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Readers are asked to re- port all cases of books marked or mutilated. arY820 *^°™" """'»™»)' Library olm,an^ ^^24 032 182 572 Do not deface books by marks and writing. XI Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924032182572 W. B. 740. U. S. DEPARTMENT OE AGRIOULTUEE, WEATHER BUREAU. INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. BY W. E, GREGG, in charge Aerological Division, ASSISTED BY Messes. V. E. JAKL, W. S. GLOUD, L. T. SAMUELS, and R. C. LANE. Prepared under direction of C. F. MARVIN, CMef U. S. Weather Bureau. ■vfrASHmGTOiT: GOVERNMENT FEINTING OrFIOE. 1021. W. B. 740. U. S. DEPARTMENT OF AGEIOULTURE, WEATHER BUREAU. INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. BY W. R. GREGG, in charge Aerological Division, ASSISTED BY Messes. V. E. JAKL, W. S. CLOUD, L. T. SAMUELS, and R. C. LANE. Prepared under direction of 0. F. MARVIN, Chief U. S. Weather Bureau. WASHINGTON: GOVERNMENT PRINTING OFFICE. 1921. TABLE OF CONTENTS. Page. Inthoduction 5 Part I. The Use of Kites 7 1. Selection and establishment of a kite station 7 2. Kite reel house 7 3. Kite reel and motor 8 Protection against lightning 9 4. Kite wire 10 Splicing the wire 10 5. Kites and kite making 11 Marvin-Hargrave kite 12 Material required for standard size kite 12 High wind kite 16 Light wind kite 16 6. Meteorograph 17 Pressure element 17 Temperature element 18 Humidity element 18 Wind element 19 Record sheet 19 Clock cylinder 19 Case or cover 20 7. Calibration of meteorographs 20 Pressure test 20 Temperature test 21 Humidity test 22 Wind test ,... 22 Time test 23 Lengths of pen arms and centers of arcs 23 Reduction of the tests: Pressure 23 Temperature 26 Temperature effect on pressure element 26 Humidity 26 Time rate 28 Wind 28 8. Making the flights 29 Carrying the kites 29 Care of meteorograph 29 Launching the kites 30 Landing the kites 30 Kite wire 31 Observation and experience 81 When to reel in 82 Number of kites to use 32 Weather types 33 Clouds 35 Diurnal series 36 Thunderstorms 36 Local conditions 37 Breakaways 37 9. Reducing records for telegraphic message 37 10. Final reduction of records 38 Hour lines 39 Baselines 39 Placing and computing levels 40 Hypsometric equation 43 Tabulation 44 11. Reduction tables 46 Determination of heights by the barometer 46 Temperature-correction factor 47 Humidity correction 48 Correction for wind velocitv 49 ]>age Part I. The Use of Kites — Continued. 11. Reduction tables — Continued. Pressure of aqueous vapor 50 Relative humidity 51 Part II. The Use of Pilot Balloons 55 1. Selection of stations and observation points 55 2. Theodolite 57 Assembling the theodolite 58 Care of the theodolite 59 Packing the theodolite 60 Carrying the theodolite 60 Adjustments of the theodolite 60 Setting up theodolite for observation 62 Determination of north -south line 63 First method , 63 Second method 64 Third method 65 Orientation of theodolite 66 3. Balloons 66 Color 66 Patching leaky balloons 67 Size 68 Weighing 68 Inflation , 68 Sealing 69 Measuring 70 4. Making an observation 70 Single-theodolite observations 74 Double-theodolite observations 75 Omission of an ascension 77 5. Computation 77 Method I. (1) Single-theodolite computation, slide- rule method 78 Plotting or the construction of the horizontal projec- tion 79 Method I. (2) Single-theodoUte, graphical method . . 81 Method I. (3) Single-theodolite, slide-rule computa- tion, graphical cosine plotting 81 Method I. (4) Single-theodolite, logarithmic computa- tion 82 Double-theodolite computation 82 Method II. (1) Double-theodolite, graphical method. 82 Method II. (2) Double-theodolite, graphical method. 82 Method II. (3) Double-theodolite, graphical method. 83 Method II. (4) Double-theodolite, logarithmic method , 84 6. Reduction of data. 86 7. Coding the message 93 No ascension 95 Code for time and date words 96 Code for wind aloft report 97 Code for altitude 105 Code for clouds 105 Code for visibility 107 8. Forms and reduction tables 107 Rate of ascent in m. p. m 109 Altitude — time tables for various rates of ascent 114 Free lift for definite inflation 115 Temperature-conversion table 115 Miles per hour into meters per second 115 Inches into milUbars 115 LIST OF ILLUSTKATIONS. Fig. 1. 2. 3. 4. 5. 6. 7. 9. 10. 11. 12. 1.3. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24, 25, 26, Plot Blowing the position of buildings and kite field at Ellendale Aerological Station Front view of ofiice and kite storage building at Broken Arrow Aerological Station Close view of kite-reel house at Ellendale Aerological Station Right front view of kite reel Left front view of kite reel View of rear of kite reel; also of variable-speed motor... Method of attaching copper cable to main "ground" pipe Method of attaching copper wire to "ground" pipes placed at stated intervals around the periphery of the reel house 10 Method of splicing kite wire by means of ' ' large twister ' ' 10 Method of turning end of loose wire around main wire by means of ' ' small twister " 11 One method of reeling wire from the kite-reel drum to a smaller drum 11 Different sizes of box kites used at aerological stations. . 12 Front or bridle face of a kite 13 Central or bridle truss of a kite 14 One of the side trusses of a kite 14 Isometric view of a kite 15 Method of making join ts, attaching bridle, etc 16 Metal angles used in fastening principal joints 16 Metal angles for intermediate joints 16 Position and method of attachment of meteorograph in a kite 12 Front view of Marvin kite meteorograph 18 Rear view of Marvin kite meteorograph 19 End view of Marvin kite meteorograph 18 Horizontal screening tube in kite meteorograph, show- ing method of mounting hairs of hygrometer Is Calibration or test of the different elements in a kite meteorograph 24 . Pressure scale values for meteorograph, as determined from tests 25 4 Page. Fig. 27. 8 28. 8 29. 8 9 8 30. 9 31. 9 32, 33 34. 35. 36. 37. 39. 40. 41. 42. 43. 44. 45. 46. 47, 48, 49, 50 51 Page. Curve showing humidity scale values for different humidities 27 Arbitrary or measuring scale: Large divigions corres- pond to divisions on meteorograph sheet 27 Percentage scale, used with scale in figure 28, for de- termining values of relative humidity for any ordi- nate on meteorograph sheet 27 Time scale for use with kite meteorograph 28 Proper method of holding a kite preparatory to launch- ing it 30 Typical meteorograph record of a kite flight 39 Diagram showing method of determining the mean tem- perature of the air column 44 Section of observation platform and theodolite stand, showing the insulation of the one from the other 57 Theodolite used in kite and balloon work 58 Theodolite vernier 58 Section of theodolite showing arrangement of verniers with horizontal and vertical circles 59 Proper method of carrying theodolite; and insulation of theodolite stand from observation platform 60 CoUimation adjustment 61 Effect of prism on line of sight 61 Horizontal axis adjustment 62 Peg adjustment 62 Constellations of Ursa Major and Cassiopeia 64 Balloon filling apparatus used for "definite" inflation. . 70 Single-theodolite plotting board 80 Plan of double-theodolite plotting board 83 Plan of triangulation showing relative positions of balloon 85 Section of plotting board, showing setting of horizontal projection for determination of direction and ve- locity 88 Graphing board for construction of Form No. 1115-Aer. 89 Sample of velocity-direction graph, Form No. 1115-Aer. 90 Graphical representation cf wind-words of balloon code. 94 INSTRUCTIONS FOR AEROLOQICAL OBSERVERS. INTRODUCTION. The value of free-air data is now universally recognized. Until a comparatively recent date these data were used very largely in studies whose purpose was to add to our knowledge of the characteristics of the free air in relation to latitude, topography, and different conditions of weather at the earth's surface. At some places monthly, seasonal, annual, and, to a less extent, diurnal values have been fairly well determined to considerable alti- tudes, and some important conclusions as to the changes in free-air conditions accompanying marked changes in those at the surface have likewise been reached. In general, however, it can truthfully be said that aero- logical investigations are still in what may be called the "pioneer" stage. Immense expansion of the work is necessary before our knowledge of free-air conditions is at all comparable to that of surface conditions. And 'even the latter is as yet far from complete, for most parts of the earth. During the past few years the practical application of free-air data has come very decidedly to the front. For this the World War and the rapid development of avia- tion are largely responsible. Average values, though constituting important information, are no longer suffi- cient. It is now necessary to know the current condi- tions. Densities are required in ballistics, and wind di- rection and force in both ballistics and aviation. More- over, free-air and surface conditions are so closely related that a study of the two, observed simultaneously and over widely distributed areas, can not fail to increase the accuracy of forecasts, not only of conditions in the higher strata, but of surface weather as well. It becomes there- fore increasingly important that this work be developed as rapidly and as thoroughly as possible. Aerological investigations are conducted for the most part by means of kites, pilot balloons, and sounding bal- loons. In the past small captive balloons have been used in calm weather, but because of difficulty of secur- ing good ventilation and because, moreover, low altitudes only could be reached, this method has been largely dis- continued. Manned balloons and kite balloons have also been used, but these are too expensive for ordinary pur- poses. Undoubtedly the airplane offers a means of ex- ploring the air in a meteorological sense, and will in the future be adapted to this use. Before this is done, however, it wiU be necessary to work out certain details of equipment, instrumental exposure, etc. Kites enable us to observe atmospheric pressure, tem- perature, humidity, wind, and electric potential at vari- ous altitudes up to 5 or 6 kilometers, but the average height reached is a little less than 3 kUometers. Kites can not be flown in very light or very strong winds, nor are they successfully used during stormy weather; never- theless, the percentage of days on which kites are flown is high, being about 93 for 5 years' work at Drexel, Nebr. Pilot balloons give us wind conditions only; they can be used in weather unfavorable for kites, i. e., in gales or light winds, but, on the other hand, can not be observed in clouds or during other conditions of poor visibility. By means of sounding balloons we obtain valuable data, including pressure, temperature, humid- ity, and wind, at much greater heights than can be reached by kites. These data, however, are not imme- diately available, as several days are necessary as a rule for the recovery and return of the balloons. In this re- spect kites and pilot balloons are decidedly superior, since the records can be used at once for the information of the forecasters and others. It is evident that all three methods have limitations, to which due consideration must always be given in discussing the results. In order to obtain reliable data it is necessary for the observers, computers, and others to become familiar with a mass of details as to construction, care, and use of apparatus; difficulties to be overcome in getting the best possible records; and reduction and interpretation of the results. Aerological investigations have been con- ducted by the Weather Bureau more or less regularly for nearly 25 years. From the experience thus gained much has been learned, but up to the present time this knowl- edge has for the most part been transmitted orally, although instructions covering certain features of the work have been furnished from time to time in type- written or printed form. The purpose of this pamphlet is to bring together all necessary information in suffi- cient detail to enable those wholly unacquainted with the work to become efficient aerological observers and com- puters. These instructions are confined entirely to work with kites and pilot balloons, since sounding balloons can not be used for some time to come, owing to lack of funds, and, besides, several changes in methods and equipment are contemplated. These instructions are in part original and in part have been prepared from the following sources: "Kite Experiments at the Weather Bureau," by C. F. Marvin, W. B. 110, 1896. "Instructions for Aerial Observers," by C. F. Marvin. Circular K, Weather Bm*eau, 1898. 5 INSTEUCTIONS FOE AEEOLOGICAL OBSEEVEES. "The Methods and Apparatus Used in Obtaining Upper Air Observations at Mount Weather, Va.," by Wm. E. Blair. Bulletin oj the Mount Weather Observatory, vol. 1, pp. 12-19, 1908. "The Construction of a Weather Bureau Kite," by A. J. Henry. Bulletin oj the Mount Weather Observatory, vol. 2, pp. 227-236, 1910. "The New Kite Eeel," by Wm. E. Blair. Bulletin oj the Mount Weather Observatory, vol. 1, pp. 237-238, 1908. "Improved Kite Hygrometer and Its Eecords," by W. E. Gregg. Monthly Weather Review, vol. 45, pp. 153- 155, 1917. "The Use of a Flag Pole in Calibrating Kite Anemome- ters and Also for Observing at Close Eange the Behavior of Kites in the Air," by B. J. Sherry. Monthly Weather Review, vol. 44, p. 327, 1916. "Notes on Kite Flying," by V. E. Jakl. Monthly Weather Review Supplement No. 13 (Aerology No. 8), pp. 7-12, 1918. "Instructions for Operation of Aerological Stations, 2d Order," issued in typewritten form by Meteorological Service, United States Signal Corps, 1918. "Instructions to Observers in Field Kite Work," is- sued in typewritten form by Aerological Division, Weather Bureau. In the preparation of these Instructions special men- tion is due Mr. V. E. Jakl, who has contributed sections 5, 8, and 9 of Part I; Messrs. W. S. Cloud and L. T. Samuels, sections 6, 7, and 10 of Part I; and Mr. E. C- Lane, who has written the major portion of Part II. Numerous helpful suggestions offered from time to time by various members of the field and Central Office force of the Aerological Division; by Mr. S. P. Fergusson, of the Instrument Division; and by Maj. Wm. E. Blair and Capt. B. J. Sherry, of the Meteorological Section, Signal Corps, have been incorporated in the Instructions. Ac- knowledgment is also due Mr. Eoy N. Covert for fur. nishing specifications, with drawings (figs. 7 and 8) , for in- stallation of kite reel to insure protection ag oinst light- ning (in Part I, section 3) ; and to Mr. Wm. C. Haines, who furnished instructions, with drawings (figs. 39, 40, 41, and 42), for adjustments of the theodolite (in Part II, section 2) . — W. R. Gregg. PART I. THE USE OF KITES. 1. SELECTION AND ESTABLISHMENT OF A IQTE STATION. Sites for kite stations must be chosen with considerable care. Experience has shown that the best location is one in level country rather than on a mountain top, the latter being undesirable because of its influence on the meteorological elements and the resulting erroneous rela- tions indicated between the surface and free-air condi- tions. The country surrounding a kite station should be as free as possible from forested tracts, lakes, marshes, rivers, etc. ; also, from towns, steam and electric railways, and high-tension power lines. Inasmuch as free-air winds in this country blow for the most part from some westerly direction, it is essential that there should be as few as possible of the undesirable features above men- tioned on the east side of the station. Fairly good roads are necessary in order that kites that have broken away may be readily recovered. In many respects kite flying can be carried on most effectively if the station is com- pletely isolated, so far as centers of population are cpncemed, but, on the other hand, difficulties of trans- portation, of procuring power and lights, and of providing good living conditions for the men render such a location inadvisable. As a compromise the Weather Bureau therefore selects sites with open country to the east, but with a small town (1,000 to 2,000 people) approximately 1 kilometer to the west. The plot used as a kite field is usually square and contains 40 acres of land, as nearly level as possible, cleared of trees, stumps, etc., and sur- rounded by a sufficiently strong fence to keep out live stock. In case there are telegraph, telephone, or high- tension lines within a distance of 2 or 3 kilometers to the north, east, or south, an extra "guard" wire is installed about 1 foot above the service wires. Power and lights are furnished from the town plant to the station by means of underground circuits. All buildings, except the reel house, and all surface instrumental equipment are located in such part of the western side of the field as is most readily accessible from the town. The instrument shelter, wind tower, etc., are installed in accordance with instructions issued by the Instrument Division. Figure 1 shows the customary arrangement of buildings and instrumental equipment, as well as the location of the kite field with respect to the adjacent town. The geographic coordinates of the stations are deter- mined in the same way as for all other Weather Bureau stations. Latitude and longitude can be found for many places in bulletins of the Geological Survey, Lippincott's Gazetteer, and other publications. The data from these sources are used, after verification as to their accuracy by reference to a recent issue of Eand McNally & Co.'s Atlas. When there are no published data, the latitude and longitude, as shown by the station's location in this atlas, are used. Altitude is determined by running a line of levels from the nearest "bench mark." The height of the barometer cistern is taken as the official station alti- tude above sea level. The methods of determining true meridian are fully described in Part II, section 2. As soon as the cardinal points are established, white posts are placed around the outer portion of the kite field, exactly north, northeast, east, etc., of the reel house, in order that wind direction, both at the surface and in the free air, may be accurately determined. The main building is of frame construction, one and one-half stories high, and is used for office quarters, carpenter shop, and kite storage. It is 26 feet wide by 48 long and approximately 24^ feet from the ground to the peak of the roof. The dimensions of the office and computing room are 25 by 14 feet; of the carpenter shop, 25 by 12 feet; and of the kite storage room, 25 by 20 feet — all inside measure. An attic provides additional room for the storage of kites, extra kite sticks, and mis- cellaneous supplies and equipment. Full specifications and sketches are on file at the Central Office of the Weather Bureau. Figure 2 gives a front view of one of these buildings. 2. KITE REEL HOUSE. It is necessary to have a small building of special design and construction in order to obtain the best results in kite flying. This building consists essentially of two parts — a turntable, by means of which the door- way may be presented to any desired direction, and a superstructure sufficiently large to accommodate the kite reel and accessory apparatus. The whole is mounted on a circular concrete wall 20 inches thick and 30 inches deep, inclosing a space 10 feet 8 inches in diameter. This inner space is excavated to a depth of 2 feet below the top of the wall, thus providing ample room for adjusting the electric wiring from time to time as it becomes twisted due to the turning of the house, and for inspecting the "ground" connections, turntable, etc. The turntable consists of five curved pieces of heavy iron rail, on which turn the wheels that carry the weight of the building, the turning being readily accom- plished by means of an endless cable leading from the trucks to a suitable hand apparatus mounted inside the house. The wooden building itself is about 15 feet in diameter at the floor, tapering to 14 feet at the eaves. The floor is about 2 feet 9 inches above the ground; the eaves, 12 feet, and the peak of the roof, 15 feet. At the front of the building is a doorway about 8 feet in width and extending from the floor to the eaves. This large doorway is provided because, in addition to the reel and the theodolite which occupy a part of this space, it is necessary for the observers to pass in and out occasion- ally in order to launch or land kites, make observations of clouds, etc. A small window at the rear of the house 7 INSTEUCTIONS FOE AEKOLOGICAL OBSEEVERS. gives additional light and ventilation, and a trapdoor provides easy access to the space inclosed by the founda- tion wall. At northern stations it has been found advantageous to have about one-third to one-half of the reel house divided off by a wooden partition, this small room being heated by an oil stove during cold weather to lessen the discomfort of the observers on duty. sun's rays. Additional protection is provided in this case by a sloping roof attached to the reel house and projecting about a foot beyond the limits of the instru- ment shelter. Generally speaking, this extra precaution is unnecessary, since there is usually a good breeze blow- ing, and therefore plenty of ventilation, while a kite flight is in progress. Citu Erlectnc Li«iit. = r- | ; — m,^ iran&torxnere ^'~\. pSD Private S.oad. to Tc;v,tj \ %■ <.