide or wind, and need not necessarily con- tain any men, so that the loss of human life would not be a certain conseciuence of their destruction by the explo.sion of amine. In order to stoi> such a system of attack, light booms Defence by or strong fishing-nets would no doubt be extremely useful, and nets™' ^° ' '°^ should be employed wherever circumstances admitted. To stop drifters with dragging grnpnels, it would seem to be a Defens- by 1 ■ 11 • ^ heiivy raooring- good plan to lay three or tour heavy chain-cables at inter- chains, vals across the channel in advance of any system of mines. The grapnels would catch in these, and the weight of the chains would be suflicient to bring up the drifters before arriving at the system of mines. The night would unquestionablv be the safest time for an Mines must be „ *' , . 1 . , 11 watched at night. enemy to carry on operations of this nature, and it would be necessary to employ boats to rpw guard in order to watch his proceedings. The mode of communication with these boats is a matter of considerable importance, and some means of rapidly transmitting intelligence is absolutely necessary. This can, of course, be done by the army and navy system of flashing signals, but the lights, in such cases, would be a disadvantage, as thej' would indicate the position of the guard-boat. In order to obviate this, a sys-^ Electrical sys- *^ > *" tem of communi- tem has been de\ised by which a boat rowing guard can be cation between ,i ^ ^ fort and guard- put in electric telegraphic communication with a fort orboat. 11 162 i;uard-sbip, by siuiply paying out an iii'sulateil wire attached to a telegrapli instnmu'iit in the fort or ship, and tarrying a second tele.nraph instrument on board tlie boat. Tlie sys- tem is so arranged that no electrical batteries need be carried in tlie boat, tbe wbole of them being retained at the headquar- ter telegraph station. Tbe instrument in the boat would be a simple 3Iorsf sounder, so that no light of any sort would be re- quired to read the message. The telegraph instrument at the headquarter station might either be a Morse sounder or a ilorse recording instrument, and, when the latter is used, the system has been so arranged that all messages, both those emanating from the headquarter station and those received from the boat, may be recorded for future refer- ence. By this means messages can be transmitted either by the Morse telegraph alphabet or by any signal code, and, when the latter is employed, any man who has been taught the army and navy system of signaling can learu to use these instruments with very little practice. The ap- paratus has been used for some time in the river Medway, in carrying on our submarine mining operations, and answers perfectly. Should the guard-boat be chased, it would be only necessary to detach the electric cable from the telegraph instrument and throw it overboard, with a buoy and line attached to it, and pull away. It could be recovered at leisure. Several systems have been devised for illuminating chan- nels at night by means of the electric light, the Drummoud Illumination ofUght, maguesium light, &c., and there is no doubt that, b J submarine where practicable, such devices should always be used. The action of the several lights named is too well known to render it necessary to describe them here, but there is one device which might be easily made use of in connectiou with a guard-boat. A substance, producing by its ignition a very bright light, (magnesium, for example, would be one of the best,) might be arranged on a float, and a guard-boat carrying a few of these might, if chased, ignite and throw one out. The apparatus should be provided with a short fuse, to enable the guard-boat to get a little distance off before the actual light burst out. In this way an enemy's vessel might be seen and tired on by tbe guns of a battery. Boxer's parachute shells, or any similar device, would also be useful for illuminating purposes. CHAPTER X. ELECTRICAL IGXITLXCt AaEX'TS. Havinj>- carried our electrical cables into tbe fort, the next l)oiiit to be ecinsidered is tbe agent by which tbemiues shall be ignited. Ignition may Ix' effected either at will or by a self-acting ignition at wiii arrangement, the vessel, iu the latter case, herself completing "„,^^' '^"■■'^"' '■ the circuit by means of a circuit-closer. The means em jiloyed in firing at will may be a magneto-current, frictional electri. city or battery-power; when a circuit-closer is used, battery- power oidy is available. First, with reference to the employment of a magneto-cnr- Firing at tcui. rent. Several instruments for the production of a current of this nature have been devised, and perhaps the most beautiful and ingenious of them is that of the well-known electrician, Professor Sir Charles Wheatstoue; a description wheatstoue's of it, which is given in the printed Cour.scof Instruction hi tef^^ '° ''^^° Milimry Engineering, published by authority, page 1.3-, will serve as a key to the coustruction of all instruments of this nature. The mode iu which the uneven succession of currents, produced by a magneto-induction apparatus, and which is not given in the Caitrse of Instruction in I\lilitrtry Engineering, is overcome is very ingenious. Sir Charles Wheatstone has placed two bobbins on each pole of the magnets instead of one, by which arrangement he obtains the result shown in . ,Q Fig. C9, where, if [n n',.s s') be the bobbins, and («) the armature revolv- ing in front of them, the latter is so arranged that, at the moment when it is breaking contact with (»') and (s,) it shall be making contact with (/() and s',) and thus the difficulty occasioned by the uneven succession of currents, which would occur if only one pair of bobbins were used, is got over; for the coils are so arranged that, for example, in the position of the armature shown, the larger or breaking- contact current, induced in the coils (?i) and (s',) is transmitted in the same direction as the smaller or making-contact cur- 164 rent, indncerlin. He states that there is always suflicieut residual magnetism in the soft iron to induce a small current in the coils, and in these instruments the re-action of mag- netism, on currents, and rice i't'r.sa, increases this residual magnetism very rapidly. wTur"i"".-''n"'s ^"^ "'"- Siemens's small instruments, weighing 28 pounds, frS-V ''''''™"' l''^'^ ^^''^'^ '^li^'*! ^^ t''*" School of ^Military Engineering, at Chatham, witli the following result: Twelve Abel's fuses, out of twenty, placed in continuous circuit in dry air, were exploded at the second discharge. Twelve Abel's fuses placed in divided circuit in dry air were fired, une at the first discharge and eleven at the second. The Instrument is so arranged that several turns of the handle are made in the first instance on short circuit, in order to accumulate a sufficient chai'ge in the coils, and on arrival at a certain point this accumulation is discharged through the main circuit in which the fuses to be fired are placed. In (nder to produce this latter resnlt, the short circuit is broken by nseans of a cam in connection with, and turned by, the handle by which the armature is put in motion, which allows a spring to descend and simultaneously to break the short and complete the firing circuit. The reason of the partial failure in the two experiments mentioned was, that the handle had been turned very nearly up to the point where the action of the cam, throwingin the filing circuit, took place, and consequently, instead of the accumulated charge produced by several turns being stored up, only that due to one or two turns was discharged through the firiug-ciicuit. It is necessary, therelbre, in using this instrument, to commence turning the handle from that i^oinfc where the maximum number of turns, before the discharge, is ob- tained. In subsequent experiments, Avhere this precaution was taken, no failure of the nature described took place. It may be assumed, therefore, that the instrument in question possesses the power to fire twelve Abel's fuses, either in cou- tinuous or divided circuit, in dry air. As the fuses are all fired by a single discharge, and not by a succession of short currents as in Wheatstone's magnetic exploder, the num- ber whicli may be relied on to be fired in earth, dry or damp, or in sea-water, depends upon the quality of the in- 167 suliition of the electric cable. To tf-^t this, a single Abel's fuse was fired with this instrument through a quarter of a mile of cable, (a strand of 7 Xo. 22 copper wires, insulated with Hoopers dielectric to a diameter of ^ inch ;) it failed to fire with a leak of jL inch. With the same cable the ebonite frictional machine failed with a leak of i inch. With a conductor consisting of IJ miles of similar cable, the dynamo-electrical machine failed to fire the fu--e with a leak of ^ inch. With the same cable the frictional ma- chine failed with a leak of J inch. As regards power to overcome a leak, therefore, a dynamo-electrical machine of this weight (28 J pounds) is about on a par with Wheatstone's exploder, weighing .31 pounds, which has been tried against it for tlie sake of comparison. Machines of this nature may 1)e made of considerable size, and, where portability is not essential, may be ar- ranged to develop a very considerable electrical current. Mr. Ladd, of Beak street, London, has invented another r.ad-i'^ lyraa■.o- , . electricaliiiacbine. instrument adapted to the explosion of mines, the principle of which is precisely similar to that of Sieinens's dynamo- electrical machine, but the arrangements differ, inasmuch as Ladd employs two armatures, one to create the electro- magnet, and the other to produce a current therefrom, with which to perform any work required. Fig. 71 gives the general arrangements of the instrument: (« a) are two soft- iron bars, around which coils of fine insulated wire (b h) Fig. 71. are wound, in metallic connection, through a commutator, with the coil of an armature, (c,) revolving between their extremities. When tlie armature (t) is made to revolve, exactly the same effect is produced as in Siemens"s instru- ment, and the result is that the two bars {a a) become very powerful electromagnets, the poles of which are so arranged as to be exjxised to each other at their extremi- ties. Now, instead of discharging the current thus induced through his working-circuit, to fire fuses or perform any other work which necessitates the beginning again, as it were, to 168 create a new current, Mr. Ladd introduces a secoTid firnia- tuie, {(J,) revolving between the soft iron bars, froai whicli he obtains his working-current; the magnetism of the bars is thus always kept np. The residual magnetism of tlie system is always suflicient to commence the action de- scribed, except, i)ossibly, when an instrument had just been made, and had never been used, when it might be neces- sary to touch the bars with a permanent magnet, or pass a voltaic current through tlie coils for au instant, to obtain the magnetism required. An instrument of this nature was exhil)ited at the Paris Exhibition of 18G7; it was only 24 inches long, 12 inches broad, and 7 inches thick, but the ef fects jiroduced by it when worked by a steaurengine of one horse-power were very great, and would seem to augur well for the future of this system, which Mr. Ladd proposes to a])ply to the production of an electric light for lighthouse purposes, the principle is, of course, equally applicable to the ignition of chai'ges of gunpowder or other explosives. The following description of another instrument of a sim- ilar nature is extracted from the report of the committee on active obstructions, page 86 : Ma;uoto.ex- "A Small magneto-clectric; exploding machine, which wns kiisctViemia. first dcviscd by Herr IMarkiTS, an Austrian philosophical- instrument maker, at the suggestion of Baron Von Ebner, (after the latter had witnessed the performances of Wheat- stone's instruments and Abel's fuses in England in 1862,) and which is stated to be employed in the Prussian service, was obtained by government for the purposes of the com- mittee from Messrs. Gessler & Co., of Berliij. This instru- ment is not more than half the size of Wheatstone's explo- ders, from which it differs materially as regards the mode by which the generation of niagneto-eleetric currents is effected. It was only disposed of to the English govern- ment upon the understanding that it was not to be exam- ined, and no detailed description of its construction can, tlierefore, be attempted, but the mode of using it aifords a suflicient indication of the manner in which the magneto- electric current is generated. The magneto-electric ap- paratus is comi)lete]y inclosed in a square oblong metal ease, to one side of which are fixed two binding-screws, (a «,) Fig. 72, for connecting the instrument with the coudncting-wires, while one of the ends forming the top of the case carries the arrangement for 'setting' the instru- ment and firing the mine. Mode of using "Bcfore this magnetic exploder is connected with the the instrument. . conducting-wires, a key, with powerful leverage, [b,) fixed upon the top of the instrument, to which it always serves 169 as a bamlle, is turned to the right as far as possible. By this oijcration the armature of the inclosed magueto-elec- Fig. 72. t"*' machine is separated from the magnet and placed under the influence of a power- ful spring. This spring is in connection with a pin (c) which projects from the top of the instrument, and moves as the key is turned in a slot of a long spring, (<7,) one end of which is fixed upon the instrument, while the other carries a knob made of ebonite, (e.) When the key has been turned to the full extent, the pin which controls the ar- =1 mature spring has become firmly fixed by irs head in the slot of the exterual spring, ((/,) and the instru- ment is now ready for action at any moment. It is then connected with both conducting-wires, and the explosion of the charge is accomplished by pressing down the eV)on- ite knob, (e,) whereupon the armature spring is released by the liberation of the pin (c) from the outer spring (^7,) and the armature returns to the magnet with great velocity, an electric current being thereby established. "This instrument is even more portable than Wheatstone's ordinary exploder, and is fully as powerful: — u v. it is ca- pable of exploding a.smany, if not more, charges in simple circuit; but it is much more limited in its power of firing charges through a divided circuit, because it is incapable of furnishing a succession of currents,, such as obtained by means of Wheatstone's and Beardslee's instruments. '• Several of these instruments of difl'erent size and power, constructed by Markus, wei'e exhibited among the collection of military implements sent to the recent Paris Exhibition by the Austrian government. The smallest of the machines was stated to be capable of exploding five or six of Von Ebner's fuses, and the largest flfteeen in simple circuit. That officer states that the magneto-electric instruments of Markus have been introduced into the Austrian service for land operations in x^lace of the frictional electrical machine. " Some very efticieut rotary magnetic exploders, similar in their powers to Wheatstone's ordinary exploders, and differing only from them in details of construction, were also shown in the exhibition of the Austrian war department at Paris." Puses adapted to electricity of high tension, may also be indactioncoii. fired by means of the induction-coil, for which they must be connected in simple divided circuit, for the same reason that it is necessarv so to arrange them for Wheatstone's mag- 170 netic exploder, viz, that the action i)roduce(l is a very rai)id succession of currents of very short duration. The defects of all these instruments for submarine mining purposes are the same as those of Wlieatstone's magnetic exi)loder, A'iz, the small quantity of the current, which ren- ders it necessary to employ a cable with very perfect insula- tion. Fiictionai .ifc- Next, as regards thi use of frictional electricity a.s an ex- plodinn- agent for submarine mines. The well-known fric- tional machine, desii^ned by Baron You Ebner, colonel of the Austrian cor[)s of engineers, is a very good type of in- struments of this class. Se\'eral instruments of this kind, but slightly differing in size and construction, were exhibited at Paris in 1867 by the Austrian war de[)artment. Some of them were made with glass disks and inclosed in a wooden box, but the best for militar_y pur[)oses are those in which the glass disks are replaced by ebonite, as described in the Cdurae of Inntruction in Military Engineering, page 150, par. 331. These instruments produce a charge of electricity much larger in quantity and higher in tension than either the usagneto-indaction or dynamo-electrical machines. One of their defects is the time required to charge the condenser, which takes from 20 to 30 seconds, and the condenser must be recharged after each explosion. There is also a certain liability for the charge to leak out of the condenser when the air is highly chai'ged with moisture, but when the instru- ment is in good working order and Abel's fuse may be fired with it through a considerable resistance, say 13 B. A. units, on a unle of No. 16 copper wire, from 15 to 20 minutes after the condenser has been charged, and under favorable cir- cumstances we have fired one after an interval of 6 hours. The chief defect of this instrument is the danger, when using it, of accidental ignition to mines, the conducting- cables of wliich may be in the vicinity of that in connection with the mine to be fired, as shown by the experiments de- tailed in page 121. Some further experiments have since been made at the School of Military Engineering, Chatham, to ascertain the limits within which the inductive action is so energetic as to render it dangerous to lay electric cables, when mines are to be fired by means of frictional and induced electricity. From these it is evident that the utmost care is necessary in using the frictional machine. On the 18th of May. 1870, two half-miles of electric cable, each ctmsisting of a straml of 7 No. 20 copper wires, insulated to a diameter of y^Q-iuch with Hooper's patent dielectric, were 171 laid out find connected with fuses. Tlie fn>is \\ < re jdaced i'O yards ai)ait, and tlie line was, in eacb case, put to earth beyond them. One of the cables was connected with the instrnment used for firin.u' the fuse, the end of tlie other, at the point fi:SQlt,. C feet . . . ■jo 3 f.et . . . do 4 Do. .■) fc-.-t . . . do 4 One fuse fired on direct ciicuit. .second fn^e nut fired i>v induction. 9fM-t... do 20 Loth fuses fired: one directlj-, one b.v induction. l-'f.-l .., do iO Do. 15 fc-Lt . . . .... do 10 One fuse fired on direct circuit, second fuse not fired by induction. 13 firt . . do 20 Do. Li feet ... do 30 Eoth fusiblired; one directly, one by induction. 20fwt ... do 20 One fu.-e fired on direct circuit, .second fuse nut fi)-ed by induction. 20 fr-ct . . . do 30 Eotli fuses fired; onediiectly, one by induction. 30 tV.-.-t . . . do 30 Do. 40 ft- Lt . . . do 30 One fuse fired on direct clrcait, second fuse not fired by inductiou. 40f.,t .. do 40 Do. 40 f..'i-t .. do 50 Do. 40 f..i.-t ... ill. 50 'Do. 3.) r.-,t . . . do 50 Do. 30 feet . do 50 induction. Touching Dynamo - electric One fuse fired on direct circuit, second fuse macbi:ie. not fired by induction. Toiicliing: do Do. Toucliin;^ Wlii-at^tinii-'8 niag- uetic exploder. Do. I'oueliiDfi d.i Do. •ThesecoTiil fuse wjs i'Ikiu^'i'iI iu tbi.s ease, in oid'-i to aseeitain tli.it tin- failure to fire did nut arise from a defective fuse, or one eomijaratively less sensitive. From this it is evident that the use of frictional electricity, Frictiun.ii eiec- . , . . , tricitv only appli- in connection with a svsteai of submarine mines, is limited cable to excep- ^ „ , I. tional ca-es. to very ext:eptioual cases, lor certain purposes, as, lor 172 cxainplt', witli isolated mines, tliis instrument is no doubt a valnable agent, but in conse()neiice of the great danger, inseparable from the induetive effect of the discharge, to AThich it is subject, it should only be intrusted to careful men who aie thoroughly acquainted with its use. T he dynamo- Taking iutocdusideration the advantages and defects of electncal machine ^ seems to be ihe ef,(.]i of the instrunieuts described, it would seem tha,t the l»est for general "SO- dynamo-electrical machine is the best adapted for use in coniuu-tion with a system of submarine mines. When madeof moderate size it is sufficiently portable for all practical pur- poses, while at the same time its ])ower to generate a charge of electricity renders it available, under nearly all conditions, for the ignition of a mine with certainty. The absence of permanent magnets gives it an advantage over Wheatstone's magnetic exploder and Markus's machine, and there is, with the smaller form of instrument, no danger of explosion by induction, as in the case of the frictional machine. This latter should never be used where any other electrical ignit- ing agent is obtainable. teiy'power!'^ ''^' Wc uow come to the ignition of submarine mines by bat- tery-power. For use in coujiection with forts, or in stationary positions, there is no doubt that the battery is by far the most important agent. Battery ior use .... ., , n ^ ^vith pittiinum W licrc a phitiuum- Wire luse is used, a current ot large quantity is necessary to insure ignition. For this purpose Grove's, or AValker's, or some battery i)rodueing electricity of the requisite nature, must be used. This question has already been discussed. See page 93 and those following. tiroYo's battery. -^^ description of Grove's battd'y, with the general principles to be borne in mind in using it, is given at page 138, par. 2!).j of The Gourxc of ItiHlnictitin in Military Engineering, and the paragraphs following. Walker's zinc- A phitiniun- wire fuse may be used in connection with Walker's constant battery. Soaie experiments have been tried at the School of Military Engineering, at Chatham, vs'itU this form of battery. Tlie battery was composed of two cylinders of zinc, each j?g- inch thick, 7 inches long, and 3 inches in diameter, con- nected together so as to form a single metallic plate, and two cylinders of graphite, each § inch thick, 7 inches long, and 3 inches in diameter, similarly connected. The cells were formed of gutta-percha pots, 7J inches in diameter and 7 inches deep, capable of containing about half a gallon of liquid. If the battwy-plates had been made in one single piece, instead of in two portions, the whole would have been very much more compact, but at the time it was made the zmc carbon battery. Experiments. 173 niaiinfacturers had no large plates in stock, and those de- scribed above were used to save time. The battery was made upon the 10th of December, ISGO. • The number of cells employed was four, and ^g inch of pla- tinum wire, weighing l.G grains to the yard, was em^^loyed as the standard of measure to ascertain the nisiiig-p(jwer of the current. The electrical resistance of one turn of the rheostat employed was A)2i'.) B. A. unit. The proportion of acid to water used in the cells was one of acid to ten of water. December 10, 18G9. — Platinum wire fused through 21 turns on rheostat. December 1.3, 1809. — Platinum wire fused through 19 turns on rheostat. December 17, 1869. — Platinum wire fused through 2S turns on rheostat. December 20, 1809. — Platinum wire fused through .31 turns on rheostat. December 23, 1869. — Platinum wire fused through '23 turns on rheostat. , December 30, 1869. — Platinum wire fused through 20 turns on rheostat. December 31, 1809. — Platinum wire fused through 28 turns on rheostat. January 3, 1870. — Platinum wire fused through 30 turns on rheostat. January i, 1870. — Platinum wire fused through 30 turns on rheostat. January o, 1870.— Platinum wire fused through 30 turns on rheostat. January 0, 1870. — Platinum wire fused through .32 turns on rheostat. January 7, 1870.— Platinum wire fused through .32 turns on rheostat. January 10, 1870.— Platinum wire fused through 30 turns on rheostat. January 12, 1870.— Platinum wire fused through 30 turns on rheostat. January 14, 1870.— Platinum wire fused through 29 turns on rheostat. January l.j, 1870.— Platinum wire fused through 28 turns on rheostat. January 17, 1870. — Platinum wire fused through 30 turns on rheostat. January 19, 1870.— Platinum wire fused through 30 turns on rheostat. 174 Janutiry 124, 1870. — Platinum wire fused tlirougb 2G turns on rheostat. January -5, 1870. — Platinum wire fused through 26 turns on rheostat. January l-'fi, 1870. — Phitinum wire fused through 21 turns on rheostat. January 2S, 1870. — Platinum wire fused through 2:j turns on rheostat. January 29, 1870. — Platiuum wire fused through 23 turns on rlieostat. January .'!1, 1870. — Platinum wire fused through 25 turns on rlieostat. February 1, 1870. — Platinum wire fused through 2.j turns on rheostat. February 2, 1870. — Platinum wire fused through 23 turns on rheostat. February 3, 1870. — Platinum wire fused through 21 turns on rheostat. February 1, 1870. — Platinum wire fused through 21 turns on rlieostat. February G, 1870. — Platinum wire fused through 21 turns on rheostat. February 8, 1870. — Platinum wire fused through 24 turns ou rheostat. February 9, 1870. — Platinum wire fused through 24 turns on rheostat. February 10, 1870. — Platinum wire fused through 23 turns on rheostat. February 11, 1S70. — Platinum wire fused through 22 turns on rheostat. February 12,* 1870. — Platinum wire fused through 18 turns on rheostat. February 14, 1870. — Platinum wire fused through 19 turns on rheostat. February 15, 1870. — Platinum wire fused through 20 turns on rheostat. February 17, 1870. — Platiuum wire fused through 20 turns on rheostat. February 18, 1870. — Platinum wire fused through 20 turns on rheostat. February 21, 1870. — Platinum wire fused through 20 turns on rheostat. February 22, 1870. — Platinum wire fused through 19 turns on rheostat. * Ou this day tho battery was removed from one table to another. 175 rebruniy 23, 1870. — Platinum wire fused through 10 turns on rhcfistat. February 21, 1870. — Platinum wire fused through 18 turns on rheostat. ret)riiary 2.">, 1870. — Platinum wire fused through 18 turns on rheostat. The battery was made up afresh on the 2.")th February, with fresh acid and water, (1 acid to 10 of water,) and zinc plates re-amalgamated. At the first test, made five minutes after filling the cells, ^-iuch platinum wire wasfused through ;j2 turns of the rheostat. The experiments were continued as follows : February L'G, 1870. — Platinum wire fused througli .32 turns on rheostot. February 28, 1870. — Platinum wire fused through .33 turns on rheostat. March 1, 1870. — Platinum wire fused through 33 turns on rheostat. March 2, 1870. — Platinum wire fused through 34 turns on rheostat. Maicli 3, 1870. — Platinum wire fused through 31 turns on rheostat. March 1, 1870. — Platinum wire fused through 31 turns on rheostat. March ~j, 1870. — Platinum wire fused through 35 turns on rheostat. ]\Iarcli 7, 1870. — Platinum wire fused through 35 turns on rheostat. March 8, 1870. — Platinum wire fused through 34 turns on rheostat. Jlarch 0, 1870. — Platinum wire fused through 31 turns on rheostat. jMarch 11, 1870. — Platinum wire fused through 32 turns on rheostat. March 14, 1870. — Platinum wire fused through 32 turns on rheostat. March 10, 1870. — Platinum wire fused through 32 turns on rheostat. March 20, 1870. — Platinum wire fused through 30 turns on rheostat. ^larch 22, 1870. — Platinum wire fused through 30 turns on rheostat. :March 25, 1870.— Platinum wire fused through 28 turns on rheostat. :\[arch 28, 1870.— Platinum wire fused through 28 turns on rheostat. 176 ^Farcli 29, 1870. — Platinum wire fused througb 27 turns on rlu'iistat. ]\Iarcli 31, 1870. — Platinum wire fused through 2.") turns on rheostat. April 3, 1870. — Platinum wire fused through 23 turns on rheostat. April 5, 1870. — Platinum wire fused through 23 turns on rheostat. Ai)ril 8, 1870. — Platinum wire fused through 21 turns on rheostat. April 10, 1870. — Platinum wire fused through 20 turns ou rheostat. ^Vpril 11, 1870. — Platinum wire fused through 20 turns ou rheostat. April 13, 1870. — Platinum wire fused through 19 turns on I'heostat. Battery proved The rcsults Obtained have proved this battery to be very vt'ry cont-tant. /. i i ' i constant, so that there ueed be uo rurther doubt on that account as to the use of the [ilatiuum-wire fuse. The want of constancy iu Grove's battery is certainly a serious con- sideration. It will be observed that on the 12th of Febru- ary, when the battery was moved from one table to another in the same room, there was a slight depreciation iu the fasing-power of the current, but that it subsequently, to a certain exteut, recovered itself. It should therefore be moved as little as possible, but ;is it is only applicable to perma- nent stations, this is not of mucli consequence. It was uoticed, too, that if the circuit was kept closed, that is to say, a constant tlow of current kept up, its working power was materially diminished, as shown by the smaller number of turns througb which the plautiuuiu wire was fused. As, however, in any system of submarine mines, the circuit would ouly be closed for an instant, as each mine was flred, and as uo continuous work would be required, this latter, though a fact to be noticed, need not interfere with its use for such a purpose. The cost of a cell of a bat- tery of this form would be comparatively large, but, on the other hand, a much smaller number of cells would do the work. Its size and weight are ill-adapted to portability, but for a permanent station this is o'f comparatively little consequence. Experiments with a much larger number of cells must he made before any definite conclusion, as to the advantage of this form of battery, can be arrived at. As far as we have yet gone, however, it promises remarkably well. 177 To fire a fuse adapted to electric-icy of tension, such as Banery foru-e ..,,,, , (• ,1 -,-' I. t. , with tenrion-fu=C'. Abels tor example, auy ot the ordinary tonus of battery used for workinj^- a line of electric telegraph may be employed; the object in such a case being to obtain electro-motive force rather than quantity. It is of importance that the battery should be constant — that is to say, that it should be capable of being allowed to remain mounted and ready for use for a considerable time, say a month, and not, like Grove's, re- quired to Ije taken to [)ieces and retitted every twelve hours; that it should generate a sutticient quantity of electricity to allow of a certain amount of leak or fault in a cable and yet lire a fuse beyond that leak; and, at the s;une time, that the electro motive force to be obtained from the battery may be such as, with a sufhcieut nuuiber of cells, to fire an Abel's fuse with certainty. The best forms of battery for this purpose seem to be Wollaston's saud-biittery, the Marie-Davy battery, audDan- iell's battery. Theordinaryformofsand-lfHtteryisshov.'ninFig. 7.3, twelve wuiia^fon'ssand- battery. Fin. 73. cellsbeiiij^united in atrough madeof gutta-percha. Theusual dimensions of t!ie plates are 3J by 4i- inches. They are alternately copper and zinc, connected together in [lairsby copper strips riveted and soldered to them. The zincplates are amalgamated with mercury, and the cells are filled vcith fine siliceonssand, moistened with sulphuric acid diluted with water in the pro])ortiou of jV. This Ijattery develops a powerful current of electricity when first made up, but, when the circuit is kept constantly closed, it is very incon- stant, and after being in use for a certain time, varying according to circumstances, it loses its power froui various causes; the sand nnist then be washed out, and the battery made up again with fresh solution and the zincs re-amalga- mated. 178 .„....„. The i;reat defect of tlie simple eoiiibinatiou of ziuc and copper in dilute acid is, that tlie bubbles of hydrogeu-gas resnlting from the deeouipositiou of the water by the electrie torce adhere to the copper plate, aud, beiug iu a state of electrical polarization, act iu oppositiou to the direct current aud reduce its strength very materially ; moreover, the hydrogen beiug iu what is termed the nascent state, com- bines ^■el■y readily with the oxygen of the sulphate of zinc, priuluced by the action of the battery, and metallic ziuc is thus deposited upon the copper plates, aud so, similar metals being opposed to each other, the action of the battery ceases. Many nsethods have been adopted to get rid of the hydrogen. In Grove's and Daniell's batteries it combines with the oxygen of the solution iu which the electro-negative metal is immersed. In Suu^e's, and its kindred forms of battery, the hydrogen is assisted in escaping from the negative plate by giving it a rough surface, x^reseutiug a multitude of small l)oints from which the bubbles separate easily. The saud is chiefly useful to prevent the acid from spilling when the battery is moved about; it tends also to make the action of the battery moi-e regular; but it should not contain carbonates, such as carbouate of lime, or a chemical action takes i)lace with the sulphuric acid, which is detrimental to the battery. In the best form of this battery a small gutta-percha pipe mprovements, ^^ inserted iu each cell, extending down to the bottom; through this fresh diluted acid is poured in from time to time to make up for waste by evaporation. Bj- thus intro- ducing the fresh acid at the bottom of the cell, where the heavy sul^jhate of ziuc gravitates, a more regular action is obtaiued. If the sulphate of ziuc be allowed to accumulate in the lower part of the cell, a cross voltaic current is estab- lished between the upper and lower portions of the plates which are iu solutions of different strengths. The effective curreut iu circulation is thus diminished, and the upper portion of the zinc plates are rapidly dissolved away. lbs. oz. The weight of the 12-cell battery is, without sand or liquid ^ 14 14 With sand 2:i 00 Sand aud liquid 23 12J It requires about 1 pound of mercury aud two pints of acid per annum for each 12 cells. For submarine mining purposes theconditions are different from those which occur in the simple working of a line of electric telegraph, in which the circuit would be closed much 179 more frequently and for longer periods; under these latter circumstauces its defects become much more apparent, a.^ the mischief is done almost entirely when the circuit is closed. This fact, however, renders it less objectionable as a tirinp a^eut for submarine mines than as a battery for telegraphic purposes. A solution of sulphate of zinc is sometimes irsed, as an exciting fluid, instead of diluted sulphuric acid; the effect under such circumstances is. to a certain extent, to reduc- the consumption of zinc, with a reduction, however, of the active force of the current generated. A battery of this form, charged witli diluted sulphuric acid, is more energetic when first made up, while one charged with sulphate of zinc is, after coming fairly into a working state, more constant and requires less attention to keep it in good order. One advan- tage of sulphate of zinc is that, being in the form of crystals. it can be more easily stored and carried about than sulphuric acid: this is a very decided advantage or board ship. This battery possesses another advantage for use on board ship, inasmuch as the liquid being kept absorbed in the sand is not liable to be .split. There are several forms of the ^Marie-Davy battery which jraric-D.ny might be used for firing Abel's fuses : it may be described ""^^' as consisting generally of plates of zinc, and carbon in a saturated solution of proto-sulphate of mercury. One form of this battery, called " Silvers Marine Battery," has been manufactured by the India-rubber, (rutta-percha, and Telegraph- works Company, of ZS'orth Woolwich, ex- pressly for use with GLsborne's system for signaling on board ship ; it consists of a combination of zinc and plat- inized graphite plates in a saturated solution of i)roto-sul- phate of mercury. This is perhaps the best and most constant formofbatteryof this nature, butitisrather bulky. It could be used on board ship, having been expressly manufactured for sea service, to stand rolling about. The smaller forms of the Marie-Davy battery, which have been tried in the electrical school at Chatham, though excellent when tirst made up, both as regards quantity and electro-motive force, deteriorate very rapidly, and are not so good for submarine mining purposes as Daniell's form. Daniell's constant battery is well known to all persons Danieir- engaged in working the electric telegraph, and consists of*""" ^ "^' ziuc and copper elements in a saturated solution of sulphate of copper. The copper plate is placed in a i^orous cell with a quantity of sulphate of copper in the form of crystals, and water is i)ouredin, which dissolves the latter and sets up an 180 Fig. 74. electrical action. An excess of sulpliate of copper must be placed in the porous cell to keep the solution, as it is termed, saturated, or, iu other words, carrying a maxiinnni of the sulphate of copper in solution. :\iniriipaa;sfOTm ^lulrlicad's form of Dauiell's battery would be a very good ile of 30 zinc, 30 flannel, and 30 copi>er disks has been co!ii[)leted. A precisely sim- ilar pile is then constructed by its side, the first plate being, however, copper in this instance, and tlie position of the copjier and zinc disks in each j)air being the op[)osite of that in th(^ lirst pile, the zinc being, therefore, the lower plate. The top disk of pile No. 1, (copper,) and the top disk of pile jS^o. 2, (zinc,) are then connected by laying a thin strip of coitjier ((/) across them. The third pile is now commenced, a thin strip of copper (/() having been laid upon the board to connect it with the second pile. A zinc plate is taken first, this time as in the case of pile i^o. 1. Lastly, a fourth pile is commenced by placing a cojjper plate upon the strips of copper, which constitutes the second pole of the battery, and this pile is built up like ISTo. 2 pile. The top disks of piles Xos. 3 and -i are then connected by a strip of copper, (/.) "A piece of hard wood, (A-,) similar to the bottom board, is well coated with pitch composition or varnish on one side, and is jjrovided with a central [lerforatiou through which the screw is to pass, and with holes of sufficient size to allow all the thin rods which support the piles of plates to pass freely through. This board is placed with its coated side downward upon the piles, anil is then pressed upon them by means of wooden nuts, {I I,) w'hich are screwed on to the central rod. The plates are thus firmly held in their places, but the pressure ai^plied by means of the screw must not be sufQcieutly great to squeeze any water out of the flannel disks. "If there is uo workman or lathe at hand to provide the screw and nuts, the pile may be firmly braced together by passing two or three turns of stout cord round the boards and tightening these cord bands by means of wooden wedges. '■ To connect the battery with the flrin,t;-wives, the cleaned end of the conducting-wire is inserted into one of the slots containing a pole of the battery, and it is maintained in close contact with the copper strip in that slot l)y passing a wire round a small wooden •wedge, which is then forced into the slot at (n.) The circnit is completed when required by bringing the return firing-wire (or earth-wire) into contact with the strip of copper forming the other pole of the bat- tery, {)i\) >r " ^Yhen the battery is taken to pieces the flannels shouhl be placed in water acidulated with vinegar or oil of vitriol, and, after having soaked for about one hour, they should be 185 washed in pure water and wrung out. The plates of zinc and copper should be thoroughly cleaned by scrubbing them with wet sand." The working-force of the current of any voltaic battery .j'^Y'''^'j'['=_,'-;'"';^"' or pile is much improved when it (the battery) stands on-aR''"^*'^ ""^ '"'"'' good insulating substance. When practicable, therefore, it is recommended that the whole battery or in\e may be ar- ranged to stand upon a sheet of thick cri>wn-glass. The reason of the improvement is, that the insulating substance prevents minutelj' small losses of current, -which occur more or less in practice, even when batteries have been put to- gether with the utmost care, and which pass to earth with- out completing the working circuit when the battery stands upon any less perfectlj' insulating material. The following table gives the internal lesistaiice and com- parative electro-motive force of several forms of voltaic battery : ^izL- of plati' !N"ame of battery. j Copper or graph- ^inc. ite. : A'Mii.-ys Danic-U ii" .^"spiraL. 5" /. 11" 10 ^ 'Jll Mairhead's Danidl ' 3!" < 4" I 3i" >: 4" 1 ' t-0 Sit.iiv.'sDaiJiell I 4" X f" | 3J" X J" ' 10 | f5- WaHaston's -and ! 34" X 4J" | 3+" X 4}" 15 i 635 ilarie-Davy I C-' X li C" loii^, i" diami-nr. . . ^ 3 j l-J-JO Leclancb§ i TJ" i i;-" C" lr.;iL', 5-li;" diain._;er ; 2 M'-r, XoTi;. — Tht-e i«--ii]ts have been obtained from .-i-ils fie.^lily made up ; the experi- mc'uts were tried at Ohviiis. 30 hours aud 54 Uoiivs iiftei'tUebatteiies weiL'put U'LjetliLi. CHAPTER XI. CLOSING ELECTRICAL CIRCTIT. Having got our mines placed in position, established the eonducting-eahles to conn<>ct tliem with our testing-room, and seleeted the most approved form of battery or igniting agent, it now becomes necessary to discuss how any par- ticular charge of a group may be fired at the right moment. This may be done at will, the position of the ship being determined by intersection, or the vessel herself may be made to complete the circuit by striking a circuit-closer. Fiviui; by cross- In firing at will, the vessel's position being determined by r.ruj^^s or inter- . 'c'io". intersection, several exiiearate arrangement should l)e prepared. Firing bj aim- A simijlificatiou of this plan may occasionally be adopted coucertGd signal . - . , i • ' i , ■, ' • ^ -, at one station. by employing a preconcerted signal at the point («,) when the bow of a \'essel came on the line («. whO For instance, if, when the bow of the vessel {s) arrived on the line (a Wj,) a flag were raised at the point (o,) the observer at(/>) would instantly notice whether she was on any of the lines of sight passing over his mines, and if she were, would at once press down the key corresponding therewith, as So. 3, shown in the Fig. 79. Directly she had passed the line {a mi,) the flag at (a) should be dropped, as she would theu be safe Fiff. 79. so far as that line was concerned. This latter system requires great coolness and nerve on the part of the obser- ver at (1),) as he has two things to do, viz, to watch the ves- sel passiug across his intersections, and to be on the alert to receive the signal from («.) In such a case it has been 189 found best to employ tvro men at station (h.) one exclusively to watch the station (a.) and on the flag being raised to give the word " fire,"' and on the flag being dropped to give the word " stop," the second man would keep his eye on the vessel, and be ready to fire the right mine at the right moment. A separate signal-flag and firing arrangement would, as before, be required for the next line (U] n,, &c.) ot mines. /j\ %80. / 1 1 ' • / I \ / ' \ x^s in many cases it would not be practicable to ha\'e a Arrangement of separate iutersec- -, - separate luiersec Station in such a position as (a) so far advanced toward the tions for each point of attack, with the corresponding danger of being cut' off by an enemy, another combination becomes necessarj^; this is shown in Fig. 80. Two stations (a) and {h,) well within Hu' defensive works, are selected in such a position that the 190 liiK's, passing from tliem over each charge, shall intersect in such a manner as to give what is termed a well-conditioned triangle, or, in other words, that they shall not intiu'sect each other at too oblique an angle. The batterj- is placed at the point («,) one pole being attached to earth, while the other is connected with a center from w^hich radiate a series of contact-keys. From the studs or contact-points of these keys a series of cables, corresponding in number to the charges in position, pass to the similar contacit-points of a similar set of keys at the station [h,) and from the pivots of the keys at {h) an electrical cable passes to each charge. In this case, therefore, each charge has a separate key at station (a) and a separate key at station (b,) each x:)erfectly distinct from every other, and well insulated therefrom, but the whole culminating at (a) in the single battery (c z.) lu each circuit, corresponding to any particular mine, there are therefore two breaks, one at its particular contact-key at the station (a,) and the other at its corresponding key at station {!>,) and till these breaks are bridged over, by pressing down the contact-keys simultaneously, the cir- cuit of the battery will not be closed and the mine will not be fired. In this way it is easily seen that if, for example, key ISTo. 1 is put down at the station («,,) and key No. 2 at station (&,) there still remains a break iu each circuit ; in circuit No. 1 at station [b) and in circuit 'So. 2 at station (<(,) and neither of these mines will be fired. The object of this arrangement is easily seen if we trace the course of the vessel (s) approaching the line of mines. She first comes on the line of (w?^) from station («,) and simultaneously on that of (mi) from station (b ;) the observer at (a) puts down key No. 5, and the observer at (6) key No. 1, without of course firing any mine ;" again, as she reaches the position («i,) the observer at (a) would put down key No. 4, and the observer at [b] key No. 2, without any circuit being closed. Let us now suppose her to reach the point (S2) when the lines from both stations over the charge {mi) intersect; both observers would now put down keys No. 3 simultaneously, the circuit of mine {m^) would be closed, the charge would be fired, and the vessel struck. Pickets may be In Carrying on the system above described, it has been "on arshortTib- found that with a series of small wooden pickets, placed in tances. ^ radiating form from a central point of observation, at a distance of about twenty feet, and with pieces of twine passing from the center over the pickets in the direction of the charges, to indicate the bearing more accurately, very good practice has been obtained, all the charges having, at a distance of a quarter of a mile, been exploded within a radius 191 of six feet of the object aimed at. The observer, with his eye at the central picket and his right hand on the contact- keys, pnts the corresponding one down as the object pa>ses the bearing of each. A man soon learns by practice the distance he may allow on one side or other of the bearing- line, and with ordinary care and nerve is soon able to make contact at the right moment. There is no doabt, however, that on actual service the steadiest and coolest men woiikl be required to work-such a system effectually. The following is a description of the firing-keys recom- mended, and shown in plan and section in Pig. SI. The 1^ \^ \i;^ F~^^ ¥ h ^ apparatus consists of an oblong wooden box, 8 inches long by 6 inches broad, and 2| inches deep, within which are firmly fixed two ebonite bars, (a) and (6,) one close to each of the larger sides; the object of these is to insulate the several wires, connected to binding-screws (c c c, &c.,) on the bar (a,) and (fZ d d, &c.,) on the bar {!),) from each other. One 192 sot of insnlattMl wives (/■/'/', &c.) may be curried into tlie liox and attaclied to the binding screws {v e c, vS;e.,) anotticv ^'^''^ {(I [I (h ^^-i) may l)c connected with tlie binding screws ((/ (I d, &c.) The firing-key (0 consists of a strong metal spring, in metallic contact with the binding screw (d) and tlieuce to the cable {g) ;ittadiedto it, and with an insnlateil knob, (//,) by which its metallic point may be pressed down npon the binding screw, (c,) wliicli latter is in metallic con- tact with the cable (/) attached to it. It is tbns easily seen how by ])ressing down any one of these keys a metallic cir- cuit is established from the cable (/,) on one sid(>, to the cor- responding cable {(I,) on the other side of the box, and that before the key is prt^ssed down tliere is no metallic circuit, and conse(iuently no path for the electric current. The box is provided with a wooden lid to keep the keys safe when not in use, and there is an India rubber diaphragm let into this lid, just over the keys, through wliich they may be depressed when the lid is shut. Two screw-holes are also provided by which the whole box may be firmly fastened to a table or bench when required. connectioiiB of In the Combination shown in Fig. 78, a single kev only ki^yB for use. !-• ^ o . ,) would be required at the station [a ;) this would be similar in construction to any single key of the set shown in Fig. 81, one pole of the battery (r z) being put to earth; the other would be connected to the binding screw (c,) while the cable counectingstations(fl)<'^iid (&,)Fig. 78, would be con- nected with the binding screw (^7,) Fig. 81, and the power of changing the cable from the tiring-battery would be ob- tained by simply putting down and holding down thefiring- Iccy. At st-.ition (/>,) Fig. 78, one firing-key would be re- quired for each mine. All the wires (,/'//, &c.,) Fig. 81, having been denuded of insulation close to the box, would be brought together and soldered carefully to the single conductor, carried from station (a) to station (&,) Fig. 7S, while from the binding screws {d d d, &c.",) Fig. 81, a separate insulated cable would be laid to each mine. For the arrange- ment shown in Fig. 79 only one set of keys would be re- quired, the battery being connected to the whole of the rear binding screws, with the separate cables radiating from the point. If used in the combination shown in Fig. SO, two c'omplete sets of keys would be required, arranged as de- scribed for Fig. 78, with this difference, that asejiarate con- nection for each nuno would be necessary fronr the front binding screws of the tiring-keys at staticm (^f) to the reiir binding screws of the set of keys at station (/;,) the bat- tery being in connection with each and e\'ery one of tin' rear binding screws of the set of keys at station (a.) 193 lu using the key.s it is necessary to press them firmly down aud hold them firmly* down, iu order to iusiire good contact at the proper moment. To work efficiently it does not seem desiralile that more than six keys shonld be intrnsted to the management of any one man. The system of pickets, above described, for giving- the Telescopic fir- bearings, might probably be used eiiectually up to half a mile, but at greater distances a more accur;;te means of obtaining the intersections becomes necessary; tlie pickets have, moreover, the disadvantage of being easily disturbed aud difficult to replace in an accurate position if once moved. In order, as far as possible, to obviate these defects, a tele- scope with cross wires has been mounted in connection with a series of contact-points and a movable key, as shown in Fig. S2. It consists of a solid and somewhat heavy cast-iron stand. Detaiu of t^ie- {(!,) on whicli is placed an iron upright {b) arranged to carry strument.""^ a telescope with cross wires, (c) the latter having a horizon- tal and vertical motion. The object of giving considerable weight to the cast-iron stand is to obviate, as far as possible, tlie chance of tlie displacement of the whole instrument by the concussion of guns fired in its vicinity. Two circular holes are cut in the body of the stand to reduce its weight, which would otherwise bi^ unnecessarily great. A circular level [d) attached to the cast-iron stand gives the means of leveling it with sufficient accuracy, by means of three cap- stan-headed screws, [c e e.) Though this instrument, in con- sequence of its weight, is not very susceptible of displace- ment by concussion, it would always be advisable to place it as far as possiljle from the neighborhood of heavy guns ia action, the concussion produced by their discharge being- very great. Between the iron upright {b,) aud insulated from it and the telescope by a ring of ebonite, is a brass portion, (/,) into which fits a brass arm, (g,) at one end of which is a wooden handle, (/;,) and at the other a binding-si'rew. This arm and the portion (/) of the upright in connection with it forms, as will be hereafter explained, a portion of the electric circuit wIjcu the instru- ment is connecti-d up for certain operations; it is therefore made of brass to prevent the chance of oxide in the con- nections, which might increase the electrical resistance. The arm [g) is rigidly connected, througli the upright (c.) with the teleseoiie and moves with it. It tra verses oxev an arc './.■) described with a radius of not less than ei.i^hteen inches, and supported at its two extremities by thick iron uprights 13 194 {I J.) This arc con.sists of an iron frame, in two pieces, di- vidud longitudinally in tlie center, the upper portions being faced with ebonite, in order to insulate the two parts from each other and from the metallic contact points (m m, &g.) in connection with them, for reasons to be hereafter explained. The arc is marked with divisions by means of which the position of' the contact points {mm, &c.) may be registered, Fig. 82. so that, in the event of their being accidentally displaced, they may again be fized in true relative position with facility. 195 These divisions sen-e also to determine the position of the whole instrument in the following manner : The telescope is directed on some distinctly marked object, such as a flagstart' or the defined angle of a building, and the number of the divi.--ion under the guiding spring of the handle (/;) of the brass rod, with the telescope in that position noted, it is thus easily seen how, even if the whole apparatus is moved, it may be replaced in the same position with facility, pro- vided the position of the point immediately beneath the upright (b) supporting the telescope and on which the in- strument revolves, or of the three capstan-headed screws. has been carefully marked. Fixed to the lower part of the brass arm (g) is a metal spring, in connection with a metal contact point; motion is given to this latter by an ebonite knob (ft) attached to it by a small upright bar, passing through the arm (tj.) In a state of rest the spring holds this contact arrangement up close to the arm (g.) but the depression of the knob {n) moves it downward sufficiently to bring it in connection with any of the contacts {m m, &c.) which maj" be directly beneath it. The knob («) is made of insulating material, because the arm (g) is always charged with elec- tricity at the moment of action, and the operator would receive a shock were the knob allowed to remain uninsulated. For the same reason it is necessary to insulate the eye-pieceof the telescope, becau.^e it. too, is in metallic connection with the arm (g.) and would consequently be similarly charged. The extremity (/;) of the arm (g) is made of an insulating material (wood) for the same reason. Fig. .S3 shows an enlarged section of the extremity of the ,a°fp^nt ° arm with the contacts and other arrangements in its vicinity ; () is pushed forward and the spring (/') released. The lower contact arrangement consists of two metallic portions (/ i,) separated and insulated from each other by an ebonite dividing-piece {I:) These metallic portions 196 are provided with sboulders made to fit upon them the upper ebonite portions of the arc {I I,) and with a thin projecting arm, giving the means of making contact with the spring (&,) as already described. The lower contact arrangement is fixed firmly in position by means of an ebonite wedge (m,) passing through it and pressing against the metal portions of the arc (c c.) In metallic connection with the brass por- tions (I i) of the lower contact arrangement are two thick copper wires (o) and (p) to which the battery or line circuits, &c., may be attached. When the ujiper contact point (cl) 7b To place mstrumeut pOHitiou. ^^^%^'k<^'A^(M^ Fig. 83. i^. is depressed, as in the position shown by the dotted lines, it will be observed that the insulated space [k] between the two sides {i i) is bridged over. the To place the instrument in position, a point from whence the lines of mines are clearly distinguishable should be chosen. This point should be as far as possible from heavy guns, and the foundation should be moderately solid. A broad flat stone, for example, would furnish a convenient foundation on which to place the apparatus. The ii'on stand of the instrument having been leveled, by means of 197 the circular level aud capstan-headed screws, the telescope should be directed on some fixed and 'n-ell-deflned object, andtheiiuiuljer of the division under the spring of the handle registered. The telescope should then be directed on each mine or line of mines, as the case may be, in succession, the position of the mines having been marked by buoys or other similar means for purposes of identification, and one of the contact arrangements brought into proper position for each, and keyed firmly up, and the number of the mine and the number of the division on the graduated arc regis- tered. This having been done at one or both stations, as required, the buoys marking the position of the mines may be removed. The points where the capstan-headed screws, carrying the instrument, rest, should be carefully marked, so that the whole may be replaced in the same position if accidentally disturbed. Should it stand on a stone, small shallow holes might be cut to receive the points of these screws with advantage. The mode of using this instrument is similar to that for (jjg'i"'^!^"^^"""^ the firing-keys. Fig. 81, already described. It is, however, adapted for longer distances. For such a combination as that shown in Fig. 78, two in- struments w;) which latter is per- manently connected with the conducting wire from the bat- 200 tory, and thus in its state of rest remains electrically charii'ed. Beyond tlie arm (n) is a small spring (.s',) perma- nently connected with the eartli,and in such a position that when the central portion is moved round, this spring («) comes in contact with the arm {n) and the plate (r) with the arm (in) simultaneously, and the circuit is completed through earth to the battery, without, however, passing through the fuse. Eeferrilig again to Fig. 84, the arms (o and ])) on oppo- site sides of the brass cylinder and consequently insulated from each other, are connected with the fuse, and the arm ((/) is permanently connected with the earth. We left the current passing from the battery through the arm (m) by the brass cylinder to the arm [n) and by the spring (6-,) then in contact therewith, to earth, and complet- ing the circuit; but by a still further pressure of the vessel on the buffer, the arm {h) is pushed beyond the spring, and in contact therewith, and consequently circuit by earth to the battery is broken, while the contact of the arm (in) and plate [r) is still retained, and the current is passed by the arm (o) through the fuse to the arm (p,) and then to earth through the arm (q,) completing the circuit through and firing the fuse. The action of the spring, in breaking the circuit, has the efi'ect of intensifying the current (by means of an intensity- coil in connection with the firing battery) to its utmost extent, and at the moment when this intens:ty is highest, passing it through the fuse. To reuder a Should a friendly vessel be approaching a line of mines ivirnrtiy vessel, arranged on this system, it woidd oulj^ be necessary to detach the firing battery, by removing the connecting plug, to render her passage perfectly safe. Should she make con- tact with any of the mines in her course, the ratchet-wheel (g,) Fig. Si, would be pushed round, the spring (s) would make and break contact, as before described, but no current would be circulated; and on the vessel leaving the mine the ratchet-wheel would be drawn back to its original position, by means of a strong spring in connection with it, and be ready again to act when ie(juired. The arrange- ment for closing the circuit is made sufliciently strong to Xjrevent chance of injury from contact with a friendly vessel. Pu^e only in It will be obscrvcd that, in the Austrian system, the fuse mem' of fiiTii°g is only put into the electrical circuit at the moment when it becomes necessary to flreit. This arrangeuient was con- sidered necessary, to obviate the chance of the accidental ignition of a change from induction, caused by atmospheric 201 electricity. According to Baron Von Ebner, accidents of this nature have occnrred to mines nsed by him. This mode of cutting the fuse out of circuit till the moment of ignition, guards most effectually against such an occurrence, but, at the same time, it renders it impossible to fire the charge at Tvill, and the ignition of the mine is thus reduced to that sin-le condition in which the action of the circuit-closer, by the contact of a vessel, is essential. Another form, designed by F. Abel, esq., F. E.' S., chem- ist of the war department, is shown in section and elevation in Fig. 85. It consists of a strong wooden case («,) bound with four iron bands (&, &, &, &,) buoyancy being given to it by means of an air-tight chamber (c.) Within the apparatus is a brass tube ((7,) into the lower extremity of which a pair of insulated wires (e) and (/) are introduced, by means of a joint {g) inclosed in a stuffing-box. This latter is rendered water-tight by a ring of India rubber, shown iu black in section, compressed agaiust the insulation of the conducting wires by the action of a screw working on the extremity of the brass tube (d.) In order to render this joint thoroughly water-tight, the insulation of the two wires (e) and (/) is, at; this point, welded into one, and made into an elongated oval form, thicker than the original insulation, by the addi- tion of layers of Chatterton's conipound and gutta-percha in a plastic state. In thus welding the insulation care must be taken to prevent the two conducting wires from being accidentally pressed into contact while the gutta-percha is softened by the heat necessarily apjjlied. Within the brass tube (d) is another tube of brass or iron (h,) extending ver- tically through the whole apparatus, and working on an universal joiat ( ;') at its lower extremity. The upper portion of this tube is rigidly connected with a metal bar (/>:,) which latter is firmly attached to a strong teak top (?,) supported on the wooden case («,) and separated from it by a vulcan- ized India-rubber ring (m.) It is thus easily seen how any blow on the top would be transmitted to the metal cylinder {h.) ' The interior of the brass cylinder {d) is kept water- tight by means of a vulcanized India-rubber collar («,) shown in black in section, connecting it with a ring projecting from the metal bar (I:) A couple of metal screws (o o) are umde to fit on a screw tapped on to the upper portion of the metal bar (/,-,) and, by means of a spanner, these may be screvred down so as to firmly connect the top of the arrangement with the wooden top (1.) One o^f the insulated conducting wires (e,) having been carried in through the metal tube (h,) is soldered on to a copper ring [p] incircling the bar (A-,) closer. 202 but insulated therefrom. The insuUited conducting-wire (/) is passed through a hole iu the tube (7t,) and its bared extremity is attached to a binding-screw (q) in connection -i Fig. 85. <&^ r^ with an insulated brass band, let into a broad ebonite ring which passes completely round a hollow, in the brass tube, made to receive it. To the base of the apparatus feet {r, r, r) 203 are attached, on which it may stand in such a way as to keep the projecting piece [g) clear of the ground. Kings are formed in these feet for the attachment of the mooring- chains. A ring (s) is attached to the upper portion of the apparatus to facilitate manipulation and moving the circuit- closer. A metal ring {t) is let into the opening of the upper l)ortion of the case (a) to take the weight of the outer case when the circuit-closer is lifted by the ring (s.) A thick ring (f) of vulcanized India rubber keeps the whole combi- nation rigid, and by its resistance, dependent on its thick- ness, regulates the force which must be used to- set the apparatus in action. This circuit-closer is designed for use, so that the fuse may Mode of uaiag ' the apparatus. either be kept entirely out of the circuit till the moment when it is required to be fired, as in the Austrian system, or it may be employed in the ordinary manner with the iuse in circuit as usual. In the latter case only one wire is re- quired, and this is connected with the copper ring {p;) the insulated brass band is not then required, and the space allotted to it is filled by metal. For the former combina,tion the electric cable from the connection with firing-battery is connected with the insulated wire (e,) the cireui"tiui'he mo- other pole of the battery being to earth, the wire (/) being™''" ° '='"'°"- attached, through an insulated conductor, to one pole of the fuse, and a metallic connection being arranged from the other pole of the fuse to earth. In order to fire the fuse it is easily seen that it is only necessary to bridge over the space between the copper ring {p,) to which the wire (e) is connected, and the brass ring (g) attached to the wire (/.) This would be done by a \-cssel striking the top (e) of the apparatus in any direction, which, being pressed on one side, would carry with it the bar (7r,) and, by the action of the universal joint (;,) bring some part of the copper ring {p) in contact with the brass band [q,) thus completing the elec- trical circuit. In this combination it is easily seen how the fuse is only introduced into the circuit at the moment when it is required to be fired. When it is desired to arrange the fuse m connection with connection this circuit-closer in the ordinary manner, the combination "rcmt as usual.'" is as follows : One pole of the firing-battery being to earth, the other is connected, through the electric cable, with one pole of The fuse, the other pole of the fuse being placed in metallic connection with the insulated wire (e,) while the insulated wire (/) is put to earth by being connected with the metallic portion of the case (a.) In this combination it is easily seen that, in order to fire the fuse, it is only neces- 204 sary to bridge over the space between the two brass rings (/*) and ((/,) which woukl be done, as already described, by the action of a vessel striking the top of the apparatus. Advantages and Wheu tlic fnse Is entirely out of the circuit till the moment nntionswitiT'iJis'., of ignition, it cannot be fired at will, and cannot Ije tested out'of circuft™ '"" except when a return wire is used ; it is, however, manifestly veiy safe from accidental ignition. On the other hand, when the fuse is arranged between the firing battery and the circuit-closer, any considerable fault in the insulation, between the fuse and the circuit-closer, would be very likely to cause an accidental explosion. ■I'o render a Jq (irdcr to rcudcr a channel safe for a friendly vessel, it channel sate for a ^ i friendly vessel, would oidy bc ncccssary, lu either of these combinations, to detach the firing battery, in which case, should a circuit- closer be struck, it would re-establish itself in its former condition bj' virtue of the action of the flat India-rubber ring (i') and the collar (ji,) and be ready to act effectively as before. AS^Scuit-cios* From experiments carried on at Chatham with several "'"■■ circuit-closers of the form described, it has been proved that they are very efficient in action, and that the strong external wooden case i)ossesses sufficient resisting power to enable them to stand a good deal of knocking about and rough nsage, withoutdamageto the internal circuit closingarrange- ments. This power to resist heavy blows is essential to the efficiency of any form of circuit-closer, as, when in position in a channel through which there is much traffic, they are always liable to be struck with considerable force by blades of screws, floats of paddles, and other hard and sharp bodies. It would be an imi^rovement if the stuffing-box (ted by Lieuten- bell, the clapper of which is insulated from the body, and re. the circuit is closed by bringing the former in metallic con- tact with the latter. This apparatus has not been suffi- ciently tried : being similar in principle to 3Iathiesou's pen- dulum, it is to be feared that it would fail from similar causes. It would no doubt stand the regular and uniform swing produced by a sea. as Mathieson's did, for a considerable time, but the slightest deranging influence caused the latter to close tlie circuit, and it is difficult to understand how it could act in one case and not in the other. Another form of circuit-closer, suggested by Quarter- M.ithie-.v.;odnai- master-Seigeant ilathieson, R. E., maybe described as fol-ci.:MnV',irfrange" lows: It consists of a glass vessel containing, and at tlie "™'' same time insulating, the earth connection. This glass ves- sel is so arranged that a .ship would come in contact with and break it, when the circuit would be completed by the earth plate through the water, and the charge fired. He proposes to moor his mines in pairs, at a depth of about 3' below the surface of the water, and to sustain them in that position by means of small surface floats, possessing just sufficient buoyancy to keep them in position without being too conspicuous, as described in page S2. Though this arrangement has not been found to answer, in couse- j^Fode of actiou. 