^araas .iS'TaTio/-? fiuildim: N 9 « ]5.a.irjL H^rid. p^;ErI, /^xOO&EJ- 0) •H L at SC.A.IJE OF FEET 100 ZOO 300 i V i i Er 1 I 2-^1^ f'erjC/e -^ COO-r'^TT-Y KiO.A.P Open T^'ield Fig. 1.— Plot showing the position of buildings and kite flold at Ellendale Aorological Station. A wind vane is attached to the top of a vertical shaft extending through the peak of the roof, and at the lower end of this shaft another arrow is fastened with the same orientation, thus making possible the determination of surface wind direction from inside the reel house. On the left side of the building, as one faces the doorway from the inside, a standard Weather Bureau instrument shelter is installed. This shelter, as is well known, has a double roof to prevent heating of the inside air by the Xi Q) ■H Complete specifications and drawings for the con- struction of reel houses arc on file at the Central OiTice of the Woathor Bureau. A general view of one of these reel houses is shown in figure 3. KITE REEL AND MOTOR. The kite reel, now in general use at Weather Bureau aerological stations, was originally designed by Prof. C. F. Marvin and later modified by Dr. Wm. E. Blair. Fig. 2.— Front view of office and kite storage building at Broken Arrow Aerological Station. Fig. 3. — Close view of Ipte-reel house at Ellendale Aerological Station- Fit!. 4.— Right Iront view or kite reel. Fig. 5.— Left front view of kite reel. .^.^--4 ^ — ' :' e--';:/;- — — - --J »-«.—- -'=-;— - 'f^^B INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. Except for the drum, it is made largely of cast iron and its weight is such as to render it stable under any pull that may be exerted by the kites. Two views are shown in figures 4 and 5. The most prominent features are the solid base and substantial frame, the drum and the three small wheels which guide the wire from the drum to the kites. One of these wheels, at the front, is so mounted that it can accommodate itself to the direction which the wire assumes under the influence of the wind's action on the Idtes. The other two wheels, at the top, are mounted on a distributor carriage which travels back and forth under the action of a cam, shown in the upper right-hand part of figure 5. Other details in this figure are the hand brake and wheel and the operating gears. In figure 4 may be seen the foot brake and wheel (auxiliary to the hand brake), a Veeder counter, and a dynamometer for indicating amount of wire out and pull exerted by the kites, respectively. The drum, which is the result of numerous trials with different types, consists of three pieces — the barrel and two spiders. The former is made of cast semi-steel and the latter of cast iron. The spiders merely center the barrel on the shaft and rotate it, but carry none of the accumulated strain to which the drum is subjected by ■the piling up of the successive strands of wire. On the same shaft with the drum are mounted the two brake wheels and two driven gears, already referred to. The latter, shown in figure 5, are of different diameter, the larger being for slower speeds. The gears engaging these are always in mesh, and power is applied to either of them by means of a double-throw friction clutch at the rear of the reel within easy reach of the operator. Complete specifications and drawings for construction of kite reels are on file at the Central Office of the Weather Bureau. The Tcite reel motor. — Power is furnished by an electric motor, so designed as to run at any speed between about 400 and 1,800 revolutions per minute, and for any pull up to that equivalent to about 5 horsepower. Such motors can be obtained for either direct or alter- nating current. Power is transmitted by means of chain and sprockets. One of these motors (for direct current, in this case) is shown in figure 6. Speed is regulated by means of the shaft leading from the motor to a position within easy reach of the operator. As already stated, the speed can be still further regulated by the use of one or the other of the two driven gears sho\STi in figure 5. Protection against lightning (contributed in part by Mr. R. N. Covert, Meteorologist). — Both in and out of the Weather Bureau service the flying of kites has been attended by danger from lightning to the persons engaged in the work, and with the continued growth of the Aero- logical Section of the service it becomes more and more necessary to use every precaution to avoid possible injuries. In addition, damage to property should be minimized. It is well known that even the wet string used in flying common kites will occasionally permit a con- siderable discharge to earth during a thunderstorm. But when steel wire is employed to hold a box kite, the metal provides a better conducting path for the lightning. A direct discharge from clouds to earth will quickly melt or vaporize the wire, but the wire will have directed the dis- charge, the air along the path becoming a good conduct- ing medium by reason of its becoming ionized. There is also occasionally a considerable inductive discharge. From the foregoing, there evidently must be some reliable means for conducting dangerous discharges to earth as well as for completely insulating the reel when it is desired to measure the atmospheric electric potential. This has been accomplished according to the following plan. The kite reel is insulated from the floor by being mounted on blocks of fiber, as indicated in figure 6, and the sprocket which is driven by the chain from the motor is composed for the most part of fiber. This insulation makes possible the measurement of elec- ^ COP/'£/? C/P5L£ TO K/r£ ^ffl Sa^^£'A'/£'SS CO/^AffCTO/? f^fmir /4 CtQP /J "g/J/LI^ P/fif Fig. 7.— Method of attaching coppercaWe to main "ground " pipe. trie current on the kite wire. Although such measure- ments have yielded little of scientific interest, they are useful, especially in summer, as indicators of possible trouble from approaching thunderstorms, of the exist- ence of which, however, there is no other evidence. Under such conditions disruptive discharges of consider- able intensity sometimes render advisable the shorten- ing of a flight which otherwise might have been continued until too late for completion before the arrival of a thunderstorm. Accordingly, Weather Bureau stations are furnished with electrostatic voltmeters of the Braun type for this purpose. A long switch, which is opened during these measurements, at other times connects the reel with a ^^^.-inch stranded copper cable to a "ground" formed by driving a 10-foot length of IJ-inch galvanized- iron pipe vertically into the earth and fitting the upper end to receive a connector, as shown in figure 7. The attachment at the reel is formed as directly as possible. 10 INSTEUCTIONS FOR AEEOLOGICAL OBSERVERS. all sharp bends being avoided. As an added precaution, a copper cable is led from the reel to the trucks which carry the wheels, and the rail upon which the kite house turns is then grounded by making four connections through No. 6 copper wire to four 10-foot lengths of f-inch galvanized-iron pipes placed 90° apart just out- side the periphery of the structure, as shown in figure 8. The foregoing description and the following instruc- tions should be supplemented by those given in Farm- ers' Bulletin No. 842, which contains general information regarding lightning protection. Attention should, in particular, be given to the grounds to see that they are well made, and it should be known with certainty that the pipes are in contact with soil that is moist throughout the year. Furthermore, the iron-pipe grounds must be periodically inspected to learn to what extent corrosion is occurring, and the pipes replaced as often as needed. After the connections have been completed to the ground pipes, paint the upper ends of the pipes and the attached fittings with two coats of metallic paint. F/iWCS OF /laiL ing extreme conditions it is even advisable to clamp the brake securely and leave the reel house, with the kites still flying, until the passing of the storm. 4. KITE WIKE. In meteorological kite flying, steel music wire, popu- larly known as "piano" wire, is generally used for the main line; it is far superior to any other material thus far tried for this purpose, because in it are combined the very desirable qualities of great and uniform strength m proportion to weight and bulk, and a smooth surface. This wire is manufactured in a large number of sizes varying between about 0.01 and 0.125 inch in diameter (Nos. to 30, music-wire gage), and usually is sold in coils of various amounts and lengths, the smaller sizes, as a rule, being in longer pieces than the larger. For the main line, the longest pieces obtainable should be used in order to avoid the necessity of making numerous splices. Obviously, assuming adequate strength, the smaller the wire the better, for convenience in handling. The sizes between 0.028 and 0.044 inch in diameter are most frequently used in kite flying. The 0.028-mch size, used by the Weather Bureau during the early days of kite flying, is quite satisfactory for small kites and ascen- sions to moderate heights, although the tendency of small ^^. /ffo// Afi^w. 5c/?efr ■5m M/iueMi£ //?o/y Cap - — ^ CAiy.P/pe Fig. 8.— Method of attaching copper wire to "ground " pipes placed at stated intervals around the periphery of the reel house. Following is a list of the material required for pro- tecting one reel house : 12 feet -j^-inch copper cable. 2 ^-inch solderlesa connectors. 1 f by I inch galvanized machine bolt. 1 IJ-inch galvanized malleable-iron cap. 10 feet Ij-inch galvanized standard pipe. 40 feet |-inch galvanized standard pipe. 4 J-inch malleable-iron caps. 8 |-inch, 12-24, round-head iron machine screws. 8 iron washers for same. 6 feet No. 6 copper wire. 1 switch for breaking "ground." In addition to the precautionary measures above out- lined, it has been found advisable for those engaged in the work to be provided with rubber gloves and boots during thunderstorms. Moreover, the utmost care should be taken in landing a secondary kite. The splice wire should be taken off at the reel house and the kite then landed at as great a distance from the wire as possible; otherwise the observer might readily form a short circuit for the lightning from the kite wire to the earth. Dur- Fig. 9.— Method of splicing tite wire by means of "large twister." wire to kink is a disadvantage. When high flights with a number of kites are desired, larger sizes of %\Tre become necessary, and the usual procedure at aerological stations of the Weather Bureau is to make up the main line of the following sizes: 0.032 inch, 500 meters (approxi- mately); 0.036 inch, 1,500 meters; 0.040 inch, 2,500 meters; 0.044 inch, 10,000 meters, or 14,500 meters in all. The proportions vary somewhat, according to the average wind conditions. In the South, for example, more of the smaller sizes can be used than in the North. The tensile strengths of the sizes indicated are, respec- tively, about 300, 330, 420, and 480 pounds, and the maximum working strains 200, 250, 300, and 350 pounds. When wire is wound on the reel, the coil is placed on a spool; the end of the wire on the inside of the coil is attached to the drum or spliced to the outer end of the wire already on the drum, as may be necessary, and the entire coil is then wound on the drum, the reel being run by power or by hand, as preferred. Splicing the wire requires considerable care. As the result of extended experience, it has been found that the best method is to twist the wires evenly about a common axis for a length of 5 or 6 feet, then turn the free ends closely around the main line for a length of about half an inch. These two processes are accomplished very Fis. 11.— One method o£ reeling wire from the kite-reel drum to a smaller drum. INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. 11 readily by means of simple tools, as shown in figures 9 and 10. The two wires to be spliced are held firmly by means of an ordinary machinist's hand vise, having brass jaws to prevent cutting the wire. This hand vise is not shown in the illustrations. The two wires are then placed in the shallow converging slots of the larger "twister," figure 9; held in position, but not clamped, by the spring and set screw above the part containing the slots; and finally twisted uniformly, each about a common axis. The free ends are then wound closely around the main wire by means of the smaller "twister," shown in figure 10, which scarcely needs explanation. Some difficulty is experienced in making an even splice of two wires of different sizes, and care must be exercised lest the smaller wire be the only one twisted. The process is aided if this smaller wire is held at a greater tension than the larger. It has not been found neces- sary or desirable to solder the splices, although that practice was followed during the earlier years of kite flying. The end of the wire to which the kite is to be o X) Fio. 10.— Method of turning end of loose wire around main wire by means of "small twister." fastened is passed through a swivel and secured to the main line by splicing in the same manner as for ordinary sphces, except that a length of about 1^ feet is sufficient. WhUe the wire is being wound on the drum, machine oil should be poured over it from time to time, in order to prevent it from rusting. This should also be done occasionally after the wire has been used during rainy or snowy weather. Vigilance in this respect is well repaid in reducing the number of breakaways due to defective wire. Moreover, it is well to examine the splices from time to time and to renew them, if the main wire at the ends of the splices shows signs of wear. Such renewal can be effected during kite flights, but a preferable method is to wind the wire from the reel on a small drum, make the splice or splices, and then rewind on the reel. Figure 11 shows one way of doing this. In winding the wire on the small drum, power is furnished, through chain and sprockets, by an automobile truck. As soon as all splices have been examined and, if necessary, renewed, the wire is rewound on the drum of the kite reel, power in this case being furnished by the motor in the usual way. During this process it is well to wipe off the old, dirty oil with a piece of waste, then pour new oil on the wire as it is being wound on the drum. 5. KITES AND KITE MAKING. In practical kite flying, as exemplified at the aerological stations of the Weather Bureau, the object is to attain as great a height as possible, without incurring serious risk to the kites or line. Obviously, the larger the size and number of kites used, the stronger — and consequently heavier — must the kite line be. Considerations of the effects of wind pressure and ease of handling restrict the diameter of steel wire that it is practicable to use for line to certain narrow limits of tensile strength. Limitations in the dimensions, etc., of the line must, therefore, be met by efficiency in kite performance. Of the qualities that an efficient kite should possess lightness, stability, and strength are the most important; but lightness must to some extent be sacrificed to realize the ideal practical kite. Of the many types and patterns of kites that have been suggested or tried the Hargrave cellular kite or some modification of it (in the work of the Weather Bureau, the Marvin-Hargrave) remains the standard. In addition to its good flying qualities, it is perhaps better adapted to the tandem method of fljang than is any other type of kite. The tandem method of flying and the design of kites and accessories best adapted to it were naturally devel- oped from experience and the knowledge of the atmos- phere obtained during early efforts to attain high altitudes by means of kites. Apart from practical reasons, the frequent stratified condition of the atmosphere as regards wind velocity and humidity imposes a limit upon the size of kites that should be used. It is not often that the wind is so uniform or increases so uniformly with altitude that a high flight can be safely made with one kite large enough to lift the necessary length of line. By distribut- ing the kites along the line, suitably to the prevailing wind and weather conditions, the maximum lifting power of a given surface can be realized, without at any time exposing the whole of this surface to sudden changes in pressure of the wind. Abrupt changes in wind and weather with time or altitude usually affect the lifting surface along only a portion of the line, the total increase of tension of the line from such causes depending largely on the area of lifting surface affected, and the methods for preventing excessive pull embodied in the construction of the kites. In the Marvin-Hargrave kite, excessive pull is prevented by its method of bridling, described in detail in a later paragraph. This feature of its construction is flexible, permitting a relatively greater margin of safety with increase in size of the kite. The ideal conditions under which a high flight could be successfully made with one kite can not be foreseen with enough certainty to warrant the necessary equipment of suitable line or large kites, even if such equipment were 12 IN.STEUCTIONS FOE AEROLOGICAL OBSERVEES. safe or practicable. There is, in addition, the fact that the tension indicated at the lower end of a line from which a single kite is flying is only one factor of the maximum tension on the line. Including the effects of wind pres- sure on the line, the maximum tension occurs where the kite is attached, and is equal to the tension indicated at the reel plus the weight of the vertical projection of the line. Under actual conditions, the tension to ^A-hich the line is subject is a complex of the action of gravity, the pressure of the wind on the line, and the pull of the kite, and departs more from the indications at the reel, the higher and farther away the kite is flying.' When the weight of the line is suspended from a number of kites at considerable intervals of distance, the difference between the maximum tension on the line and that indicated at the reel is practically negligible. Under the adopted method of tandem flying, the range or variety in size of kites that it is advisable to build is established by the experience of the kite flier, the mechanical skill of the kite builder, and a knowledge of the tensile strength of the different sections of the line employed. It is unnecessary to build a kite much smaller than one which, under the most severe conditions, will exert a pull nearly equaling the tensile strength of the smallest diameter of line used. In the other extreme, the size of a kite should not go beyond that defined by caution in flying and limit in permissible fragility. One or two intermediate sizes in addition give a complement of Idtes that serves all purposes of every-day flying, and admits of easy standardization for manufacture. The Marvin-Hargrave hltes now used are essentially of the same type and construction as those devised by Prof. Marvin,^ and used at 17 stations during the Weather Bureau kite campaign of 1898. The only important modifications that have been introduced since that date are in the dimensions and in the adoption of the elastic bridle, experience having shown that a smaller and stronger size of kite is required for high winds, while for light winds a greater spread of sustaining or lifting sur- face is necessary. Three sizes of kites are most frequently used. They are illustrated in figure 12. They may be classed as high-wind kites, moderate-wind or standard kites, and light-wind kites. A fourth size, slightly larger than the standard but smaller than the light-wind kites, is some- times used. The details of construction for the different 'Monograph, "The Mechanics and Equihbrium of Kites," by Pnif. C. F. Marvin, particularly pp. 64 to 70. (See Monthly Weather Review, April, 1897.) This mono- graph was submitted in competition for, and was awarded, the Chanute prize ofl'ered in 1896 by the Boston Aeronautical Society "for the best monograph on the kite, giving a full theory of its mechanics and stabiUty, with quantitative computal ions appended." It was written at a time when the mechanics of the cellular i^itc— the progenitor of the heavier-than-air machine— wa; being closely studied. The student of the equilibrium of kites is referred to this monograph in its entirety for a full mathematical trcuimcnt of the subject. ' Concerning the history of the meteorological Itites now used in the United States, it maybe of interest to note that in the early days of kite flying at JJhicHill Observatory, Massachusetts, H. Helm Clayton made many improvcrucnl:. on the Hargrave box Icite of 189.5. The most important modiilcation was the use of longitudiiialsticksconneeting the two cells at their outer corners, thereby greatly increasing the strength and stability of this kite. Prof. Marvin added the excellent folding feature, which not only makes it easy to ship kites, but also allows ready reassemblage with unimpaired strength . sizes are precisely the same, the only differences being in the dimensions and proportions. As will be under- stood from the description and detail drawings which follow, this form of construction has certain advantages and disadvantages. One of the chief disadvantages is its frailty. Collision with the ground or other object almost invariably causes a bad smash of the kite; like- wse, when the sails become water-logged the shrinkage of the cloth combined with the pressure of the wind is frequently powerful enough to crush the framework of the kite. On the other hand, broken sticks are easily and quickly replaced and the kite itself is conveniently collapsed for shipment. This is a very important point, since occasionally the kites have to be returned from the surrounding country. As is well known, the kite consists of two cells joined together by longitudinal strips or sticks of straight- grained spruce. The front cell has a middle plane, and in this respect it differs from the original Hargrave pat- tern. The details which follow refer to what is l-inown as the "standard kite." This size, modeled after the pattern used in 1898, has been found to be the most suitable for a wide range of wind velocity and weather conditions. When properly built it will fly well in winds of from 12 to 30 miles an hour (5 to 13 meters per second) near the ground, and 70 miles an hour (31 meters per second) when 2 or 3 miles high. Its extreme dimen- sions are as follows : Ft. In. cm. Length or distance fore and aft 6 8 J 204 Width or distance between the outside vertical surfaces... 6 4J 194 Height or distance from top to bottom of cell 2 8^ 83 The area of sustaining or lifting surface is 63.8 square feet (5.9 square meters), and of steering or neutral sur- face 21.7 square feet (2 square meters). The kite weighs about 9 pounds (4.1 Idlos). The material required in the construction of ihe standard- size Icite includes: (a) Forty-tloree sticks of the following dimensions: li i l^y i inch by 7 feet 6 inches. Center bridle stick: square edges. li S by ^ inch by 6 feet 10 inches. Back center; square edges. 4, S by -f^ inch by 6 feet 10 inches. Corners; square edges. 8, t by T^ inch by 6 feet 6^ inches. Horizontal front and back edges of kite; rounded edges. 12, I by ^ inch by 2 feet 7^ inches. Horizontal sides; rounded edges. 8, I by -^ inch by 2 feet 7^ inches. Horizontal intermediates, bracing horizontal front and back edges of kite; rounded edges. 6, I by -^ inch by 3 feet 2 inches. Horizontal centers, bracing hori- zontal sides, rounded edges. 3, I inch by ^ inch by 2 feet. Vertical center; rounded edges. (&) The sticks are made of straight-grained spruce. All horizontal sticks should have their edges rounded, so that the end resistance of the kites to the wind will be as small as possible. Fourteen yards of Lonsdale cam- bric ^ 26 inches wide arc used for the sails; some coarse waxed linen thread for lashing angles to sticks; 192 feet of No. 11 piano wire, diameter 0.024 inch, for guys. (c) Forty-eight metal angles of the pattern shown in detail in figure 18 form the principal joints, 1 to 24 ]|'IG. 12.— DifEerent sizes of box kites used at aerological stations. Fig. 20.— Position and method of attachment ol meteorograph in a kite. INSTEUCTIONS FOE AEROLOGICAL OBSERVERS. 13 figure 16; 34 metal angles of another pattern, shown in figure 19, are used for all intermediate joints, excepting at h'. d' , n, p, y, and w, which are simply Figure 13 is an elevation of the front or bridle face of the kite — i. e., the lower sxuface when flying. The opposite face — i. e., the upper or rear surface of the / %"ji'/2 t6'-/0" 3 n"xW>^Z' /f/te 37"/c/rs squars. rounded iges ] 43 Mefaf clomps- Fig. ^3'--y " '/ « 192 ry. 0. 024 " piano w'lrg 14 yds, Lonsdcfe Cam- It/'c or metcen'z- \ ed si/k 26 " wide. lashed with waxed thread. The isometric detail, figure 18, shows how these joints are fastened. These metal angles are made especially for the Weather Bureau. kite — is the same except as to the size and length of the bridle stick. Figure 14 is a sectional elevation showing the central or bridle truss, and figure 15 is an elevation of one of the two side trusses. The fine diago- INSTEUCTIONS FOR AEROLOGICAL OBSERVERS. 14 nal lines in figures 13, 14, 15, and 16 show the system of wire bracing necessary to preserve the form and rigidity of the framework. This bracing is all done with very fine piano wire secured to the metal angles, as shown in figure 18, for the vertical cross bracing. In the hori- zontal and long vertical bracing the wire is looped over Lonsdale cambric,^ 2 feet 2 inches wide and 18 feet 4 inches long, and are double hemmed one-half inch on each edge and each end. A strong cord should be passed through this hem to lessen the danger of tearing. The sails are stretched around the kite frame and lashed to the horizontal and vertical sticks with waxed thread jr=" CENTER Fig! /4 ENDS ng. /5 the small bolt head in the metal angles before the bolt is tightened up. All metal angles are lashed to the sticks with well waxed linen thread. After the frame is put together and securely braced, care being taken that all angles are true and square, the kite is ready for the sails. These are made from white A middle sail is placed in the center of the top section, extending from MV to QZ (see fig. 16). This sail should s The roar cell and sometimes both colls aro covered with a black tahric known to the trade as "mercerized" silk or French porcaline, "batiste," etc. It has the property of shedding water to a much iiroater extent than cambrio. For that reason kites covered with It are preferred during fog. Most kites are made with a white front cell and a black rear coll, the contrasting colors being very desirable for visibility. IlSrSTRUCTIONS FOR AEROLOGICAL OBSERVERS. 15 be exactly 2 feet wide and 6 feet 4^ inches long after this bridle is attached another stout cord in the form of being hemmed, as described for the main sails, and a double loop about 18 inches long, having at its end a should be lashed to the sticks in a similar manner. strong brass ring. This cord extends as shown and is lis Fij^. 16 /somefn'c view The bridle and the method of attaching the kite to the fastened to the extreme front end of the bridle stick, line wire are shown in the isometric detail, figure 17. A From this point a wire extends back and is fastened at stout cord about 18 inches long is fastened to the bridle point 14, as seen in figure 14. The elastic cord used in stick at point 11, and to this is attached a cloth-bound making bridles is manufactured especially for the elastic bridle, formed as shown. To the outer end of Weather Bureau. It consists of thin strips of rubber 16 INSTEUCTIONS FOE AEEOLOGICAL OBSEEVEES. about one-quarter of an inch wide tightly bound in a cloth cover, in the form of a small braided rope about five-eighths inch in diameter. On account of the elas- ticity of the rubber this arrangement protects the kite and wire from injury by sudden gusts or strong winds by allowing the kite to fly at a smaller angle of incidence, thus diminishing the pull. The head kite, which carries the meteorograph, is fas- tened directly to the line by means of the brass ring in the outer end of its bridle. The secondary kites are flown by means of cords about 125 feet long. These cords are attached to the main line in the following manner: A piece of No. 9 soft iron wire about 6 feet long is bent so that a small open ring about an inch in In the light-wind lite the change in proportions from the standard is the reverse of that of the high-wind kite— i. e., the width is increased in proportion to the length fore and aft. The dimensions are increased over all, giving this kite a lifting surface of 93 square feet (8.6 square meters) and a weight of Hi pounds (5.2 kilos). It will fly in a slightly lighter wmA than the standard, but its chief advantage is characteristic of all large kites — it will lift more line after it has ascended into a current stronger than necessary to lift itseK. Its ability to fly in a lighter vnnd is due to the fact that it is lighter for the same lifting surface than the other kites. The frailty of this kite is partly compensated for by the fact that it is used only when 'surface winds are light to Brass ring for affachinq y^ "* ^>^ Fr^lar^ed Metal Chrrtps diameter is formed near one end. About an inch of the wire at each end is then bent at right angles, thus: I o — I. This piece of iron wire is wrapped tightly about the main line, and the cord holding the secondary kite is tied into the ring. The method of attaching the meteorograph to the head kite is shown in figure 20. In the high-wind Tcite the proportions and dimensions of the standard size are preserved, except that the width is made 11 inches less, thus reducing the width of the lifting surfaces and relatively increasing the area of neutral surface. It has a lifting surface of 54.6 square feet (5.1 square meters). This kite has been successfully flown in an 80 mile per hour (36 m. p. s.) wind at an altitude of 1 mile (1,600 meters) above the ground. moderate, and the chances of the kite's striking the ground consequently small. It is not used when wind velocities aloft exceeding 30 miles per hour (13 m. p. s.) are expected, for, while it has been found to possess fairly good flying qualities in a 50 mile per hour (22 m. p. s.) wind at an altitude of 2 miles (3,200 meters) smaller kites can be more easily handled and more advanta- geously used in the stronger winds. With a given pattern of kite, any increase in size, without a more than corresponding increase in weight, will be at the sacrifice of rigidity of the framework. In the three sizes of kites described and illustrated, and other sizes and shapes that have been experimented with in the past, there is only a small range in the minimum wind velocities in which they will rise from the ground. The INOTRUCTIONS FOE AEEOLOGICAL OBSERVERS. 17 excess of wind velocity above that necessary to fly the unburdened kite will be available to lift a weight roughly in proportion to its lifting surface. The lifting capacity of a Hargrave kite is partly a function of its shape. For a given area of horizontal sail surface, the lifting capacity can be increased by making it wider relative to its length, since, in all kites the pres- sure of the wiad is greatest near the front edge of the sails.' By increasing the length and depth relative to the width, the lifting capacity is lessened, but the stability of the kite improved. However, not much latitude is permitted the kite builder in either direction, as on the one hand a kite proportionally too wide will fly badly in any consid- erable wind, while a kite too long and deep will not have lifting power enough, in relation to the pull it is capable of, to justify its use. A certain sturdiness of framework is necessary in all kites, not only to minimize breakage from inevitable collisions with the ground, but also to maintain good flying properties in strong wind. The wire ties in the Marvin-Hargrave kite serve to hold the framework symmetrical as a whole, and add little to the weight. A kite so braced will not collapse in any wind in which it is advisable to fly. An exception occurs when the sails become wet, but under such circumstances frailty is sometimes an advantage, by preventing a possible break- age of the line. However, unless the sticks are given an adequate thickness, distortion or deformation of the frame and sail surfaces, and consequent erratic action of the kite, will result during strong winds. The stability of any kite is observed to increase with height above the groimd, especially the first few hundred meters. For a considerable distance above the ground, the ability of a kite to withstand strong wind increases at a rate greater than can be accounted for by the dimiuishing density of the air. There seems little doubt that this can be explained entirely by turbulence, gustiness, eddies, and convectional cxu-rents, the effects of which on the kite are strongest near the ground. 6. METEOROGRAPH. It is apparent that an instrument adapted to the pur- pose of exploring the atmosphere by means of kites must be accurate, light, durable, and compact. The meteorograph designed by Prof. Marvin is very satisfac- tory in all these respects, and is simply an ingenious combination of well-known devices used in recording pressure, temperature, relative humidity, and wind velocity. As shown in figures 21, 22, and 23, the essen- tials of this instrmnent are a light, rigid tube and frame- work, firmly united, which serve as supports for the several recording devices and provide satisfactory ex- posure for the sensitive elements. The anemometer, temperature element and hygrograph hairs are mounted inside this tube, and the pressure element is secured to the frame in which, also, is clamped the clock drum. The four pen arms are mounted on the outside of the tube • For footnote see page 12. 46329—21- and connected with the sensitive elements by means of a simple linkage, adjustable in order that the range of movement of the pens or their position on the record sheet (as explained in detail hereinafter) may be changed if necessary. With the exception of the clock movement, the bearings and links (which are of German silver) and the brass screws and nuts, the instrument is constructed of aluminum, and weighs but 2.5 pounds. A removable cover protects the mechanisms from injury when the instrument is in use. The screening tube is insulated from this cover by strips of bakelite. During a flight the meteorograph is secured inside the kite in such a position that the wind passes freely through the tube containing the temperature element and hygro- graph hairs. In this way a very satisfactory exposure is obtained; the ventilation is good, since the wind is always strong enough to support the kite, and insulation is further minimized or eliminated by the shading of the instrument by the kite. A brief description of each ele- ment and its characteristics wiU, perhaps, lead to a clearer understanding of the workings of the meteoro- graph. Reference should be made to figiu^es 21, 22, and 23 for illustration of the parts described. Pressure element. — ^Two nickel-plated, steel vacuum cells, such as are used in aneroid barographs, are pre- vented from collapsing by a strong steel spring. Any change in the air pressure causes an expansion or con- traction of the cells and a consequent movement of the free end of the spring (the other end being rigid), and this causes the connecting arm to be raised or lowered the same amomit. This vertical movement caused by the expansion or contraction of the cells is changed to a hori- zontal movement of the pen resting on the record sheet, and at the same time considerably magnified by a simple right-angle lever connection. Since the instrumentis often carried to an altitude of 5 kilometers or more, and since this distance is recorded in a space of about 5 centimeters on the "record sheet, it is very important that the pen record accurately. The usual difficulties met with in the aneroid cell are overcome as far as possible. The link is so simple and direct that there is httle chance for lost motion or friction. These must be watched for, however. The combination of two cells gives twice the power of one to the spring and consequently the pen arm, and also makes the movement " stiff er;" that is, it takes a greater jar or vibration to move the pen from its proper position at any time, and any possible friction in the bearings or connections has a smaller effect on the movement of the pen arm. Since, then, a change in the pressure expands or contracts the cells, the movement of which is multiplied by the link and recorded by the pen, it is simply a matter of determining how much any certain change in pressure moves the pen on the sheet. The methods of deter- mining this and similar values will be described in section 7. AU aneroid cells are affected by changes in temperature, an increase in temperature lessening the resistance of the spring and vice versa. To "compensate" for this a little air is allowed to remain in the cell and then after testing 18 INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. at the factory a bimetallic strip is introduced in the link to "compensate" the element with still greater refine- ment. The compensation, however, is never perfect; hence, it is necessary to determine just what effect any temperature change will have on the pressure element and make allowance for it. The pressure pen is usually placed in the middle of the record sheet. Sometimes, however, it may be advisable to change this position, for example, if an unusually high flight is expected, and this is easily done by simply turning the adjusting screw on the pressure element. This screw should always press against the frame, as otherwise the element will be loose. If we wish the pen to move farther than it does for any definite change in pressure, we can loosen the small set screw in the link and push this lever arm in toward the linear fimction of the temperature, it is found that the movement of the pen arm is in direct ratio to the tem- perature change; in other words, the scale value for any one instriunent is a constant. The exposure of the ele- ment being excellent, there is no appreciable sluggishness on account of lack of ventilation, and therefore the ele- ment adjusts itself quickly to any change in temperature. The temperature pen is set near the top of the sheet, allowance being made for any increase in temperature with altitude. The position of the pen on the sheet may be changed by loosening the brass set screw and then turning the pinion situated just above this set screw and between two other small brass screws. One end of the temperature element is rigidly connected to a rack which is moved by this pinion. The other end of the element is connected to the lever arm and link. Moving the pen # f^ . ^^^^ ^ wh 1 Si ^^^^^ ^^^ €^ L-— 3? ^^r^ ^^^^^^ ^^ ^^^^^ ^^•* ^'''oC^g'^^ ^**^^^^^^^ V ,^^0^^^^^^^^ S^v ^^^ » Fig. 24. — Horizontal screening tube in kite meteorograpli, showing metlioa of mounting hairs of hygrometer (a, taed post; 6, pivoted arm; c, pen arm; i, spring for holding hairs at constant tension). center; then the same motion of the element and its con- necting arm will cause a larger angular motion of the adjusted arm and the pen. In this way the amount of motion of the pen arm compared to the actual change in the element, called the "scale value," can be made practically anything desired. Temiperature element. — The temperature element is made of "thermostatic" metal which consists of closely united strips of "invar" and bronze 25 mm. wide, bent into nearly a complete circle. A small steel spring inserted inside the element and attached to its ends increases its elasticity. The invar does not expand or contract with a rise or fall in temperature, but the bronze does, thereby causing the element to open or close; this motion is transmitted directly to the pen arm by means of a simple link. Since the coefficient of expansion of bronze is a in this manner does not change the scale value, which is altered in exactly the same manner as is that of the pressure element. In some of the newer meteorographs the link has been so constructed that the scale value may be changed in any of several ways. The principle of the mechanism, however, is the same in every case. Moving the connect- ing point toward the center of rotation causes that point to move through a greater angle with the same change of the element, and vice versa. Humidity element. — Free-air relative humidities are usually obtained by means of the hair hygrometer. Human hair has the property of lengthening or contract- ing about 2 per cent, when subjected to extremes of moisture. The hairs are mounted longitudinally in the horizontal screening tube. (See fig. 24.) The individual tr INSTEUCTIONS FOE AEEOLOGICAL OBSEEVEES. 