21-2 qneuce of the reasons giveo in tlie description referred to, tliere is no leason why tlie mines tlicmselxx's juiglit not bo floated np from sinkers on the bottom in the usual Avay, though they would uot, under such circumstances, be effect- ive at all times of tide. He proposes to connect each of the mines to a hermetically-sealed vessel, placed midway be- tween them , by means of strong lines. He proposes to carry his electric cable from the firiog battery on shore to a point on the bottom nearly midway between the pair of mines, conlaining the electrical connection by branches thence to the fuse in each mine, and from each fuse to an earth-])late inclosed within the glass vessel between them. A ship passing between a pair of such mines would throw a strain on the lines connecting them with the glass vessel, the mines themselves would be drawn toward the ship's sides, the glass vessel would be broken, the earth-plate con- tained in it would be brought in contact with the water, and the pole of the firing battery not connected with the electric cable being to earth, the charge would be fired. In the event of a vessel being observed to pass without exploding the mines, Quartermaster- Sergeant Mathiesou proposes an alternate mode of firing by the frictional elec- trical machine ; by means of a switch-pin the battery would be disconnected and the frictional machine, with its con- denser ready charged and earth connection made good, thrown into circuit. On the condenser being discharged, the small length of cable beyond the fuse would act, in con- junction with the surrounding water, as a Leyden jar, aud the tension of the charge produced by this very i^owerful machine, combined with the inductive action set up between fhe metallic conductor forming the inner, and the water, forming the outer coating of the Leyden jar, would be suf- ficient to fire a high-tension fuse. The platinum-wire fuse could not be used in this combination. ExiH-riments to Experiments were tried at Chatham on the ISth of May, ing by tnctionailSTO, to tcst tlic powcT of the frictioual machine to tire a Si' leugtu of charge by induction in this way. ^V cable, half a mile long, L'^a Leydeu'jar!'^ consistiug of a straud of 7 Xo. 22 B. W. G. copper wires, in- sulated to jjj inch with Hooper's patent di-electric, was laid out on the ground and a fuse attached to the fuse end with 12 feet of electric cable beyond it, the latter imm'ersed in water, but with its end carefully insulated. Under these conditions Abel's fuses were fired with certainty by a port- able ebonite Austrian frictional machine, not only when applied directly to the cable to which the fuse was attached, but by induction when a charge was passed through half 213 a mile of similar cable, laid parallel to it on the groiiud at a distance of three feet. A battery of 100 DaiiieH's cells failed to fire the fuse by induction under either of the cir- cumstances specified. In such a combination care must be taken to leave i)leuty of slack in the electric cable, so that the strain may not come on them, but on the lines connecting the glass vessel with the mines. This system possesses the disadvantage that, unless it Disadvantages of ■was so arranged that the mines could be drawn down out ''^y"'™- of the way, the first vessel, friendly or otherwise, which passed through would break the glass vessel and probably also the electric cables connecting it with the mines. By simply detaching the firing-battery no injury need occur to a friendly vessel ; but even if the electrical connections remained in working order, the mines would be reduced to the condition of being capable of being fired at will only. Charges might be arranged to be hauled down, under certain circumstances, to allow friendly vessels to pass, but as a rule this would be a very difficult operation and probably not appli- cable to the majority of cases. The power of the frictional ma- chine to fire charges arranged in this way is. no doubt, very great, but the danger of induction when using it must not ^ be lost sight of, — see description in pages 170, 171, and 172, — and its employment must therefore be limited to con- ditions in which this serious disadvantage may not be pro- ductive of unintended results. These are some of the most practical forms of circuit- closers capable of application under various conditions, but no doubt others might be designed suitable for the purpose. ilost circuit-closers are capable of being used either in circuitcioier the same case as the charge, or detached from it and only m^h mines or'de- conuected by a suitable mooring line and electric cable. In ™ ^ ™™ the Austrian system the circuit-closer and charge are in part of the same case, and are so arranged that the charge will only explode when a vessel is in actual contact with it, or nearly so. The reason of this is that the Austrian mili- tary authorities were of opinion that, to be effective, a charge must be fired in very close proximity to a vessel's hull. One advantage arising from a combination, in a single case, of the circuit-closer and charge, is the additional inertia thus obtained proportioned to the weight of the latter. The general tendency of any body floating in water, on being struck by a ship, is to move easily on one side, and thus to lessen the force of the blow; the greater inertia 214 of the combined charge aucl circuit-closer is therefore iu favor of the effective action of the circuit-closing appa- ratus. ciPu-dMe'l 'Vo- '^^^^ floating obstruction committee have proposed a de- r"sert by floating tached circuit-closer, trusting to the extension of the de- obstructiou com- ' '=' ^'t'e"?- strnctive effect due to the explosion of any given charge extending to a certain distance from it. What this distance is has yet to be definitely determined, but exjieriments prove that it is not limited to actual contact with the charge, though it diminishes rapidly in proportion to the increased cushion of water intervening, as the distance from the side of a vessel increases. There is no doubt that in a tidal harbor or estuary, a detached circuit-closer presents many advantages, one of which is that the ijositiou of the actual charge may be arranged so as to suit the ever-varying depths of water over it with greater facility, when the cir- cuit-closer is detached from it. It is probable that neither detached circuit-closers nor thosepermanently combined with the charge can be universally adopted ; measures have therefore been taken to design different cases for each com- bination. Mathieson's circuit-closer is readilj?- adaptable to either. Bnc-mj- would The flrst object of an enemy in attacking a harbor Ae- Zv\7mls\aesZ'-f^^'^'^^ ^J Submarine mines would be,if possible, to explode '''■'■■ those mines, and thus render the ground in his front safe; or, failing to do this, to get hold of and carry off the cir- cuit-closers, and, if i>ossible, to dispose of the electrical cables in connection with them in such a way as to render the charges unexplodable ; and as is it not desirable to throw away large charges upon boats and small craft, such as would be employed in tlie duty of searching for mines, means must be taken to retain the charges intact and effective, even should the circuit-closer be carried away. Power of filing Should an enemy simply break away a circuit-closer, and tnired!TpossiWe; allo^^ tl'G cud of thc clcctric cable to fall off, there would, drc\'it-do°e™^ °''of course, be no difficulty iu still firing at will, if the fuse were arranged iu circuit as in Fig. 88. Supposing the cir- cuit-closer (•«) removed, the fractured conducting cable would still, in most cases, be sufficient to pass the current to earth in the circuit of the battery {c s) being completed, and this operation could easily be performed within the testing-room. Under these circumstances the mine would remain as effect- ive as ever, provided the means of ascertaining the posi- tion of a vessel existed. Supposing, however, that an enemy, knowing the arrangements prepared for his recep- tion, were, before casting off the broken end of the conductor, 215 00 I after detaching the circuit-closer carefully to insulate the fracture, the charge (?») would, uuder .such circumstances, be almost harmless. It might possibly be fired by in- duction with thefriction- al machiue, as already described, if there were a suflflcieut length of conductor beyond the fuse and a high-tension fuse were used, but this would be a difficult and uncertain result to ob- tain. In order to obviate such a contingency a different combination has been proposed by Quartermaster- Sergeant 3Iathieson, E. E., which is well deser\ing of at- tention, from the great in- genuity displayed in all its arrano-ements. Fig. 89 shows the general de- sign of the system. The electric cable passes di- rect from the battery (c z) to one pale of the fuse in the charge (m,) the other pole being di- rectly connected to earth, and there is a branch to the circuit- closer (n,) starting from a point (a) between the battery and the fuse. In this case the circuit-closer is simply used as a a indicator, and may be made to work a relay in a manner to be hereafter described. When in a state of rest the extremity of the cable, passing from («) to (»,) is manifestly insulated, and it is evident that the charge (m) may be exploded at any mo- ment at will, by simply completing the circuit of the battery (c z) in the testing-room. Let us now suppose that an enemy, knowing the system of firing adopted by the defenders, has got possession of the circuit-closer («,) he would, uuder such cii'cumstances, detach, and having removed the insu- lation from a considerable portion of the extremity of the 216 couductiug vrire, he •would throw it into the sea, so that the current, finding au easier path through the hare end of the wire^than through the fuse, would pass almost entirely in T) UHli ilir IV rih a iiathieson's (jis-that directiou and not fire the fuse. The following arrange- ment would, however, prevent such a contingency. Fig. 90 Fig. SO, 4& ,i if K7?v. m shows in section a combination by which the two extremities (f( a') of a break in the electric cable, leading from the fork or branch in the vicinity of the charge, are introduced into an ebonite vessel (?»,) so that, when held in an upright posi- tion, a small quantity of mercury (c) placed therein would complete the circuit. If the vessel '\b) were inverted the mercury would fall down to its larger extremity, and the circuit would be broken. Should the vessel only fall over on one side the same effect would be secured, for directly the contact between the mercury and the two extremities of the wire {a a') ceased, the electrical circuit would be broken, and the extremity (a) of the cable, to all intents and purposes, efiectually insulated. If au enemy, therefore, were to get possession of a ciruit-closer attached to a cable 217 arranged iu this way, and cut and cast it off, under the sup- position that he was connecting the circuit to earth and thus rendering himself secure, the falling away of tlie mer- cury would insure the insulation of the point («,) and the mine (to,) Fig. 89, would still remain as efficient as ever. A modification of the device aljove described, suggested Disconnectar de- hy Lieutenant Anderson, E. E., consists iu the substitution of aS^Anckion'R! a platinized metal ball in a platinized metalcup for the mer- ^' cury. One of the wires is attached to each side of the metal cup, and the two sides of the cup, and conse- quently the points of the wires are insulated from each other. As long as the ebonite vessel remains upright, the ', ball completes the circuit between the two extremities of the wire, but directly it is turned over the ball falls out, and the two sides of the cup, one attached to each wire, being insulated from each other, the circuit would be imme- diately broken. Suppose now that an enemy, knowing that an arrange- Eiectro-ma^iietic ment of the nature above described was used, were to get possession of a circuit-closer, he would carefully detach it, make the end of the wire bare, so as to complete the circuit to earth, and bury it, so as to keep the ebonite cup up- right, and retain the mercury or platinized ball iu such a position as to complete the circuit. To guard against such a contingency another arrangement has been suggested by Quartermaster-Sergeant J: Mathieson. He proposes to intro- duce an electro-magnet between the point («,) Fig. 89, and the circuit-closer, the armature of which should be in con nection with a spring, arranged as in the p>riuiary circuit of Ehumkofi's induction coil, so that it -would make and break the circuit mechanically with great rapidity. With such a combination as this it is easily seen that every alter- nate instantaneous current would pass through the fuse in the mine (m) and fire it. With such arrangement it would not 2natter whether au enemy were to insulate the wire, after detaching the circuit-closer, or not, as the power of firing the charge at will would remain iu the hands of the defenders under both conditions. It would not, however, he available for use with the frictional machine. These disconnecting arrangements, in the form described. Further trials have none of them been sufficiently tried to enable a definite '^'"^'^^'"'^■ opinion to be given as to their j)ractical use. They are, nevertheless, interesting, as illustrations of the general foi'm of combinations which might be used to counteract an enemy's attempts to render a system of submarine mines ineffective. Should any modification of the branch system, 218 sliown in Fig. 89, be adopted, it is manifest that some dis- connecting arrangement must be employed, in order to meet the contingency of a removal of a circuit-closer, and there seems to be no reason wljy one or other of the very ingeni- ous expedients projiosed may not be made capable of prac- tical application. There is no doubt that it would be a very great waste of power to fire large mines, of 500 pounds of gun-cotton, for example, at boats engaged in searching for tl>em, and such boats might, relying on the immunity thus secured, carry on their operations with comparative boldness. In day- J light it is probable that they might be kept off by the guns covering a system of mines, or l)y boats manned by the defenders; bat at night, or in a fog, they might carry on their operations in comparative security as regards such means of defense ; the question is, therefore, whether some plan might uot be adoi)ted to act as a deterrent without, at Avrangemrat of the sauic time,. Sacrificing the principal mine. It has been drcuit-cioac?.^ ™ Suggested, for example, that a small charge, sufficient to sink a boat without damaging the large charge, might be placed in the circuit-closer and arranged to be fired when that cir- cuit-closer was touched. In order to secure this effect some such combination as the Ibllowijig might be adopted : A single fuse might be placed in the charge in the circuit- closer, the latter being connected, as shown in Fig. 89, with a branch circuitfrom the point («-,) while in the main charge a number of fuses might be placed in continuous circuit, or with a considerable electrical resistance, in the shape of a coil, or an ordinary lightning protector might be arranged 'oetwoen the point ■(«,) and the fuses in the charge {m.) Now, if a battery sufficient to fire a single fuse were arranged in connection with a circuit so constituted, directly the circuit through the circuit closer was completed, by touching the latter tlie charge therein would be fired, and any small boat in its vicinity sunk or damaged, while from the great resistance introduced between the point («) and the fuses in the main ciiarge those latter would remain intact, but could still be fired by a considerable increase in the power of the firing-battery, or by the fri(;tional or dynamo-electric machine, provided the end or the branch connecting the point (a) with the circuit-closer were insulated when blown off, and this could be effected by means of the mercury-cup or other arrangements already described. Difficulties af- Such a Combination, however, must be attended with tending n»eof rj-i jc^i -i j. ciiarare of circuit- ditticultu^s. lu thc first placo. It bccomes necessary so to ' "''"' balance the respjctive resistiUices of the fuse in the circuit- 219 closer and those in the main charge, as to render the sun- ultaaeous explosion of the two cliarges impossible. To do this a largely preponderating resistance must be given to the circuit in the main charge, and in order subsequently to fire the latter with certainty a large increase of battery- power would be necessary. This adjustment of resistances in the fuses, as well as subsequently in the batteiy-power, would at all times be a delicate operation and require the greatest care: Again, the circuit-closer must be at such a distance from the mine itself that the explosion of the charge contained in it shall not damage the case or connec- tions of the latter. A charge of 5 pounds of gun-cotton would '■ probably be sufficient to sink any boat, but it would be necessary to ascertain how far such a charge must be placed from others iii its neighborhood to insure their safety. Again, it is not desirable to expend the circuit-closer attached to a mine, except as a last resource, because as soon as it is gone the mine can onl^- be fired by judgment. It is a choice of evils, however, and preferable to allowing an enemy to carry off the circnit-closer without damage to himself. In order to determine whether such a system can be prac- tically worked, carefully conducted experiments are neces- sary. Another mode of keeping oft' boats would be to place a A7G-TABLES. We now eoiiie to the'consideratiou of testing-tables, or, in otlier words, the mode of arranging the wires in connection with the charges in a convenient form in the electrical-room M'ithiu a fort. When a very large unmber of wires must be introduced into a fort, it becomes necessary to arrange them in such a manner that they shall be easily iclentified, and that the operations of testing and firing, &c., may be con- ducted with the greatest amount of simplicity. Several forms of tables have been designed with this object in view. The Austrian government exhibited several instruments of this nature at Paris in 1867. One of these, which gives a good general idea of their system, may be described as follows : Austrian testing- able. Its design is shown in Fig 91 ; Fig. 91. z) represents the bat- X J 2 4 -4. f, ^ f S S 9 ff :}'<' , tery with one pole to earth at (e,) and the other in counec- tion with an intensity coil («,) through which the current passes to the contact plate (6.) When it is desired to put the system of mines, iu connection with the table, in a state of preparation to be fired by the contact of a vessel, a plug is inserted between the contact plates (& and /,) and the 221 current passes through and electrically charges the conduct- ing -wires, showu by dotted lines, connecting the charges with the battery, through the several binding screws (r/, g, g, &c. ;) as soon, therefore, as a vessel makes contact, the circuit is completed, as already described, (see paj^'e ISO,) and the charge flted. It then becomes necessary to ascertain which particular Te^t to discover mine of the system has been exploded ; for this purpose the ciLge.''''''"^'"' plug is placed so as to connect the contact plates (b and d.) the current is then pas.sed on to the testing circuit, shown by the firm lines, in which a galvanometer, (h,) is placed, and which is iu connection with two metal bars (i 1:, i A;) on these bars, and slipping freely along them, are metal keys {I and »?,) sufficiently long to complete the circuit from them to the binding-screws {g, g, g, &c.) In a state of rest these keys are thrown back into the posi- tion in which (l) is shown, and no current passes beyond the bars (^ 1:, i Ic ;) when, however, the key is turned over into the position in which (m) is shown, the current passes into and electrically charges the insulated wire communi- cating with the n:ine.: iu this way each of the binding-screws (g, g, g, &c.) is put in circuit iu succession, and on arrival at that lately in connection, with the charge that has been fired, the galvanometer will be deflected, as the circuit will be completed by the broken end of the conducting wire, through the water, and back by the earth- plate to the battery. In order to test the insulation of the electric cables con- lusuiation n-fi. necting the mines with the battery, (the firing circuit,) it is only necessary to place the plug between the contact-plates (b and d) and touch each of the binding-screws {g, g,g, &c.,) in succession with the testing key; should the galvanometer (/t) remain stationery, the insulation is good; but should aleak exist, the current passing through it would act on and deflect the galvanometer, indicating the particular line iu which it exists, and, roughly, the extent of the leak in proportion to the deflection shown; should the leak be con- siderable, the defective cable should be at once detached, as the current lost through it might so diminish the working power of the battery as to prevent its firing any of the fuses attached to the group in connection with the same battery. For tlie same reason the conducting wire of an exploded charge should be at once disconnected from its binding screw. By the above arrangement the insulation of each line can be tested at any moment required. In order to make the channel safe for a friendly vessel, it is only necessary to remove the plug from between the con- chaDnei safe. 222 tact plates (b and/) and insert it between [b and d,) or leave it out altogether ; this disconnects the battery from the firing' circnit. Great cure sluiuld be taken to keoi) the metal keys {I and Hi) always thrown back, except at the moment when re- quired for use in testing, in order to avoid the chance of accidents. srparatetesting- j^ would bc Convenient in most cases to employ a sepa- oattery geaernlly i. -2,) by the action of a circuit-closer, on,e of' a set placed ou a series of branches, as ()( n n, 6L'c.,) so as for 223 tbe moment to cut out the fuses {m m m, &c.) iu the man- ner already described. Another series of contact ])oints {fff, &c.) are in connection with one pole of a firing-bat- tery (fi .~i,) the other pole being to earth. In order to fire any of the mines at will, it is evident that it only remains to close the circuit of the battery (Ci Ci) by completing the connection between the points (d d d, &c.) and (///, &c. ;) this is eltected by the simple depression of a key which is arranged to be done by hand. Another set of contact points (« a u. &"c.) are in connection, through a vcrv delicate Testing and galvanometer [g,) with a testing battery (C3 -,.) Fig. 93 '^'«°"'"« """"'• shows an enlarged plan and elevation of a firing-key. Con- tact plugs are provided, which, iu their ordinary position, 224 ^Tould remaiu between the contact plates (& and e ;) and the front avm of the firing-key being in connection, when in a state of rest, with the point {b) and pivoted on the contact Fig. 03. point {(!,) the cnrrent of the signaling battery (C2 Sj) would be free to pass through the contact points (c h) and {d,) and ah^ng tlie line wire; and the completion of any individual circuit, through its own circuit-closer, would be indicated on its corresponding galvanometer of the series {g g g, &c.) In order to test any individual line and fuse it would only be necessary to remove the contact plug from between the plates {b and c) and insert it between (a and &,) by which operation the signaliug-battery (c^ So) would be thrown out, and the testing-batte'ry {c- c^) and galvanometer (g) would be thrown into the circuit, and the deflection of the latter would indicate whether all was right as regards insulation and conductivity. During this process of testing, it will be observed that the line and charge tested would only be thrown out of the ordinary conditions ; the remainder of the charges would remain in stfftu quo and be ready to indicate that a vessel was within the radius of destruction at auy moment. The ordinary ga.lvanometers {g g g, &c.) would at all times give a rough indication of the effectiveness or otherwise of the line and fuse. The key employed for firing is precisely of the form used with the ordinary Morse telegraph histrument. In a state of rest the front contact is held down on the plate ('^) by mea-us of ;i spiral spring (s,) and to fire it is only necessary to depress the handle (h) and make contact with the plate (/,) and, the key being pivoted on the point [d,) the effect of this depression would be simultaneously to break contact with the point (&.) Thus, the firing-battery would be thrown into circuit and the signaling-battery cut out simultaneously by the depression of the key. u detach CU-- "^Vlieu any given charge has been fired, it would only be of expencied ueccssary to remove the plug from between the plates {b iig-key. 225 and c) in order to cut off the conducting cables which would otherwise interfere detrimentally with the action of the in- tact circuits, and which, after a charge has been fired, should be detached with as little delay as possible. If the circuit were cut off in this way the line wire itself would be dis- connected from the system at leisure, an operation vi'hich it might not be convenient to perform immediately, in the heat of action with an enemy's vessels in the act of passing over the mines. In this system it will be observed that the firing battery is only thrown into the circuit at the wish of the operator, and that no miue can be exploded without the depression of its corresponding key. In order, however, to render the system perfectly safe, and to guard against the accidental depression of the key, which would produce a Ijremature explosion, a plug has been provided between the firing-battery and the apparatus, at the point (p;) when this plug is out the firing-battery cannot be accidentally thrown into circuit. The construction of a testing and firing table of this con-nmiion .u nature is so simple that it could be very easily put together very sL',!,.! ''*''''' by an ordiuuvy workman, and the materials of which it is composed are obtainable anywhere. The mines in connec- tion with it are capable of being fired by judgment, aud, for this purpose, would only rerpiire the addition of signaling apparatus, somewhat similar to that desoribed on page ISO aud those following, to complete the system, which could thus be used for firing by intersection when the position of the mines was clearly visible, while capable of being used at night or in a fog, on the signal being made by a vessel in contact, as first described. It is, however, dependent for effective service upon the vigilance and dexterity of the man in charge, which is a defect common to all systems in which firing by judgment is employed. This arrangement of testing-table may be used either May be u^-.i on the circuit-closing or circuit-breaking system. ^Yith the cait"ic"i' g or c'r- circuit-closing system it would be connected precisely astem. '^''""''° ~'~ shown in Fig. 89 ; with the circuit-breaking system, the circuit-breaker would be placed beyond the fuse, and this signaling current, passing through it, would keep the gal- vanometers deflected on a vessel striking any one of them, the action on the galvauometer would cease, and its needle would fall back to the position due to terrestrial magnetic attraction, and this motion of the needle would indicate the fact of the ship's contact. The system above described is so arranged as to indicate a vessel in contact with a circuit-closer, and as in many 15 226 cases it may be couvenient or even necessary to perform tbe operation of throwing in the firing-battery without the aid of a personal operator, the following self-acting system has been devised: By making the ai)paratus purely self- acting, all chance of error, consequent upon the inattention or want of dexterity of the man in charge, is, of course, eliminated, and this may be done without complicating the connections of the instrument to any considerable degree. Fif;. 94. SujnxdLuig / \ Bcuren/ • '? * ,' ».» ^ tice^ esrst .§^ irirr s \ a 1 ^ Shutter-signal- ing and firing-ap paratus. Fig. 94 shows a diagram of the airangemeuts by which a ves- sel striking a circuit-closer may be made to shift, by means of a relay, the conducting cable from the signaling to the firing-circuit and explode the charge; called the "shutter- signaling and firing-apparatus." (a) is an armature, working on a pivot between the two horns of an electro-magnet {h &,) and held in iDosition by a spiral spring (c;) the latter is in connection with a regula- ting screw, by which more or less pressure may be brought to bear in an opposite direction to that of the attractive action of the electro-magnet. A small stud (i) regulates the distance to which the armature may be drawn back ; [d) is a shutter, on which a reference number is clearly indicated, at- 227 tached to a lever pivoted at the point (e,) the iiiiiei- arm of whicli is just long enough to catch under the point of the armature (ix;) when a current is passed through the coils (6 b) of the electro-magnet, the armature (a) being attracted, the lever attached to the shutter is released, and the latter falls by its own weight into the position shown by the dotted lines. The pivot (e) is formed of an ebonite cylinder, with a metal cen- ter, from which latter two metal points project through the ebonite. When the lever (/) is held up by the armature (a,) one of thesemetal points projects downward andisin contact with a metal spring {g,) which forms a portion of the circuit of the signaling-battery. When the shutter falls into the posi- tion indicated by the dotted lines, the other metal point, projecting through the ebonite cylinder, comes in contact with a metal spring {h,) which forms a portion of the circuit of the firing-battery, while the connection between the spring ((/) and its corresponding point is broken in consequence of the revolution of the pivot bringing the ebonite part of the cylinder upon it. The metallic portion of the axis (e,) being ijermanently connected with the line wire terminal, and through it with the electric cable and fuse in the charge, it is easily understood how the action of dropping the shut- ter throws the firing-battery into circuit, and simultane- ously cuts out the signaling-battery and explodes the mine. The points of the metal projections on the pivot (e) and the faces of the springs (g and h) are platinized, to prevent oxide and insure good metallic contact between the j)arts. The armature (a) is prevented from coming into actual con- tact with the horns of the electro-magnet, by two small studs. The object of this is to prevent any effect of residual magnetism which might interfere with the rapidity of action of the armature when released and drawn back by the spring (c.) The siaualinff-battery should be so constituted as to be coustitutinn of " '^ signaling-balteiy, capable of working the electro-magnet effectually when the cii'cuit is closed direct to earth, and attracting the arma- ture with sufficient force to release the lever (/) with cer- tainty, and yet not so powerful as, by the continuous pas- sage of the current generated by it, to fire the fuse in the mine. Plentj' of power may be given to this batterj-, when used in connection with a platinum fuse, without any chance of accidental explosion from this cause, but when Abel's fuse is employed it is necessary to be very careful in order to guard against such a contingency. The testing arrangements are precisely the same as those ^Jg^4*„\° « "• shown in Fig. 93 ; it is, however, necessary to disconnect 228 tlie firing battery iu tbis latter combiuatiou, wheu testing, as any accidental dropping of the shutter would produce a premature explosion, pinng-batteiy. The flriiig-battery should be suited to the nature of the fuse employed, and should possess considerable excess of power iu order to overcome accidental defects, such as in- creased resistance in the connections or defectiv^e insulation iu the electric cable in connection with the mine. A battery, just sufficiently powerful to fire a fuse on shore, with the electric cable, &c., in circuit, but not submerged, would not be unlikely to fail after' the cable had been immersed in sea- water; in such a case it is recommended that the battery power determined by such an experiment on shore should be doubled for actual work. jio.ie of action If uscd iu couuectiou with a group of mines, arranged of tiie apparatus, ^^j^]^ clrcuit-closers ou the branch system, as shown in Pig. 89, the mode of action of the apparatus would be as follows ; while at rest the current of the signaling-battery wonld be divided between the several fuses in circuit; each of these fuses, possessing a very high electrical resistance, would, by its presence in the circuit, i^revent the battery current, passing the coils of the instrument, acting with sufficient force to form an electro- magnet, sufficiently power- ful to overcome the resistance of the spring (c) and draw the armature («) over to it. Directly, however, one of the circuit-closers on a branch was struck, the whole of the fuses would be, for an instant, practically cut out of circuit, because the resistance of those fuses, compared with that of the earth connection of the circuit-closer, is so great that practically the whole current would pass through the one particular circuit-closer that had beeu struck. Wheu this took place the comparatively feeble current of the signaling- battery would therefore practically be passed through a single electro-magnet, (that in connection with the circuit- closer struck,) and would consequently act with sufficient force to attract the armature, which it had uot power to do wheu divided between the several fuses (each possessing a A'ery high electrical resistance) iu the group. The arma- ture (d) being attracted, the lever (/) would be released, the shutter would fall, and the firing-battery would be thrown into circuit, through the spring [li,) and the metal point in contact with the pivot (e ;) the coils of the electro- magnet being simultaneously cut out of circuit, as already described, the current of the firing-battery, having a direct metallic circuit through the fuse to earth, would pass instan- taneously through and fire the mine. The action of the 229 ■whole ixS so rapid that practically the instant a vessel struck the circuit-closer the mine would be fired. In order to test the capabilities of the shutter arrange- . '^^p"™™* "!. ■*- o test the stability or ment for standing the concussion of heavy guns fired in its shattejsignaiinp: ^ ^ and finng-appa- vicinity, experiments were tried at Sheerness with a working i-atus during con- ^ cuKsion produced model constructed on the principles above described. It by firing gnus. was placed on the parapet of the work, at a few yards dis- tance, during artillery practice with a seven-inch muzzle- loading rifled gun; subsequentlj' advanced close to the muzzle of the gun, and finally placed on the gun platform, and the only case in which the shutter fell was when the whole apparatus was knocked over by the recoil of the gun. The instrument was made to work by closing the circuit electrically between each round, in order to ascertain that its stability was not caused by any undue tension of the regulating spring. It would seem therefore that, with moderate care, there would be no danger of a shutter dropping by concussion, but experience has proved that it is necessary to balance the force of attraction, exercised by the electro-magnet, against the mechanical effect of the spring, with some degree of nicety, as in guarding against an accident due to the falling of a shutter, one is sometimes apt to apply the spring- too strongly. Several modifications of the shutter-signaling apparatus have been made, but before any one of them can be consid- ered sufiQciently perfect to be received into the service, fur- ther experiments to determine their action when subjected to the effect of concussion, produced by the firing of heavy guns, must be made. Though the experiments tried at Sheerness were sufficiently conclusive as to the particular specimen tested, it is necessary that the instrument should be thoroughly tried under every possible condition which might occur in actual work. The stability of the shutter is a point vitally essential to its use, as in many instances it would be impossible to put it in such a position as to be out of reach of concussion. The question of the stability or instability of the shutter involves a condition of balance between the force exerted by the regulating spring pulling the armature in one direction, and the attraction of the electro-magnet acting in the opposite direction. In the circuit-closing system the spring must hold the armature sufficiently firmly to prevent the accidental fall of the shut- ter by concussion, while the battery must be so constituted as to act effectually when the circuit is closed. In the cir- cuit-breaking system the battery must, on the contrary, 230 hold the armature steady, while the spring ought to be able to act with sufficient force the moment the circuit is broken. It is not desirable to draw absolutely definite conclusions from the single experiment referred to, even though it was a very severe one on the instrument, and the conditions were infinitely less favorable than those which would ever occur on service. N iiuttfi -signal- When the circuit-breaking system is used with the shutter- "ifc^ut-'break/ng signaling apparatus, the action of the armature in releas- systpm. j^jjg ^]^g lever must be reversed ; that is to say. that when the current is passing and the armature attracted to the horns of the electro-magnet, the shutter must be held up, and when the current ceases and the armature is drawn back by the action of the spring, it must release the lever and allow the shutter to fall. This is done by the arrange- ment shown in Fig. 95. The extremity of the lever (/) is bent up and passes round and under a projection (£f,) at- tached to the lower portion of the armature (a;) when, F^. 95. therefore, the current ceases for a moment and the arma- ture falls back, carrying the projection [g) with it, the lever (/) is detached and the shutter becomes free to fall. The l^rojection [g) and the extremity of the lever (/) are made wedge-form, in order the more readily to become discon- nected from each other when the apparatus is put in action. Another form of shutter-signaling apparatus, designed 231 for use with a circuit breaker, is shown in Fig. 96. In this s hat ter signa i- instrument the shutter (a) is pivoted on a metal axis (b) with "fth stiaightTie"- two projections, insulated as before, with ebonite. The elec- *''°"^°'^'- tro-magnet (e) is, in this case, composed of a single coil, and two levers, {d) and {d',) one attached to each extremity of ^•^Q-^jl|Jjl|5f--- Si'tMaltinq Battery D-H|i .--j ! (ijGaluarwmeler — ' l--^\\\\\\\—^arm^ Testing Mattery |!lsMl|l|S|l[!|!|!|l|!|!l FirLruj Baltefy he axis (6) on which the shutter is pivoted, are so arranged that they may be attracted to and held by the electro-mag- uet as long as the current is passing, {d) being held by the front and (cZ') by the rear point of the electro-magnet. A small capstan-headed screw (/t) regulates the distance be- tween the electro-magnet and the armature j it prevents 232 absolute contact, -wbich might be detrimental in tlie case of residual magnetism, and by it tbe sensitiveness of the appa- ratus may be regulated. When the current ceases the shut- ter falls down into the position shown by the dotted lines, and, the springs and connections being precisely similar to those already described, the firing-battery is thrown into circuit as before. Fig. 96 shows the connections of the apparatus; (/) is the terminal to which the firing-battery must be attached, (g) the terminal for the testing-battery and galvanometer, (c) the terminal for the signaling-bat- tery, and (l) for the electric cable to connect the fuse iu the charge. A plug {p) provides the means of rapidly detnching the firing-battery; this latter is entirely out of cii'cuit, and no mine in connection with the group can be fired unless the plug (2?) is inserted between the two brass plates pro- vided for it. A second plug is used to connect the signal- ing-battery by insertion between the brass plates provided for that irarpose; if removed from (g) and inserted at the point {■)',) the signaling-battery is cut off from the circuit and the testing-battery is thrown iu. When the plug (q) is taken out for testing purposes there would, of course, be a cessation of current through the coils of the electro-magnet, and the shutter would fall down and complete the circuit of the firing-battery ; to guard against such an accident it would be necessary, therefore, when testing, previously to remove the plug {p.) With the exception of the action of the electro-magnet in dropping the shutter being the reverse of that previously described, that is to say, dependent upon the cessation of the current and not on its action, the mode of operation of this apparatus is precisely similar to that already given, and need not therefore be again described. Shutter signal- Another form of this instrument is shown in Pig. 97. Its «"th merrar^'col' amiature, electro-magnet, regulating spring, stud, shutter, "' '*""''■ and attached lever are precisely similar to those first de- scribed, (see page 226,) but the connections are made by two mercury cups, («) and (&.) When the lever is horizontal and the shutter drawn up and ready for action, the circuit of the signaling-battery is completed through the mercury- cup («,) along an arm (o) projecting downward from the lever (d,) and thence to the shutter-pivot and line terminal as before. When the shutter is down, as shown by the dotted lines, another arm, (e,) a prolongation of the lever (d,) falls into the mercury cup (c,) which latter is permanently connected with the firing-battery. The object of the mer- cury-cups is to get rid of the springs in the original design, Wg. 97. t IHiH -HiIl|i|l[i|i!ltH- 233 electrical circuits, dependent on the pressure of spring, being always liable to interruption from dirt or oxide intervening between the points of contact. There would be much less danger of such a contingency if mercury-cups were used. Fig. 98 shows apian of the apparatus ; (/&) is the firing-battery terminal, (s b) the signaling-battery terminal, and {g) the testing-battery and galvanometer terminal. These are con- 234 iiected with brass plates, as showji by the dotted lines, and plugs are provided, as before, for altering the connections. There is an electrical bell in the tiring circuit to give notice by striking when a mine has been fired. iug''"*!ippa'ratus The shutter-signaling apparatus may be so arranged as i'liTk'yt''^'*'^*''^ to be worked on the circuit-closing .system, by a combination of firing-keys, in connection with observant stations, in any of the systems described at page 18G, and those following, (Figs. 78, 79, and 80.) It would only be necessary to con- nect a battery of similar constitution to the signaling-battery, so that its circuit might be closed and current passed through the coils of the electromagnet of tlie shutter appa- ratus, by means of the depression of firing-keys, and the shutter, corresponding to the particular mine to be fired, would thus be released at the proper moment and the firing battery thrown in. In this way a system might readily be used, if required, for firing by intersection when the posi- tion of the mines are distinctly visible, while a simple change of connections would render itself acting at very short notice. Should the circuit-breaking system be used, the combi- nation would not be so simple. The visual circuit-closing system is dependent, in two out of three of the cases described, (Figs. 78 and 80,) on the closing of the circuit at two dis- tinct i)oints, while the breaking of the circuit at one point would cause the shutter to fall. If, therefore, a circuit- breaking combination were used, it would be necessary to arrange an entirely separate, system on the circuit-closing principle for signaling; in this way the number of a mine might be readily indicated to an operator, and he might throw down the shutter by hand. If a system of firing by intersection, combined in this way with a self-acting system, were used, the observing- stations would frequently be some distance from the testing- room; they (theobserviug-statious) ought to be, if possible, well clear of the smoke of guns in action, while the testing- ■' room ought to be within a fort and in a bomb-i)roof case- mate, well covered from an enemy's direct and vertical fire. It ought not, in point of fact, to present any opening in the direction of the enemy's guns. There would, however, be no difficulty in arranging a combined system under such conditions, either for the circuit closing or breaking system. Arrangemrat of The shutter-signaliug apparatus may be conveniently rf huttPi' -.signaling • i -i i • n apparatus in box. arranged in a compact form, with a long box to contain the coils, which box should be made to shut up and lock, to prevent interference by unauthorized persons. The battery 235 terminals, brass plates, pings, &c., shonld he placed on a board in front and ontside the box itself, so as to be acces- sible at all times. The coils of the electro-magnets may be conveniently placed side by side: in this way six coils, with their necessary terminals, brass connecting-plates, &c., would occupy a space of 30 inches in length, 9 inches in breadth, and 7 inches in height. The bell would stand 6 inches high over the top of the center of the box. A form of testing and firing table has been designed in woohvichtest- ^ "^ ing and firing t^i- the chemical department, Woolwich, adapted for a self-acting tie. system of mines, the general arrangement of which is shown in Fig. 99. The electric cables, in connection with the mines, having been brought into the fort, are each attached to a series of screw-plugs, inserted into perforated metal plates insulated by ebonite rings (« a a, &c.,) which latter are numbered to correspond with the number of the mine or system of mines to which each belongs. A second series of screw-plugs {b h b, &c.,) in metallic connection with (« a a, &c.,) is arranged to receive a series of insulated wires, connecting the electric cables with a metal plate (c,) by means of a series of binding-screws {d d d, &c.) This metal plate (c) is permanently connected with the firing-battery; if, therefore, a vessel were to strike one of the circuit-closers of the system, the circuit of the firing-battery would be comj)leted through the fuse and the fuse would be fired. The positive (copper or carbon) pole of the firing-battery is connected with the plate (p,) containing three holes for screw-plugs, which are brought into metallic connection by it; the negative (zinc) pole of the battery is connected with a similar plate (n.) Another insulated plate (e,) made to receive three plugs, the center one of which is connected to earth, is placed in a convenient position on the table to facilitate such changes of connection as may be required in using the apparatus ; three holes are supplied in each case, so that one or more connections may be made at each of the points (2^ n e) if required, as it may be necessary to use more than one such connection at a time in testing the condition of the lines. When arranged for action, the posi- tive pole [p) of the firing-battery is connected to (e,) and the negative pole («) to the plate (c,) as shown by the dotted lines. The positive (copper) pole of the testing-battery is connected by means of a screw-plug with the plate (p',) and the negative (zinc) pole with the plate (7i',) two other screw-plugs in each case being, as before, disposable for any required connec- tions. Another insulated plate (y) is in connection with one binding-screw of an astatic galvanometer [g') placed in a for testing firing- battery 23G convenient position on the table, -while an insulated wire, (/,) long enough to reach to any one of the screw-plugs of the combination, is attached to the other terminal of the galva- nometer. The positive pole (j/) of the testing-battery is permanently connected for work with one of the earth ter- minals at (e,) while the negative pole {n') is connected with one of the terminals at (g.) The whole object of these nu- merous binding-screws is to give facility for changing the several circuits with the least possible delay. Us.- in testing. In order to test any one of the electric cables for insula- tion, conductivity, or for any other purpose, it would only be necessary to disconnect it for the time from the firing circuit, by removing the connection between the screw-plug (b) and the plate (e,) and to insert in its place the wire (I;) the testing-battery would thus be put in the circuit, through the galvanometer, with the particular line to be operated upon, apd its efficiency as regards insulation, conductivity, &c., indicated by the movement of the needle of the instru. ment. Airaugemcotg To tcst the couditiou of the firing-battery, Mr. Abel pro- poses to use a small set of resistance-coils in connection with a thermo-galvanometer or bridge, in which he proposes to place a definite short length of fine platinum wire of known electrical resistance. The working power of the battery would be tested by the fusion of the thin ijlatinum wire through a given electrical resistance, as indicated by resist- ance-coils put in circuit, and a practical test of its efficiency would thus be obtained with great facility. This test would of course only be applicable in the case of a battery pos- sessing the power to fuse a fine platinum wire, and it would be necessary actually to fuse and not to simply heat the wire more or less red, in order to obtain defluite knowledge concerning the battery, as previous to actual fusion no defi- nite information as to the degree of heat produced by the battery could be obtained by this means, as a measure of its working powers. To test a battery which would not fuse a short length of fine platinum wire, some other means must be adopted, but the same kind of information might be obtained by firing an ordinary tension fuse, of known resist- ance and through a known resistance as indicated by the re- sistance-coils. The battery power required to fire a tension fuse would not perhaps be determined within such small lim- its as that necessary to fuse the platinum wire, but it would answer perfectly well for practical purposes. Whether the platinum or tension fuse were employed, it would not do to rely on the results of such an experiment to determine abso- 237 lately the number of battery-cells to be used in practice. If a certain number of cells, tried in this way, just fired the fuse through a resistance equivalent to that of the electric cable, &c., it would be desirable in practice to double that number of cells. It must be remembered that the condi- tions in the experiment are always far more perfect as regards insulations, &c., than can ever occur in practice, where all sorts of deteriorating influences must necessarily exist to mar, at least in a degree, the perfection of the combination. The resistance coils and connections for this test must be wire oi coiis suited to the nature of the firing-battery used, for example, taiter/cmr'i^nt. " thick wires in the resistance coils if a quantity battery is employed, and fine for a battery of high electromotive force. The whole might be arranged in any convenient position on the testing-table. ft is also proposed to provide the testing-table with a commutator, by which means the number of battery-cells used for testing purposes may be rapidly and conveniently altered. CHAPTER XIII. :\IECHANICAL AND ELECTEICAL TESTS. Having now given a general description of the arrange- ments wliich seem to be best suited for working out any system of defense by submarine mines, it only remains to explain how the several component parts of the system may- be put in proper practical working order and kept so after submersion. Tcstsempioyed. rpg iusurc this it becomcs necessary to test the different component parts of the system carefully before they are placed in position, and to retain the power of ascertaining their efficiency, as far as possible, at any period after they have been combined and put in the water. The tests em- ployed are of two kinds, mechanical and electrical. Mecii.mica; tests. Mcchanlcal tests should be applied to ascertain that the mechanical arrangements of the shutter apparatus, circuit- closers, and all similar appliances work easily and efficiently ; that the several parts of the case to contain the charge, when put together complete, are water-tight; and that it is sufficiently strong to bear the external pressure due to the depth at which it is to be submerged, for a considerable time without leaking. Electrical iv^tn. Elcctrical tests are those which must be applied to the several component parts of the system to ascertain that the electrical conditions, necessary to a successful result, exist; for example, that the electric cable possesses a sufficient amount of insulation and conductivity; that the firing-bat- tery is in such order as to insure certain ignition ; that the electrical connections of the circuit-closers are correct, and other similar information. By means of certain electrical tests we can also ascertain after immersion, with a consid- erable degree of certainty, whether the several combinations of a system are in such a condition that it will work effi- ciently. This is a very important fact; for the whole thought, trouble, and previous preparation bestowed on a submarine mine is undertaken in order that it may act effi- ciently at a single instant of time, and it becomes valueless unless it does so act without failure. Testa bciove and Each portiou of the apparatus should be tested separatelv, after submersion. i i • n • i ^ x .- and combined m the form in which it is to be used before submersion, and the whole should be again tested immedi- ately after submersion. 239 As a preliminary- to all electrical testing it is necessary to Tests of instru- ascertain that the instruments, batteries, &c., used iu making "™*'' the tests, are themselves in good working order, otherwise defects which exist in the testing instruments may produce results which might be mistaken for defects in the apparatus under trial ; for example, a want of proper connection in the construction of a galvanometer might be mistaken for want of conductivity in an electric cable, or for a high condition of insulation which might not exist. The follpwing modes of testing the several component parts of the system may be adopted : The exi^losive used would be either gunpowder, gun-cot- Tests of expio- ton, or some similar compound ; as a general rule these might be accepted as of good quality, but should any sus- picious appearances present themselves, or should facilities be at hand, tests should be made. Gunpowder may be tested by an eprouvette, or by tiring small charges out of a mortar and measuring the range obtained. Gun-cotton may be tested chemically, or practically, to see that it possesses detonating qualities. Any other explosive of a similar nature could be tested in a similar manner. The case to contain the charge should be tested to ascer- Tests of case. tain that it is thoroughly water-tight, and capable of bear- ing external pressure to the extent required, according to the depth at which it is to be submerged. This test may be applied by forcing in water bj' means of a hydraulic press, to any given pressure, and observing the joints, &c., to see that nothing comes through them or through the body of the plates themselves. This should be done during the process of manufacture, and the leaks at the joints, should any exist, should then and there be calked. Any leak through the body of the metal itself would necessitate the rejection of the entire case. Cases of J-iuch boiler- plate iron should bear a j)ressuie from within of forty pounds on the square inch without a suspicion of leak. To test for capacity to bear external pressure, the cases, having flrst been made complete with mouth-piece, &c., to close the loading-hole, as for service, may be submerged to a depth somewhat exceeding that at which they are eventu- ally to be used. After remaining thus submerged for not less than forty-eight hours, they should be lifted, opened, and carefully examined, to see that they remain perfectly dry inside. In making this examination it would be neces- sary, in the event of damp having penetrated, to ascertain whether it had forced its way in at the junction of the mouth-piece, or through the joints or metal plates composing 240 tlie body of the case. ISTo electrical test can be applied as far as the simple metal is concerned ; when complete, liowr ever, with mouth-piece, fuse, &c., before submersion an electrical test, to be hereafter described, should be applied to ascertain the condition of the apparatus as a whole. Tests of moor- All moorinff apparatus should be tested mechanicall?: ing apparatus. o x i. ..7 first, to ascertain that the weights of anchors or sinkers are such, considering the buoj'ancy of the case, rate of current in which it is to be moored, and nature of bottom or holding ground, as to keep the mine in its proper position after sub- mersion. Second, the chains, wire cables, and ropes to be employed should be examined to see that they are of sound construction ; and, if the slightest doubt exists as to their quality, they should be further tested mechanically, by applying a strain of a measureable nature, to ascertain whether they are fit to perform the work required. No electrical tests are applicable to this part of the apparatus. Tests of me- Mcchanical fuses, such as the sulphuric acid fuse, &c., might often be improvised and should be practically tested in course of construction. A fuse of this nature which may at any future time be made an article of store, to be drawn out as required for use, must be tested practically, by selecting a certain percentage of those issued and firing them ; should the results be good the whole may be accei^ted as of good quality; if failures to fire occurred they would indicate more or less deterioration or imperfection in the whole. Abel's torpedo primers should be tested in this way. Mechanical fuses cannot be tested electrically. Tests of piati- The platinum wire fuse may be very simply tested electri- nxim wii-e fuse for n -j-j-' 1 1 • • -j •.^ ,. -., ^. ■, , ^ couductiyity. cally. It placccl in circuit with a few cells of a battery (c z,) Fig. 100, and a common detector galvanometer (g,) as shown in Fig. 100, before the fine platinum wire {p) is soldered across between the wire points there should be no deflection of the needle, for no metallic circuit should exist; if it did it would be fatal to the efficiency of the fuse. If placed in circuit 241 101. with the same battery and galvanometer, after the liue pla- tinum wire had been connected to the extremities of the larger wire points, a considerable deflection of the needle should re- sult, such deflection being due to the current passing through tlie platinum wire bridge, which, to be efilcient, ought to be the sole medium through which the circuit is completed. This test should be made with a few cells of Daniell's, or other similarly constituted battery, the current generated by this form of battery being of such a nature that no sen- sible heat would be produced in the platinum wire, and no chance of an explosion of the fuse incurred. This is espe- cially necessary in testing the fuse after it has been placed in the charge, when a premature explosion would of course be a very serious matter. The current of Grove's, or other battery, so constituted as to fire a platinum fuse, would moreover injure, if not destroy, the coils of tbe galvanome- ter unless specially constructed for use with it, and should never be thus employed. The continuity of a platinum wire fuse may also be tested by means of a water-decomposer, as shown in Fig. 101. The passage of the electric current through the water would decompose it, and hydrogen bubbles would be deposited on the point in connection with the negative pole of the battery. Should a want of continuity exist in the fuse, no current would pass and no water would be decom- Ijosed. The apparatus consists simply of a glass bottle (a) to contain the liquid, into which a pair of wires, {b &,) insulated from each other, have been introduced, by simply passing them through a cork. A single cell of Grove's, or any battery by which a -platinum wire may be fused, may be used in testing for continuity with this apparatus, provided the insulation between the wires passing into the bottle is sufficiently good, and the space between them, within the bottle, is sufficiently great to obviate the chance of premature explosion. In testing with a Grove's cell, extreme care is necessary to pre- vent the accidental closing of the circuit directly through • the fuse by bringing the terminals in contact with each other, witliout the intervention of the resistance of the liquid in the bottle ; in order to guard against this the wire terminals, outside the bottle, should be bent well apart. Salt, or acidulated, water is better than fresh for testing 16 24-2 purposes, ;is exhibiting the eft'ect of its decomposition more rapidly. auM "if "piJimim Tlic electrieal resistance of a platinum wire fuse may he wire fuse. ascertained by balancing, by means of a set of resistaiicc- coils (/■) and a. deferential gahauometer {(j.) Any number of Daniell's cells required may be used for this operation, but, for the reasons already given, GroA'e's battery is inad- missible for such a purpose. Fig. 102 shows the connec- tions to be employed for a test of this nature. The resist- Fig. 102. |Sii|i[i|i|l- auce of the coils is adjusted, by taking out plugs till tlie needle of the galvanometer is brought to zero, when the sum of the resistances indicated by the unplugged coils will be equal to that of the fuse. The electrical resistance of j\" of fine platinum wire, weighing 1.9 grains to the yard, is j^ of a B. A. unit nearly, (Schaw ;) this is its resistance at the moment of fnsion. The resistance of ^g", obtained by balancing with a set of resistance-coils, as in Fig. Klli, is about -f^ of a B. A. unit ; yV is a good length of wire to em]iloy as a fuse, and may be adopted as a standard. Tests of high- Fuses adapted to be fired by electricity of high tension, ronductivity.^ *"' such for example as Abel's fuse, require much more careful and delicate management in order to test them; they may, however, be tested for conductivity and resistance, and this must always be done before they are used in any operations connected with submarine mines, to insure the maximum of efficiency at the proper moment. The test for conducti\'ity must be made with a few Daniell's or other similar batten cells of small surface, adapted for tests of this nature, and an astatic gah'auometer. The high electrical resistance of fuses of this nature, amounting in the case of Abel's fuse to as much as 1,500 or 2,000 B. A. units of resistancie, combined Avith the danger of prematni^e explosion when testing with even a small number of battery cells, renders it necessary to employ the astatic galvanometer, on which, in consequence of its greatly superior sensitiveness, a deflection is produced 243 by a comparatively small current. A reflecting galvanom- eter would of coarse be preferable for such work, but is much more expensive and not a very portable instrument. The resistance of a high-tension fuse may be obtained in f.sts of .esist- connection with a differential galvanometer, by balancin"-8i°o"'^f"°'"< '^ ' ° by means of a set of resistance-coils, as in the case of tbe platinum wire fuse. For the reasons already given, ii very moderate battery power must be employed, and a more sensitive galvanometer used in this operation. The resistance of this form of fuse may be very accurately determined by means of Wheatstone's bridge and a, re- flecting galvanometer. For general work, however, an astatic galvanometer will give results sufiicient for all practical purposes. The precautions necessary in testing Abel's fuse are given at pages 94 to 96, and these must be adopted generally in testing high-tension fuses of any forai. The tests to be employed for detonating fuses would be Test»ofdcto»a- precisely similar to those for ordinary fuses of the same con- "°s fuses. struction, the only difference being in the priming, (fulmin- ate of mercury instead of gunpowder.) They should, however, be subjected to a further test to ascertain that their detonating properties are sufiicient to insure success ; a deficiency of detonating composition will often prodaue imperfect detonation In the explosive itself, when used with compressed gun-cotton. A percentage should, therefore, be tried to ascertain their efficiency in this respect. Each fuse should be tested before and after it is placed in the charge, subsequentl.y as a part of the general combina- tion in which it is to be submerged, and finally, directly it has been placed in position for work. Any change in the results obtained by the first and subsequent tests applied would indicate a change in the electrical conditions, as well as give such information as would indicate efficiency or otherwise of the system, as will be hereafter explained. It is, i)erhai>s, almost unnecessary to test electric cables, Tests of electric suitable for submarine mining purposes, mechanically for al'^^^J; "'"^''"""'" tensile strength ; extraordinary precautions are taken by giving them strong outer protecting covering of iron wire, lieiiq), &c., intended not only to give tensile strength but to protect them from injury by rubbing against rocks, &c. .Special precautions too are employed to prevent any great strain bein!"