19 hairs are mounted separately instead of in a bundle. This method makes the element more quickly respon- sive to any change in himaidity. The hairs are connected as directly as possible with the recording pen, thus re- ducing to a minimum the possibility of lost motion or friction in the bearings. Two sets of hairs are used — one running from an adjustable post at a to the pivoted arm at h, this arm also being connected with an adjust- able post; the other from the lower end of the arm at 6 to the pen arm at c. A small spring at d, or outside the tube on new instruments, keeps the hairs at constant tension. This tension should simply be sxifficient to take up any slack in the hairs and to overcome any possi- ble friction in the movement of the pen arm. The dou- bling of the strands of hairs in this fashion is equivalent to extending the hairs for twice the distance of either strand alone and hence the movement of the pen arm is twice that of a single length. Before moimting, all of the hairs are subjected to the same conditions of tempera- tm-e and humidity and the same tension and are fastened firmly with shellac. It has been found that an element in which the hairs are thus mounted responds very quickly to changes in humidity, whereas, when the hairs are arranged in a bundle they reqiiire a relatively long time to . change from dry to wet conditions and especially from wet to dry. Any change in the relative humidity, then, changes the length of the hairs, and this change is commxmicated directly to the pen arm. The change, however, is not linear with respect to the humidity change. Thus it is found that twice the change in hmnidity does not cause the pen to move twice the distance that a imit change would cause it to move as was found iu the case of the temperature element. For this reason a special scale has to be made up for each humidity element showing the movement of the pen arm for any definite change in humidity. The position of the humidity pen on the sheet may be easily changed. The two adjustable posts mentioned above are held iu position by small thumbscrews on the outside of the screening tube and may be moved either way by loosening the thtmibscrews. This either increases or decreases the distance between the posts, the slack or tension being adjusted by the small spring connected to the axle of the pen arm. The post that is connected directly with the pen arm is threaded and the position of the small clamp nuts holding the hairs on this post may be changed by moving the clamp nuts up or down. In later instruments the adjustment is made by means of a set screw in a small cylindrical block which can be made to slide up or down the post. In either case a movement up or down causes a change in the scale value of the humidity element. Thus, when the device that holds the hairs is moved downward, the post moves through a greater angle than before for the same change in himaidity. This greater angular motion of the pen arm causes the pen, of course, to move over a greater distance on the sheet. Thus by trial and adjustment the scale value can be made any- thing desired. The humidity pen should be placed in such a position that when the humidity is about 100 per cent the pen will be a little above the humidity space on the record sheet. Wiind element. — The velocity of the wind is recorded by a small anemometer fan placed in the forward end (that facing the wind) of the screening tube. In appear- ance it closely resembles a diminutive electric fan, except that the pitch of the blades is much greater. The wind passing through the screening tube causes the windmiU to rotate; this rotation is transmitted through worm gearing to a cam against which bears a lever secured to the pivot of the recording pen; when the cam comes to the proper position the lever is sud- denly pulled down and the pen makes a mark on the record sheet. It then returns slowly to its former posi- tion. The scale value of this element is changed only by changing the pitch of the blades on the fan. The entire anemometer fan and its immediate connections, called the "anemometer head," may be removed by unscrewing the three Httle brass screws in the coUar running around the tube. This should be done only when absolutely necessary, as, for example, when it is desired to test the instrument in a small beU jar, for damage is easily done when replacing this head. The pen may be shifted forcibly when necessary to change its position on the sheet. The record sheet used is the same for all instruments. The wide space at the top side of the sheet is for the wind record. The temperature pen should record be- tween this space and the center of the sheet. The space for pressure rims from near this center line to the begin- ning of the space occupied by the humidity record. Here the lines are double spaced, for the record of hu- midity is not as accurate as are those of the pressure and temperature elements. Under extreme conditions it should be possible for the pens to record outside their ordinary limits. Thus at an altitude of about 7 kilo- meters the pressure pen could record on the humidity space and the temperature pen on the pressure space and there would probably be no interference. The dock cylinder may be removed from the frame by loosening the thumbscrews on each end of the axis. Inside the cylinder is a specially made clock. The axis of the cylinder is one of the arbors of the clock and, when it is clamped in the frame at one end, the clock and cylinder rotate around it once in eight horn's. The other end, the one with the large knurled thumbscrew, is used for winding the clock and rests lightly on the frame. The clock is wound by turning this large knurled nut, holding the cylinder at the same time. The paper on which the record is to be made is properly trimmed and placed on the cyhnder, the latter being, of course, removed from the frame while winding the clock and attaching the paper. The record sheet is held in place by a brass strip which presses down upon the sheet and 20 IN8TEUCTI0NS FOE AEROLOGICAL OBSERVERS. fastens in the side of the cyhnder. The outer end of the sheet is always placed beneath the chp so as to give the greatest possible length of record before the pens have to pass over the chp. A pen lifter is provided by which, when the instru- ment is in the case or otherwise, the pens may be raised from the sheet. The lifter should always be worked by the lever inside the screening tube. The case or cover. — The instriunent fits snugly iato a hght aluminum case in such a way that no part of the instrument except the inside of the screening tube and the anemometer head is exposed to the weather. Two bakehte strips insulate the tube from the case. A piece of mica in the case allows the action of the pens, whether they are inking properly, etc., to be seen while the instru- ment is stUl ia the case. The case is fastened into the kite as explained in section 8. 7. CAIJBEATION OF METEOROGRAPHS. Before beginning any tests on an instrument it should be carefully examined to see that it is in good working condition. The cylinder should be removed from the frame and the clock wound. A record sheet should be trimmed along the line above the wind space and on the center line of the three close lines below the humidity space. The sheet is then placed on the cylinder so that the wind space is near the large knurled nut used to wind the clock. Where the ends of the sheet overlap the lines should be made to coincide and the paper should fit snugly against the front (wind) side of the cylinder. The brass strip is then put in place and the cylinder set in the frame in such a way that the pens are directly above the brass strip. The knurled nut at the right is tightened securely, but with the fingers only. The larger knurled nut is simply screwed up, not tight- ened. For convenience in testing these instruments a stand is made of two parallel strips of wood with ridges pro- vided for the lower part of the frame. This stand holds the instrument in the proper position and allows the cylinder to move freely. The pens are filled with the special ink provided and the adjusting nuts on the pen arms screwed down until the pens press lightly against the paper. The pressure should be sufficient to hold the pen against the sheet when the instrument is tilted about 20° from the vertical. The pens should be made to ink properly. It is sometimes necessary to draw a thin slip of paper between the points of the pens in order to start the liquid flowing through them. With new pens it may be necessary to smooth the points a very little to prevent their catching in the paper. The pressure pen should then be run down to the center of the humidity space and back, this being done by turning the adjusting screw resting against the frame. If there is any mechanical obstruction to this motion it should be removed. If the difiiculty can not be easily remedied the instrument should be returned to the instrument maker. No attempt should be made to repair the instrument. This applies to any adjustments, other than very simple ones, which may be found neces- sary. When repaired by other than an expert instru- ment maker the instrument suffers. While running the pen down and back it should be noticed whether it marks all the way or whether it rises from the sheet part of the way. (This may be due to a twisting of the frame and if serious the instrument should be returned for repairs.) The pen should then be forced two or three spaces to either side of its position of rest and allowed to return by itself. When the instrument is tapped lightly the pen should return to within at least two or three tenths of a space to its original position. If it does not do this there is something wrong. It may be lost motion or friction in the connecting link or perhaps the pressure of the pen against the sheet is too great. The latter may be tested by loosening the pen arm a bit and allowing the pen to rise slightly from the sheet. If it still fails to return the trouble is evidently elsewhere. The con- nections should be examined for tightness or looseness and altered, if necessary. The trouble may possibly be due to the fact that the adjusting screw is not resting tightly against the frame. If, after these and other trials that may suggest themselves, the pen does not return properly it is probably due to a weak or defective element which should be replaced by a new one. The temperature element should then be tested in about the same way, making sure that the pen can go as far as the wind and pressure spaces. The pen is moved by loosening the brass set screw and turning the pinion above it as described previously. The set screw should be tightened again, of course. The humidity pen is tested similarly by moving either of the adjusting posts. If this pen does not return when slightly displaced and jarred it may be due to the tension of the little spring on the pen-arm axle being too small or too great. Too great a tension will tend to cause a lag in the element. If the instrument is working properly to this point it is ready for the individual tests. These wiU be described separately and in detail; first, however, a brief descrip- tion of the special apparatus necessary in testing each element will be given. Pressure test. — For this test an ordinary bell jar large enough to hold the instrument, preferably without remov- ing the anemometer head, an exhaust pimip of the Geryk or other good type, a U-tube manometer, with attached thermometer, or other means of accurately measuring the pressure within the jar, together with the necessary connections, etc., are needed. Two pressure tests are necessary — a prelimmary one for the purpose of adjust- ing the range of the pen, and an intensive one to deter- mine scale values. The instrument is placed upon the wooden stand and the pressure pen lowered against the sheet. The time should be noted. (See Table 1 for entries refen-ed to.) The instrument and stand are placed under the bell jar, and the pimip is then started INSTKUCTIONS FOR AEROLOGICAL OBSERVERS. 21 for the preliminary test. The pressure should be lowered gradually until the pen has run down to the top of the humidity space, and should then be about the minimum anticipated in any flight. If it is not, then the jar should be slowly refilled, the instrument removed, and the con- necting link changed. In ordinary kite work the highest altitude often reached is about 5 kilometers, at which height the pressure is about 400 mm. Therefore the pen should be at the bottom of the pressure space at about this pressure. In a record flight the pen could go still lower, of course, since the htmiidity pen would doubtless be out of the way. Suppose, for example, that we run the pen down to the top of the humidity space and find the left arm of the manometer to read 260 and the right arm 275. The sum of these is 535 which, subtracted from the average pressure 760, gives 225 mm. as the pressure at that point. The pen has evidently moved over too small a distance for the indicated change; there- fore the little connecting lever should be pushed in toward the axis of rotation so that the pen arm will move through a greater angle for the same change in pressure. Having adjusted the connecting lever until the desired range is reached, the intensive test follows. With the instru- ment still under the bell jar the clock is allowed to run ujitil the pressure pen makes a straight or steady line. Then the air is pumped out until the pen has gone down about five spaces. The instrument is allowed to stay under this pressure until a straight line has been traced. The instrument should be jarred slightly a minute or so after the pump is stopped. When the steady line has been made, the pressure, as recorded by the arms of the manometer, and the temperature are read and entered and the pump started again. When the pen has gone down about five lines more the pmnp is again stopped for a similar period. These steps are repeated until the pen is about at the center of the humidity space. It is then allowed to return at about the same successive steps, the air being let into the jar by opening the stop- cock or by some other convenient method. The times of the beginnings and endings of each of these stops may be noted in the proper column if desired. When the air in the jar is again at atmospheric pressure, the pen is given sufiicient time to return to its original level. It should be jarred several times if necessary. If the pres- sure in the room has not changed during the test the pen should return to very approximately its original level in five minutes or so. A complete test usually occupies about one hour and a half or two hours. Since the instrument, when in the kite, is seldom or never subjected to changes as rapid as these, and since it is always under more or less vibration which tends to adjust the pens, it seems reasonable to assume that, if the element is work- ing properly and the pen returns properly under these conditions, it is working all right and that it will work satisfactorily when in actual use. When this result is attained it is hardly necessary to simulate the actual conditions of flight by taking a longer time, etc., for the tests. If, however, the pen does not return to within at least several tenths of a space of its origiaal level (pro- viding the pressure has not changed) the element and its connections should again be examined and the ele- ment replaced if necessary. In performing these tests it is always desirable to notice the general behavior of the elements. Thus the pen should move smoothly and should move every time the pump exhausts air, etc. If there is a leak in the connections or bell jar, as indicated by the manometer, this leak should be shown by the trace. A leak is rather an advantage if it is not too great, for a small leak in- dicated by the trace shows that the pen and element are working properly and smoothly and that the element is responsive to very small changes in pressure. The above test is repeated at least once, since a single test is not sufficient to give accurate values for making up the necessary tables. The method of working up these tests to give the tables will be treated later on. HaAang obtained two or three pressure tests which are apparently satisfactory the temperature test is then made. Temperature test. — For testing the temperature element there will be needed a warm and a cold room, box, or other receptacle in which the ventilation, produced by an electric fan or otherwise, is good. If a box is used it should have a glass window, so that a thermometer placed iaside the box may be read from outside. In cold weather the instrument may be placed indoors and out- doors alternately. In warm weather it may be possible to secure a low enough temperature by placing the instrument ui a tight box containing chopped ice naixed with salt. Other means of securing still lower tempera- tures are very convenient but not necessary. To secure the proper ventilation an electric fan is usually placed in the box or other compartment in such a way that the air current caused by it blows through the screening tube. An ordinary mercurial thermometer is suspended or placed in such a position that the bulb is exposed to the same current of air as the temperature element and can be read through the glass window. In this test both the temperature and the pressure pens are allowed to record, for we wish to know the effect of temperature change on the pressure element as well as on the temperature element. The general method is the same as that followed in the pressm-e test. The instrument is set up before an electric fan and allowed to run for about five minutes or until straight fines are traced by the pens. The thermometer is then read and the instrument subjected to a temperature differing from the first by 25° to 30° C, if possible. It is placed in front of a fan in this compartment and allowed to run until a straight line is made at this new temperature. The temperature is then read again, this time through the window. After one or two such changes the nmnber of lines which the pen has moved over should be compared with the temperature change as indicated by the ther- 22 INSTEUCTIONS FOE AEROLOGICAL OBSEEVEES. mometers. The recorded change in ordinate divided into the change ia temperature gives the scale value, and if this is not approximately that desired the connect- ing link should be adjusted so as to give the desired value. In aerological work a factor between 0.9 and 1.0 is sought; that is, one space on the sheet should correspond to a temperature change between 0°.9 C and 1°.0 C. There are several reasons for this limitation of the scale value. It is evident that the farther the pen moves the easier it will be to read more accurately any definite temperature change. On the other hand, the distance that the pen can move is limited by the width of the record, sheet; for, if it goes beyond its proper space, it is likely to inter- fere with the pressure trace and both records will be lost or useless. Hence, it is necessary to ascertain the extreme temperatures that are apt to be met with and then adjust the pen or connectiug link in such a way that either extreme will be recorded, the lower usually being re- corded about the middle of the sheet and the upper near the wind space. It has been found that within the limiting range stated little difhculty is ever met with on account of interference, but any smaller scale value with a greater movement of the pen arm would be hable to cause such trouble. If the factor, as determined roughly from the first two or three changes, is approximately that desired the pro- cedure is repeated at least half a dozen times. This will give about 12 changes in all which, when averaged, should give a good mean value. The number of values necessary to give a good mean depends mainly on the consistency of the values; and if this is good, 15 or 20 values seem to be sufficient. Two series of the above tests should therefore give a satisfactory scale value. Humidity test. — Some kind of a humidity chest or box is necessary for this test. Any box which is nearly air- tight and provided with a glass window and containing a ventilating fan will be found satisfactory. The tem- perature box, if such was used, may be made to serve this purpose also. The inside of this box should be lined or otherwise covered with blotting or absorbing paper which should be saturated with water. With the cover on tight and an electric fan going, the humidity inside will soon reach 90 per cent or higher. This gives a standard value of liigh, humidity. A standard low humidity may often be reached in the open room. In winter when the temperature and humidity are low outside it is possible to get a very low humidity in a warm room. If such conditions obtain nothing further is needed. If not, then another box or a readjustment of the conditions in the same box is necessary. This time calcium chloride or sulphuric acid is placed in the box. The moisture present is soon absorbed by either of these and the humidity becomes very low. In addition to the box and electric fan some kind of a psychrometer is necessary. The ordinary psychrometer exposed to the electric fan will serve this purpose, but an Assmann ventilated psychrometer is more convenient. The humidity pen is made to record, and the instru- ment is placed in front of the fan in either the wet or dry compartment until a straight line is made. The psychrometer is then read and the instrument changed to the opposite condition of humidity and the procedure repeated. A trial determination of the scale value is made as in the temperature test and the scale value changed if desired. If the hairs are lowered the pen will, of course, move farther for the same change in humidity. As has been stated, the scale value is a variable depend- ing on the humidity. For this reason humidities ranging from about 10 per cent to nearly 100 per cent should be used to derive the proper changes in the scale value. By allowing the blotters to dry out partially the high humidity may be lowered and then by Hmiting the amount of the drying reagent the low humidity may be raised until all possible values are obtained. Wherever possible about fifty changes should be secured and these should be as evenly distributed as possible among the different possible percentages. The range of hu- midity for each test should not necessarily be large. A range of 20 per cent is sufficient to give a good test and is more desirable in some ways than a larger range. It is often possible, especially in preliminary tests, to make the humidity and temperature tests at the same time. The instrument is placed in a room or box where the temperature is high and the humidity low. It is then changed to a box containing soaked blotters and cracked ice with salt. The temperature range secured in this way may be 20 or more degrees and the humidity range 30 per cent or more. The temperature and humidity pens in these tests should be watched to see that they are responding prop- erly; that is, they should respond immediately to any change in the temperature or himiidity. The humidity pen, however, usually takes a few minutes, or more some- times, to adjust itself. This does not happen very often in actual flight, for sudden changes are not the rule, and the vibration of the kite and instrument assists the pen in adjusting itself to any change. If the elements do not respond to the changes as quickly as desired they should be examined for friction, etc., or replaced if necessary. Wind test. — In this test an anemometer, for recording the number of miles of wind passing a certain point, and an anemoscope or wind vane are necessary. Ordinarily the station anemometer and vane are used for this purpose. The anemometer pen of the meteorograph is adjusted to touch the sheet and the time is noted. The meteoro- graph is then suspended from the anemoscope so that the ventilating tube carrying the anemometer always faces the wind. The time at which it is suspended should also be noted. The wind should be somewhere near the aver- age met with in actual flights. At any rate it should not be an extremely light or high wind. The instrument is allowed to record for three or four hours or more and is then taken down, the time being noted. The nimiber of INSTKUOTIONS FOE AEEOLOGICAL OBSEEVERS. 23 miles of wind that have passed the instrument is taken from the record of the station anemometer. Two or more of these tests should be made. In all the foregoing tests if the scale values as deduced later on do not agree fairly well, further tests should be made. A disagreement or lack of consistency may indi- cate a poor element or a poor test. At any rate tabular values for standard use should not be dependent on in- consistent tests. Time test. — ^This test may be made separately or the times noted on the other tests may be used. If it is de- sired to make a special test on the clock, all that is necessary is to allow any pen to record for about three or four hours and raise it at a noted time. At least two such tests should be made. Lengths of fen arms and centers of arcs. — For drawing the hour lines (see section 10) it is necessary to know the length of each pen arm and the point on the record sheet at which the pivot of the pen arm falls. To find these the length of each pen arm from the center of the pivoting point to the pen is measured. The inked pen is then run up and down the sheet making as large an arc as con- venient. The record sheet is then removed and with the length of the pen arm as a radius and each end of the arc as a center small arcs are drawn. The point of intersec- tion of these arcs is the center of the arc made by the pen arm. The position of each center is thus found and stated with reference to the number of lines that this center is below a certain point. Thus the temperature is measured from the top temperatiu'e line and the pres- sure from the middle line of the sheet, etc. All the in- struments now made by the Weather Bureau instrument shop have standard lengths of pen arms and centers of arcs so that it is not necessary to make these measure- ments on the new instruments. These measurements are as follows: Lengths: Wind, 86 mm.; temperature, 130 TTiTn.; pressure, 130 mm.; humidity, 99 mm. Center of arcs: Temperature, 25 lines below top temperature line; pressure, 20 lines below top pressure line; humidity, 5 lines below top humidity line; wind, center of wind space. Reduction of the tests: Pressure. — Table 1 shows a pres- sure test that has been made in accordance with the method outlined above. If reference is made to this table the following procedure will be simple. The columns headed "Notes," "Time,""Att.ther.," "Manom- eter," "Left," and "Eight" have already been filled iu as described. The figures under the "Eight" and "Left" columns are added and the total is entered under "Sum." Now, any change in the temperature of the mercury in the manometer will cause that mercury to expand or con- tract a certain amount, dependent on the height of the column and the coefiicient of expansion of mercury. For this reason all readings are reduced to zero degrees centi- grade. The glass also expands or contracts when heated or cooled, and so what we really wish to determine is the difference between these two expansions. The easiest way to do this is to make up a table or graph showing this result. The values generally used are given in the Smith- sonian Meteorological Tables, 1918 edition, Table 47, but special graphs have been made up to faciUtate these reductions. By reference to one of these graphs or to the original table the corrections indicated in Table 1, "Temp, cor." column, will be found to apply. The argu- ments are the "smn" and the "attached thermometer." Since the temperatures recorded are above zero, the mercury is occupying greater volume than it would at zero, and hence the corrections are subtracted. This gives the "corrected reading" in mm. In aerological work millibars are the units used, so mm. have to be converted to mb. by mtdtiplying by 1.333224. This gives the corrected reading in mb. (For these corrected valuesi see. Table 12, S. I. Metl. Tables, 1918 ed.) Table 1. (Washington, D. C, Dec. 24, 1919. Pressure tests Nos. 1 and 2. Meteorograph No. 25.] Notes. Time. Att. ther. Manometer. Stun. Temp, cor. Corrected reading. Ordi- nate. Scale value. Left. Right. mm. mh. Pens down 9:04a 25.0 14.5 14.5 29.0 0.1 28.9 38.6 3.4 11.32 25.0 26.0 26.5 52.5 .2 62.3 69.7 6.2 11.24 25.0 37.0 38.5 75.5 .3 76.2 100.3 8.9 11.27 25.0 49.5 51.5 101.0 .4 100.6 134.1 12.4 10.81 25.0 65.0 68.0 133.0 .6 132.5 176.7 16.3 10.84 25.0 83.0 87.5 170.5 .7 169.8 226.4 21.2 10.68 25.0 109.0 116.5 224.5 .9 223.6 298.1 28.4 10.60 25.0 131.5 139.5 271.0 1.1 269.9 359.8 35.4 10.16 25.0 159.5 170.5 330.0 1.4 328.6 438. 1 ) 3 9.91 24.5 188.5 201.5 390.0 1.6 388.4 517.8 153.6 9.54 9.66 24.5 159.5 170.0 329.5 1.3 328.2 437.6 43.3 10. XI 24.5 121.0 128.5 249.5 1.0 248.6 331.3 31.8 10.42 24.5 103.0 108.5 211.5 .9 210.6 280.8 26.8 10.48 24.5 81.5 86.0 167.5 .7 166.8 222.4 21.4 10.39 24.5 70.0 73.5 143.5 .6 142.9 190.5 18.3 10.41 24.5 54.0 56.8 110.8 .4 110.4 147.2 14.1 10.44 24.5 42.0 44.0 86.0 .4 85.6 114.1 10.9 10.47 24.5 29.5 30.0 59.5 .2 69.3 79.1 7.4 10.69 24.5 19.4 19.7 39.1 .2 38.9 61.9 4.8 10.81 24.5 17.6 17.9 36.5 .1 35.4 47.2 4.1 11.61 24.5 34.8 36.3 71.1 .3 70.8 94.4 8.3 11.37 24.5 53.0 56.0 109.0 .4 108.6 144.8 13.0 11.14 24.5 73.5 77.0 160.6 .6 149.9 199.8 18.4 10.86 24.5 96.0 101.0 197.0 .8 196.2 261.6 24.7 10.69 24.5 120.5 127.6 248.0 1.0 247.0 329.3 31.9 10.32 24.5 147.0 167.0 304.0 1.2 302.8 403.7 40.0 10.10 24.5 182.0 195.5 377.5 1.5 376.0 501.3 /51.1 \61.3 39.2 9.81 9.77 24.5 144.0 154.0 298.0 1.2 296.8 395.7 10.09 24.5 113.0 119.5 232.5 .9 231.6 308.8 29.9 10.33 24.5 98.0 103.0 201.0 .8 200.2 266.9 26.1 10.23 24.5 78.0 82.5 160.5 .6 1.59.9 213.2 20.5 10.40 24.5 50.2 54.0 104.2 .4 103.8 138.4 12.9 10.73 24.5 36.0 37.1 73.1 .3 72.8 97.1 9.2 10.55 24.6 18.0 18.6 36.6 .1 36.5 48.7 4.6 10.69 Pens up 12;01p The next step is to determine the values of the ordi- nates. To do this we find the number of spaces and tenths of a space or division that the pressure pen moved from its initial position when each stop was made. Thus in figure 25 the starting line is 0.4 division above the line next below it. Then on the first stop, just before the pump was started or just at the time the pressure reading was made, the trace shows that the pen moved 3.4 divisions from the original point. The total number of whole divisions over which it has moved is 3. The lower point is exactly on the line, and hence its frac- tional ordinate is zero, and the addition of these values gives the ordinate stated. Each successive step is determined in the same way and entered as indicated in Table I under "ordinate." From the lowest point. 24 INSTEUCnONS FOE AEEOLOGICAL OBSEEVEES. coming back, all the points are computed in exactly the same way but from the last position of the pen. This is about 0.3 of a division above the line below it, and on refilling the bell jar all points are computed from this point. By the side of each step in figure 25 is placed a numeral which is the number of tenths of a space that the point at which the pressure reading was taken is below the line above it. This facilitates reading the trace and assists the computers in checking the work. The starting and ending points are computed from the line below rather ), where h is the vertical height, I, the length of wire out in meters and 4>, the angular altitude of the kite. It has been found that on the average a deduction of about 2 per cent must be made from the altitude obtained in this way to allow for the sag in wire, number of kites out, etc. This altitude is used principally as a check on the former. The altitudes of observed values of electric potential are computed trigonometrically whenever possible, but in those flights made at night or when the kites are obscured by clouds it is necessary to employ another method. The pressure ordinate at the time at which the potential reading was made is corrected for temperature, and with this corrected ordinate those two levels are taken which occur immediately before and after the time of the potential reading. Using the corrected pressure ordi- nates of these levels, the altitude of the potential reading is directly interpolated, since the altitude varies inversely as the pressure or, rather, approximately so, for the comparatively short intervals between two levels. Form No. 1104-Aer., Table 11, is used for computing the electric potential data. Tabulation. — The data are now ready for tabulation and Form No. 1105-Aer., Table 12, is used for this purpose. The first entry is taken from the data sheet and gives the values observed at the time at which the instrument kite is launched, the altitude of the station above sea level being entered as the first altitude. Between the computed levels spaces are left for inter- polated levels at altitudes above sea level 250 meters apart, except that the intervals are increased to 500 mctci-s for altitudes greater than 1,500 meters above sea level. The last entry is taken from the data sheet at the time the head kite is landed. In the first and last entries the data for both the surface and aloft are iden- tical. For the computed levels, the surface data are entered to the left of the double line and the data aloft to the right. INSTEUCTIONS FOE AEEOLOGICAL OBSEEVEES. 45 [Form No. 1104r-Aer.] Station, Table H. u. a. depaetment of aqeiculttibe, weatheb bueeatj. Altitudes at Times or Eiecteic Potentul BEAcraas. Date, Time (a.m.) 7:11 7:21 7:34 7:52 8:27 8:38 8:55 P. ordinate 21.0 .1 20.9 -1.2 -1.1 3.5 2.4 0.5 1.9 2,417 6,000 27 6 T. correction Cor. P. ordinate 27 6 T. ordinate Same as 7:34 level. T. ordinate X factor 6 6 T.ol base line Temperature 3 Initial T 5 T . change Altitude, S. L 645 938 565 1,191 1,600 1,607 2,000 2,636 5,600 Electric potential 7 400 Time (a. m.) 9:11 9:35 9:50 10:05 10:23 10:37 10.47 P . ordinate 28.5 .2 28.7 -8.6 -7.9 3.5 -4.4 0.5 -3.9 3,272 7,600 27.0 .1 27.1 -7.0 -6.5 3.5 -3.0 0.5 -2.5 3,086 6,200 T. ordinate Same as 9:50 level. T. ordinate x factor T. of base Une Initial T Altitude, S. L 2,458 4,300 1,940 2,600 1,331 1,200 770' 490 598 [Form No. 1105-Aer.] Table 12. u. o. depaetment of ageicultube, weatheb bubeau. FEEE-Am Data Feom Kite Flights. Station, Meteorograph,.. ... Date, Surface. At different heights above sea. * Pres- sure. Tem- pera- ture. Eela- tive humid- ity. Wind. Alti- tude. Pres- sure. Tem- pera- ture. At 100 m. Humidity. Wind. Potential. Eemarks. Time. Direc- tion. Veloc- ity. Rela- tive. Vapor pres- sure. Direc- tion. Veloc- ity. Grav- ity. Elec- tric. 0. m. mb. 984.7 984.5 984.4 984.0 983.9 983.6 983.2 982.8 982.6 982.4 982.3 982.2 °C. 0.5 0.6 0.6 1.6 1.6 1.9 3.0 3.8 5.0 5.8 5.9 6.6 % 87 89 89 86 86 86 84 83 79 79 79 79 ese. ese. ese. ese. se. se. se. se. se. sse. se. se. m.p.s. 5.4 4.5 4.9 5.S 6.3 6.3 5.4 6.3 5.8 5.4 4.9 6.4 771. 396 500 750 799 1,000 1,191 1,2.50 1,600 1,567 2,000 2,070 2,487 2,600 3,000 3,500 3,723 3,600 3,000 2,600 2,458 2,000 1,778 1,500 1,260 1,121 1,000 750 671 500 396 m&. 984.7 973.0 943.0 936.5 914.2 892.4 886.0 860.0 852.6 808.9 801.2 761.0 760.1 714.0 670.1 661.1 670.1 713.2 759.2 763.0 807.4 829.8 859.1 885.2 898.8 913.3 942.0 949.6 971.0 982.2 0.5 1.0 2.1 2.3 4.8 7.2 7.1 6.9 6.8 3.8 3.3 1.6 1.5 -2.3 -6.1 -7.8 -6.0 -2.1 1.9 2.2 4.4 5.6 6.2 6.8 7.1 6.0 3.6 2.9 6.2 6.6 ■-6.'45" ■-i.'25' ■■'o.'ii' ■■'6.' 76' 0.41 ■"'6.' 78' """6.49' ■"6.' 24' "-6." 93' "i'.u % 87 89 92 93 75 68 68 59 59 39 36 100 99 80 60 51 58 72 87 88 53 36 52 67 75 78 85 87 82 79 mb. 5.61 5.84 6.63 6.71 6.45 5.89 5.85 5.87 5.83 3.13 2.79 6.86 6.74 4.03 2.19 1.61 2.13 3.69 6.09 6.30 4.43 3.25 4.93 6.62 7.57 7.29 6.72 6.64 7.25 7.69 ese. se. s. s. sse. sse. sse. sse. sse. s. s. ssw. ssw. ssw. sw. sw. sw. ssw. ssw. ssw. s. s. s. s. s. s. sse. sse. se. se. m. p. s. 5.4 6.6 9.4 9.9 11.8 13.6 13.3 12.0 11.7 16.2 16.9 19.0 19.0 18.7 18.3 18.2 18.3 18.6 18.9 18.9 17.6 16.9 16.3 16.9 16.6 13.9 10.2 9.1 6.8 5.4 i06 ergs. VoUs. 4/10 St. Cu. ssw.; changing to 7/10 St ssw. by 9:06 a. m. and to 9/10 St. Cu. by end of flight. Altitude of St. Cu. base about 2,250 b 8:30 and 2,300 m. at 9:50 a. m. r.n ssw. 7'29 560 1,600 8:12 2,000 8:40 6,000 9:19 7,400 7,600 5,200 9:50 10:11 4,300 2,600 1,200 10:29 10:40 10:63 490 Linear interpolations are made for the intermediate values of temperature, relative humidity, wind direction, and velocity. The atmospheric pressures for these levels are determined by plotting the pressures for the calculated levels, using the altitudes as ordinates and the pressures as abscissas. This is necessary because in this instance the interpolation is not a linear one but approaches a logarithmic curve. This, however, is dependent upon the temperature at the various levels. The column headed jqq is the change in temperature per 100 meters, or the temperature gradient. The gradient values are obtained by dividing the difference in temperature between two adjacent levels by the number of himdred meters difference in their elevation, and the results are given to two decimal places. The gradient is positive when the temperature decreases with altitude, and negative when the the temperature increases with altitude. The vapor pressures are obtained from the corre- sponding temperature and relative humidity as in the case of the computed levels. (See Table 17.) The values of electric potential are entered to the nearest 10 opposite the altitudes nearest which they occur. Under "Eemarks" are recorded all meteorological phe- nomena observed during the flight, including cloud changes, halos, thunderstorms, begirming and ending of precipi- tation, etc. Whenever kites are observed to enter or leave the cloud base, a reading of the theodoUte is made and the altitude above sea level computed; the result is 46 INSTEUCTIONS FOE AEROLOGICAL OBSERVERS. expressed to the nearest even 50 meters below the com- puted value. This result is entered under "Remarks" with a brief statement, together with a record of the kind and direction of the clouds. 11. REDUCTION TABLES. Tables 13 to 18, inclusive, are regularly used in the reduction of every free-air record obtained by means of kites. Tables 13, 14, and 15 are exactly the same as Tables 57, 58, and 61 of the 1918 edition, Smithsonian Meteorological Tables, and a description of their use may be found in the introduction of that work. The values in Table 16 were obtained by dividing the number of meters indicated at the tops of the columns by the number of seconds in the minutes listed in the extreme left-hand column. Table 17 corresponds to Tables 71 and 72 in the Smithsonian Meteorological Tables, 1918 edition, except that vapor pressures are expressed in millibars instead of millimeters. Table 18 gives values of relative humidity, or per- centage of saturation, for air temperatures from — 39° C. to -1-44° C. (side argument) and for depressions of the wet-bulb thermometer at 0.1° C. intervals (top argu- ment). Thus, only a single interpolation is necessary. The values have been computed for a barometric pressure of 990 mb., this being approximately the average pressure at the kite stations now maintained by the Weather Bureau. When the air is very dry, errors of 1 or 2 per cent in the relative humidity are possible with pressures markedly differing from the mean here adopted, but such instances are infrequent, and even then the errors are no greater than those of observation. Hence, it is deemed unnecessary to use two or three different sets of tables, the one, computed for an average pressure, being sufficiently accurate for aU practical purposes. Table 13. — Determination of heights by the barometer. (values of 18400 log 1^^^ 1 2 3 4 5 6 7 8 9 Pressure P.P. (mb.) METERS. 500 510 5645 5486 6629 6471 5613 5456 5697 6439 5681 6424 6565 5408 6549 6393 5533 5377 5518 5362 5602 5346 16 15 0.1 2 2 520 5331 6316 5300 52S5 6270 6256 6239 5224 5209 5194 .2 3 3 530 5179 6164 6140 5134 6119 6104 6089 6074 5059 6044 .3 5 4 540 5030 5015 6000 4985 4971 4956 4941 4927 4912 4898 .4 6 6 550 4883 4868 4S54 4839 4825 4811 4796 4782 4768 4753 .5 8 8 560 4739 4725 4710 4696 4682 4668 4654 4640 4626 4612 .6 10 9 570 4598 4583 4669 4556 4542 4528 4614 4600 4456 4472 .7 11 10 580 4439 4445 4431 4417 4404 4390 4376 4363 4349 4335 .8 13 12 590 too 610 4322 4188 4056 4308 4174 4042 4295 4161 4029 4281 4148 4016 4268 4134 4003 4254 4121 3990 4241 4108 3977 4228 4096 3964 4214 4082 3951 4201 4069 3939 .9 14 14 14 13 0.1 1 1 620 3926 3913 3900 3887 3874 3861 3849 3836 3823 3810 .2 3 3 630 3798 3785 3772 3760 3747 3736 3722 3709 3697 3684 .3 4 4 640 3672 3659 3647 3635 3622 3810 3697 3585 3673 3560 .4 6 5 650 3548 3636 3523 3511 3499 3487 3475 3462 3450 3438 .6 7 6 660 3426 3414 3402 3390 3378 3366 3354 3342 3330 3318 .6 s g 670 3306 3294 3282 3270 3258 3246 3235 3223 3211 3199 .7 10 g 680 3187 3176 3164 3162 3141 3129 3117 3106 3094 3082 .8 11 10 690 700 3071 2956 3059 2944 3048 2933 3038 2922 3025 2910 3013 2899 3002 2888 2990 2878 2979 2865 2967 2854 .9 13 12 12 11 710 2842 2831 2820 2809 2798 2786 2775 2764 2753 2742 0.1 1 1 720 2731 2720 2708 2697 2686 2676 2664 2653 2642 2631 _ 2 2 2 730 2621 2609 2699 2588 2577 2566 2555 2544 2533 2523 is 4 3 740 2512 2501 2490 2479 2469 2458 2447 2437 2426 2415 .4 5 4 750 2405 2394 23S3 2373 2362 2361 2341 2330 2320 2309 .5 Q 760 2299 2288 2278 2267 2257 2246 2236 2225 2215 2205 .6 7 7 S g 770 2194 2184 2173 2163 2163 2142 2132 2122 2112 2101 .7 s 780 2091 20S1 2071 2060 2050 2040 2030 2020 2009 1999 .8 10 790 800 1989 1889 1979 1879 1969 1SG9 1959 1869 1949 1849 1939 1839 1929 1829 1919 1819 1909 1809 1899 1799 .9 11 10 9 8 810 1789 1780 1770 1760 1750 1740 1731 1721 1711 1701 0.1 1 1 2 2 3 820 1692 1682 1672 1662 1653 1643 1633 1623 1614 1604 .2 830 1595 1685 1575 1666 1556 1547 1637 1527 151S 1608 "J 3 840 1(99 1489 1480 1470 1461 1451 1442 1433 1423 1414 .4 4 850 1404 1396 1386 1376 1367 1367 1348 1339 1329 1320 .5 4 5 4 860 1311 1302 1292 1283 1274 1264 1266 1246 1237 1228 ,6 870 1218 1209 1200 1191 1182 1173 1164 1154 1145 1136 .7 Q 6 6 7 880 1127 1118 1109 1100 1091 1082 1073 1064 1055 1046 .8 7 8 890 900 910 1037 948 859 1028 939 860 1019 930 842 1010 921 833 1001 912 824 992 903 815 983 894 974 886 966 877 956 S6S .9 7 807 798 789 781 0. 1 1 1 2 3 920 772 763 755 746 737 729 720 711 703 694 .2 930 686 677 668 660 651 643 634 626 617 60S .3 940 600 692 583 676 666 558 549 641 532 524 .4 950 616 607 499 490 482 474 465 457 448 440 .5 4 4 5 6 6 960 432 424 416 407 399 390 382 374 365 357 .6 970 349 341 332 324 316 308 300 292 2S3 276 .7 980 267 259 251 243 234 226 218 210 202 194 .8 990 186 178 170 162 154 146 138 130 122 114 .9 1000 108 08 90 82 74 66 68 50 42 .34 1010 26 18 10 2 -6 -13 -21 -29 -37 —45 1020 -53 -61 -68 -76 -84 -92 -100 -107 -115 -123 1030 -131 -138 -146 -154 -162 -160 -177 -186 -192 -200 1040 -208 -216 -223 -231 -238 -246 -264 -281 -269 -277 INISTEUCTIONS FOR AEEOLOGICAL OBSERVERS. 