- brought to bear upon them, either daring or subsequent to submersion. Should, however, any donbt arise as the ability of a cable to sustain a strain likely to be put upon it, it may be tested for tensile strength in the same manner as an ordinary rope. When an improvised 244 lu^iulution tost cir electric cables. (electric cable is employed it would always be advisable to ascertain its tensile stveiigtli before putting it to practical use. Electric cables should be tested electrically for insula- tion, conductivity, and electrical resistance. To test for insulation the cable should be put in a tank of water and allowed to soak for 48 hours. The object of this soaking is allow the water to penetrate through the outer protect- ing covering of hemp and iron wires, and to search out and get into any weak places there may be in the insulation. After soaking, one end («.) of it should be reconnected, as shown in Fig. 103, with an astatic galvanometer {g,} and Figi. 103. .J^_ -III I|i|i|f|l|l|l|l^ battery (c s) of not less than 50 Daniell's cells, while the other end (6) should be carefully insulated. The battery circuit should be completed by an earth-plate (e) in the tank {t) through the galvanometer (g,) and the deflection of the latter should be observed. It is manifest that in such a combination any current, passing through and deflecting the galvanome- ter, could only comx^lete the circuit by passing through the insulation of the cable. A very slight deflection would fre- quently be observed on a moderately sensitive galvanome- ter in such a combination as that indicated in the figure, even with a well insulated cable. This would be due to the current passing through the insulation ; its whole length being immersed, the surface through which such a current would pass would be large, and the sum of the intinitesi- mally small quantities, escaping over the whole length, would, in the aggregate, be sufiieient to deflect the galvan- ometer to a small extent in completing the circuit of the 245 battery. Should any considerable deflection occur, it would indicate a defect, or leak, in the insulation of tlie cable, the extent of which would be roughly measured by the amount of such deflection. In making a test of this nature a large number of battery-cells, at least 50, and, if possible, more should be used, the object being to obtain high electro-motive force to drive the current through any defects which may exist. The battery-current should not be kept circulating longer than necessary during a test of this nature, and in order to close and break the circuit with facility, it would be convenient to insert a manipulating key, (A,) Fig. 103, in the combination. Should a leak exist in the cable, the effect of the continuous passage of electricity would be to polarize that leak, and thus to intro- duce a conflicting element into the combination which would be likely to interfere with the value of the test. If the tank in which the cable was coiled away were of iron or other metal, the earth-plate (e) might be dispensed with, and the circuit simply connected by a wire to the tank itself. When no tank is available an electric cable may, for testing purposes, be immersed in the sea or in any water, and equally good information obtained by testing it in the manner described. Having completed the test for insulation, an electric Test of ei«tiic cable should next be tested for conductivity. To do this it tivitj' would only be necessary to remove the insulation from the end (6,) Fig. 103, of the cable, so as to expose the metallic conductor, and put it in the water of the tank. If the con- ductivity were good, the whole of the battery-current would then pass through the cable, and the galvanometer would be violently deflected. If the continuity were broken no deflection of the galvanometer would occur. Very much more delicate tests for insulation might be obtained by substituting a reflecting for an astatic galvan- ometer, but for the comparatively short lengths of electric cable required for use in submarine mining operations, such minute accuracy is seldom necessary, though, at important stations, the more delicate apparatus might be very usefully employed. It must be borne in mind, however, that whatever instru- ^^omltrs best "mentis used, the deflection of a galvanometer only conveys a foj-^'e»*i"g p"'- comparative idea of a current passing through its coils. A current which would produce absolutely no motion on an insensitive galvanometer, would cause a considerable deflec- tion in the needle of even a moderately sensitive instru- ment. An operator should, therefore, know the nature of rent best for te 24*; the iiistruuieiit with which he is working, iind it is prefera- ble for him to euii>loy a toler;ibly sensitive instrnmeut, with the use of which he is thoroughly ac(]uaiute(l, than a rough one witli which the more delicate observations could not be made. The negative (zinc) pole of a battery should always be ng rmrpo»<"s. attached to a. table for testing purjioses, because if the positive (copper) pole were attached, a salt of the metal of which the conductor was formed would be iunnediately de- posited in any defect which miglit exist in the insulation if the metallic conductor were in the slightest degree exposed. This would occui' in ;iny water, unless absolutely free from impurities, and would be especially the case in salt watei', in which a chloride of the metal would be quickly formed. This would almost immediately insulate the defect to a certain extent, and a true deflection would not be obtained on the galvanometer. The effect of a negative current would be to decomi:)ose any such salt and to deposit the metallic component on the conductor, and thus, so to sjieak, to clear the defect and expose a j)urely metallic surface at the point required. Tests lor nniiti- To tcst a multiple cable for insulation and conductivity, pleciibles. . .[ , -, , , a similar course should be pursued with each conductor as has been described for a single cable. In testing each single core, the conductors of all the others should be put to earth to obviate the effect of induction which would, more or less, according to the length of the cable, interfere with the results of the observations obtained. T.i discover po- Should a defcot in insulation be indicated by the tests sitiiin of a defect "^ of insulation. abovc described, its position might be readily ascertained, by keeping a continuous current on from the battery, and gradually taking the cable oat of the tank. If the imper- fection existed at a single point, the defection of the gal- vanometer would be suddenly much reduced at the moment the defect was raised out of the water, and its position would thus be determined with considerable accuracy. Should several defects exist, as each was lifted out, a sud- den reduction of deflection would occui\ Discharge teet. Want of coutiuuity in an electric cable maj- co-exist with perfect insulation; for example, the conductor might be parted within the insulation, while the latter remained good. Under such circumstances the tests above described would indicate good insulation but no conductivity, without giv- ing any information as to the position of the severance of the conductor. To ascertain this the following test may be applied: Having put one pole of a battery of 200 or 247 more Dauiell's cells to earth, charge one end of the defective cable, and immediately discharge through a reflecting gal- vanometer, noting the extreme limit of the swin g of the needle, then charge the other end of the cable in a similar manner, and discharge it through the same galvanometer, noting the swing of the needle as before. This should be done three or four times, and an average of the deflections taken. The position of the break in the conductor would be indi- cated by the proportion between the average deflections in each case, and the cable might safely be cut at the point so determined, which, if the tests were carefnlly made, would not be very far from the defect. Should the precise position of the fault not be discovered in thus cutting the cable, each section should then be again tested for conductivity, and that in which the fault was still found to exist should be again tested by the discliarge as before. In this way the exact point would finally be discovered. The deflection of the needle is dependent upon the quan- tity of current, at a given potential discharged through the coils of the galvanometer, and the quantity is again depend- ent on the electrical capacity of the conductor of the cable to contain a charge forced into it at a given potential, and its electrical capacity is direct^ in proportion to its length, snpx)osing the conductor to be of uniform size throughout. The swing of the galvanometer-needle meas- ures the quantity of the charge passed through its coils, in proportion to the sine of half the angle deflected, (.Jeukin;) hence on a reflecting galvanometer the information would be given directly, in proportion to the number of divisions on the scale, as indicated by the extreme motion of the s[iot of light, while on the galvanometer reading the angular measure in degrees, &c., the sines of half the angles de- flected would give the required proportion. Few galvan- ometers, except the reflecting instrument, are siifQciently sensitive to enable the " discharge-test" to be employed. After testing for insulation and conductivity, the electri- Test r,t L-ioctn- cal resistance of an insuhited cable should be measured. caWe. This should be done by balancing it agaiust a set of resist- ance-coils, in ct)iinectiou M'ith a dift'erential galvanometer, in a similar manner to that shown for the fuse in Fig. H)2. The coils should be unplugged till its galvanometer-needle is brought to zero, when the sum of the unplugged coils would be equal to the electrical resistance of the cable. A more delicate test of this nature may be made by Wheat- sf one's bridge and a reflecting galvanometer. The electrical 248 resistance of tlie couductor of a cable affords a very cor- rect indication of the (jnality of the metal of which it is composed. In making these tests Daniell's or some similar form of battery shonld be employed, so that the delicate coils of the galvanometers, &e., may not be injured. MLcbauicattcsts Water-tight ioints and connections should be tested of nater-liglil ° -^ i"'"'*- mechanically, by immersion, for not less than i8 hours, at depths somewhat greater than those at which they are to be eventuall5' used, after which they should be raised, opened, and examined to see that they remain dry. offMuiated •otafs'* lusulated joiuts and connections, whether of a permanent or temporary nature, should be tested electrically, in a precisely similar manner to that described for electric cables. They should be soaked for 48 hours and then tested for insulation, conductivity, and electrical resistance. In testing the permanent joiuts made in a line of subma- rine electric cable, special precautions are taken, which are described by ^.Ir. Culley as follows: "A joint should insulate as well, or nearly as well, as an equal length of the perfect core, and the object of the test is to ascertain if this be the case. The leakage, even from a considerable length of good core, is too small to affect the galvanometer ; although the electricity which escapes mo- ment by moment cannot be measured, still, if it were possible to store up the loss during a minute and compel it to pass instantaneously through the coils, it would produce a sen- sible deflectiou. Deiicaie tcbt of " lu Order to effect this, recourse is had to induction. A iqlpuraiul. '''"^°"' mctallic trough, sufficiently large to contain two or three feet of the core, is suspended by straps or rods of polished ebonite, two or three feet long. A small condenser is at- tached to increase its inductive capacity, and enable it to store up the electricity which may leak through the iusula- tioji. The testing-battery, of not less thau 200 cells, is in- sulated in a similar manner, and all loss over the surface of the conducting wires is prevented by paring their ends, so as to exijose a fresh clean surface, or even by coating them with hot iDaraffiue. To tin tbe ap- " To asccrtaiu if the apparatus is sufficiently insulated, the trough and condenser are charged, and the swing of the needle, from an immediate discharge, noted. They are then recharged and left free for a time equal to that to be occupied by the test and again discharged. The difference in the swing shows the loss in the time, and should be very small. Itaiatus. 249 "The joint is placed in the ti'ough, a negative current is applied to the cable, and the positive pole of the battery is connected to the outside coating of the condenser. Any leakage which may occur through the insulation is, by this arrangement, accumulated in the condenser, and may be discharged through the galvanometer after any given inter- val. "It is possible to find how much is lost by deflective in- sulation duringthe joint-test itself; but as both core and joint are. subjected to the same conditions, and the object is sim- ply to see if one insulates as well as the other, this precau- tion does not seem to be absolutely necessary. "To make the test. 1st. Place the ioint in the trough — Modeofmakia •' '^ the test. leave one end of the cable free; connect the copper pole of the battery to the galvanometer ; connect the other terminal of the galvanometer to the trough, and, finally, charge the cable by applying the zinc pole. "The charge within the cable acts inductively upon the natural electricity of the trough, the wire being in fact the inner, and the water the outer coating of a Leyden jar. A portion of the negative electricity of the water is set free, and an equal quantity of the positive is held fast or disguised by the negative charge within the cable. The free electricity is at once neutralized by the action of the battery ; if it were not so arranged, it would increase the apparent leakage from the cable, being of a similar sign. "The deflection or swing due to the discharge being in- stantaneous, it follows that if the needle remains deflected after the discharge, the joint is very bad or there is leakage over the surface of the insulation. The latter may be con- ducted to earth so as not to interfere with the test, by wrapping- an earth wire round the core a few feet from the free end. "2d. Without disturbing the charge of either cable or trough, connect one coating of the condenser to the trough, the other coating to the positive pole of the battery, the zinc being to the cable as before. " Any negative electricity which may leak from the cable will now accumulate in the condenser. Allow one minute for this. "3d. Disconnect the condenser from the trough and bat- tery and discharge it through the galvanometer. If the trough and other parts of the apparatus have been well insulated, the swing will show the accumulated leakage from the portion of core under test. It is evident that these changes must be made by perfectly insulated keys and commutators. 250 ■.:iivot.ii indue- "It. ofteu occurs, when there are several wires in the liun \vneD several ^ i.iii;ts:,ieMrauita- enable, that the aniiareiit leakaue is greater from the joint which is tirsttestetl than from any of the other joints tested at the same time. This arises from the charge in the first wire acting upon the others inductively. Tlie wires not under test should therefore be put to earth until they are wanted, and the condenser and trough should be perfectly discharged between each test. " It will be understood that the results are simply compara- tive, not absolute; all that the method effects is to show the difference between the insulation of a joint and that of any other part of the core. " This method somewhat differs from that ordinarily adopted. It is usual to put one pole of the battery to earth ; but in tills case leakage takes place over the whole cable, however long it may be. By the plan described, the leak- age is confined to the part in the trough: the whole force of the battery is concentrated there and the axiparent leakage exaggerated." Though such miiinte accuracy is not absolutely essential in the short lengths of electric cable used for submarine mining purposi-s, it must be borne in mind that the higher the condition of insulation, the greater will be the eflicieney of the system, and the longer the line, the greater the neces- sity for perfection, as far as it can possibly be attained. stonoV exploder, All clectrical instruments used for firing mines at will, "mi'stoiiai^appa- such as Wheatstoiic's exploder, Siemens's dynamo-electrical ™*"'*' machine, and the Austrian frictioual machine, should be carefully examined and tested to see that their mechanical arrangements are in good working order. They should fur- thei' be tested, with a fuse and known electrical resistance in circuit, to ascertain their power to fire that fuse with cer- tainty. If the electrical resistance in circuit is considerably greater, (say double,) than that through which they are required to work in iiractice, it may be assnmed that they are in good order. The Austrian frictioual machine has a special arrangement, by which its working condition may be ascertained, on short circuit, by the length of the spark passing across a given space on closing the circuit between the armatures of the condenser. ies, ^° Electrical batteries should be tested for potential, internal resistance, and electro-motive force. '"^"'™*"''' To test the potential of a battery, one pole should be put to earth, and the other to charge one pair of the quadrants of a reflecting electrometer; when this is done a certain deflection of the spot of light will be observed. 251 and the amount of the deflection, as compared with that produced by a standard cell applied to the instrument in a similar manner, would give the relative value of the poten- tial of the battery. In making such observations it is neces- sary to take care that the condition of the electrometer, as regards charge in the Leyden jar, «fec., is the same, while the deflections with the batteries under comparison are observed. The reflecting electrometer is not a very porta- ble instrument, and requires very careful and delicate ar- rangements in connection with it, and the beautifully minute and accurate Information obtained by it is not absolutely essential to efQciency, in connection with the comparatively short lines of electric cable necessarily used for submarine mining purposes; its employment may therefore be limited to the more delicate observations necessary at important stations. The internal resistance of a battery maybe readily obtained ,.eaS;ance o°'%a^ by means of a double shunt differential ' galvanometer and fo^tes?™'""''"'"^ set of resistance-coils, as recommended by Mr. Latimer Clark, in his book on electrical measurements in the follow- ing manner : " Connect the battery and a set of resistance-coils in cir- cuit between the terminals A and D, and insert plugs iu the resistance coils so that they give no resistance; insert plugs at A and 0, and also both the shunt plugs at A and D. The battery current will now flow through one-half of the galvanometer circuit only, being, however, reduced to xooth of its amount by the shunt D : the deflection of the needle must be carefulljr read. The plug A must now be removed to B, which causes the battery current to flow through both halves of the galvanometer, (each being shunted.) The cir- cuit will now be as shown in Fig. 105, and the needle will, of course, be deflected somewhat more than before. Xow unplug the resistance-coils which are in circuit with the battery until the deflection of the needle is reduced to its original amount, and the resistances unplugged will be equal to the internal resistance of the battery. Fur example, assuming the resistance of the half coil to be ninety-nine ohms, and that of the shunt wire one ohm, thejoint resist- ance of the two circuits will be : Galvanometer X shunt ^^ 99^1=0.99 ohm. Galvanometer -f shunt 99+1 Suppose the resistance of the battery to be four ohms, the two together=1.99 ohms, and the current acts on the gal- vanometer needle through one-half of its circuit only ; when tlie second half of the galvauometer is tlirown iuto circuit, by shifting- the plug from A to r>. the resistance becomes 4.1(9 + (».00=.j.!)S, and therefore less current passes; but, since it acts upon the needle through both coils insteadof one. the deflection is greater than before. The resistance coils are now varied until the needle recedes to its original deflec- Fig. 104. tion, which will necessitate the unplugging of a resistance of four ohms, making the total resistance now 5.9S + 4:=9.98, wliich is exactly double the first resistance ; that is to say, in the one case we had a current acting upon one coil through 4.99 ohms, and in the other case acting upon the two coils through 9.0S ohms, the deflecting power on the needle hav- ing been increased in the same ratio as the resistance.'' This measure is obtained in terms of B. A. units of elec- trical resistance, and is thus at once comparable with any other electrical resistance required. 253 The comparative electromotive force of a battery mar be Electro- mcnive 1 1 ■ 1 , ^ '' ^ • force, teat of bat- aetermineu by means of a differentiali" galvanometer andt^y. set of resistaace-coils, in a very simple manner. Fig. 104 shows a diagram of a double-shunt differential galvanome- ter and the mode of finding the electro-motive force with Fig, 105. ^13^ this instrument, as recommended by Mr. Latimer Clark, is as follows : "This can only be done relatively in terms of some other connectioDs for tlie test standard battery. The method is as follows : Determine " . the resistance of the standard and of the other cells to be measured ; insert the shunt-plugs at A and D, Fig. 104, and also at and B, as in the former case, and join up the standard cell in circuit with a resistance-coil to the terminals A and D, and unplug the resistance-coils until a convenient deflection is obtained, say 15° ; note the sum of the resistances in circuit, including that of the battery, galvanometer, resistance-coil, and connecting wires; now change the cell for another, and by unplugging the resist- ance-coils bring the needle again to the same deflection, 15": having again found the total resistance in circuit, the rela- tive electro-motive forces of the two cells will be directly proportional to these resistances." The electro-motive force thus determined is comparative ; that is to say, the result given by one battery may be com- pared with that obtained from another, and assuming- any given cell as a standard, the value of each, as compared therewith, is obtainable. The electromotive force and internal resistance of a bat- ^^?^^ "force^Tnd tery which is callable of fusing a fine platinum wire, mav '°;«™a' "distance >■' ■*■ ox ^ -^ ot quantity bat- be found in the manner described in The Course of In- '"y. •254 ■•:fnictwn ill Military Engineering, page 140, paragrapli o03, ftr Grove's battery. jMr. .Vbel proposes to lit up a simple aiTaiigeineut of tliermo-galvanometer aud resistauee-coils, suitable for tliis purpose, ou his testing-table. (See page 23C.) Tests of system Havliig carefally tested the several parts of the appa- whnie. ratus, both mechanieally aud electrically m the mautier de- scriht'd. they may be put together precisely in the combi- uatiou iu which they are to be submerged. When elec- tricity is to be theiguitiiig ageut the system should be agaiu tested electrically, as a whole, for insulation, conductivity, aud electrical resistance. The results thus obtained would at once indicate whether the whole was iu working order or uot, and would be strictlj' comparable with the informa- tion obtain I'd by similar tests, applied at any period after the mines had been submerged. A careful record should be kept of the results of all of the electrical tests applied, as by preserving the electrical historj", so to speak, of any combination a defect in its electrical condition may be readily discovered, aud the nature, position, and extent of such defectindicated with a considerable degreeof certainty, without the necessity of raising the mine out of the water, or in any way disturbing the arrangements employed. Alter a uiiue has been submerged with electiic cable. &c., complete, it should be immediately tested to ascertain tlmt all is right, aud similar tests should be applied at in- tervals to ascertain that the charge remains dry, aud, in consequence, efBcicut; that the electrical resistance of the fuse is such as to indicate certainty of ignition ; that the insulation and conductivity of the electric cable remains good, and that its electrical resistance indicates a state of efficiency. The nature of the tests applied to ascertain these points depends upon the nature of the combination in which the mine is arranged ; that is to say, whether it is ou a circuit closing or circuit-breaking system, whether the cir- cuit-closer is ou a branch, or otherwise connected, and the nature of fuse used. The amount of accuracy with which the information, derived from electric tests, may be ob- tained, depends entirely upon the manner in which the several electrical circuits are connected up, and the nature of the tests to be applied must be determiued accordingly. i.sttoasreitaiQ The arrangements for testing to ascertain whether a that the cbai-ge is *- '=' ■I'T charge is dry, at any i^eriod after submersion, are showu in Fig. 106. A plate of zinc is introduced at the point ((() within the charge, in connection with the conductor of the electric cable, and between the fuse and the shore, while a Ti'sts after ni'-isiou. :oo plate of uaibon (&) is conuected \vitb tLie electric cable, be- youd tlie fuse, to form the ordinary earth couuectiou of the system at that point, and a copper earth-plate (c) is used at the home end of the cable. Taking advantage of the fact that if two plates, of suitable metal to form a voltaic bat- tery, are placed in salt water and connected by a metallic conductor, a battery is at once formed, capable of producing Fig. 106. f ^\ f considerable deflection on a moderately delicate galvan- ometer; the combination shown in Fig. 106 has been made available for testing purposes. This arrangement has been termed the " sea-cell." The length of the conductor be- tween the plates is, within reasonable limits, (up to two or three miles,) no practical impediment to the action of the current set up, as far as the deflections produced on the needle are concerned. Let us suppose in the first instance that the eliarge is dr^', and the insulation and conductivity of the cable good ; under these circumstances we sliould have a sea-cell, composed of a copper and carbon pair, (c aud b,) which would iwoduce a deflection on a galvanome- ter [g) in circuit, in a certain direction, say from right to left. Suppose now that the charge had become wet by leakage through the case : under these circumstances the zinc plate («) would come in contact with the salt water, and a sea-cell, composed of a copper and zinc pair, would result ; this would give a ditferent deflection on the galvan- ometer, and the needle would swing in the opposite direc- tion, or from left to right. This would at once indicate that the charge had become wet. Again, suppose that the insulation of the electric cable; s^='-':«'" '■-• <«' had become damaged to such an extent as to expose the copper conductor. Under these circumstances the sea-cell would be formed of two copper plates, one the permanent earth-plate, the other the exposed copper conductor, and a ' insulation of ciibl*- -256 eertain definite deflection would be oliser ved. This deflection would differ in character from that produced by the copper carbon sea-cell, which would exist under the conditions of <;()od insulation, and would thus indicate a chaugo iu the electrical conditions of the combination, at the same time giv- ing such information as to lead to the supposition that an injury to the insulation of thecable had occurred. If the earth- plate at the home end of the cable were changed from copper to zinc, or to carbon, a fresh set of combiuatious would result giving different indications on the galvanometer, and these would provide the means of determiuiug, with considerable accuracy, the reason for the change in the electrical condi- tions of the combination which they indicated. In this way the fact that a lealc existed in the insulation of a cable might be discovered. Its exitent and position might subsequently be approximately ascertained by tests to be hereafter described. Sea-cell test for Should the coucluctor of an electric cable be fractured contiuuity. withm the insulation without injury to the latter, the fact would be ascertained by the sea-cell test. In such a case the contiuuity of the conductor being destroyed no deflec- tion on the galvanometer would result. Want of conduc- tivity or inefficient connections iu the fuse would be simi- larly indicated. Disturbing in- In tcstiug IU this maimer with the sea-cell, certain dis- fluences to sea-celi -,.^ -, • -, ii--,^ f'st. turbmg innuences occur, which must be obviated as far as possible. For example, the carbon earth-plate (b) beyond the charge becomes ijolarized, and acts in opposition to the current produced by the copper-carbon sea-cell; in order to obviate this it is necessary to depolarize the system, by the application of a short current of opposite sign from a few cells of a voltaic battery, to bring the plate to what may be termed a neutral state, under which circumstances alone it is iu a condition to give a correct deflection on the galva- nometer. The exposed metallic conductor of an electric cable becomes similarly polarized when subjected to the passage of a continuous battery current, and it must be depolarized by similar means. The polarization of the car- bon plates of any voltaic battery, into the composition of which this metal enters, is very rapid. The moment the battery-circuit is cl sed, the carbon plates become polarized, and much care and dexterity is required to depolarize them, when making the test for the internal resistance of the bat- tery, as described at page -51. Unless they are carefully depolarized, the internal resistance of the battery, found in tliio manner, will appear to be very much larger than it really is. It will be, in fact, the resistance after the current has circulated, aucl not the resistance when the battery cir- cuit is first closed. The following demou^ration of the general principle on which the liquid resistance of a battery is calculated by the differential galvanometer, shows that the result fouud by that method is not correct in the case of batteries in which the electronegative plate is carbon, or any other element which assumes a different degree of polarity according to the altered resistance in the circuit in each case. Let g be the resistance of each coil of the galvanometer. s be the resistance of the shunt. X l)e the resistance of the battery. ic be the resistance unplugged. e be the electromotive force when the current passes through one coil. Ci be the electro-motive force when the current passes through two coils. c be the current in the first case. Ci be the current in the second case. By Ohm's law we have (1) and X + — -^ c But Ci only equals tt as it passes through twice as many coils to produce the same deflection. e 2 Ci X + -1^ X + 2 -111- + »' 9 + s (j + s (3) Now if e = gj as is the case in the Dauiell battery or others in which the electro-negative plate does not polarize rapidly, from equation (3) we get + s . ^ (J + s But if e were not equal to e„ as would be the case when the electro-negative plate was carbon, equation (4) would not hold good. In such cases the currents would have to be measured by the swing of a needle or the fusion of ijlatiuum wire for the establishment of equations (1) and (2.) The outer-) uotectiug covering of the form of electric contact of gai- l o . ^ vamzed protecting cable used for submariue-miuiug purposes, being partly wires. 17 formed of "alvanize'd iron wires, any aeeidental contact of tliesf, introduced into the system, would produce a copper- * zinc sea-cell, and give a deflection similar iu character to that produced by the zinc plate in a wet charge. This might be obviated by substituting a carbon plate, within the charge at («,) Fig. 106, for the zinc, and [)uttiug a zinc one at {h.) The plan hitherto adopted in the ex()eriments conducted at Chatham has been to place the carbon plate outside, because it is not liable to be decomposed, by the passage of a continuous current of electricity through it, vrhen immersed iu sea water. Value of eiectri- ^y\i elcctrical tcsts, made at anv period after the submer- cil testy depends ' * i n,i comp.irisoD. j,ion of a charge, are simx:)ly comparisons with the elec- trical conditions necessary to practical working perfection, which, to insure success, must have existed when it was first placed iu position. Any deviation from these conditions ■would indicate iaults iu the system, and woukl be deraou- strated by the difference between the results of the tests obtained, as compared with those which ought to exist in a perfect combination. It is very essential, therefore, that a strict record should be kept of all tests applied to each mine and cable, with the results obtained. Trstin-arrange- Different tcstiug arrangements must be adoiited according mentsfor platinum -z^ o a o iind tension fuse to the systcui ou which thc mines are to be tired. If a differ. platinum wire fuse and circuit-breaker be employed, as in Fig. Ss, page i'lo, a large number of Danielfs cells may be employed without danger, and every part of the system may be tested directly, induing the fuse and circuit breaker beyond it. If a high-tension fuse and circuit-closer, ar- ranged as in Fig. S'J, page 21.j, be employed, a small num- ber of DiUiiell's or some similar cells must be used with a very sensitive galvanometer. The system may be tested through the fuse on the direct circuit aud^to earth, but the continuity of the electrical connection to the circuit-closer, ou the branch, can only be ascertained by actually sending a boat out and closing the circuit by ruuniug against it. i..rMvte*"; -Tor'dis^ Sliould au iujury to the insulation of the electric cable, r.neiy.if position either between the fuse and the shore, or bevond and be- ot tault. " ^ tween it and the circuit-closer, be indicated by means of the sea-cell test, when the platinum wire fuse and circuit- breaker is used, its position may be discovered in the man- ner shown in Fig. 107. The positive pole of the battery (c z) being jmt to earth at (c,) the negative pole should be attached to a differential galvanometer, one terminal of which should be coniiected tothedefective cable {I,) while the other should be connected with one terminal of a set of 259 resistance coils (r.) A well insulated cable {I') of knowa electiical resistance sboukl be attached to the other termi- nal of the resistance C(iils (r,) and should be paid out to J^g. 107. ©H'liWiW reach the circuit-breaker attached to the defective line. The electric cable attached to the circuit-breaker should be disconnected therefrom, and attached by a temporary insu- lated joint or Mathieson's connector with the line (?'