47 Table 14. — Temperature correction factor, (a.) (Multiply values of Z,— Z, by a; add correction when mean temperature is above 0° C; subtract when below 0" C.) Mean Temp. e. .0 .1 .2 .3 .4 .5 .6 .7 .8 .9 °C. a a ' a a a a a a a a 0.000 0.000 0.001 0.001 0.001 0.002 0.002 0.003 0.003 0.003 1 .004 .004 .004 .005 .005 .006 .006 .006 .007 .007 2 .007 .008 .008 .008 .009 .009 .010 .010 .010 .011 3 .011 .011 .012 .012 .012 .013 .013 .014 .014 .014 i .015 .015 .015 .016 .016 .017 .017 .017 .018 .018 5 .018 .019 .019 .019 .020 .020 .021 .021 .021 .022 6 .022 .022 .023 .023 .023 .024 .024 .025 .025 .025 7 .026 .026 .026 .027 .027 .028 .028 .028 .029 .029 8 .029 .030 .030 .030 .031 .031 .032 .032 .032 .033 9 .033 .033 .034 .034 .034 .035 .035 .036 .036 .036 10 .037 .037 .037 .038 .038 .039 .039 .039 .040 .040 11 .040 .041 .041 .041 .042 .042 .043 .043 .043 .044 12 .044 .044 .045 .045 .048 .046 .046 .047 .047 .047 13 .048 .048 .048 .049 .049 .060 .050 .060 .051 .051 U .061 .052 .052 .052 .053 .063 .054 .054 .054 .055 15 .055 .055 .056 .056 .067 .057 .057 .058 .068 .058 16 .059 .059 .059 .060 .060 .061 .061 .061 .062 .062 17 .062 .063 .063 .063 .064 .064 .065 .065 .065 .066 18 .066 .066 .067 .067 .068 .068 .068 .069 .069 .069 19 .070 .070 .070 .071 .071 .072 .072 .072 .073 .073 20 .073 .074 .074 .076 .075 .075 .076 .076 .076 .077 21 .077 .077 .078 .078 .079 .079 .079 .080 .080 .080 22 .081 .081 .081 .082 .082 .083 .083 .083 .084 .084 23 .084 .085 .085 .086 .086 .086 .087 .087 .087 .088 24 .088 .088 .089 .089 .090 .090 .090 .091 .091 .091 25 .092 .092 .092 .093 .093 .094 .094 .094 .095 .095 26 .095 .096 .096 .097 .097 .097 .098 .098 .098 .099 27 .099 .099 .100 .100 .101 .101 .101 .102 .102 .102 28 .103 .103 .103 .104 .104 .105 .105 .105 .106 .106 29 .106 .107 .107 .108 .108 .108 .109 .109 .109 .110 30 .110 .110 .111 .111 .112 .112 .112 .113 .113 .113 31 .114 .114 .115 .115 .115 .116 .116 .116 .117 .117 32 .117 .118 .118 .119 .119 .119 .120 .120 .120 .121 33 .121 .121 .122 .122 .123 .123 .123 .124 .124 .124 34 .125 .125 .126 .126 .126 .127 .127 .127 .128 .128 35 .128 .129 .129 .130 .130 .130 .131 .131 .131 .132 36 .132 .132 .133 .133 .134 .134 .134 .135 .135 .136 37 .136 .136 .137 .137 .137 .138 .138 .138 .139 .139 38 .139 .140 .140 .141 .141 .141 .142 .142 .142 .143 39 .143 .143 .144 .144 .145 .145 .145 .146 .146 .146 48 INSTRUCTIONS FOE AEEOLOGICAL OBSERVERS. Table 15. — Humidity correction — Add to mean temperature. Air pressure VAPOR PRESSURE (MB.) i (mb.) 0.5 1 2 3 4 5 6 7 8 9 10 20 30 40 "C. °c. "C. °C. "C. 'C. "C. "C. °C "C. °c. "C. °C. °C. 1040 0.0 0.0 0.1 0.1 0.2 0.3 0.3 0.3 0.4 0.4 0.5 1.0 1.5 2.0 1020 .0 .1 .1 .2 .2 .3 .3 .4 .4 .5 .5 1.0 1.5 2.0 1000 .0 .1 .1 .2 .2 .3 .3 .4 .4 .5 .5 1.0 1.5 2.1 980 .0 .1 .1 .2 _ 2 .3 .3 .4 .4 .5 .5 1.1 1.6 2.1 960 .0 .1 .1 .2 !2 .3 .3 .4 .4 .5 .5 1.1 1.6 2.1 940 .0 .1 .1 .2 .2 .3 .3 .4 .4 .5 .5 1.1 1.6 a.2 920 .0 .1 .] .2 .2 .3 .3 .4 .4 .5 .6 1.1 1.7 2.2 900 .0 .1 .1 .2 .2 .3 .3 .4 .5 .5 .6 1.1 1.7 2.3 880 .0 .1 .1 .2 .2 .3 .4 .5 .5 .6 1.2 1.8 2.3 860 .0 .1 .1 .2 .2 .3 .4 .5 .5 .6 1.2 1.8 2.4 840 .0 .1 .1 .2 .2 .3 .4 .5 .6 .6 1.2 1.8 820 .0 .1 .1 .2 .3 .3 .4 .5 .6 .6 1.3 1.9 800 .0 .1 .1 .2 .3 .3 .5 .6 .6 .6 1.3 1.9 780 .0 .1 .1 .2 .3 .3 .5 .5 .6 .7 1.3 2.0 760 .0 .1 .1 .2 .3 .3 .5 .5 .6 .7 1.4 740 .0 .1 .1 .2 .3 .3 .5 .6 .6 .7 1.4 720 .0 .1 .1 .2 .3 .4 .5 .6 .6 .7 1.4 700 .0 .1 .1 .2 .3 .4 .5 .6 .7 .7 1.5 680 .0 .1 .2 .2 .3 .4 .5 .5 .6 .7 .8 660 .0 .1 .2 .2 .3 .4 .6 .5 .6 .7 .8 640 .0 .1 .2 .2 .3 .4 .5 .6 .6 .7 .8 620 .0 .1 .2 .2 .3 .4 .5 .6 .7 .7 600 .0 .1 .2 .3 .3 .4 .6 .6 .7 .8 580 .0 .1 .2 .3 .4 .4 .5 .6 .7 .8 560 .0 .1 .2 .3 .4 .5 .6 .6 .7 540 .0 .1 .2 .3 .4 .5 .6 .7 .8 520 .0 .1 .2 .3 .4 .5 .6 .7 .8 500 .1 .1 .2 .3 .4 .5 .6 .7 480 .1 .2 .3 .4 .5 .6 .8 460 .1 .2 .3 .4 .6 .7 .8 440 .1 .2 .4 .5 .6 .7 420 .1 .2 .4 .5 .6 .7 400 .1 .3 .4 .5 .6 .8 380 .1 .3 .4 .5 .7 360 .1 .3 .4 .6 .7 340 .2 .3 .5 .6 .8 320 .2 .3 .5 .6 300 .2 .3 .5 .7 280 .2 .4 .6 .7 260 .2 .4 .6 240 .2 .4 .6 220 .2 .5 .7 200 .3 .5 180 .1 .3 .6 160 .2 .3 .6 140 .2 .4 120 .2 .4 100 .3 .5 SO .3 60 .4 40 .6 20 1.3 10 2.6 INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. 49 Heeling onT+. Table 16. — Correction for wind velocity. [In meters per second.] Eeelino in — TIME AND DISTANCE BETWEEN OBSBKVATIONS Minutes. m. 500 m. 600 m. 700 m. 800 m. 900 m. 1,000 m. 1,100 m. 1,200 m. 1,300 m. 1,400 m. 1,500 m. 1,600 m. 1,700 m. 1,800 m. 1,900 m. 2,000 i 4 5 6 7 8 » 10 11 12 13 14 15 16 17 18 19 20 31 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 2.8 2.1 1.7 1.4 1.2 1.0 0.9 0.8 0.8 0.7 0.6 0.6 0.6 0.5 0.6 0.5 0.4 0.4 3.3 2.5 2.0 1.7 1.4 1.2 1.1 1.0 0.9 0.8 0.8 0.7 0.7 0.6 0.6 0.6 0.5 0.6 0.8 2.9 2.3 2.0 1.7 1.5 1.3 1.2 1.1 1.0 0.9 0.8 0.8 0.7 0.7 0.0 0.6 0.6 0.6 0.6 3.3 2.7 2.2 1.9 1.7 1.5 1.3 1.2 1.1 1.0 1.0 0.9 0.8 0.8 0.7 0.7 0.7 0.6 0.6 0.6 0.6 0.5 3.0 2.5 2.2 1.9 1.7 1.5 1.4 1.2 1.2 1.1 1.0 0.9 0.9 0.8 0.8 0.8 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.5 3.3 2.8 2.4 2.1 1.8 1.7 1.5 1.4 1.3 1.2 1.1 1.0 1.0 0.9 0.9 0.8 0.8 0.8 0.7 0.7 0.7 0.6 0.6 0.0 0.0 0.6 0.5 3.0 2.6 2.3 2.0 1.8 1.7 1.6 1.4 1.3 1.2 1.1 1.1 1.0 1.0 0.9 0.9 0.8 0.8 0.8 0.7 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.5 3.3 2.8 2.6 2.2 2.0 1.8 1.7 1.5 1.4 1.3 1.2 1.2 1.1 1.0 1.0 1.0 0.9 0.9 0.8 0.8 0.8 0.7 0.7 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.6 0.5 3.1 2.7 2.4 2.2 2.0 1.8 1.7 1.6 1.4 1.4 1.3 1.2 1.1 1.1 1.0 1.0 1.0 0.9 0.9 0.8 0.8 0.8 0.8 0.7 0.7 0.7 0.6 0.6 0.6 0.6 0.6 0.8 0.6 0.5 3.:i 2.9 2.6 2.3 2.1 2.0 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.2 1.1 1.1 1.0 1.0 0.9 0.9 0.9 0.8 0.8 0.8 0.8 0.7 0.7 0.7 0.7 0.6 0.6 0.6 0.6 0.6 3.1 2.8 2.6 2.3 2.1 1.9 1.8 1.7 1.6 1.6 1.4 1.3 1.2 1.2 1.1 1.1 1.0 1.0 1.0 0.9 0.9 0.9 0.8 0.8 0.8 0.8 0.7 0.7 0.7 0.7 0.6 0.6 0.6 3.3 3.0 2.7 2.4 2.2 2.0 1.9 1.8 1.7 1.6 1.5 1.4 1.3 1.3 1.2 1.2 1.1 1.1 1.0 1.0 1.0 1.0 0.9 0.9 0.8 0.8 0.8 0.8 0.7 0.7 0.7 0.7 0.7 3.2 2.8 2.6 2.4 2.2 2.0 1.9 1.8 1.7 1.6 1.5 1.4 1.4 1.3 1.2 1.2 1.1 1.1 1.0 1.0 1.0 1.0 0.9 0.9 0.8 0.8 0.8 0.8 0.8 0.8 0.7 0.7 3.3 3.0 2.7 2.6 2.3 2.2 2.0 1.9 1.8 1.7 1.6 1.6 1.4 1.4 1.3 1.2 1.2 1.2 1.1 1.0 1.0 1.0 1.0 0.9 0.9 0.9 0.8 0.8 0.8 0.8 0.8 0.8 3.2 2.9 2.6 2.4 2.3 2.1 2.0 1.9 1.8 1.7 1.6 1.5 1.4 1.4 1.3 1.3 1.2 1.2 1.1 1.1 1.0 1.0 1.0 1.0 0.9 0.9 0.9 0.8 0.8 0.8 0.8 3.3 3.0 2.8 2.6 2.4 2.2 2.1 2.0 1.8 1.8 1.7 1.6 1.5 1.5 1.4 1.3 1.3 1.2 1.2 1.2 1.1 1.1 1.0 1.0 1.0 1.0 0.9 0.9 0.9 0.8 0.8 46329—21- 50 INSTRUCTIONS FOE AEEOLOGICAL OBSERVERS. Table 17. — Pressure of aqueov^ vapor. .0 .1 .2 .3 .4 .5 .6 .7 .8 .9 Temp. MILLIBARS. -34 0.25 0.26 0.24 0.24 0.24 0.24 0.24 0.23 0.23 0.23 -33 .28 .28 .27 .27 .27 .26 .26 .26 .26 .25 -32 .31 .31 .30 .30 .30 .30 .29 .29 .28 .28 -31 .34 .34 .34 .34 .33 .33 .32 .32 .32 .31 -30 .38 .38 .38 .37 .37 .36 .36 .36 .35 .35 -29 .43 .42 .42 .41 .41 .40 .40 .40 .39 .39 -28 .47 .47 .46 .46 .46 .45 .44 .44 .44 .43 -27 .52 .52 .61 .51 .60 .50 .49 .49 .48 .48 -26 .68 .67 .67 .56 .66 .65 .54 .54 .,53 .63 -25 .64 .63 .63 .62 .62 .61 .60 .60 .59 .58 -24 .71 .70 .69 .69 .68 .67 .67 .66 .65 .65 -23 .78 .77 .77 .76 .76 .74 .74 .73 .72 .71 -22 .86 .85 .84 .84 .83 .82 .81 .80 .80 .79 -21 .96 .94 .93 .92 .91 .90 .89 .89 .88 .87 -20 1.04 1.03 1.02 1.01 1.00 1.00 .99 .98 .97 .96 -19 1.16 1.14 1.13 1.12 1.11 1.10 1.09 1.07 1.06 1.05 -18 1.26 1.26 1.24 1.23 1.22 1.20 1.19 1.18 1.17 1.16 -17 1.39 1.37 1.36 1.35 1.34 1.32 1.31 1.30 1.29 1.27 -16 1.52 1.51 1.49 1.48 1.47 1.46 1.44 1.43 1.41 1.40 -15 1.67 1.65 1.64 1.62 1.61 1.59 1.58 1.67 1.55 1.54 -14 1.83 1.81 1.80 1.78 1.70 1.75 1.73 1.72 1.70 1.69 -13 2.00 1.99 1.97 1.95 1.93 1.92 1.90 1.S3 1.S6 1.85 -12 2.19 2.17 2.15 2.13 2.12 2.10 2.08 2.06 2.04 2.02 -11 2.40 2.38 2.35 2.33 2.31 2.29 2.27 2.25 2.23 2.21 -10 2.62 2.60 2.67 2.55 2.63 2.61 2.48 2.46 2.44 2.42 - 9 2.86 2.83 2.81 2.78 2.76 2.74 2.71 2.69 2.67 2.64 - 8 3.12 3.09 3.07 3.04 3.01 2.99 2.96 2.93 2.91 2.88 - 7 3.40 3.37 3.34 3.31 3.29 3.26 3.23 3.20 3.17 3.15 - 6 3.70 3.07 .3.64 3.01 3.68 3.65 3.52 3.49 3.46 3.43 - 5 4.03 4.00 .3.97 3.93 3.90 3.87 3.83 3.80 3.77 3.74 - 4 4.39 4.35 4.31 4.28 4.24 4.21 4.17 4.14 4.10 4.07 - 3 4.77 4.73 4.69 4.65 4.61 4.5S 4.54 4.50 4.46 4.42 - 2 6.18 5.14 6.10 6.06 6.01 4.97 4.93 4.89 4.85 4.81 - 1 5.63 6.68 6.53 6.49 5.44 5.40 5.36 5.31 6.27 6.23 - 6.11 6.06 6.01 6.96 6.91 6.86 5.81 6.77 6.72 5.67 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 6.11 6.66 7.05 7.68 8.13 8.72 9.33 10.02 10.73 11.48 12.28 13.13 14.03 14. 98 16.99 17.06 18.19 19.38 20.65 21.98 23.40 24.88 26. 46 28.11 29.86 31.70 33.04 33.09 37.84 40.10 42.48 44.98 47.00 50. 36 53.26 56.30 59.49 62.83 66. 34 70.01 73. K6 77. >;.s K2. 10 86.51 91.33 6.16 6.61 7.10 7.63 8.19 8.78 9.41 10.09 10. SO 11.66 12.36 13.21 14.12 15.08 16.09 17.17 18.30 19.61 20.78 22.12 23.64 25. 04 26.62 28.28 30.04 31.89 33. 84 35.90 38.06 40.33 42.72 45. 2?, 47.87 50.65 53.56 56.61 59.81 03.17 66.69 70.38 74.25 7X. 30 82.53 86.96 01.60 6.20 6.66 7.16 7.68 8.25 8.84 9.48 10.16 10.87 11.64 12.44 13.30 14.21 16.18 16.20 17.28 18. .12 19.63 20.91 22. 26 23.69 25.19 26.78 2S.46 30.22 32. 1)K 34.04 30. U io.m 4L'. 97 4.3. 49 48. 14 50.93 63. 85 56.92 60.14 63. ,52 67.06 70.76 74.65 7N. 71 K2. 97 87. 12 92.07 6.24 6.71 7.21 7.74 8.30 8.91 9.64 10.22 10.95 11.71 12.63 13.39 14.31 15.28 16.30 17.39 18. .34 19.76 21.04 22.40 23.83 25.35 26.94 28.63 30.40 32. 28 :! 1. 25 30. 32 3S. 30 40.80 43.21 45. 75 48.42 51.22 54. 16 67.24 00.47 63. Hi 67. 42 71.14 7,5. 04 79.13 83.40 87.87 02.66 6.29 6.76 7.26 7.79 8.36 8.97 9.61 10.30 11.02 n.79 12.61 13.48 14.40 13.38 16. 41 17.60 18. 66 19. 88 21.17 22. 64 23.98 25.50 27.11 28.80 30.69 32.47 34. 45 36.63 38. 73 41.04 43. .10 40.01 48.69 61. 50 31.40 ,37. 50 60.81 64.21 67.78 71.53 73.44 79.55 83. 84 88. 33 93.03 6.33 6.81 7.31 7.85 8.42 9.03 9.68 10.37 11.10 11.87 12.70 13.57 14.60 15.48 16.61 17.61 18.78 20.01 21.31 22.68 24.13 25. 66 27.27 28. 98 30.77 32.68 34.66 36. 75 38. 95 41.27 43.71 46.27 48.97 51.79 61.76 57.87 61.14 04,56 68. 13 71.91 75.83 79, 97 84.28 88.79 93.61 6.38 6.86 7.36 7.90 8.48 9.09 9.74 10.44 11.17 11.96 12.78 13.66 14.59 15,58 16.62 17.73 18.90 20. 13 21. 44 22, 82 24.28 23. 82 27.44 29.15 30.96 32. 86 34.86 36.96 39. 18 41.51 43.98 46,54 49, 24 62.08 55.06 68, 19 01,47 64,91 US, 52 72,30 76, 25 SO, 39 8t,72 89.26 93. 99 6.42 6.90 7.42 7.96 8.54 9.16 9.81 10.51 11.25 12.03 12.87 13,75 14.69 16.68 16.73 17. 84 lU. 03 20. 26 21. 3 ^ 22,96 24,43 23. 98 27.61 29, 33 31.14 33.05 35.06 37.18 39.41 41.75 44.21 46. 80 J!1. 52 52. 37 .35. 37 5S. 51 61.81 65, 27 CS. vaaA--v. j,...Ay^ r>.'-y\/^ Af^^^ |'lHv^>^A> l»^>v\AM>i LvvvW^ ^^^^,^^^ W^^VVaJ UyVA/^ Fio. 34.— Section of observation platform and tlieodolite stand, showing tlie insulation of the one from the other. transmitted to the theodolite is the vibration of the roof of the building. 2. THEODOLITE. The theodolite, figure 35, is a specially designed and The telescope is bent through an angle of 90 degrees. The eyepiece is produced through the angle of the bend to act as the horizontal axis of the telescope, while the object end turns freely in the vertical plane about this axis. In a cubical chamber about the right-angle constructed instrument similar in many respects to the bend of the telescope a 45-degree triangular prism, transit yet possessing distinctive features which make it acting as a muTor, is rigidly fixed in such a position that 58 INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. the shorter sides of the prism are perpendicular to the central line along the two tubes. The function of this prism is to turn the line of sight with the bend of the telescope and give a clear, well-defined image. The eyepiece is further provided with cross hairs stretched over a reticle for centering the objective and a rack and pinion for focusing the telescope. The objective end terminates in a cylindrical sleeve, which acts as a sun- shade to protect the object lens. The mass of both eye- piece and object end of telescope are compensated by counterweights, thus providing a free, even movement of little resistance. The telescope is supported over the center of the hori- zontal plate by a yoke standard. A vertical circle for elevation and a horizontal circle for direction are pro- vided for determining the relative movement of the telescope. Both vertical and horizontal circles are graduated in whole degrees. More accurate readings may be made by using verniers. Essentially, the vernier, fio hv MC \ 3H> 1 h V "? He 3bO Fis. 36.— Theodolite vernier. figure 36, liv, consists of a small graduated scale the imit divisions of which are just a certain amount smaller than the divisiofis of the scale upon which it is applied. This is accomplished on the circles of the theodolite by taking a space equal to 9 degrees, laying it off on the vernier, and dividing it into 10 equal parts. In figure 36, drawing A, let HG be the horizontal circle divided into degrees, and liv the horizontal vernier. Note that while the zero of both HC and 'hv are coincident, the tenth division of liv is coincident with only the ninth division on B.C. Thus, each division of hv is one-tenth degree less than each division on TIO. When two such scales are placed together, some particular line of the one will always be coincident or nearly coincident, with one of the divi- sions on the other. The position of the coinciding divi- sions, or the nearly coinciding divisions, determines the vernier reading. For example, when the third, fourth, or sixth division of }iv is coincident with some division on RC, the fractional parts of degree will be 0.3, 0,4, or 0.6, respectively. On drawing B of figure 36, the ver- nier reading is 0.6 of a degree, and on drawing O, it will be noticed that no one division of Iw is coincident with any other of the scale RC but that the seventh and eighth of Tiv are both between two of the divisions of EC, which shows that the vernier reading is more than 0.7 and less than 0.8 of a degree. The second place of the vernier reading must be gained by estimating the frac- tional part of one of the vernier divisions, which is rep- resented by the space between 6 on RC, and 7 on Tiv. In drawing C of figure 36, this space is about half of one-tenth, or 0.05 of 1 degree. Thus we see the vernier reading in this particular case is 0.75 of a degree, which, added to the index reading of the scale, determines the degrees and hundredths. The practical application of these verniers is shown by the sectional view of the theodolite in figure 37. The accompanying table gives the reading of each vernier in figures 36 and 37. Figure 36 A. Figure 38 B. Figure 36 C Figure 37.... VV 85.71 HV 00.00 \v 0.00 .60 359. 75 315.00 The levels are arranged on the horizontal plate, one parallel to the horizontal axis called the plate level. Pi, figure 35, while the other, perpendicular to the first, is knowm as the standard level, 8Ti, figure 35. The instrument thus far assembled revolves about a vertical axis, whose bearing is a sleeve and spindle, at the center of a graduated horizontal circle known as the base plate. An extension of the vertical axis, or the sleeve and spindle, passes through the shifting center and terminates in a spring and knurled nut to form the shifting center tension. The base plate is capable of revolution about this center but is ordinarily held in a rigid position by plate clamp screw, P, figure 35. The shifting center, S, assembled with and encircled by a heavy ring or handle, R, is supported above the tripod head, T, by means of three leveling screws, LB. Each leveling screw is provided with a tension or clamp screw, L. Pendent from the vertical axis and center of instrument VA is a small chain and hook, p, for the attachment of the plumb bob and line. Assembling the theodolite. — Assuming that the crates have been removed and that no damage has been done either in shipping or unpacking, the tripod will be opened up and planted fii-mly upon the floor with legs well spread and securely set to prevent slipping. Loosen the milled tension nut of the shifting center, figure 35, and run well down to the knurled head of spindle. Then remove the round wooden cap. Loosen the shifting-center nut or clamp ring, CR, figure 35, and adjust the shiftmg center 8, so that the seats of the leveling screws, LS, are sym- metrically arranged over their respective plates of the tripod head T. After tightening the clamp ring to retain the shifting center in that position, the tripod is in readiness for the instrument itself. Fig 35 —Theodolite used in k-ite and balloon work (B, back otinslrument; BA , bubble adjustment screw ; BP, base plate; C, cap or cover block; CK, clamp ring; CH',back counterweight; cw, front counter- weight- £T eyepiece; /, focusing screw: ]•', front of instrument; Zf, handle or ring; H^, horizontal axis- HC, horizontal circle; hv, horizontal limb and 45° vernier; HV, horizontal limb and right vernier; HT horizontal tangent screw: £, leveling clamp screw; iS, leveling screws; p, plumb bob hook; P, plate Clamp screw; PL, plate level or bubble; P/J', jirism housing; jes, reticle screws- « ^hiftini. center: SL, standard level or bubble; 3S, sun shade; ST, shifting center tension: TS, telescope stop; VA, vertical axis; VC, vertical circle; VV, vertical limb and vei tangent screw; r, yoke standard). S, shifting T, tripod head; vernier; VT, vertical 'mj^r^-'^^m ^^^^^lEl ^^^BH 1 ■ 1^ : feWEJwi iB^r F^^^mi ^^^^^^^^^H f^l^ pioEirnaw ^ L^tftidflHH BBB ^^^^^S^^^^^"^' ' BK Fig. 37.— Scclion of theodolite showing arranj^emenl of verniers with horizontal and vertical circles ( // 1', horizontal limb and right vernier; hv, horizontnl limb and 45° vernier; I'C, vertical circle. VY, vertical limb and vernier). INSTEUCTIONS FOE AEEOLOGICAL OBSEEVEES. 59 In most cases it will be found that the telescope has been removed from its bearings and packed in a separate rack in the case above the carriage. When so packed, the procedure will be as follows : The door of the theodo- lite case must be wide open to allow the removal of the lower shelf supporting the assembled yoke standard, base plate, and shifting center. These parts, so assembled, when removed from the case are placed upon a table or bench. With a firm grip on one edge of the shelf or rack tilt the whole upon one edge to allow access to the underside where a brass thumb nut retains the assembly to the rack. Unscrew this thumb nut but do not remove instrument from rack. When returned to the initial position as it was placed on the table or bench, remove the string tied about the horizontal tangent screw and right telescope stop, HT and TS, figure 35, and disengage tangent screw from horizontal circle, HC, by pulling the head of the screw away from the circle. Turn the yoke standard and base plate upon its axis, VA, until both elevation and azimuth tangent screws, VT and HT, are on the extreme right; then throw in the azimuth tangent screw, HT, to retain the base plate in that position. The two telescope bearings of the yoke standard will now be equi- distant from the observer as he stands before the instrument. With a small thin-bladed screw driver, remove the screws in each end of the cap or cover block, 0, over the telescope bearing of each yoke standard, Y. Eemove each cover block carefully, with both screws in their rela- tive positions in the block, and lay to one side in such a manner that there will be no confusion as to the exact position from which it was removed ; that is, observe that the screws are not changed about in the immediate cover block and that the cover blocks do not become exchanged for one another, or reversed end for end. In short, when they are replaced see that they are in no other position than that from which they were removed. The carriage is now ready for the telescope. The telescope is removed from the shipping case in the same manner as is the carriage itself. It is placed upon the table by the side of the carriage and with the object end of the telescope toward the observer. To set upon the standard, grasp the telescope at both ends of the main tube and, holding in this position, move to the carriage and carefully set in its bearings, which, if the preceding instructions have been carried out, will be properly set to receive. Caution: Do not let moisture or oil from the hands come in contact with the brass bearings of either telescope or yoke standard; likewise the silvered vertical circle and vernier. Note that the graduations on the vertical circle are coincident with the vernier on the right standard. Making sure that the telescope is firmly set in its bearings, replace the caps or cover plates in the same position as that from which they were removed. Turn in the screws firmly but do not force them. Under no consideration should the leather- ized bushing screw at the middle of the cover plates or the Y-block screw on the underside of the left bearing be touched at this time. These materially affect the ad- justment of the instrument and should not be disturbed. Eeplace the brass cap on the object end of the tele- scope with the aluminum cylinder, or sun shade, found in the back right-hand corner of the shipping case. The function of this shade is to protect the object lens, and the instrument should never be used without it. Direct rays of the sun or strong light will cause the cement between the sections of the object lens to run to one side, causing a "fern leaf" which interferes with the visibility through the lens. The cap on the axis of the telescope, just above the right horizontal tangent screw, is now removed. The eyepiece is taken from its rack in the back left-hand corner of the shipping case, freed from its protecting cap on the lower end, where it is screwed to the axis of the telescope in place of the cap which was just re- moved therefrom. This eyepiece is provided with a spe- cial pivoted attachment containing a disc of colored glass (dark green) for use when the the balloon is near the sun. The assembled instrument is now lifted from the sup- porting rack by the ring or handle and carefully placed upon the tripod, making sure that the chain and hook, f, figure 35, drop straight through the hoUow spindle of shifting center ST, and that the three leveling screws, LS, are properly seated in the grooves in the respective arms of the shifting center plate. Insuring that the ten- sion nut is run down well to the knurled end of the spindle, the shifting center tension, ST, is now raised until the threaded socket engages the threaded end of the vertical axis, VA, and turned on securely. The ten- sion nut is then run up on the spindle to compress the spring and hold the instrument firmly on the tripod. However, the nut must not be run up too far, so that there is no room left between the turns of the spring for equalizing the adjustment of the leveling screws. The theodolite is now completely assembled, and after adjust- ment and checking will be ready for observation work. Care of the theodolite. — The theodolite, being a delicate and costly instrument, should be given particular care and attention. It should never be left standing without the assurance (1) that the instrument is securely fastened upon the tripod, accomplished by the complete union of the vertical axis of instrument with the spindle of the shift- ing center tension; (2) that the tripod is well opened— that is, the free ends of the legs not too close together; and (3) that the legs are firmly planted to prevent slipping — a slight pressure of the foot upon the projecting plate of the tip of the tripod leg will accomplish the last. When left standing, the instrument should be pro- tected from all dust and foreign matter by covering with a light cloth and frequently wiping off the exposed parts. Should it become necessary to remove dust or moisture from the object lens, only a clean, dry chamois should be used on the exterior side of the lens. The lens is not to be removed from the tube for this purpose. The joints and seams of the telescope are so closely fitted that it is 60 INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. practically impossible for dust to get on the inside of the tube. Therefore, there will be no reason for taking the instrument apart for cleaning purposes. The lens at the eyepiece will rarely need this attention, and in such event is easily accessible by removing the aperture disk only on the extreme end of the eyepiece or front of the tele- scope. Attempts at further removal and cleaning of this lens are most certain to result in the destruction or dis- arrangement of the cross hairs on the reticle. Special attention should be given to the tangent screws of both vertical and horizontal circles. A little light clock oil in limited amounts and applied properly will eliminate much friction and reduce the wear on the base plate. Close examination of the instrument from time to time will reveal small parts and screws which have become loosened. These should be attended to immediately, so far as possible without the interference of proper adjust- ment; that is, if the parts which have become loosened materially affect the adjustment of the instrument it will be necessary to readjust and check the instrument after such parts have been tightened. The instrument is not to be taken apart more than is necessary for packing and shipment. Further taking apart for the purpose of cleaning or repairs should be done only by one experienced with the construction of the instrument, or by a competent person, and upon the receipt of authoritative instructions from the Central Office. Care should be taken that the hands do not come in contact with silvered surfaces of the circles or the verniers, for the moistiu'e and oil thereby deposited tend to oxidize the surfaces, making the graduations indistinct and diffi- cult to read. If these parts do become tarnished they may be brightened to some extent with a soft rubber pencil eraser. PacTcing the theodolite^WheneTeT it becomes necessary to ship the theodolite, a great deal of care must be given to the packing and preparation for shipment. The pack- ing case in which the instrument is received should be preserved for this purpose. The style of case oidLnarily used necessitates the separation of telescope from the assembled standard and base plate. This is accomplished by reversing the instructions given in section 2, under "Assembling the theodolite." In addition, the hori- zontal tangent screw HT, figure 35, is to be thrown in mesh with the base plate BP and secured there by wrap- ping and tying a short length of string about the hori- zontal tangent screw ET and telescope stop TS. See that the vertical tangent screw VT is disengaged and that the base-plate clamp screw P is loosened. Place the assembled standard and base plate, which has been secured to auxiliary shelf for that purpose, in the bottom part of the case so that the right horizontal vernier HV is about midway and toward the front of the case. Now prepare 4 rolls of excelsior about 6 inches long and 2 inches in diameter for packing the assembled standard. These rolls are to be placed one on either side of each telescope standard, in such a way that the ends of each roll will be against the side wall of the shipping case and the right or left edge of the telescope standard. When the last of these excelsior rolls is in position the telescope standard will be held rigidly from moving about on the rack. In placing the excelsior roll against the left hand edge of the forward yoke standard ie sure that it does not press too hard against the vertical tangent screw VT, figure 35. The telescope, with sunshade and eyepiece tube removed, is then laid in its supporting rack and placed in the upper part of the shipping case, with a piece of folded paper inserted between the telescope tube and the stay-blocks on underside of top of packing case. After closing and securely locking the door, fasten the key to case by means of a screw through the head. Each theodolite should be packed in its own case — that is the case bearing the same serial number. For shipment from station to station the shipping case containing the theodolite must be substantially crated. Carrying the theodolite. — The best method for carrying the theodolite is shown in figure 38. This position is obtained from the standing theodolite as follows: The observer, with the instrument close to his left, grasps it firmly on opposite sides of the ring or handle, then, placing his right foot in front of the nearest leg of tripod to prevent slipping, pushes the instrument forward to rest entirely upon that one leg and closes the others in by its side. Resuming the handhold upon the ring and turning a little to the right, followed by a step forward, will allow the observer to place the left hip in front of the closed tripod, and a second step forward with the lowering of the instru- ment head turning over the hip as a pivot will obtain the illustrated position. The advantage of carrying the instrument in this manner, rather than over the shoulder, is that the particular part of the instrument needing the most attention is right before the observer where he can watch it while passing through doorways, up and down stairs, or close to walls and buildings. When the theo- dolite is carried over the shoulder, the mass of the instru- ment itself exerts a strain upon the vertical axis, VA, figure 35, but when carried in the above-described position the strain is overcome, since the mass of the instrument is supported by the ring or handle designed for that pm-pose. It also affords more ease and comfort to the observer if the instrument is to be carried any distance. Adjustments of the theodolite. — Before the new theodolite is used it must be thoroughly adjusted and checked. This will be done at the Central Office before the instru- ment is assigned to any station. However, due to rough handling in shipment, it becomes necessary to recheck and sometimes to readjust the theodolite at the field station. An instrument in daily use should be checked occasionally — at least once every four months. If the initial adjustment is carried out carefully and accurately, these periodic corrections will be slight if at all noticeable, yet they should not be neglected. When the theodolite adjustment has been completed, the entire series of tests should be gone over as a means Fig. 38.— Proper method o£ carrying theodolite, and insulation of theodolite stand ( T) from observa- •/ tion platform (0) INSTEUCTIONS FOR AEEOLOGICAL OBSEEVEE.S. 61 of checking. It will often be found necessary to make slight corrections which exemplify the need of much attention during the initial adjustment. Before making any one of the adjustments, note that the instrument is properly seated at leveling screws and that the horizontal base plate is level. Check for levels before each of adjustments 2, 3, and 4 is attempted. The instructions for the adjustment and checking of instruments follow and are to be closely adhered to. They were prepared by Mr. William C. Haines, Observer, FiQ. 39.— Collimation adjustment. as the result of extended experience with these instru- ments. The adjustments of the theodolite are such as to cause (1) the instrument to revolve in a horizontal plane about a vertical axis, (2) the line of collimation to generate a vertical plane through the instrument axis when the telescope is revolved on its horizontal axis, and (3) the vernier on the vertical circle to give true readings of the angle of elevation of the line of collimation. These results may be brought about by the following adjustments: 1. The plate-level adjustment: To make the axis of each plate level lie in a plane perpendicular to the vertical axis, bring one of the level tubes in line with two of the leveling screws. Level with leveling screws, revolve the instrument 180° in azimuth, correct one-half the move- ment of the bubble on the leveling screws and the other half by raising or lowering the adjustable end of the level tube. Now level up again and revolve 180°, and the bubbles should remain in the center. If not, adjust for one-half the amount as before, and so con- tinue until the bubbles re- main in the center for all posi- tions. 2. The coUimation adjustment: To make the line of sight perpendicular to the horizontal axis of the telescope. When this is done the line of sight will generate a plane when the telescope is revolved on its horizontal axis. Set up the theodolite on level ground where a view can be had in opposite directions. (If the ground is not level a small error may be introduced into this test due to the horizontal axis.) With the telescope pointing to the left, set the line .of sight on a definite point A, figure 39, a few hundred feet away. Revolve the telescope about its horizontal axis and set another point B in the opposite direction. Now rotate the instrument in azimuth until the line of sight comes upon the first point A. Revolve the telescope about its horizontal axis again and fix a third point C on the line of sight beside the second point B. From the last point set, measure off one-fourth the distance between these two points to a point D and bring the line of sight to this position by moving the reticle laterally. This movement is reversed in the theodolite, as it is an inverted instrument. This adjust- ment should be repeated as a check. It is often found that the line of sight can not be brought to position without moving the reticle too far from the center of the tube. In this case adjustment must be made on the 45° glass prism which is placed in the cube at the axis of the telescope for the purpose of deflecting the line of sight at right angles. Unless the reflecting surface of the prism makes an angle of 45° with the incident beam of light, the deflection is no longer at right angles, but may be either greater or less than 90°, depending upon the relative position of the prism. Before attempting to adjust the prism, first determine whether the angle of deflection is greater or less than 90°. This may readily be done from the above test. If point C, the last point set, falls to the left of point B (the observer facing the points), the angle of deflection is apparently less than 90°. If it faUs to the right of point B, the angle of deflection is apparently greater than 90°. The reverse of the above is actually true, however, because of the fact that the theodolite inverts the objects. In the first case the angle of deflection is in reality greater \N > N' Fio. 40.— Efleot of prism on line of sight. than 90°, and the prism must be moved so as to increase the angle made by its reflecting surface to that of the incident beam of light. In the second case the angle of deflection is in reality less than 90°, and the reflecting siu-face must be moved so that it wfll make a smaller angle with the incident beam. In figure 40 (neglecting the effects of refraction of light in the glass) (a) shows position of prism with reference to incident beam of light to cause deflection greater than 90° and (b) posi- tion to cause deflection less than 90°. 62 mSTBUCTIONS FOE AEEOLOGICAL OBSERVERS. To make this adjustment, the prism must be removed from the telescope. This is accomphshed by removing the small brass screws from the plate covering the cube at the axis of the telescope. The prism is attached to this plate and is removed with it. Tv/o set screws hold the prism in position on the plate. Its reflecting surface may be moved with reference to the line of sight by loosening one set screw and tightening the other. Care should be taken not to overadjust the prism, for a glance at figure 40 will show that any movement in the reflecting surface to the incident beam of light will be doubled in the reflected rays. In this instance, the assumed move- ment of 5 degrees in the reflecting surface produces 10 degrees difference in the angle of deflection. In so far as the deflection of the line of sight is concerned, the 45-degree prism produces the same effect as a plane mirror placed in the position of the reflecting surface of the prism. Any refraction that is produced at the en- trant face of the prism is nullified by corresponding re- fraction on emergence of the ray of light. 4. The vernier adjustment: To make the vernier read zero when the line of sight is horizontal. This adjust- ment is usually made by one of the peg methods. The following is perhaps the simplest: The instrument is set up midway between two pegs N and S, figure 42. With the vernier set on zero the rod is held and read on these two points. Care should be taken that the vernier setting is not disturbed while making this test. Even if out of adjustment the dif- ference between the rod readings gives the true difference in level between iV and S. The instrument is next set up near the higher peg so that looking through the tele- scope with the eye at the object end a point can be set in the exact center of the small field of view and the reading taken. The rod is next held on the distant peg and read in the usual way. If the true difference in level between the pegs be added to the near peg reading it will give what the distant rod reading should be if the instrument is in adjustment. The difference between this amount and the actual distant rod reading represents the error in adjustment. To correct the error, set line of sight on correct reading on distant rod, then shift the FlG. 41.— Horizontal axis adjustment. 3. The standard adjustment: To make the horizontal axis of the telescope perpendicular to the vertical axis of the instrument, carefully level the theodolite and sight on some high point, as a steeple S, figure 41, lower the telescope and set a point R below S on about the same level as the instrument. Revolve the telescope about its horizontal axis and turn the instrument upon its vertical axis and again sight at S. Lower the telescope as before and set a point L opposite R. A point S' mid- way between R and L must be in the same vertical plane with S. Now raise or lower the adjustable end of the horizontal axis by means of the capstan-headed screws at the one end of the axis. The high end of the axis is always on the same side as the last point set. If this end of the axis is not adjustable, the other end can be raised instead. The test should be repeated until the line of sight coincides with S S'. Care should be taken to leave the cap screws tight enough to insure that the axis rests on its bearing but not tight enough to cause friction in turning the axis. Fig. 42.— Peg adjustment. vernier and carefully adjust it to read zero in this new position. Setting up tJieodolite for observation. — Place the theo- dolite over the observation point so that the base plate of the instrument is nearly level and centered over the exact point selected. To do this, see that the tripod is well opened, with legs firmly and symmetrically im- planted about, and equidistant from, the exact point. It is well to arrange the theodolite, when setting up for observation, with plate clamp screw, P, figure 35, on the opposite side of vertical axis, VA, from the orientation point which is being sighted upon. The significance of this will be understood later. To level the theodolite, turn the telescope upon the horizontal axis HA, figure 35, until it is about perpen- dicular to the base plate (the vertical circle set at or near 90 degrees, see reading of T'T', figure 37). Disen- gage the horizontal tangent screw ET, figure 35, and turn the instrument about its vertical axis until one of the levels, preferably the standard level SL, is parallel with the line joining any two of the leveling screws, LS. As a guide for this setting bring the right horizontal vernier, HV, over one of the three spokes of the ring or handle, and use the leveling screws on each side. See INSTKUCTIONS FOE AEROLOGICAL OBSERVERS. 