.) Sup- pose the defect in the line to exist atthe point (/,) it is easily seen, on reference to the diagram, that the current from the battery would divide itself between the two circuits open to it, returning through the leak at (/) to the earth-plate (e,) and if the resistance in these two circuits were ecpral, the needle would stand at zero^ and this ec[uality would be es- tablished by unplugging the coils (r.) Let a? = the distance, in terms of electrical resistance, of the fault from the galvanometer {g,) y=the distance from the fault to the circuit-breaker, L=the total resistance of the circuit (l,) including fuse and electvic cable up to and connecting the circuit-breaker, (this should be ascertained by previous tests Avheu the cable and connections were in good working order,) Li = the resistance of the line (I',) and E=the unplugged resistance in the coils when the galvan- ometer needle stands at zeio. In this way we obtain two equations, viz : and X = R+Li-I-^ from which the values of x and y, in terms of electrical resist- ance, which would be readily convertible into length, would be easily determined. Should the fault exist near the home- end of the line, it would be necessary to place the resistance, coils in connection with the same coil of the galvanometer as the defective line, in order to make the two circuits bal- ance, the resistance of x being necessarily small under such circumstances. In this combination it will be observed that the electrical resistance of the defect is ecxually divided between the two circuits, and its effect does not in any way Earth cniiiiec tion iu top of (.'ir cuit-l)n?aker I'ni convenience of 260 disturb the conditions uecessiiry to the truth of the equa- tiony employed. A large munber ^)^ liuiie uiimber of Daiilell's cells raay be used in makiug of DaniellM cells ' ^ i:> maybe used with this tcst with the platiuum wire fuse, without any chance of platinum fuse. an accident. In working a circuit-breaking system in con- nection with a platinum wire fuse, it would be convenient to keeji an electric cable, from the electrical room in the fort to the vicinity of the mines, permanently in position, for the tests described. This line would also serve for tele- graphic communication, w'hich would in the majority of cases be required under any circumstances. In order to render this system for the discovery of the position of a fault effective, some means must be adopted testing. by which a connection with the electric cable in the vicin- ity of a circuit-breaker may be rapidly made. The circuit- breakers of a. system would generally be xvvy close to the surface at low Avater, and a little e.xtra length of electric cable, sufficient to enable its extremity to be brought well above the surface, with a joint capable of being readily opened — one of Matbieson's connectors, for example — would, answer every purpose. This and other testing arrange- ments might be much facilitated by arranging the connection with the earth-plate in the top of the wooden jacket of the circuit-breaker. Experiments should be made to test this system, and to bring it into a good practical working form. Biavier's form- Whcu uo rcturu wire, as (I',) Fig. 107, is used, the position ula for discovery 7 \ 7/ o 7 7 x of extent and post- and extcut of a fault may be determined by means of Biavier's tion ot a fault. ' formula, as follows : Let {a &,) Fig. 108, represent the line, (a) being the home and {b) the distant extremity, and sup- pose a fault of unknown electrical resistance to exist at (c.) Let ,)■ = the resistance of the portion (a c) from the home Fig. 108. a> c ■I end to the fault ; let y = the resistance of the portion (c V) from the fault to the earth connection of the circuit-breaker; and let z = the electrical resistance of the fault itself. Let E. = the resistancie of the line and fuse when in good -working order, derived from previous experiment ; let S = the resist- ance of the faulty bi"ie when to earth at {b-,) and let T = 261 tbe resistance of the faulty line when insulated at (&.) From these we derive the following equations;: X + 2/ = R (1) x+z — T (2) X + 1^ = S (3) From (1) %j — 'Si — x (4) {2)z = T~x (5) Substituting these values in equation (3) we have I\Iultiplying both sides by the denominator, we get (R + T) X — L'^-' + R.T — (E + T) j + .i^ = (R + T) S — 2a;. S (7) From which we obtain R.T — a^ = (R+T).S — 2^''S (8) and 2^ — 2 S . .T + R . S + T . S — R . T = (9) : • *■ = S ± a/ S' + T.R — T.S — RT 8 (10) or .r = S ± -/ (R — tt) x (T — ti) (11) Substituting this value of .r in equation (3) we have Z = T — S± V(R— ti) X (T — S) (12) From these equations the values of ,r, y, and i, in terms of electrical resistance, are readily obtainable, and the posi- tion of the fault may be discovered by converting the values of a; and y into length. If the value of x has been previously obtained, by means of Varley's loop-test, that of z is readily obtainable from equation (2.) In making tests of this nature much dexterity and previous practice is required, as well as considerable electrical skill. The difficulty of the problem arises from several causes, # described by Mr. CuUey as follows : " 1. As the metallic conductor is exposed it forms gal- cabie current. vanic elements or batteries with the iron sheath and salt water, so that a positive current flows from the cable, through the testing galvanometer, to earth; this is steady and con- stant if the cable is not disturbed. "2. We have to deal with two unknown resistances: that of the wire itself and that between the esposed part and the earth ; the first is constant, the second very variable, because — ' " 3. The action of the current alters the resistance at the point at which the metal touches the water, by coating it with substances which difier in conductibility ; and, at the same time, the apparent resistance is still further altered by the currents of polarization set up by these substances. 262 '• The action which talccs phice can be shown by phxciiig a piece of cable in a glass filknl with salt water and applying- a ciuTcnt from 40 or 50 cells, one pole of the battery being connected to the iron sheath, the other to the copper condiicting wire. The portion of the cable couaected to the zinc gives off a stream of hydrogen, while the other becomes coated with a chloride of the metal. Thus, if tbe negative pole is connected to the conductor and the iiositive to the sheath, chloride of iron is formed ; and if th^ connections are reversed, chloride of copper is prodaced. " Let us now connect a galvanometer to the cable la such a manner that the current from the cable-battery of copper and iron in salt water, called the 'cable-current,' shall deflect the needle to the r'ujht ; the iron element being, of course, always on the earth. < " If a negative current is now sent into the cable, its direction coincides with that of the cable-current, and does not affect the direction of tbe deflection. " But the superior force of the testing-battery overcomes the cable-current and polarizes its elements. Thecoitper wire becomes coated with hydrogen, the iron sheath with chlo- ride of iron, so that when tlie testing-battery current is cut off and the cable-batti>ry is again free to act, its action is reA'ersed, and tbe needle moves to the left, under the influ- ence of the current of polarization. " But the hydrogen gradually enters into combination and disappears from the wire, the polarization ceases, the needle returns toward zero, passes it, and finally takes up its former position to the right, under the influence of the cable-battery in its normal state. ecial method of test is to produce this condition. " The test for distance is best made witli a differential i^f°^2,tljet^it. galvanometer. First ascertain the ap[)roximate resislance in the ordinary way, and clean the exposed wire from the dirt and the salts with which it will be coated, by applying a zinc current for several hours, occasionally reversing it to get rid of any deposit of soda which may occur. The sur- face will be roughened l>y the redepo.sit of the copper which has IxM'n dissolved, and will therefore more readily throw off the hydrogen evolved by the zinc current. Next apply a positive current for the purpose of coating the .wire with chloride of copper, and finally test with the negative cur- rent. The action of the current set up by the chloride of copper will uiake the resistance appear less than it really is ; but as the chloride is gradually reduced by the testing- current, in the manner which has just been explained, the resistance will appear to increase, moment by moment, and the resistance-coils must be lengthened, unit by unit, to balance. the resistance of the cable, so as to keep the needle at zero, until it passes over to the opposite side suddenly, under the influence of the change of polarization, calised by the cofiious evolution of hydrogen which will follow. The increase of apparent resistance, and the consequent move- ment' of the needle, is slow and gradual so long as the hy- drogen is employed in reducing the chloride, but after the reduction is complete and the chloride has disappeared, the increase in resistance is enormous and almost instantaneous. Unless, therefore, the resistance of the cable has been care- fully balanced, so as to follow the variation of the current throughout, the test will not succeed, because the neutral condition lasts too short a time to permit the adjustment of the resistance-coils. " In any case a certain dexteritv is required, which can mucIj dexterity ^ '' . re(|uirpd ill mak- only be obtained by practice; but fortunately the practice mgie,istance-tL-»t may be had conveniently upon an artificial fault, or a piece of insulated wive in a tin can filled with salt water and connected to a set of resistance-coils. Induction does not 2G4: affect the test, and as iu any ordiuary cable the iiisniatiou is practically perfect, its resistance can be represented as accurately by a rheostat as by an actual cable. The higher the tension of the battery the less does the opposing current of polarization affect the result, for its force seldom exceeds two or three cells. The measureuieut is therefore made with a battery of as high a tension as can be conveniently procured, CO cells or more. fauifdlpendf on " ^lic bchavior of a fault varies with the length of wire posed" °' ^'™ "^^ '^^1'°®^*^^ ! a short fault polarizes and depolarizes very rap- idly ; its changes iu resistance are correspondingly rapid, and its resistance great. If the exposed wire is long, the changes are slower and more readily observed ; the resistance of the fault is also less. " After haviug well studied the changes of the fault itself, make au artificial fault by placing a piece of the cable core iu a tin can filled with salt water, aud alter the length of the exposed wire until it behaves iu the same manner as the cable, aud then find its resistance, which will be very nearly the same as that of the real fault ; so that the distance of the break will be the tested resistance of the cal)le less that of the artificial fault. "It is a couvenient plau to form a table of the resistance of exposed wire of various lengths with 6 aud 60 cells, adding resistances by a rheostat, using the negative current and allowing the exposed wire to take up its maximum re- sistance. The tests with the 6 cells will be always higher than those with GO, that is to say, the resistance of the fault will always appear higher when tested with the lowtir power, aud the differeuce between the apparent and real resistance will also increase gradually, as the length of the cable itself, or the resistance added by a rheostat, increases; the length of exposed wire being coustant. "If a cable is found to give, with 6 and CO cells, two results corresponding to some two in the table, it is probable that the length and resistance of the exposed wire is the same as that of the aitificial fault used in the formation of the table, and therefore that the resistance bet weeu the test ing station and the fault is equal to the resistance added to the artificial fault. p.rsnuai equa- " go much, howcvcr, dcpcuds upon the manner in which tiOD ot observer. ^ the tests for the table were takeu, or u-pou what ^^■e may call the ' personal equation' of the observer, that e\'ery one should form a table for himself. The cable must be treated iu precisely the same manner as the artificial fault, and therefore no table will be perfectly correct unless it is made 265 just before the cable is tested, in order that the precise manipulation may not be forgotten." The above remarks are made with reference to the tests of submarine cables of considerable length, and though there is not so much difficulty in testing the short lines used for submarine mines, still the same conditions exist and must be guarded against and taken into consideration on all occasions. Unless this is done, anomalous results, caused by the disturbing influences above mentioned, ^Yill be obtained, and it is necessary to guard against their ac- ceptance as due to defects of insulation alone. lujurv to the insulation of the electric cable necessarily insuiatioa in- *^ jured at poiQt:^ occurs at those points where it is subjected to friction, aud^^-iiere motion oc- in practice the points where it is attached to the sinker or mooring a^iparatus, where it enters the case and where it joins the circuit-closer, are those where injury has been most frequently found. This is due to the slight motion produced by the action of the water,' and special precautions must be adopted to protect the cable at such points. The high electrical resistance of the tension fuse, com- T''"''^ of combi- ^ ' nation when a hined witli the necessitv for using a very small batterv-cur- hiswension fuse ° -^ •' is used. rent in connection with it for testing purposes, renders it necessary to adopt a totally different arrangement for testing when a tension fuse and circuit-closing system is adopted. If used with the circuit-closer on a branch, as in Fig. 8!), p. 21.J, any test current employed would show a certain permanent definite deflection on the galvanometer, due to the passage of such current through the fuse itself. Any increase in, this deflection would indicate a fault in the in- sulation of the electric cable, and the extent of such fault would be roughly determined by the amount of deflection of the needle. Its position could not be determined in the manner described for the circuit-breaking system, even with very delicate instruments, because the nature of the fuse precludes the use of any considerable battery power for testing purposes, and there is a permanent passage for the current to earth, through the fuse, at a point considerably below the surface of the water, where it would be impossible temporarily to iu.sulate for testing purposes without bring- ing the entire charge to the surface, a proceeding entailing much trouble, and to avoid which is one of the principal objects of test of this nature. A want of conductivity in the conductor of the electric cable would be indicated by a cessation or considerable diminution of deflection in the galvanometer. To test the conductivity of the portion of the electric cable between 266 the cluirge find circuit-closer ou a braueli, as in Fig-. 89, it would be necessary to send a boat out aud close tlie circuit by ruunini;' apiiiist it. If a circuit closer were employed beyond the fuse, a defect in tlie electric cable would be indicated by a deflection of greater or less amount on the galvanometer. If a fuse of Ligh electrical resistance were employed in such a combi- nation, it would be extremely difficult to detect a -eH. the latter to see the operation owing to the darkne.-s or fog. Where electrical igniting apparatus is suspected, the banks of the river or roadstead would, if possible, be searched with a view to iuterce.pt the wires. The advanced booms and nets, if any, would be blown up, or, if secrecy be an object, cut, or turned by boats rowing round their shore ends. Lines of boats would then advance in couples, towing small hawsers between them weighted about the center, with a view to sweep the suspected waters for buoyant mines and circuit-closers, their own light draught giving them sutticieut immunity. When a submarine mine or circuit-closer was thus caught, a signal would be made to other boats to avoid the locality, while the two boats concerned, crossing the ends of their hawser, would cautiously pull the mine up to the end of a long outrigger, (or davit,) and, carefully cutting the mooring rope, tow the mine into shallow water. Other lines of boats might follow, dragging small grapnels, in the hope of intercepting the wires of such ground mines as were uui^rovided with circuit-closers. Tlie channel being thus partially cleared, small steam-vessels might advance in pairs, dragging between them large hawsers, weighted with chains and armed with grapuels; while pushing some sixty feet before each vessel a submerged framework, armed with hooks and nets, extending below the keel and beyond the broadsides, which might intercept aud explode harm- lessly the usual nlechauical submarine mines. Even with very slow speed aud every precaution great danger would be incurred for steam-vessels iu the case of circuit-closers 272 attached to ground mines, as tlie former might be dragged forward by tlie projfctiug frame and close the circuit when its mine was actually under the bottom of the shix). The breadth of channel so cleared should be carefully marked to prevent advancing vessels passing over uusearched ground. It is obvious that such operations could only be undertaken in undefended and unguarded waters. And it is worthy of remark that most of the United States vessels destroyed by submarine mines were lost wliile advancing in waters pre- viously dragged or otherwise examined by boats. The introduction of electrical apparatus increases the difficulty of clearing channels, and too much precaution cannot be observed in uavigating waters which are supposed to have beeu defended by submarine mines, even after they have been most carefully searched. If advanced booms or nets are not used by the defense, barges or rafts, with submerged frames to give deep draught, mightbe employed to drift overthesus- pected waters, with a view of exploding the mines by con- tact, should the conformation of the river or roadstead admit of it. If the tidal stream be very strong, light grap- nels might be dragged over the bottom by these drifters, with a view ol fouling the electrical cables or mooring ropes should the nature of the ground favor the proceeding. It is evident that a rough or rocky bottom, or the employment, by the defense, of a heavy chain laid across the channel in advance of the mines on hard gi-ound might convert the grapnels into anchofs, and thus defeat the primary object of exploding self acting mechanical mines by contact. In many places, in the Medway for example, a heavy chain would soon sink into the mud, and become as far covered as to offer a small chance for catching the grapnel: under the same conditions, however, the electric cables would equally sink into the bottom and be less likely to be fouled. projectingframes In their Operations against the confederates, the Federal or nets carried in . " . ^. ,. i i ' • advance of a ves-neets m mauy cascs used projecting frames and nets, in front of the bows of the leading vessels, in which the sub- marine mines, arranged for mechanical ignition, were in- tended to be caught without danger to the ships, l^otwith- standiiig this precaution several vessels were sunk and damaged. In many cases the charges were not fired at all, but this was due more to the failure of the igniting apparatus than to any special value attaching to the mode in which the machines themselves were caught _; with the more effi- cient means we now possess for finding mechanical mines, combined with the vastly increased size of the charges pro- posed to be employed, it is probable that tljismode of clear- ing a channel would be a far more dangerous and difficult operarion: the mines would be fired with far ;;reater cer- tainty, and their radius of destructive effect would be so much increased as to lieeessitate a frame, extemliug to a much greater distance in front of a vessel than those usi^d in the ox)eratioiJS alluded to. In the case of mines fired by electrical agency, the ilauucr to a vessel using a projecting fender would be still yiHan/r if circuit closers, in connection with grcjimd mines, were to be attacked. In such a case the circuit-cl i>er only would be caught by the fender, and the vessel would be more or less over the actual mine, when the collision, with its con- sequent explosion, would take place. Fenders of this nature should, in all cases, be constructed to extend to as great a depth as possible below the water level, so as to catch mines and circuit-closers not only near the surface but to a considerable depth below it. The cour-e adopted by the Federal fleet, in searching channels for submarine mines, was first to send ibrward boats to drag for them and to follow the boats np with ves- sels fitted with fenders of the nature described. This system seems to be that best calcidated to instire success. The following mode of operation, which mav or mav not Sog^e-ti"n vn ^ ^ ' V. ,iig a^g oi train be capable of practical emplovment, is siiciie^ted for the moo''''-^ fi"ii ^i- consideration of naval and artillerv authorities. It consists ^earchinz fir in simultaneously firing a couple of mortars, pointed in such a manner as to cause their shells to diverge from each other, by electricity, using very small charges of powder, only just sufticient to give a range of 100 or 3()i) feet : and having pie- viously attached a chain to each of the shells, and another con- necting the two shells together, the effect would be tu cast the chains out and inclose a certain area. By hauling on the two extremities of these chains, any mine within that area would be caught and proliably injured or destpoyed. In certain parts of the world, at Bermuda for example, the sea water is so extremely clear that, in fine weather, such an object as a submarine mine would be easily distinguish- able from a vessel's tops at a considerable distance and at a j;reat depth; in such a case this mode of clearing a channel, by throwing out a chaiu attached to a couple of shells, nii-ht be successfully employed. Very clear water would be a favorable condition, as regards the search f(jr sulnnariue mines, whatever mode of proceeding may be em- ployed. In this, as in all operations of a similar nature, the same difficulties, as regards interruption caused by the fire of guns defending the system of mines, would still exist. 1^ (Jleaiiiifi acliaa nel by siibmiirioe Hxtjlosiniis. ■274 To be eftcctive it is probable tliat a specially fitted vessel and a special crew would be retpiired. Such an operation would be comparatively easy if the uiortars were fired from the shore or from a vessel anchored iu a harbor in smooth water, but it must be borne in mind that, to be eifeetive, it should be capable of being used iu moderately rough water and from a vessel uot necessarily at anchor. Another method, which has suggested itself iu the i^ourse of experiments carried on at the school of military engineer- ing, Chatbam, during the autumn of 1S70, is to fire large charges of gun-cotton in positions which are supposed to be studded with submarine mines, with a view to destroy- ing any charges which may be within the radius of explo- sive effect; to proceed, in point of fact, on the same princi- ples which have been found etfectual in attacking a laftd fortress defended by counter-mines. The experiments made last autumn demonstrated that a charge of 431^ pounds of gunJ:. The corvette was sunk, but nothing was ever again heard of the torpedo-boat. This was the only successful attack out of five attempts made by the confederates with boats of this nature, and the results were so discouraging that they turned their attention to the use of ordinary ship's boats for this service. pedMsHned *To 'T^"' I'esults as regards ship's boats carrying torpedoes ou ord'iuary^coDsmic'*^"'^'-''^^^'^^ ^^ spars, to be pushed out and fired in close *'""■ proximity to a vessel's hull, were more satisfactory. Several steam-1-aunches were adopted for service in this way by both Federals and confederates. Their general arrangements con- sisted of one or more long spars, to the extremities ot each of which a torpedo was attached, carried in such a way as to be readily pushed out from the bow of the boat imme- diately before the absolute moment of attack, the charge being fired by the percussion of a self-acting mechanical fuse ou the hull of the enemy's vessel, or by means of an arrangement fired by a trigger line ; this latter combination was generally employed by the Federals. The confederate torpedo-boat " Squib," which attacked and so seriously dam. aged the United States frigate " 3Iinuesota," lying at anchor iu Newport News, at 2 a. m. ou the morning of the 9th of April, 186J:, TN'as a steam launch fitted in this way. A very more satisfactoiy. good aci'ount of this opcratlou is given in Captain Harding Stewart's Notes onSiiintarinc 2Iines. The torpedo-boat, with which Lieutenant Gushing, of the United States Navy, suc- cessfully attacked and destroyed the confederate ram "Albe- marle," which was, at the time, alongside the wharf at Plymouth, eight miles above the mouth of the Eoanoke Iviver and carefully protected by a strong timber boom and other obstructions, was an ordinary man-of-war's steam- launch. A good account of this very daring enterprise, which was carried out at 3 a. m. on the 2Sth of October, ISGJr, is given in a book entitled Siibmuruie Warfare, Offensive and Defensive, by Commander Barnes, United States Navy, page 142. In this latter work, at page 151, there is also a very good account of the United States torpedo-vessel 277 "Spuyten Duyvil," of 200 tons, especiallv designeil for use . sp»yieu Dny- ». / 7 L ^ o ^,j^ construction With an outrigg-ei' torpedo to be pushed out, below her water iisapproved by , ' committee on nne, through a water-tight opening in her bow. This vessel floating obstmc- is very completely fitted up, but no opportunity has liitherto occurred of trying her against an enemy's vessel. The con- struction and general arrangements of the "Spuyteu Duy- vil " were condemned by the committee on floating obstruc- tions, as may be seen from the following extract from their report, page 138 : " In the beginning of 1865, the plans of 3Ir. Wood's outrigger torpedo apparatus were ofiered to Her Majesty's government, but a careful examination con- firmed the opinion originally entertained as to the too com- plicated nature of the machinery. The arrangement for giving lateral motion to the outrigger is obviously unneces- sary, inasmuch as this may be accomplished by the use of the helm ; it is also dangerous, because it renders the out- rigger liable to get across the stem at high speeds, when the spar might snap, the torpedo being thus under the bottom. The separation of the torpedo from the outrigger before exploding, as proposed, would involve the danger to the operating ship of advancing within the sphere of its destruc- tive action when the explosion takes place. The committee therefore fully concur in the opinion expressed by Rear- Admiral A. Cooper Key, C. B., then captain of Her Majesty's ship 'Excellent,' that this. plan 'is not worth adoption, or even of trial with a view to adoption in our Xavy.'" In addition to this vessel the United States possessed a number of steam-launclies, each carrying one 12-pounder boat how- itzer, and a crew of 15 men, fitted for outrigger torpedo service, the torpedoes being carried on spars resting on crutches, and ready to be run out and fired at short notice. Six low free-board monitors were also similarly fitted. No attempt has been made in this country to fit up any special vessel, such as the '' Spuyten Uuyvil," for offensive torpedo service, our naval authorities being, it is understood, of opinion that such operations as the attack of a vessel by a torpedo-boat would be similar in character to the cutting out of a ship at anchor in an enemy's harbor, which was so successfully performed during the French wars in former times; they therefore propose to adopt boats and small vessels, of classes already existing in the Eoyal Xavy, for this service. The following description, extracted from a book entitled " A Short Course of Ulectricity," by Lieutenant (now Commander) Fisher, R. N., late instructor in electricity and torpedoes on board Her Majesty's ship " Excellent," gives a good idea of the arrangements proposed as most suitable for the purpose required. 278 rhiiiigs of Ex- u^ iicnci'iil descriiitioii will be giveu of the manner in lauiichi.iitoipcao whicli a slcaDi-luuncli aud aiff are fitted in Her Majestv'.s I rvK'i.-. sliip '■Excellent"' for torpedo purposes, as shown iu Fig. 100, both giving most successfnl results. " The fore part of the boat is covered over with a canopy, which is spread over a fore-and-aft pole, resting on two wooden crutches, and is tightly laced down to a foot-board that extends round the fore part of the boat, just inside the gunwale, to allow the crew to work outside when required. At about two feet abaft the stem a projecting cross-piece is .secured to l.ioth gunwales, having at either end an iron crutch, in which rests the outer part of the torpedo-pole when not in use, and which serves as a fulcrum for the pole when rigged out; a pin across the crutch prevents any chance of the pole being lifted out of it. An upright, similar to a rocket stanchion, ships into a step on either side of the boat, outside of the gunwale, and is secured to it by iron clamj)s ; these stanchions, which are about six feet in length, have attached to, and projecting from, their exterior sides, an iron rod, the torpedo-pole working between the iron rod and the stanchion, so that when the heel of the torpedo-pole is triced up to the head of the stanchion, (thus rigging it out and at the same time submerging its outer extremity,) the pole is confined between them, and thus any lateral movement is prevented. " The rigging-ont rope of the torpedo-pole is led from the stern-sheets through a small block at the head of the stan- chion, and made fast to the pole about a foot from the heel. A back rope is secured to the heel, for the purpose of easing out the pole, and of rigging it in again when required. AVhen the poles are rigged iu, their heels rest on crutclies on the outside of the after part of the boat. The height of the stanchion, its distance from the fulcrum-crutch, and the length of the pole, de])eud on the depth to which the torpedo is required to be submerged and on its charge ; but appended are the dimensions of the " Excellent's " torpedo-gig and fittings, constructed to admit of 50 pounds of gunpowder, submerged nine feet, being fired with perfect safety to the boat and its crew. Such a charge so placed, we know from experiment, would inflict irreparable damage on any ship as at present constructed, if exploded in contact with her bottom ; and as it is probable that the horizontal section of its ellipsoid of destruction at the depth of nine feet would not be less than a circle of five feet radius, great mischief would doubtless be caused by it even when not exploded iu perfect contact, but withiu the assumed five-feet limit. 279 "The 'Excellent's' steain-launcli, fitted up in a similar manner, carried a torpedo charged with 100 pounds of fine- grained powder, the only exceptions to the torpedo gig ar- rangements being that it was submerged to a depth of 10 feet, and the torpedo when in position was 25 feet (instead of 17^ feet) from the stem, in the direction of the pole. Ifo water was shipped on the explosion being effected, nor was there the slightest inconvenience of any sort experienced. Dimensions of torpedo (jig and fiitiiujs. Length of boat 30 feet. Beam .5 J feet. Length of canopy lOf feet. Distance of cross-piece from stem 2 feet. Length of poles 28 feet. Thickness of butt-end of poles IJ inches. Length of stanchion 6 feet. Distance from stanchion to the cross-piece in stem .J feet. Distance from after crutch to stanchion 10| feet. " Each stanchion is supported by two |-inch iron stays, one going to the opposite gunwale and the other supporting it in a fore-and-aft direction." Eear- Admiral A. Cooper Key, C. B., F. E. S., then di- rector general of naval ordnance, remarked upon the above apparatusand experiments : "Tliatit wouldbe rarely advisa- ble to risk a boat's crew for the purpose of using a charge of 40 pounds, which must be placed in actual contact with the bottom of the ship it is intended to di'stroj'. The uncer- tainty attending such an attempt must lead to failures. I consider that 100 pounds of gunpowder, or its equivalent in gun-cotton, is the least clianje that should be used." The use of such service-charges would involve a greater streugtli in the apparatus and longer poles. Fig. 109 is copied from the Report of the Committee on Description , . , , fitments. Floating Obstructionsin the following description as extracted from it; (a) shows the canvas covering, (b) the outrigger rigged in, (c) a stanchion, (d) the guide rod, (e) the fore-and- aft stays of iron, (/) the stays athwart-shlps, {g) the torpedo for 40 pounds of gunpowder or 10 pounds of gun-cotton ; {g') the torpedo for 100 pounds of gunpowder, and 25 pounds of gun-cotton ; the dotted lines showthe arrangement of boom recommendedby the committee on floating obstructions, the firm lines the form adapted for a charge of 40 pounds of powder only, (h) the foremost crutch, {h') the pin to retain the out- rigger in the crutch, (i) the after crutch, (Ic) the fore-and- aft mooring pole, (?) the securing screw of the stanchion, {m) the securing screw of the cross-piece, («) the step for 280 the staiieliion, (o) the secnriug clamp for the stauchion, (p) the foot-board, (q) the cross-piece,. (r) the topping-lift, (s) the iuhaul, (t) the outhaul, («) the coudnctiug wire. "Only one outrigger should be placed in position for action at a time, otherwise the first explosion might injare the other torpedo. "It would be -necessary to impart increased strength to these flttiugs to enable them to withstand the explosion of serviceable charges of 100 pounds and upward of gun- powder. In an experiment of this description material injury was sustained by the apparatus. "The dotted line thus — represents thecom- 15uted area of principal destruction of 100 pounds of gun- powder at the depth of greatest effect." Outrigger torpedoes are applicable for the attack of booms, pouton-bridges, vessels at anchor or moving very slowly, and similar objects. iiarvcys 98a Harvey's sea torpedo also belongs to the first class of torpedo: descrip- t • i /. i ■ - x- -rj. • fion. weapons, benig maneuvered trom a ship m motion. It is a joint invention of Captain Johu Harvey and Commander Frederick Harvey, E. K., and consists of a case (a) of B'o. IS B. W. G. sheet-copper, of the form shown in Fig. 110. This case may be made of any size ; the dimensions, as shown in the figure, are those calculated to contain a charge of 76 pounds of gun-cotton, or an equal bulk of other explosive. This charge would be sufficient to sink any vessel if fired in contact with her hull, and is of convenient size to work with facility from a ship's deck. The form adopted is similar to the machine called an "otter," used by poachers for fishing purposes, and its mode of proiralsiou through the water is identical therewith. Outside the sheet-copper, which forms the internal water-tight portion of the apparatus, is a thick wooden casing strengthened with iron plates, to preserve the former from injury. To the bottom of this wooden casing is attached a keel of iron, (Z>,) with a leaden covering on the lower side, to keep the apparatus upright while floating in the water. The weight of iron used is regulated by the speed of the vessel from which the torpedo is to be maneuvered, and it sliould be sufficiently great to sink the whole apparatus when complete with charge, &c. This capacity to be submerged at will is essential to the proper maneuvering of the apparatus, and, when the towing line is cut away, its effect is to sink the whole to the bottom, and thus prevent chance of injury to a friendly vessel. Lines are arranged, as shown at (c,) to enable the torpedo to be towed at an angle diverging about 15'= from the direction of 281 the course of the vessel from which it is worked. The towing liue is composed of several strands of galvanized steel wires over a hemp core, forming a l^-inch wire rope. The towing line passes through a ring in connection with the guiding ropes (c,j thence through another ring (d) on the stern of ^. ! 10. ■4 10 £leyatimv. the apparatus, and is connected with a buoy, arranged to prevent the torpedo sinking too deeply for subseciuent work during any temporary slackening of the towing line. A knot on the towing line prevents the buoy being drawn too closely up to the torpedo, but being beyond the uiig 282 (r7,) tlireetly the towins' line is cut at any point, the latter sliiis throiigli, and tlie torpedo itself is diseuL;ayed and siuks. x,.tureofexpio- Tlie charire of a'uii-eottou or other explosive is contaiiieil >n>- used. ^ ^ in two compartments within tlie sheet-copper case which is divided iu the middle. A loading hole, li inches in diam- eter, to be closed by a water-tight screw plug, is provided for each compartment. Mode ot fliicg-. The charge is arranged to be fired by means of a metal bolt (/) in connection with a sulphuric acid fuse. When the bolt is forced down it breaks a glass vessel containing sulphuric acid, which, falling on a chemical mixture, pro- duces heat and fires the priming of the fuse, which in its turn ignites the charge. The priming charge is contained iu a vertical copper cylinder, placed in the center of the torjiedo, and only divided from the two sections of the charge by the thin metal of which the cylinder is composed. The fuse i)iece. with firing-bolts, &c., complete, is carried sejia- rate from the charge, and only screwed into it just before the torpedo is launched overboard for the attack of a vessel. The firing-bolt is provided with a safety-key, passing through a hole iu the former, and till it is removed the bolt cannot be pressed down and the charge cannot be fired ; this key is drawn out by means of a line attached to it and veered out from the ship simultaneously with the tow-line. The firing-bolt may be arranged to explode the firse on any given pressure being applied; for this purpose a i^ressure of about GO pounds has been found to be convenient. The i^ressure required to withdraw the safety-key should be arranged at about 30 pounds. Pivoted on the bow of the torpedo are two levers {(j) and (/;,) one {(j) passing vertically over it toward the rear, the other [li) on the side of the apparatus which is most likely to come iu contact with the vessel to be attacked, always on the opposite side to the directing lines (c.) The lever {g) is arranged over the head of the fir- ing-bolt; on coming in contact with the bilge of a vessel, it would be pressed down, carrying with it the lever (t) and the firing-bolt, which would break the glass capsule containing the siili>huric acid, and thus fire the fuse and consequently exi)lode the charge. The lever [h) performs the same office when acted on by side pressure against a vessel ; when pushed in toward a topedo, it draws in a lanyard in connec- with the lever (/) and pulls this latter down, acting on the flring-bolt with the same result as before. Differentformsof Different forms of torpedo are employed for each side of the torpedo i-L-quived for each ^ide of vcsscl, the Icvcr (ft) bcuig alwajs SO arranged as to bc ou that side of that apparatus which, when floating in the water, is 283 away from the sliip from wliicTi it is maueuvered, the tow- liues being on tlie side nearest to the vessel. In order to maneuver torpedoes of this nature, the ship ^^j"'^''' °'™'''"''"" should be provided with a couple of drums, with brakes attached, on either quarter. One of these drums carries the tow-line, the other the safety-key line, which are veered out uniformly together; they should be of such dimensions as to hold a length of 2i0 fathoms of each. To atrack a ves- sel the proper torpedols launched overboard by its towing- line and gradually veered out to any distance required, usually about 150 yards, the vessel being kept in motion during the whole process. The brake is then put on, which has the effect of bringing the torpedo to the surface and carrying it along in a line parallel to the ship's course and diverging from her quarter at an angle of 45 degrees, and at any distance from 150 yards upward, that may be re- quired. A reserve of about 150 yards of line is kept on the drum for future use. The torpedo is visible from the deck of the vessel usiug it during the whole of this operation, and its approach toward the vessel to be attacked may be readily watched. As it approaches its object the safety-key is with- drawn by means of the line provided for the purpose, the brake is relaxed, and, the pressure on the towing-line being thus removed, the torpedo sinks for a moment, the brake is again applied just at the time when it is supposed the tor- pedo is under the vessel to be attacked, it rises in conse- quence of the pressure thus applied to the towing-line, comes in contact with the bilge, one or both levers are forced down and act on the firing-bolt, and the charge is fired. Commander Harvey has ai_>i)lied Captain McEvoy's circuit- Electrical mode -' '^ '■ ^ •' of ignition. closer for firing his torpedo by electricity ; he seems, how- ever, to prefer mechanic;il ignition on contact, in consequence of the danger of fracture or injury to be apprehended in veering out the insulated conducting wire, which must be made in the center of the towing-line and consequently be subjected to a considerable strain. He is of opinion, more- over, tliat electrical ignition would not, under any circum- stances, be so certain in its action as mechanical action. Experiments with this form of torpedo have been carried Most useful ap- plication. ou by the government at Portsmouth and Plymouth, and it was maueuvered with great success. To render it thoroughly efficient, however, in rough water and in the open sea, much skill and practice are necessary. This apparatus is adapted for the attack of vessels at anchor or in motion, but it is in the latter service, either in a rough sea or smooth water, that 284 its peculiar advanta,u-es are most appareut. It lias been ap- lirovc'd by our naval authorities, and is about to be issued to some of Her iMajesty's sliips. H-SifHamiiMuv- ^^^ Order to maneuver this torpedo to advantage, Gom- tor^Mi?"'"^ ""™ mander Harvey prefers a high speed. He is of opinion that' it cannot act well at a less speed than six knots an hour. This fact has an important bearing in limiting its use, es- pecially at night and in narrow waters. The following obserx'ations, on tUe subject of outrigger torpedoes, are extracted from the Report of the Committee on Floating Olt.strueiions, published in 18C8: Outrigger tor- " The succcss wMch appears to have attended the use of pedoes. torpedoes as a means of attack by the Americans, led the committee, at an early stage of their labors, to devote con- siderable attention to the plans which were submitted for their consideration by Captain H. H. Doty and others, for projecting torpedoes from the bows of small steam -vessels hy means of outrigger fittings. " The plans suggested for the arrangement of outrigger torpedo steam-ships, among which the most efficient appears to be that proposed by Captain Doty, all involve tlie appli- cation of special machinery and fittings for the vessel, of more or less complicated and costly character, and it ap- peared to the committee, upon a careful consideration of the subject, that the objects for which the various mechani- cal appliances were designed could be sufficiently attained by easily extemporized devices of a comparatively very simple nature, readily adaptable to the many varieties of small vessels propelled by steam which are now constantly employed in all ports and rivers frequented by shipping. ™'"ss '^"s- "In March, 1865, the committee submitted to the sec- gevtedbythecom- " ? mittee. rctary of state for war, plans for applying extejuporized outrigger fittings to small steam-vessels, and since that time they have endeavored to ascertain experimentally, with the assistance of the cajitaiu of Her Majestj-'s ship "Excel- lent,'- at Portsmouth, whether any obstacles presented themselves to the rapid api^lication and ready manipulation of such outrigger fittings. Another object of their experi- ments has been to ascertain whether a torpedo containing a charge of gunpowder or gun-cotton, calculated to produce seriously destructive effects when exploded in close prox- imity to a ship's bottom, could be fired from a small vessel such as a steam-launch, if attached to the end of an outrigger spar, without risk of injury to the attacking vessel and her crew. The conclusions which the committee believe the>' are warranted in drawing from these experiments are as follows : 2S5 "(1-) One hundretl pounds of gimpowder, inclosed in a suflQ- cieutly strong ease for the proper development of its destruc- tive action, can be manipulated with sufficient ease when at- tached to the end of a spar pi-ojected i'.j feet from the bows of a steam-launch, and fitted with the gear descriljed at page 151 and Plate XXXYIII, page li-1. ■• (2.) A cliarge of 25 pounds of compressed gun-cotton, which may be relied upon to produce a destructive effect equal to that of 100 pounds of powder, furnishes a con- siderably lighter and less bulky torpedo thau the latter, and is therefore decidedly the most convenient for boat service. '' (3.) Either of the above charges may be exploded from a steam-launch, with safety to its crew and engine, if sub- merged at a depth of 10 feet below the surface, and fired at a horizontal distance of 20 feet from the launch. For this purpose the outrigger spar should project about 23 feet from the vessel. "Some experiments are still needed for the purpose of determining whether, when the torpedo has been lowered and the outrigger spar fixed at the proper angle, the launch may be navigated over a moderate distance of water with- out difficulty. "Captain A. W. A. Hood, li. X., of Her ]Maiestv's ship Fittings for gis. "Excellent," has instituted some additional instructive ex- suggested by cap ■ • IT 1 ^^^^ Hood. periments for the purpose ot ascertaining whether much smaller craft, such, for examx)le, as gigs or wliale-boats, can be safely and effectively applied as outrigger torioedo boats, and the conclusion to which he has been led is, that charges exceeding 40 pounds of powder, submerged at a depth of 10 feet, cannot be exploded with safety from a 30 feet gig at a horizontal distance of 14 feet. " Though a 40-pounds charge, exploded at sucb a depth size of charge of immersion, might prove effective if in absolute contact with a ship, yet the committee are of opinion that the uncer- tainty which would attend the attempt to secure such con tact in the various contingencies of actual service must inevitably lead to failures, as it repeatedly did in the Ameri- can experience. For this reason they consider that 100 pounds of gunpowder, or its ecxnivaleut in gun-cotton, is the least charge that should be employed. The explosion of such serviceable charges within a horizontal distance of 14 feet from the operating boat was never contemplated by the committee, but it is evident that these charges may be exploded with safety from any sbip of war's boat capable of projecting a torpedo, at the extremity of an outrigger, to a horizontal distance of not less thau 20 feet. 2sn '-''--'"s-out ap- " Caiitaiu Hood has devised a verv couvenient arranue- ment for handling outriggers in small boats, which has the advantage of enabling a second torpedo to be brongh^ very readily into action. Though no explosions have been. made with 100-pound charges attached to this appa- ratus from boats smaller than a launch, the committee have reason to believe that it can be easily adapted for employ- ment with such torpedoes, projected by outriggers of suita- ble length, from most of the boats carried by ships of war. In determining, therefore, the class of boat to which the outrigger apparatus should be fitted, it will only be necessary to select that which is best adapted for this service by its ability to carry the outrigger with ease, its speed and handi- ness, and by such other qualities as may be most suitable to the particular time and place of attack, whether it be by day or night, in a harbor or river, or in the open sea. Simplicity in <' The implements and manipulations connected with the ■^'iti'ii- explosion of outrigger torpedoes need only be of the most siuiple kind. JIany plans have come to the notice of the committee for exploding this class of torpedoes by mechan- ical agency ; thus it has been proposed to apply friction tubes to their explosion, a method of flriug which- embraces several elements of uncertainty ; various mechanical arrange- ments, (some of which appear to have been used by the Americans,) to be fitted into the heads of the torpedoes, and to explode upon collision with the ship's side, have also been suggested, that of Mr. C. A. McEvoy being decidedly the best of this class of contrivances, but the committee consider that any mechanical arrangement for explosion by a blow must involve elements of danger or uncertainty: either the torpedo is liable to accidental explosion from a blow or fall in the course of the manipulation to be per- formed after the "exploder" has been fixed into it, or the latter must be provided with a safety- guard— the removal of which at the last moment may be neglected : moreover, the employment of such an arrangement would necessarily limit the direction from which a ship could be attacked with a pros[)ect of success. Simplicity in " Thc gTcat simplicity to which the voltaic arrangements, ment3°t-ssentSi.^^ rcqulrcd for boat service, have been reduced by the experi- ments conducted at Woolwich during last year under 3Ir. Abel's direction, has placed beyond doubt the advisability of exploding outrigger torijedoes exclusively by electrical agency. The simple pile battery, which is readily con- structed and pat into working order by seamen afrer a very brief instruction, is in'epared from materials everywhere at 287 hand, has no special fittiugs wliatever, remains in contin- uous working order for at least 24 hours, and may be used in open boats in au,y weather. A small length of covered wire is all that is specially required in addition to this bat- tery and the electric fuses for exploding the torpedoes, and even the coated wire and fuses, suitable for this simple boat equipment, may be extemi^orized on board ship. The only operation to be performed by the man in charge of the boat battery, in order to explode the torpedo upon receipt of the word of command, is to touch a metal plate on the battery with the end of the conducting-wire which he holds in his hand ; but if it be desired to render the firing. of the torpedo quite independent of any operator, and also to insure its explosion at the instant of its collision with the ship's side, it should be fitted with the electrical percussion-fuse, devised for that purpose by Mr. Abel. This fuse, which is perfectly harmless unless placed in an electric circuit, may be fitted to the torpedoes either in the boat or previously to their being jjlaced on board. Just before the torpedo is lowered into the water, or before the outrigger is projected from the bows, one end of a conducting-wire is screwed into the fuse; as the Ijoat approaches the vessel to be attacked, the other end of this conducting-wire is attached to the battery, (which is already connected to earth,) and the torpedo is then ready to be fired by collision with the ship. "The committee entertain a strong opinion that the sim- ple system of applying torpedoes by means of outriggers referred to in the- preceding paragraphs, if carried out by men well trained in the management of the outrigger boat and its fittings, under cover of the night, is likely to prove a most formidable means of attack. " It was deemed proper, however, to submit to actual experi- Exp.rimenn to % 1. i 7 / (gy^ apparatus. ment an expedient of this kind, suitable for the use ot boats of ships of war ; and on the 15th of May, 1860, a trial was made by the officers of Her ilajesty's ship " Excellent," in concert with the committee. A small spar was inclined over the stem of the launch, so that the charge at its ex- tremity was at the horizontal distance of 23 feet from the boat, and G feet below the surface of the water. The charge was inclosed in a J-inch wrought-iron case, and consisted of 9 pounds 10 ounces of gun-cotton, which is equivalent to about 40 pounds of gunpowder. The boat was placed only 6 to 8 feet from, and holding the charge nearly in contact with the bow of the "America" frigate; ignition was eftected by electricity. The explosion tore away 15 feet of the shi]i"s outer planking, laying bare 11 timbers, starting back an iron 288 knee aud an inner plank, and showing daylight through the bottom, the oblique thickness of which at that spot was 30 inches. The launch, however, did not suffer in the least ; the ontrigger was broken 6 feet from the charge, where an iron rod, bearing the torpedo, had been lashed, but the three or four turns of spun-yarn, employed as a slight lash- ing to retain the spar in position, remained undisturbed, showing that no strain had been experienced by the boat. "To lest the probable effect on the operating vessel more thoroughly, a second experiment was made, in which the launcli was placed with the outrigger at right angles to aud the charge in contact with the sunken " America," so that the boat might receive the fall shock of the recoil due to the explosion. The charge consisted of 74 pounds of gun- powder mclosed in a strengthened barricoe, ignition being effected by a friction tub(>.. The horizontal distance of the charge from the boat was 19 feet Si inches, and its depth below the surface was iucreased to 11 feet. The explosion did not in any way affect the boat, or the lashings aud guys of the outrigger, but the outer end of the sp)ar was broken off' at a weak point about 8 feet from the charge. " On the J:th April, 18G7, a further experiment Was made against the sunken frigate "America," with a launch fitted with an outiigger torpedo. The only special litting made for the boat was a movable iron crutch on the stem-head, to receive a spar 6 inches in diameter and of 30 feet in length. The inner end of the spar had an iron hoop with three eyes for small heel-tackles; the outer end had hooped on it a 4- foot rod of round iron, 1^ inches in diameter, to which the torpedo was attached ; when required for irse tlie crutch was fastened on the stem, and the outrigger launched through it, leaving 6 or 8 feet of the s^iar inboard. The outiigger was inclined at such an angle as submerged the torpedo about 10 feet beneath the surface, and 13 feet 9 inches to 17 feet C inches horizontally from the boat at the water-line, and was confined in this position by three small heel-tackles inboard, and externally by a martingale. Charges of 50 pounds and 100 pounds of gunpowder, and 21 pounds of compressed gun-cotton, which is equivalent to about SO pounds of gunpowder, were employed ; these were confined in wrought-irou cases J-inch thick, aud were ex- ploded by electricity. The boat was in each case secured in position with the outrigger at right angles with and a few feet from the bot( om of the sunken ship. At each explosion the spar was broken off' at a weak point, some 6 to 13J- feet from the outer end, but when the torpedo was projected to 289 a suitable distance from tlie stem, no injury whatever was sustained by the boat or its fittings, and only a small quantity of water was shipped. On the 20th of December, 1867, these results were confirmed by the explosion of a 100-ponnd charge immersed 10 feet, and projected by an outrigger in a line with the keel, from the side of the bow of a steam-launch, to a horizontal distance of i'S feet 10 inches from the stem at the water-line ; no injury whatever being sustained by the boat or the machinery. "To determine the limits of the destructive results to be .ReBuUsof explo- sion of 100 pounds anticipated from similar chargesexplodedatincreased depths °.f po^aer at va- > o i c nouB depths and of immersion, two 100-pound gunpowder torpedoes were, in^8tano,<. July, 18G8, fired from outriggers projected from a launch to a depth of 20 feet, at a horizontal distance from the stem at the water-line of 22 feet 4 inches and 17 feet C inches respectively. In neither case was the launch injured, though sufficient water fell in-board from the column thrown up by the nearer explosion to have swamped the boat, had not the fore part been protected by a sloinng canvas cover which extended to 15 feet abaft the stem. The depth of greatest effect of 100-pound charges is estimated to be less than 15 feet, and the lateral destructive action of a serious nature to be anticipated is computed to extend over an area of 9^ feet radius; but it is supposed that a minor destructive effort may extend beyond that distance sufficient to do in- jury to boats. These experiments tend to confirm the pre- vious estimations of the limited extent of the destructive area, while they show that the falling water must also be taiien into consideration in determining the maximum dis- tance at which torpedoes can be exploded from open boats with safety to the operators. " With a view to the ai>plication of outrigger torpedoes sizes of boat, ■*-■'■ ocj *. moHt suitable fnr to the smaller boats of ships of war, a series of experiments outrigger torpedo were conducted with a 27-foot whale-boat, and a 30-foot gig, fitted with outriggers projecting from the broad part of their bows. These side outriggers were found very con- venient for carrying and handling torpedoes in light boats, the weight being thrown further aft, and the outriggers being manipulated, without any movement of the crew, by persons in the stern sheets. A canvass awning was stretched over the fore part of the boat to deflect any falling water raised by the explosion. The ignition was in all cases ef- fected by electricity. The length of the outriggers employed in these experiments did not admit of the explosion of the torpedo at a greater horizontal distance than 15 feet IJ inches, which, with an immersion of 9 feet, was found inade- 19 servict;. 290 quate to tlie safety of the boat and crew with a greater charge thau 40 pounds of gunpowder. Though this charge would snftice for the destruction of a ship of war, if exploded in absolute contact, the difficulties of insuring this in actual service, would render it inexpedient to risk undecided re- sults by the employment of such a doubtful charge. If four- oared gigs cannot be fitted to carry outriggers capable of projecting 100-pouud torpedoes to a horizontal distance of 20 feet, their application to torpedo service must be very limited. The means, however, devised for carrying side outriggers in gigs, are equally applicable to galleys and cutters, and there is no reason why these boats should not project serviceable charges to safe distances. " These experiments show that outrigger torpedo appli- ances, to project destructive charges, can be employed in any ordinary ship's boat capable of carrying a spar of sutfi- cient length, with perfect safety to the boat and crew. "A series of torpedo-boat experiments was therefore con- ducted by the officers of Her Majesty's ship "Excellent," at the suggestion of the committee. By these it was demonstrated that 100 pounds of gunpowder and 21 pounds of gun-cotton can be exploded with perfect safety to the boat and crew, from the extremity of an outrigger projected from the bow, at such an angle that when the charge is immersed 10 feet beneath the surface its horizontal distance from the stem at the water-line shall be 20 feet. A charge of 40 pounds of gunpowder, immersed lOJ feet, was also exploded with safety from a four-oared gig with the crew embarked, at the horizontal distance of 14 feet; but a 50-pound charge im- mersed 9 feet, and exploded at a horizontal distance of 15 feet 1 J inches from a whale-boat, swamped the boat. These distances were much less than were at any time contem- plated by the committee as calculated to secure immunity to the operating vessel, while the uncertainty of securing, in actual warfare, the absolute contact essential to the destru('tiou of an enemy's ship by the explosion of such small charges must preclude their employment on service. " The committee are of opinion that outriggers sufficiently long to project lOOpound charges to a horizontal distance of 20 feet may be carried in boats of much sihaller capacity than launches ; but whether fittings can be applied to four- oared gigs, by which they can do .so, is j'et a matter for ex- periment. The best means of projecting outriggers from steamships of various sizes, and of maintaining them in posi- tion at different speeds, and their influence on the steering 291 capabilities of the vessels, are problems which have yet to be submitted to experimental investigation."' As regards the second class, or projectile torpedoes, one of ^^^^"^p^"^,^ ''^J^ the most promising is that invented by ^Messrs. Lupin and "■■p«'*°- Whitehead. A considerable ii mount of secrecy has been observed with reference to this machine, but the following, as far as can be ascertained, is a description of it ; It is fusiform in shape, and is provided with projections constrnction . resembbng fins and some kind of rudder, by means of which it may be set to run in any particular direction, and at the same time the depth at which it is to move below the surface of the water is regulated. The fins also serve to guide it in passing out of the tube through which it is discharged into the sea. ^lotive-power is given by means of com- pressed air, which is made to turn a four-bladed screw pro- peller. The speed obtained is about eight and a half knots an hour. Direction is given to the torpedo by means of an iron tube fitted into a vessel in such a position as to dis- charge it at a considerable depth below the surface of the water. The tube constructed in Her Majesty's ship Oberon, for experiments tried with this torpedo last autumn at Sheerness, was 2 feet in diameter, 28 feet long, and di- rected horizontally through the bow ; its outer extremity was covered by a metal cap. The tube was divided into two portions, and was provided with two vertical sluices to keep the water out. The rear sluices having been opened, the torpedo is Mode of project passed into the tube on rollers; the rear sluice is then closed, the front one opened, and the cap covering the outer extremity of the tube having been removed, the torpedo is expelled from the ship by means of a piston ; during this process the fins serve to prevent any turning motion by bearing upon four rails, the upper and under ones being pro\ided with friction rollers placed within the tube to serve as guides for this purpose. As it passes out a tripper catches against a stud in the tube and puts in action the propelling power. Direction is given, or, in other words, aim is taken by moving the ship herself as required. The charge, which may be of gunpowder, gun-cotton, or position of any other explosive, is carried in a chamber in the head of' "'''^' the torpedo, and ignition is effected by means of a percus- sion fuse. ^'umerons experiments were tried during the autumn of Experiments to , „,,. . .,. T. *''»< 'be use of tor- 1870 with torpedoes of this nature without an explosive p«ao. charge, to ascertain their capacity to move at given depths below, and in a given direction through the water, and these SIOU 292 baving proved fairly successful, an experiment with a loaded torpedo was decided on and ciu-ried out at Slieeniess on the 8th of October, 1870. The charge used on this occa- sion 'sras (17 pounds of gun-cotton; the torpedo was dis- charged from a distance of about 150 yards at an old hulk called the Aigle, moored at the mouth of the ^ledway; the hulk was struck and sank immediately. The explosion threw up a columu of si)ray aud smoke mixed with coal- dust to a height of about 70 feet. The spray was perfectly distinct from the smoke aud coal-dust, and proceeded from the water disturbed outside the yessel's hull ; the smoke and coal-dust beiug probably due to the exi)losiou acting inwards, through the vessel's side, and the column of gns driven through the interior of the ship. The two sec- tions of the column, viz, the white spray and black smoke aud coal-dust were entirely distinct from each other and not mingled in any way. Effect of expio- rfjj^. (jamagc do'ue by thisexplosion consisted of a clear hole on the side struck, (the starboard side,) '26 feet long and 9 feet in depth, and extending down to the keel ; about 4 feet of the planking above this hole was broken and the copper more or less torn off for a length of about 40 feet. luside the hulk half the main deck, up to the mizen hatchway, was carried away, and the remainder much torn aud injured. On the upper deck the planks round the hole, left by the removal of the mizeu-mast were displaced and forced up- wards for a distance of about 12 feet. The planking on the port side of the vessel was blown outward for a length of 16 feet, and to a depth of 2 feet, while it was shaken for a further distance, and the copper more or less stripped over an area extending considerably beyond the space mentioned. In considering the extent of damage done, it must be borne in mind that the Aigle was an old wooden ship, probably somewhat rotten, aud it is scarcely likely that this amouut of damage would have occurred had the same torpedo been exploded against the side of a ship so strongly built as a modern iron-clad. This is, however, a question for the con- sideration of naval architects. Fish torpedo A suiall torpedo of the same class, 14 feet long-, 14 iuches rii-ed from boat. ; h) iu diameter, and carrying a charge of 18 pounds of glyoxa- line, was subsequently fired from an ap]jaratus suspended beneath a boat which' was placed at a distance of about 150 yards from the Aigle, and directed at some netting arranged to protect the vessel against an attack of this nature. The torpedo was fired by contact with the netting, but did no 293 apparent injury to the ship. The netting was hung about 16 feet clear of the vessel's side. This torpedo must necessarily start with a low velocity, conflicting in- , . ^ ^ ' fluence of cur- ancl even at its best, as at present arranged, does not attain '■™»«' '^<^- a speed of more than eight miles an hour, which would ren- der it very liable to disturbance from the effects of currents. This, combined with the extreme care and the amount of trouble which seemed to be necessary in taking 'aim from a distance of only 150 yards, in perfectly smooth water, in the experiment above described, seems to indicate that there would be a considerable amount of uncertainty in direction ai the distance of 800 yards at sea, at which the inventors claim that it is practically effective. Destruction would no doubt result from striking a ship with this or any other tor- pedo ; but the great difficulty would seem to be experienced in attempting to hit a ship, with this or any other known projectile torpedo, at a serviceable distance with any approach to certainty. Mr. Lancaster, the gun-maker, made a proposition to the Torpedoes pio- JO J ft pelled by rocket Groverniuent some years ago, to propel a torpedo through composition. the water, by means of rocket composition carried in the body of the apparatus. His ideas, however, were not approved, and consequently were never worked out. More recently Mr. Quick, engineer of the royal navy, has brought forward a similar proposition, and an experiment has been recommended by the royal engineer committee to test its value. This experiment has not yet been carried out. Mr. (Quick's idea seems to be similar to that of Messrs. Lupin and Whitehead, the chief difference being in the pro- pelling agent, rocket composition, suggested in the former, instead of compressed air, as in the latter case. Should efficient projectile torpedoes be devised they might ,„JJ,fH°L^™'''"^''''' be used against ships at anchor, or perhaps moving slowly, also for the destruction of obstructions extending to any con- siderable depth below the surface of the water. They do not seem applicable to the attack of ponton-bridges or booms as the chance of striking such objects would be comparatively small, unless the power of regulating the depth at which they would move below the surface is capable of being very nicely adjusted. Their direction with such a comparatively low velocity as can be attained, is so easily disturbed by currents and other conflicting causes, that they would seem applicable only to the attack of objects presenting a con- siderable breadth of front, and the chance of hitting a ship in motion, at a distance of even one or two hundred yards, would appear to be extremely small. torpedoeu. 294 Drifting torpe- Amoiig tliG various devices suggested at diflfereut times for tlie third class or drifting torpedoes, tbe mostpromisiug seem to be those designed by Captain McEvoj-, of the late confederate torpedo service, and by Lieutenant J. F. Lewis, E. E. McEvoy'a (jrift- The followiug dcscriptiou of McEvoy's self-acting drifting ing torpedo. torpcdo, is cxtracted from the report of the committee on floating obstructions, published in 1868 : Construction. "The torpcdo case is to be suspended from a float, and permitted to drift down upon an enemy's floating bridge in a river, or against a vessel at anchor, but specially suitable for the former purpose. " On the top of the exterior, protected by iron bars, is a sensitive percussion fuse, with a hammer retained at full cock by a lever, which is acted upon by the threads of a screw. To this screw is attached a many-bladed screw pro- pellor of sheet tin, balanced by a fan or rudder blade on the opposite extremity, the whole pivoting round the percussion fuse, and occupying little space. mode of action. " So loug as the torpedo continues to drift, the apparatus on its top will be unaffected by the current, but as soon as the motion of the torpedo is interrupted, the current run- ning past will act on the fan or rudder blade and turn tbe screw propeller to the current, when a given number of turns will liberate the hammer and cause explosion." Fig. Ill shows the general design of the apparatus ; A is the sensitive fuse, B the hammer, retained at full cock by pressure against the catch K, which works in the threads of the screw ; C is the fan to turn the screw propeller, pivoted round the fuse A to the current when the torpedo ceases to drift : D is the screw propeller of sheet tin, to be revolved by the current when the torpedo fouls anything and ceases to drift ; this action would disengage the catch K and allow the hammer to fall and ignite the sensitive fuse A ; E E are circular guards to x>rotect the igniting apparatus, F F iron slings, G the suspension rod, and H the surface buoy. This figure is copied from the report of the committee on floating obstructions : Lewis's drifting The foUowlug dcscrlption of Lieutenant Lewis's self-acting torpedo. drifting torpedo, is extracted from the report of the committee on floating obstructions : "This is a contrivance for projecting drifting torpedoes under booms or other floating obstructions employed for the defense of ships at anchor. coDstruciioD. " The torpedo consists of a cubical box capable of contain- ing 5~> pounds of powder, and furnished with five detonat- ing fuses in one of its sides. Vig. HI. S- I)ri/'lM/j Bu/jy^ ^OTV the ■SK.rf'ace. Top Fhcuh. £' 295 "This torpedo is attached to one side of a beam, and within six_ inches of one extremity — the beam being- i'O feet long and 7 inches square. To the opposite side of the same end of the beam a 60-pound iron weight, resting in a shoe, is attached by a long iron rod which reaches to the other extremity of the beam, and is there connected to a bell-crauk lever and spring, a pressure on which detaches the weight. A chain 18 feet long connects the weight loosely with the upper end of the beam, and another chain, 9 feet 6 inches long, connects it with a point more tljan two feet below the center of the beam. The whole arrangement floats nearly vertically with the top of the beam, just above the surface of the water. "When the apparatus drifts against the boom or other Mode ot iiciion. obstruction, the spring or lever at the upper extremity is pressed down, thus raising the long iron rod and releasing the weight, which, falling, becomes suspended by the two chains, throwing the beam into an inclined position. The weight of this mass of iron and the chain suspending it are suddenly brought to bear on the top of the beam, drag- ging it under water and clear of the floating obstructions, at the same time the lower end, released from the weight, rises and the whole apparatus is carried forward by the current against the side of the vessel, on striking which the torpedo explodes." Fig. 112 shows the general form of the apparatus ; (a) is the box containing the charge ; (b) the beam to which it is attached; (c) the 60-pound weight resting on the shoe {d; ) (e) is the iron rod connecting it to the bell-crank lever and spring (/;) [g) and (h) are the two chains connecting the weight to the beam. Machines of this nature might be used for the attack of Nature of opera- ^ tlODS to whicli ponton-bridges, booms, and obstructions generally ; those iosive should be compressed gun-cotton, fired with a detonating fuse; where gun-cotton is not procurable, gunpowder fired, if possible, with a detonating fuse may be used. ' "'-" The cases should be of wrought iron, with a cast-iron loading-hole, which also serves to receive the fuse or circuit- closer. Oases to contain charges of the following sizes are recommended, viz: 100 pounds, 250 pounds, 500 pounds, and 1,000 pounds. (jiir. -luindiea The general design and dimensions of the 100-pound case ijouiitl case, con- c? o ^tvllction Bud di- are shown in section in Fig. 113. It consists of a wrought- iron cylinder [a) of i^o. 1'2 B. W. G. iron plate, riveted ; the upper end {h) to be dished and of the same thickness of metal ; (c) is the mouth-piece, riveted directly to the cylin- drical iron plate of the body ; this opening is circular, 6 inches in diameter, and serves as a loading-hole and for the introduction of a circuit-closer of Mathieson's form, which is arranged to be placed within the case; {d) is a screw- piece to keep everything water-tight, as described in page 9(3, Fig. 33; (e) is a wooden jacket of fir, conical in form, to protect the iron cylinder from injury when subjected to blows from friendly passing ships. The wood of which the jacket is composed should be well seasoned, thoroughly saturated in tar, and subsequently painted to keep the water as much as possible from entering into its pores after sub- mersion, so that the buoyancy of the wooden jacket may increase the flotation. The case is intended essentially for a contact charge, and a maximum of buoyancy is absolutely necessary. The wooden jacket is bound together by iron bands and provided with a ring (/) at the top, from which to suspend the case for mooring purposes. The whole of the iron work of the case should be painted two coats, and tested up to a pressure of 10 pounds on the square inch, mensions. 299 gradually increasing from within. The calculated weight of this case, complete with circuit closer and charge, is Pig. 113. SecAioTV. -BoCWm.Plaju. about 470 pounds, and its available buoyancy, that is to say, ,w.f,-,ni iir>woT- r.f fliitntimi. cibnnt 140 nounds. 300 Two hundred The ffeiieral desijra and dimensions of the 250-pouTul case tind lifty pound ^ o no 0- pound case. The whole of the iron- work should be painted two coats; the case should be tested to a pressure of 40 pounds on the square inch, gradually increasing from within. The calculated weight of the case, with charge complete, is about 1,000 pounds ; this exceeds the total buoyancy by about 190 pounds; it has, therefore, no floating xjower, and if required to be floated up from the bottom the necessary buoyancy must be attached. Xo definite pattern of case to contain a charge of 1,000 pounds has yet been mad«: it should, however, be similar*'™"^!'™ ""^ •" in form to the 500-pound case, and be composed of i-inch best iron boiler-plate, and of such cubic space as to contain the requisite charge, viz, "J feet 9 inches by 3 feet i inches, not including the dish of the ends. The mouth-piece should be the same as before, in order that the fuse-pieces may be interchangeable; the attachments for the moorings should be similar to those of the ."iOO pound case, but of pro- portionately larger dimensions. The dimensions of all these cases are calculated for com- ^'>>°'''<' , '",'"<■'>• sions calc'iliiti'n pressed gun-cotton, and their thickness is not sufficient to de- f°'' co!iipiv,-e,i gun-cotton. Telop the maximum explosive force of guni^owder ; if, there- fore, this latter explosive be used, detonating fuses and sev- eral centers of ignition must be employed. The cubic space occupied by a given charge of gunpowder is slightly less than that required for an equal weight of comx^ressed gun- cotton ; for practical purposes, however, the cases described may be taken as the same for both. The best special mooring apparatus for general purposes rJ„"'"'mushroom seems to be the mushroom sinker, somewhat similar to that '>°'^'»°''- shown in Fig. 20, and describetl in pages 72 and 73. Its weight would depend upon the buoyancy to be overcome, and would generall\ be from five hundred-weight, upward. Ordinary mooring-chains and hemp cables may generally be employed in connecting the charges or circuit-closers with the sinkers. Where there is any tendency to twist, a «ire cable is the best to counteract it. Any considerable amount of twisting must be checked, as it is liable to en- tangle the moorings and to rub and injure the electric cables. The strength of the chains or cables employed must depend upon the amount of buoyancy possessed by the mine or circuit-closer.. The cable connected with the circuit-closer would also frequently be subjected to a severe strain if caught by the paddles, screws, &<:., of a friendly vessel i)ass- iug over the mine. For this reason stron.ger cables, both electric and mooi'ing, must be provided at that point. fill 304 )rh,l'o''r' ' '°''i"^*' For mechanical iguition Abel's torpedo primer, described at page SS, and shown in Figs. 26 and 27, may be used. piRtmuiu wire -pov elcctrical iguition a platinum wire fuse, primed with fulminate of mercury, somewhat similar to that shown in Fig. 51, page 133, seems most suitable. Mr. Abi'l is now engaged in experiments with a new form of tension-fuse for submarine mining purposes, but as yet it is impossible to decide whether it will eventually supersede the platinum wire fuse or not. Kiectiic cables. The electric cables which seem best suited for submarine mining-service, are the following: sini;!,. ,ai)ic. rphc Single cablc, to consist of a strand of four No. 20 B. W. G. copper wires tinned, insulated with vulcanized In- dia rubber to a diameter of jYo i^clij over which a layer of felt is wound; the whole is then submitted to a tempera- ture of about 300° F. to consolidate the dielectric. Over the core thus formed a covering of tarred hemp should be wound on spirally, followed by 8 ITo. 13 galvanized iron wires, each wire separatelj' covered with tarred hemp. The whole to be finally covered with two coatings of hemp and eom{)osition, (consisting of tar and some bituminous sub- stance,) wound on with a short twist in opposite directions. The external diameter of the whole would be about § inch. The weight of this cable would be about 2G|-cwt. per nauti- cal mile. Multiple cable. The multiple cable, to consist of seven single cores, as above described, formed into a strand. The whole covered with tarred hemp, laid on spirally, subsequently with 16 ISTo. B. W. G-. galvanized iron wires, (each wire separately covered with tarred tape,) laid on spirally over the hemp covering. The wliole finally covered with a layer of hemp and composition laid on with a short twist. The diameter of a multiple cable, constructed in this way, would be about 1;^ inches and its weight 5 tons per nautical mile. Either Hooper's or Grny's patent di-electric is very suitable for this service. They are both combinations of vulcanized India rubber, which forms a very flexible covering to the copper conductor, and may be stored either wet or dry. It must, however, be kept always wet or always dry, as any alternation of these conditions would tend to rot the hemp covering and di-electric. Should it be necessary to store an electric cable insulated with gutta-percha, it must be kept under water. When so treated it may be preserved in a sound state for a considerable length of time. Dry air has a very deleterious effect upon gutta-percha, causing It to become brittle and crack when bent after exposure to its influeuce for a comparath'ely sbort time. When giitta- perclia cables, therefore, are to be stored, tanks must be provided for their reception. The voltaic battery temporarily adopted is 'Vralker">. _FHing-battery, (zinc and carbon plates in diluted sulphuric acid.) The zinc element consists of a plate 11- inches by il inches, amalga- mated with mercury, the carbon pole being formed of a pair of plates each G J inches by 4i inches, connected together to form one element. The dimensions of the outer cell are .j inches by 2i inches and 7 inches deep. The greater depth of the zinc i)late brings its lower extremity to the bottom of the outer cell, in which a small quantity of mercury is placed to keep the zinc amalgamated. The graphite i^lates do not reach down so far as to touch the mercury. The slipper generally used in this form of battery to hold the mercury may thus be dispensed with. They should be ar- ranged in a wooden frame, so that the battery-plates may be lifted out of the liquid when not in use. This may be readily done by means of a small chain, or rope and i)ulley. They need only to be lifted a very short distance, just clear of the diluted acid, and not absolutely out of the cell. This will prevent the chance of damage to the plates which was found to occur when they were lifted to any great height, by striking against the eilges of the cells when sub- sequently lowered. Experiments are now being made with a large form of ls cianchs bat- Le Clanche battery, to ascertain whether it is not better ''''^^ ' than Walker's for submarine mining purjioses. The Le Clanche battery is no doubt preferable to Walker's in many important res[iects ; its constancy, for example, is greatly superior, but till the experiments are completed no definite opinion can be given. For firing at will, when it is desirable to dispense with Dvnamoeiectric- battery power, the dynamo-electrical machine seems to be the best form of instrument for submarine mining purposes. The size adopted as the field-service pattern for the engi- neer equipment, seems to be a very convenient form of in- strument for this work. Its weight complete, with carrying- case and straps, is I'S pounds. For firing by intersection at long distances, telescopic . Ttieecopic sr- keys, somewhat similar to that described at page 19J:, Fig. 82, would be required. The radius of the arc on which the firing-contacts are to be fixed, should be increased to a minimum of 36 inches, and the eye-piece of the telescope should be placed farther back, so as to be easily seen through when the hand is employed in moving the appa- 20 306 ratns round iu following a ship. A pair of improved instru- ments of this nature are now being made for the trial of this S3 stem. Mathieson'? cir- Whcu a platinum wire fuse is used, a circuit-closer or cuit-cIoser and ^ ' breaker. breaker of Mathieson's form, as described at page 209, Fig. 87, seems to be the most generally useful instrument of this class. When simple contact mines are used the instru- ment may be connected as a circuit-closer. When the mines are arranged with a detached circuit-breaker to be fired by the contact of a sbip, with an alternative mode of ignition by intersection, the ajiparatus should be connected as a circuit-breaker. An improvement has recently been introduced into this instrument, which consists in reducing the number of supporting pillars and spiings, with their corresponding connections, to three instead of four, as shown in Fig. 87. The reason why this instrument is so well adapted for use with the platinum wire fuse is, that the springs produce a slight prolongation of the contacts when the apx^aratus is used as a circuit-closer, and this gives an almost inappreciably prolonged interval for the circulation of the battery-current which is desirable to produce the heating power necessarj- to fuse the tine platinum wire forming the fuse. .lot^r*'" '''"""" Experiments are now being carried on with Abel's circuit- closer, somewhat modified on that described at page 202, Fig. 85, with a view to test its capabilities as compared with Mathieson's circuit-closer and breaker. It is probable that, with a tension fuse, either may be used, and no definite deci- sion can be made till the experiments are completed. With the platinum wire fuse, however, Mathieson's apparatus is preferable to Abel's, as the latter is at present constructed for the reasons already gi^-en. Shutter signal- rpj^g fQj.j^ ^f shutter-sigualing apparatus, which seems ing and nring ap- & & i i 5 paratua. "begi; adapted for submarine mining purposes, is that described at page 232, Fig. 97, in which the contacts are made by means of mercury-cups in place of the springs which were first used. Further experiments, however, are required with this form of instrument before it is possible to decide definitely whether it is the best suited for the pur- pose, or even whether it may be found convenient to use an apparatus of the shutter form at all. THE END. I3>^r)EX A. Page. Action, electrical, ■between metals in sea-water 64 Agents, explosive 2s "America," Her Majesty's ship, experiments on, to determine the efifect of a given charge ^3 Anchor, mushroom, Austrian (^4 most approved form 30:j Anchors, ordinary Sa Astatic galvanometer 2(i* B. Bag, gun-cotton, to surround charge, suggestion ^ 11:; Bags, India-rubber, Captain Harding Steward's ' 52 Balance, electrical, Wheatstone's 2G'J Barge, mooring, Austrian, arrangement of. ... _ gO Barrels, employment as make-shift cases 59 Battery, voltaic, Austrian, for submarine mines 131 Daniell's I79 Muirhead's l,'^i) Varley's ISO firing, Walker's, most approved form 305 for use with platinum wire-fuse 172 tension fuse 177 Grove's 172 and platinum fuse, experim en ts with 94 defects of ys ignition by 172 Le Clan ch6 182-30.5 Mari^-Davy 179 sand, Wollastou's 177 Walker's ■. 98-172 Batteries, quantity, tests of 25:1 voltaic, testing 2i;0 tests of - a.'iO Beach, open, defense of, by submarine mines V-i Blavier's formula to discover position of fault 2(iO Boat service, torpedo outrigger for 27.5 Boats, clearing channel by 27 1 size most suitable for outrigger torpedoes 2^9 Boiler, steam, as a makeshift case - 60 Boom, electric cable in connection with 12-< Booms, defense of mines by 101 Box, testing, for connection of multiple cable 124 Breakers, circuit, Matliieson's 2IIS most approved form 30i> Bridge, electrical, Wheatstone's - -i'-' Buoyancy, necessary for mines moored from bottom o.j 308 c. Page. Cable, coudition of, best suited for resistaiici> test )iC<2 Cable, electric, multiple, most apju'oved form 304 single, luost apiiroved form 304 testa of 243 test of electrical resistance of- 247 Cables, electric, Austrian 115 branch system - l'-!4 Gray's core 118 Hooper's core 117 improvised 129 in connection with booms 128 introduction into a fort • 157 mode of paying out 151 multiple 119 multiple, defects of 121 outer protection of ordinary rope 127 permanent joints in 137 protection from wash of sea 154 qualifications required 115 Siemens', protected by copper tape 116 multiple, tests of 246 Case, conical, for small mechanical mines J 49 cylindrical, for large charges 50 100 pound, description of approved form 298 2.')0 pound, description of approved form 300 500 pound, description of approved form 302 1,000 pound, description of approved form 303 experiments on strength by floating obstruction committee 3f7 form of, Austrian 51 general form of 49 internal, sheet-tin or India rubber 60 must be thoroughly water-tight 60 strength required for gunpowder and gun-cotton 60-303 strong, required when gunpowder is used ^ 28-113 tests of 239 Cases, boiler-plate iron, construction, calculated strength, &o 54 buoyancy necessary 85 make-shift 59-60 materials for construction of 51 not to be loaded in the sun or at high temperatures 54 Catch, mooring. Austrian 63 barbed 65 Cell, sea, disturbing influences during test , 256 test for insulation by 255 Channels, illumination of 162 Charge, effect of, when fired under water ; general conclusions 44 ignition of, at will 163 maximum, to be fired with a single fuse 109 size -of 40 approximate rule for 45 confederate rules for 40 experiments on, by floating obstruction committee 42 used in destruction of wrecks in Eiver Hoqgly 42 309 Page. Charge, small, mode of mooring 1,7 test to ascertain -whether dry 2r,4 Charges submerged, examination of 77 when visible to be disguised ,S:3 Circuit-breaker, ilathieson's 2i IS Circuit-closer, Abel's- -201-306 Aiistrian jag dual-electric, Matlileson's 211 Mathieson's 204 pendulum.. 211 and breaker, most approved form 306 Circuit-closers combined with or detached from mines 213 mechanical I99 when visible to be disguised 83 Clearing channel by small boats ■ , 271 ^ by submarine explosions 274 Coils, resistance 269 wire, of instruments must be suited to current to be conveyed 237-270 Committee on floating obstructions, appointed 9 Company, constitution of, for submarine mining duty , 270 Connection, water-tight, temporary 134 clay 135 Contact mines for defense against boats 219 Cost of submarine mines, small 15 Course of instruction at Chatham 9 Cross-bearings, firing by 13!) Current, negative, used for testing purposes 246 D. Defense by submarine mines, especially applicable to United Kingdom and colonies 14 increase to, by use of submarine mines 15 of a channel ; distribution of mines • 23 of a first-class fortress 11 of a mercantile harbor by submarine mines 12 of an open beach by submarine mines 13 of an open roadstead by submarine mines 26 of mines by booms and fishing-nets 161 from drifters 161 Detachment, number of, for submarine mining duty 270 Detector galvanometer 268 Detonating fuse, experiments with gun-cotton and glyoxaline 30 fuses, tests of 243 Differential galvanometer 26S Disconnector, Anderson's 217 electro-magnetic 217 Mathieson's 216 Distribution of mines for defense of a channel 23 Drifters, defense of mines from - 161 Drifting torpedo, Lewis' 294 McEvoy's 294 Drifting topedoes 275-294 nature of operations suitable for 2'J5 Dummies, use of ^ -•^ Dynamite, experiments with, against hull of frigate 38 3ia Page. Dynamo-electrical macliine, Ladd's , . 167 Siemeus' 165 most approved form of - 305 E. Eartli coiinectioDS Tv-ith Grove's battery and platinnm fnpe 94 Effect, comparative, of gunpowder and guu-cottoa fired under water with de- tonating fuse - 35 of charge when fired under water ; general conclusions 44 Electric cable, multiple, most ajiprovcd form 304 single, most appi oved form 304 testes of 243 Electric cables, Austrian 115 branch system 124 Gray's core 118 Hooper's core 117 improvised 129 in connection with booms 12S introduction into a fort 157 mode of paying out 151 multijjle 119 multiple, defects of 121 outer protection of ordinary rope. 127 permaneut joints in- 137 protection from wash of sea 154 qualifieations required 115 Siemens', protected with copper tape 116 Electric telegraxih from fort to guard-boat 161 Electrical balance or bridge, "Wheatstone's 269 ignition 93 instruments used in testing 268 machine, dynamo, description of 165 most approved form 305 frictional 170 resistance of cable, test of ; 247 submarine mines 17 advantages and disadvantages 17 tests 238 value due to comparison 258 Electro-magnetic disconnector 217 Electrometer, reflecting 268 Equation, personal, of observer • _ 264 Exploder, magnetic, Beardslee's 164 Marcus' 168 ■\Yheatstone's 163 tests of 250 Explosive agents 28-298 best suited for submarine mines 298 Explosives, tests of 239 Extent of fault, determination of, Lieutenant Eisher's method 266 F. Fault, extent of. Lieutenant Fi.sher's method of determining 286 Firing-battery, AValker's, most approved form 305 by cross-bearings 286 311 Pase. Firing-key and iixed telescope, use of l!ii^ attacLied to testing-table > '-H keys •. 191 telescopic 193 most approved form 'MC> Fishing nets, defense of mines by 161 Fish torpedo, Lupin and "Whitehead's 291 fired from boat 'i9'2 Fleet, inferior, protection of, by submarine mines .-. 13 Formula, Blavier's, to discover position of fault '2*iO Fortress, first-class, defense of 11 Frames, projecting, carried ou vessel's bows 'J71 Frictional, electrical machine 170 tests of 250 Frictional electricity, induction experiments 212 Fuse, Abel's 101 detonating K'4 precautions in testing — 104 Beardslee's 99 Brook's 87 chemical - ^"7 detonating, experiments ^Yith, to fire gun-cotton and glyoxaline oO electrical, high tension, extemporized 106 Fisher's 108 introduction into metal case 130-133 barrel V->2 platinum wire 93-95 advantages of - - 93 battery for use with - 172 most approved form - - ■ '04 tests of - 240 with gun-cotton priming 97 Prussian - - 101 sodium or potassium 88 surrounded with gun-cotton - 113 tension, butterv for use with 177 tests of i:42 VonEbner's - 100 Fuses, detonating, tests of - 243 distribution of, in charge - - lf'9 electric, for current of high tension 99 mechanical defects of - 90 Harding Steward's safety 91 tests of.... - 240 mode of fixing, in position -- 113 position of, in charge 108 two, to be used at each center of ignition - 113 G. Galvanometer, astatic 268 detector - 2G8 diilerential - - • 268 reflecting 268 seositive, for testing purposes 24,j tbermo '"^"- 312 Pago. Glyoxaline '. 39 experiuiouts with, iired •with detonating-fuse 30 Gray's c'.ectiie calde 118 Grove's Ijatteiy and platiuum fuse, experiments with 94 defects of 98 Gnarding mines at night 161 Gun-cotton 29 and gunpowder, comparaiivc effect when fired under water by de- tonating fuse - - 35 liag to surround charge; suggestion 113 CI impressed -- 29 Abel's improvement in manufacture 29 experiments with, wlien tired with detonating-fuse -.. 30 exjilosive effect of, examined theoretically 3G most suitable for submarine mines 298 not explosive when wet 36 priming for jilatinum- wire fuse 97 Gunpowder and gun-cotton, comparati\-c eifect when fired under water by a detonating-fuse 35 exp]i)sive effect of, examined tlieoretically 36 proporlion of charge as compared with other explosives 46 use of, for submarine mines 23-'398 Gutta-percha insulation, defects of 115 H. Harding Steward's improvement in mechanical mines ]8 Harvey's sea-torpedo 280 I-Iooper's core 117 I. Ignition by battery power. 172 electrical 93 mechanical modes of 87 of charge at will 163 Illumination of channels 162 Improvements in mechanical mines, Harding Steward's 18 India-rubber bags, Harding Steward's 52 insulation 116 Induction coil 169 eifect of, in testing several joints together 250 when frictional electricity is used 121 experiments with frictional electricity 212 Injury to insulation, points most liable to 265 Instruction, course of, at Chatham 9 Instruments, coils of, must be suited to the current to be ciniveyed 237-270 electrical, used in testing 268 tests of 239 Insulated and water-tight joints 130 joints, test of , 24!-! delicate tests by special apparatus 248 Insulation, gutta-percha, defects of 115 India rubber 116 advantages and defects , 220 points where most liable to injury 265 313 Pa.ie. Intervals to insure safety to adjoining mines -46 Introduction of electric caWes into a fort ,. l-'iT of fuse into barrel ' l:>-2 of fuse into metal case 130 133 J. Joint, Beardslee's : 146 bottle, Dent's 142 Glover's 145 India-rubber, permanent 139 tube, advantages and disadvantages li'i Mathieson's 147 for electric cable with outer protecting covering 14'J metallic, Nicoll's 14-2 vv-ater-tiglit, clay 135 Joints, India-rubber tube 141 insulated and water-tight 130 permanent in electric cables, , 137 teniporar3', insulated 140 water-tight and insulated, tests of 2 i -' K. Key, firing, and fixed telescope, use of 193 for simple testing-table 224 Keys, firing ■_ 191 telescopic 193 most approved form 305 L. Lateral pressure on buoyant mines, calculation for 86 Le Clanch(5 voltaic battery 182-305 Line, single, of mines, disadvantage of 22 Lines, disadvantages of arrangement of mines in Ifil Loop-test, Varley 's 253 M. Machine, frictioual electrical 170 Magnetic exploder, Beardslee's 10 4 Marcus' --- 163 Wheatstone's 163 Materials for construction of cases 51 for submarine mines, easily obtainable 16 Maximum cbargr to be fired with a single fuse 109 Mechanical circuit-closers 199 fuses, defects of 90 Harding Steward's safety 91 tests of '- 240 ignition ''^7 submarine mines -- lf> advantages of 17 danger in submerging 18 disadvantages of 16 tests ~-53 Men, qualifications of, for submarine mining duty 270 Mercantile harbor, defense of, by submarine mines 12 314 Page. Mine, ground, must be heavy .• sd submarine, definition oi^ 7 Jlines, circuit-elosers combined ■with or deti.ched from 213 contact, for defense against boats 219 defense of, from drifters 161 disadvantage of arrangement in lines - 161 mode of marking position 151 placing in position 80 moored from bottom, buoyancy required ^^5 must be guarded at night 161 offensive, or torpedoes 9-275 position of to be concealed 157 submarine, American rt Austrian 8 Chinese 8 cost of, small 15 defensive 10 electrical 17 advantages and disadvantages 17 intervals between to insure safety to adjoining mines 46 materials for, easily obtainable 15 mechanical 16 nature of 16 Eussian 8 Mooring apparatus, most approved form 303 tests of 240 Mooring, Austrian arrangement of barge 80 mode of 63 by single cable j 71 experiments in Medway 66-7 1 extemporized 83 faulty arrangements to be avoided 66 fore and aft 69 from ponton-raft 81 Harding Steward's, for mechanical mines 92 ladder method 6> operations, favorable weather necessary 76 running gear in couuectiou with, power of working 78 ship's launch fitted for 72 small charges, mode of. 67 tea heavy chain cable 74 weight of 84 with considerable rise and fall of tide 82 with directing hawser 75 Mortars, twin, suggestions for use in clearing channels 273 Jluddy bottom favorable for mushroom anchor 73-36 Multiple cables, tests of 216 Mushroom anchor, Austrian 64 sinker, most approved form 303 N. Negative current used for testing purposes 246 Nitro-glycerine 37 explosive efiect of, examined theoretically 36 Number of a company and detachment for submarine mining duty 270 315 o. Obstructions, passive, combination Tvith submarine mines 24-iT 1 Oilicers and men, qualification for submarine mining duty 270 Outrigger torpedo fitted to steam-launcli '. 278 torpedoes 07.-, for boat service 27.1 observations of iloating obstruction committee 2^4 sizes of boats most suitable for 2s9 P. Passive obstructions, combination of, \rith submarine mines 24-271 Paying out electric cables, mode of , 151 Personal equation of observer 264 Pickets, use of for cross-bearings at sbort distances 190 Pile, voltaic, extemporized 183 Platinum wire fuse 93-95 battery for use with 172 most approved form 304 tests of 240 Polarization, effect in disturbing tests 2o(i Porter, Admiral, United States Navy, opinion of 11 Position of mines, mode of marking jol to be concealed 157 Pressure, lateral, on buoj'ant mine, calculation for. 66 Primer, torpedo, Abel's, most approved form 86-304 Principles, general, in defending a channel 22 Projectile torpedoes -. ... 275 use of 293 Protection, outer, for glectric cables 127 Q- Qaalifications of cases for submarine mines 49 of electric cables 115 of officers and men for submarine mining duty 270 Quantity batteries, tests of 253 E. Eetlecting electrometer 208 galvanometer 20-! Eesistanoe coils 269 electrical, of cable, test of 247 Eheostat 269 Eoadstead, open, defense by submarine mines 26 Socket composition, torpedoes propelled by 293 Eoom, testing, in a fort 159 Eope protection for electric cables 127 Eule, approximate, for determining size of charge 45 Eules, general, in using submarine mines, 20 Sea-cell, disturbing influence, during test 256 test for insulation by - 255 torpedo, Harvey's 260 316 Page. Sbutter signaliug-apparatua for circnit-brealcer 2:!0 combined ^ritb tiriug keys 234 and firing apparatus 226 most approved form 306 Siemens Brothers', electric cables 116 Si;:;naling from fort to guard-boat and back 161 Single line of mines, disadvantage of 22 Sinker, nmsliroom, most approvi'd form 303 Slack to be allowed in paying out electric cables 1-52 Special torpcilci-vessrls 275 Speed to be slow when searching for submarine mines 274 " Spuyten Duy vil," opinion of floating obstruction committee 277 Steam-launch fitted with outrigger torpedo 278 Submarine explosions, clearing channel by 274 mine, definition of - 7 mines, American 8 Austrian 8 Chinese Ts defensive 10 electrical 17 advantages and disadvantages 17 especially api)licab]e to defense of the United Kingdom and colonies c 14 increase to defense by use of 15 materials for, easily obtainable 15 mechanical... 16 advantages 17 danger in sul.'niersion 18 disadvantages 16 moral effect of 14 n.atnre of 16 Eu,ssian 8 small, cost of 15 Submer.sion, electrical tests during 1-56 tests before and after 238-254 T. Table, testing, Austrian 220 simple 222 and firing, Woolwich 235 Telegraph, electric, from fort to guard-boat 161 Telescope, fixed, and firing-key, use of... 198 Telescopic firing-keys 193 most approved form 305 Tension-fuse, battery for use with 177 'tests of 242 "Terpsichore," Her Majesty's ship, experiments on, to determine etfect of a given charge _ 43 Test for insulation by sea-cell - 255 discharge 246 loop, Varley's 253 of electrical resistance of cable 247 to ascertain whether charge is dry 254 to discover position of fault in insulation 246 Testing-ljatteries -ifjd ami firiug-taUe, AVdolwich 235 boX; for coniieclion of multiple cable 124 electric;il instruments used in inS room in a fort 159 table, Austrian 220 simple _ 222 Tests before and after submersion 233 electrical 233 during submergence 156 of electric cables 245 value due to comparison 258 mechanical-- - 233 of electric cables 243 of case - 239 of combined system before and after submersion 254 of detonating fuses 243 of explosives - - 239 of fnctional electrical machine 250 of instruments 239 of mechanical fuses 240 of mooring apparatus 240 of multiple cables 24o of platinum wire fuse 240 of quantity batteries 253 of tension fuse 242-205 of voltaic batteries 250 of water-tight and insulated joints 243 of Wheatstone's exploder 250 Thermo-galvanometer 269 Tide, mooring when rise and fall is considerable 52 Toritedo, definition of 7 drifting, Lewis' - 294 McEvoy's -- 294 fish, Lupin and ^Yhitehead's 291 fired from boat 292 outrigger, fitted to steam-launch - 278 primer, Abel's approved form 33-304 sea, Harvey's 230 Torpedoes, drifting 275-294 nature of operations suitable for 295 or offensive mines - 9 outrigger 275 for boat service - 275 observations of floating obstruction committee :J34 sizes of boats most suitable for 239 projectile 275 use of 293 propelled by rocket composition 293 Tube, firing. Captain Harding Steward's 109 Y. Vark-y's loop-test 258 A'enice, project for defense by submarine mines 19 318 Paje. Visual signaling from fort to guard-boat and back 161 Voltaic battery, Austrian, for submarine mines 181 DanieU's .. , 179 Muirhead's IHO Varley's IKi) for use ■with platinum fuse 172 tension fuse 177 Grove's 172 ignition by 172 LeClancli6 , 182-305 Mari6-Davy 179 sand, Wollaston's 177 Walker's 98-172 batteries, tests of 25 pile, extemporized 183 Von Scheliha, observation on submarine mines 19 W. Walker's voltaic battery 98-172 Wash of sea, protection of electric cables from 154 Water-tight connection, temporary 134 clay 135 joints 130 tests of 248 Weather, favorable, necessary for mooring purposes 75 Wire coils of instruments must be suited to currents to be conveyed 237 55 511:: >■>:>■> ^ _• >9 tf-12 >)> J>-i»-S> >v .0 _3*^.^afc>> J>*£>-^g^ >>»"> v>^j»:: O^^C" - ^ ,»j- »3.->_i IMO'^ll^b '^ji » :»> . sTfy^ t»A^ :»v ■>:,>» ^JpT^rJ^^ x;> ~>>vj»,r ^^^^>IVI0 > .j»:i 13»>'>')'j J^^^'^?^? » >>>'X>0>. 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