63 that the shifting center tension spring is sufficiently loosened to allow ample adjustment of leveling screws, then bring the bubble between the marks of the standard level by turning the two leveling screws in opposite directions; that is, both in or both out as the occasion demands. While in this position, adjust plate level, PL, by raising or lowering with third leveling screw. Attach plumb bob to hook and chain, f, pendent from the vertical axis, and adjust until the bob just swings freely over the point. When the bob comes to rest, if not centered over the point of observation, loosen the thumb plate, CR, clamping the triangular shifting center, S, and shift theodolite head to the position in which the point of the plumb bob, when at rest, is pendent directly over the observation point, then lock by means of the thumb plate. If necessary, relevel the instrument by the above method, noting that each bubble is equally spaced between the marks on the appropriate tube. Now turn the instrument about its vertical axis successively through 90, 180, and 270 degrees, and observe that the bubbles are still in the central positions. If they are not, then return the telescope to the initial position and readjust until this is accomplished. The theodolite now beiug leveled, turn the instrument about its vertical axis until either the right horizontal vernier, HV, figure 35, or the 45-degree horizontal vernier, Tiv, figure 35, is set on the azimuth bearing of the reference point, then lock by throwing in the hori- zontal tangent screw, HT. Set the vertical circle of the telescope at or near zero, loosen plate clamp screw and turn the locked telescope and base plate about the vertical axis until the telescope is sighted upon reference point of orientation, accomplished by means of the ball and V sights along the main tube of the telescope. Be sure that the azimuth setting on base plate for the par- ticular reference point has not been disturbed, then lock base plate to the horizontal axis by tightening the plate clamp screw P. Upon sighting through telescope, if it is found that intersection of cross hairs is not coincident with reference point, raise or lower by iheans of the vertical tangent screw, VT, and shift horizontally by means of the slow- motion or base-plate adjustment screw. This final hori- zontal adjustment must not be made with the horizontal tangent screw, since this would disturb the orientation setting of the particular reference point. Adjustment of the eyepiece, by turning the aperture disk either in or out, to obtain the maximum sharpness of cross hairs, and focusing the telescope by use of the rack and pinion, wUl complete the orientation and setting of the theodolite for observation work. Orientation of the theodolite is the process of placing the telescope in the vertical plane of a particular meridian and is accomplished by the method which immediately precedes. However, before orientation can be accom- plished, the exact position of a north-south line must be determined, and this line must also be determined for each point of observation, with the exception of second- ary stations at the far end of a base line. The line for this observation point may be derived from the azimuth bearing of base line from the primary station. Three distinct methods are here given for the determination of the north-south line. Determination of north-south line. — The first method is by the culmination of Delta Cassiopeia and Mizar; the second, by determining the hour angle and azimuth bearing of Polaris by observations on that star; and, third, the azimuth bearing between some terrestrial object and any definite celestial object. The culmination method is much the simplest of the three, requiring neither computation nor tables; it is necessary to know only the approximate time of culmina- tion. However, during certain periods it will be incon- venient to determine the north-south line by the cul- mination method, due to clouds obscuring one or both constellations, or culmination occurring at a time when the sky is so well lighted that the stars can not be seen. Such conditions lead to the second and third methods, which are adapted for any time at which Polaris or other celestial object selected for the observation may be seen. Both of the latter methods involve simple computation and the use of the American Ephemeris and Nautical Almanac. Much care and attention should be given to adjust- ment and leveling of the instrument, determination of angles, and the disposition of decimals in computation. All angles should be read to the nearest hundredth of a degree. Whichever method is used, the theodolite must be in perfect adjustment and the actual point of observation selected and permanently marked. The observer's watch will be compared with the standard of time in local use, and corrections made as become necessary. The theodolite will be placed centrally over the point to be determined and the greatest care given to leveling. In either the first or second method, it will be necessary to provide a means of illuminating the cross hairs. Any method whereby a beam of light can be reflected or thrown into the object end of telescope giving suflicient illumination to set forth the intersection of cross hairs and not flood the field with light to the extent that the image of the star is lost will answer the purpose. First method. — Delta Cassiopeia is the lower left hand star in the constellation Cassiopeia, figure 43, when this constellation is in the position of the letter W. During culmination this star crosses the north-south line 10 minutes in advance of Polaris and at the same time as Mizar, or the middle star in the handle of Ursa Major. These two stars mentioned are on opposite sides and nearly equidistant from Polaris. Culmination of tliese two stars occurs twice in 24 hours, and is followed within 10 minutes by Polaris crossing the same meridian. These facts, with the aid of an instrument, aft'ord a simple means of determining the north-south line. 64 INSTEUCTIONS FOE AEROLOGICAL OBSERVERS. Having determined the approximate time of culmina- tion of Delta Cassiopeia and Mizar, the theodolite is set over the exact point for which the meridian is. to he deter- mined, plumbed, and leveled very carefully. It is well to do this while it is yet light. Be sure that the base plate is firmly locked and that both vertical and hori- zontal tangent screws can be turned freely without resistance. Sight the telescope upon some prominent point, as the tip of church spii'e, peak of gable roof, sharp corner of building, etc., and note the azimuth reading of this point on either the right or the 45-degree horizontal vernier. Take particular care that all subse- Delta Cassiopeia* "" B FiQ. 43.— Constellations of Ursa Major and Cassiopeia. quent azimuth readings during this observation are made from the same horizontal vernier. A little time before culmination occurs, say half to three-quarters of an hour, a little practice should be gained by sighting upon the upper of the two stars and rapidly shifting the sight to the lower one. By the time culmination occurs, if the practice of raising and depressing telescope has been carried out, the observer will have gained considerable proficiency in the act, and the final movement at time of culmination will be performed with little or no difficulty. Have the cross hairs illuminated as mentioned above and the telescope properly focussed. Engage both verti- cal and horizontal tangent screws and bring the inter- section of the cross hairs centrally over the star in ques- tion. Quickly note the readings on the respective ver- niers and rapidly depress the telescope to elevation of the lower star by turning the vertical tangent screw, but do not disturb the horizontal tangent screw during the depression. The lower of the two stars will appear to the left of the vertical cross hair, but it will gradually approach the vertical hair as the time of culmination is approached. Raise the telescope to the upper of the two stars again, reset, read the angles from the same two verniers, and immediately depress the telescope as before. Repeat the foregoing operation until it is observed that the lower of the two stars also falls upon the vertical cross hair when the telescope is depressed. When this is obtained, raise the telescope to the altitude position of Polaris, hut do not disturb the azimuth setting, or the result of the observation will be of no avail. As a check, note that Polaris culminates just 10 minutes after the culmination of Delta Cassiopeia and Mizar. Note and record the azimuth setting, then depress the telescope to sight upon some conveniently accessible object where a distinct point coincident with the intersection of cross hau's will be placed. This point so placed will be true north. Example 1 : Suppose the theodolite is first sighted upon the cross of a church spire to the right of north, and the azimuth bearing, read from the right horizontal vernier, is 126.15 degrees. Let 98.4 degrees be the reading from the same vernier when Delta Cassiopeia and Mizar are in culmination. The difference between these two readings will give the angle at observation point between true north and the reference point, or the bearing of reference point from north: 126°.15-98°.4 = 27°.75; thus, when theodolite is set up with zero of base plate on north, the azimuth bearing of cross on church spire will be 27.75 degrees. But, if the theodolite is set up with zero of base plate on south then the azimuth bearing of the church spire will be 180.0 degrees more, or 207°. 75. Second method. — Polaris, in its apparent counter- clockwise revolution about the pole, takes 23 hours 56.1 minutes of our regular 24-hour day, thus culminating or crossing the meridian twice in 24 hours, and nearly 4 minutes earlier each day. From this we see that the position of Polaris east or west of the meridian for any specified time will vary from day to day. Knowing the correct local mean time and the time of upper culmination, the horn- angle of Polaris (or the angle at the pole be- tween the north-south line and the hour circle passing through Polaris), may be found. From the hour angle of Polaris, with the aid of the American Ephemeris and Nautical Almanac, the true azimuth of Polaris may be easily computed. The observations are made on Polaris at any convenient time after it becomes visible. The theodolite is carefully set and leveled over the exact point of observation as in the preceding method, the cross hairs are likewise illuminated, and the watch compared with the correct local mean time. After the INSTKUCTIONS FOE AEROLOGICAL OBSERVERS. 65 base plate is locked, the telescope is sighted upon some well-defined point as a reference mark, and the azimuth reading carefully noted and recorded. The telescope is then trained upon Polaris, and at the instant that the intersection of cross hairs is brought centrally over Polaris, the exact watch time to seconds is first noted, followed by the reading on the same azimuth vernier from which the azimuth reading of the reference point was made. All angles will be read to the nearest hun- dredth of a degree. A series of three or more observa- tions, 10 to 15 minutes apart, should be taken as a check on the first and the computation as a whole. The final result of each computation should be no more than 0.02 or 0.03 of a degree from the mean result. Example 2: On July 2, 1919, in lat. 42° 27' N., long. 76° 29' W., or 5 h. 06 m. earlier than Greenwich, a series of three observations was made at 8 h. 42 m. 00 s., 8 h. 55 m. 00 s., and 9 h. 10 m. 00 s., seventy-fifth meridian time. The base-plate reading of the right azimuth vernier, when sighted upon a definite point on the left of north, was 189.64 degrees. The azimuth readings from the same vernier when sighted upon Polaris during the obser- vations were 237°.80, 237°.89, and 237°.98, respectively. Date, July 2, 1919. Position, lat. 42° 27' N., long. 7^° 29' W. — 5 h. 06 m. earlier than Greenwich. H. m. s. H. m. s. H. m. s. Time of observation (St. 75th). 8' 42 00 8 55 00 9 10 00 Earlier than seventy-fifth me- ridian 06 00 06 00 06 00 Local mean time 8 36 00 8 49 00 9 04 00 Reduction to sidereal time (A. E. and N. A., Table III)... -fOl 25 +01 25 +01 25 Sidereal time mean noon Greenwich, or right ascen- cension of mean sun this date (A. E. and N. A., for Greenwich mean noon) 6 37 54 6 37 54 6 37 54 Correction for long., 5 h. 06 m. 00 s., (A. E. and N. A., Ta- ble III) +00 50 +00 50 +00 50 Local sidereal time 15 16 09 15 29 09 15 44 09 Apparent right ascension of Polaris this dale (A. E. and N. A., apparent place of stars) 1 31 34 1 31 34 1 31 34 Hour angle of Polaris before upper culmination 10 15 25 10 02 25 9 47 25 H. m. H. m. H. m. Same in decimals of minutes 10 15.42 10 02.42 9 47.42 Azimuth of Polaris at this hour angle and latitude (A. E. and N. A., Table IV) 39.58 44.23 50.29 Same reduced to degrees .66 .74 .84 Observed azimuth of Polaris.... 237°. 80 237°. 89 237°. 98 237°. 15 237°. 14 True north on base plate 237°. 14 Accepting 237°. 14 as the direction of true north when the theodolite is set with 189°. 64 on the reference point, the bearing or horizontal angle between the reference point and true north will be the difference between 237°. 14 46329—21 5 and 189°.64 or 47°.50. Now, then, with the zero of base-plate setting on north, the azimuth bearing of the reference point is 360° minus i:7°.50, or 212°. 50. Third method. — The method of determining the north- south meridian by observation on the sun necessitates the use of a ray filter or smoked glass placed over the eyepiece during the observation. In the absence of both, the observer may wear smoked glasses or if these are not at hand, an image of the sun may be cast on a piece of white paper held at a distance from the eyepiece. By adjusting the focus the shadow of cross hairs will be seen on the paper and thus facilitate proper centering over the sun. Do not leave the object lens of the telescope exposed to the direct rays of the sun for any length of time. Such continued exposure is likely to render the lens unfit for use, as already explained. The preparation and setting of theodolite for this method is essentially the same as for the other two methods mentioned above, namely, properly place, level, and check the theodolite, lock base-plate, estab- lish reference point, and note the actual time of observa- tion. By the foUovfing method of computation, the north-south line may be determined from observations upon any known celestial body, it being only necessary to substitute the other definitely known body for the sun. However, the sun affords the most convenient object for the determination. The factors resolve themselves into a spherical triangle, which may be com- puted by the following formulaa : Let S = ^ (polar distance + co-latitude) , p + co-lat. ; Let Z> = ^ (polar distance — co-latitude) , p — co-lat. Let ii = i hour angle; Let Z = true azimuth; Then tan A" = sin B cosec S cot ^t tan Y = cos D sec S cot -?fi andiZ = X+ Y, ov X~Y. Example 3: On June 19, 1920, in latitude 38° 54' 12" N., longitude 77° 03' 03" W., or 5 h. 08 m. 12 s. earlier than Greenwich, observations were made on the sun at 1 h. 36 m. 44 s., seventy-fifth meridian time. The baseplate reading of the right azimuth vernier when sighted upon reference point to the left of sun was. . . . Observed azimuth reading of sun, same vernier Azimuth difference of points 142°. 28 239°. 78 97°. 50 Time of observation, seventy-fifth meridian 1 Earlier than seventy-fifth meridian time Local mean time of observation Equation of time (apparent— mean, A. E. and N. A.). . Local apparent time 1 Hour angle of sun (t) 1 ¥ The same converted to degrees ' 10° 1 36 44 08 12 1 28 32 -01 04 27 28 27 28 43 44 56' 00" 1 If S is less than 90 degrees, and (a) polar distance greater than co-lat., use sum of X and Y; (fi) polar distance less than co-lat., use diHerenoe ot X and Y. If S is greater than 90 degrees, always use diflerence of X and Y, which, subtracted from 180 degrees, results in the true azimuth. 2 Since 15°=one hour in time, the hour angle may be converted to degrees by using 15 as a factor, and reducing the whole to the simplest form in degrees, minutes, and seconds. 66 INSTEUCTIONS FOE AEKOLOGICAL OBSERVERS. H. m. s. co-lat. (90° -latitude of station) 51° 06' 00'' Polar distance of sun (90° - declination) 66° 34' 00" p+co-lat 117° 40' 00" S, or i(p+ co-lat.) 58° 50' 00" p-co-lat 15° 28' 00'/ -D, or i(p- co-lat.) 7° 44' 00" J£=10° 56' 00" log cot }i=0. 71405 log cot it=0. 7140S 5=58° 50' 00" log cosec -S=0. 06770 log sec S=0. 28607 D= 7° 44/ 00" log sin D=9. 12892 log cos .0=9. 99603 log tan X=9. 91067 log tan Y=0. 99615 X=39° 08' 55" r=84° 14' 20" X+Y=123° 23' 15", or 123°.39 True bearing of sun from north through west 123°. 39 Azimuth difference 97°. 50 Bearing of reference point from north through west 220°. 89 True bearing of reference point from north, 360°-22O°.89, or 139.11 degrees. Whenever it is possible all computations should be made before the theodolite is disturbed or moved from its setting. When the true north-south line has been determined, the true bearing of reference point from ob- servation point with at least two others at different dis- tances should be determined. These points with their bearings from north or south will constitute the orienta- tion points of the station. A plan of these points will be constructed to some convenient scale on a card 4 inches by 6 inches and mailed to Central Office for file, along with a brief description of the arrangement of equip- ment. At double-theodolite stations, a second card will show the length, bearing, and arrangement of base lines. Orientation of theodolite. — In single theodolite work, zero of the base plate will be set on north, for when the data are plotted upon the regular single-theodolite plotting board, the wind directions are more easily determined than otherwise. Further explanation will be given in later sections. For double-theodolite work, the setting of zero on the base plate may vary with the different methods used in plotting the data obtained. In any event both instru- ments should be homologously oriented, that is, the Keros of the base plates of both instruments on the same geographic point. Three methods of double-theodolite orientation are accepted. Namely, base-line orienta- tion, north orientation, and south orientation. In all metkods of plotting, base-line orientation is preferred, wherein the theodolite at primary station is set with zero of base plate on the base line, or secondary station, and the theodolite at the secondary station is set with 180° on base line or primary station. In ntirth orienta- tion and south orientation, both theodolites are set with the zero of base plate on north and south respec- tively. These latter methods are well adapted for the graphical method of two-theodolite plotting, but in- volve azimuth corrections equal to the base-lino bear- ing with north-south line, when the slide-rule method is used. The same exception holds for logarithms. There- fore when the flight is to be computed by slide rule or logs and then plotted, orientation by the base line method should be adopted. 3. BALLOONS. The balloons in use for pilot balloon work are made from the best grades of raw gum rubber to be obtained. They are manufactured by the "dip" process, and are therefore without seams and nearly spherical in shape. An extension of the longer axis about 2 inches in length and 1-h inches in diameter, terminating in a rolled edge, forms the neck or appendix through which inflation is accomplished. Balloons of two sizes are used, the first, 6 inches in diameter when uninflated, for single-theodo- Hte work, and the second, 9 inches in diameter uninflated, for special double-theodolite work. Both sizes of bal- loons may be procured either uncolored or colored. Color. — The uncolored balloons are those of natural gum, appearing to be a light tan or pale gray, while the colored may be either vermillion, maroon, blue, or pur- ple. The color of balloons when inflated is much less intense, and frequently of different color, than when un- inflated. As a ^^'hole, the appearance of balloons when at full inflation rnay be classed as transparent, translu- cent, or opaque. Balloons colored with a pigment in the body of the rubber are likely to be opaque when inflated, and those colored by a stain will be opaque only when colored witli a dense stain, and even then are more likely to belong to the translucent class. The \mcol- ored balloon becomes transparent under ordinary con- ditions of inflation. If the sky were of one color continuously, it would be necessary to have but one color of balloon for all times. That color would be one which would present a strong contrast with the color of the sky. Since the sky color- ing may be either blue, white, or gray, the balloons most easily seen with the aid of the theodolite will necessarily be those which present the strongest contrast to these sky colors. In general, the strongest contrast of colors is that of black and white. Next in order come the asso- ciation, or juxtaposition, (1) of two primary colors, (2) of one primary and one complementary secondary, and (3) of a light tint of one primary and a dark shade of the same or another primary, the strength of contrast de- creasing in the order given. If we let the primary colors be red, blue, and yellow, the secondaries pairs of prima- ries combined in equal volumes, and a complementary secondary to a primary be a secondary composed of two other primaries, then the above scheme of contrasts used by the United States Coast and Geodetic Survey is represented by the following table : For color contrasts, juxtapose. (1) Piimaiy with other primary. Red with— Blue or yellow. Blue with — Red or yellow. Yellow with — Red or blue. (2) Primary with complemen- tary secondary. Red with— Blue and yellow or green. Blue with— Red and yellow or orange. Vellow with— Red and blue or violet. (3) Light tint of primary with dark shade of same or other primary. Light red with— Dark red, dark blue, or dark yellow. Light blue with— Dark blue, dark yellow, or dark red. Light yellow with — Dark yellow, dark red, or dark blue. IISrSTRUCTIONS FOR AEROLOGICAL OBSERVERS. 67 From the above we see that the strongest contrast formed against a blue sky would be obtained by using a red or a yellow balloon, and a strong contrast, though less marked, would be obtained by the use of an orange- colored balloon. When the sky is a light blue or fading into white and finally becoming gray, a strong contrast is obtained by the use of dark shades of blue, yellow, or red. The same relative principles would hold if the sky coloring were red or yellow instead of blue. Since these colors but rarely exist at the times of balloon observation, and even then in but the lightest of tints, we may confine our interest to the method of contrasts by (3). The application is similar to and essentially the same as for light blue. Cloudiness, haze, or mist is nearly always associated with the sky colors. Tints of red, blue, and yellow, in the majority of cases, fade into the whites or gradually deepen into the grays so common during cloudiness. But these conditions of sky coloring, we learn from the above table, are most strongly contrasted by the use of dark red, blue, or yellow. Experience has shown that dark-red balloons, or even light red, if the coloring has rendered the balloons opaque, are best adapted for all round use whether the sky be blue, white, or gray. When the sky is cloudless and well tinted with blue, remark- able results may be gained by the use of an uncolored or gray balloon. But this is nothing more than a reversal of contrast by (3) method. However, the successful use of the uncolored balloon is measured by the degree of clearness, the absence of haze and mist, and the predominance of bright sunlight throughout the flight, for the uncolored balloon against a white or gray back- ground readily blends and becomes invisible. In bright sunlight, the uncolored balloon possesses the main properties of a mirror, for the light upon it from the sun is reflected to the observer so long as the balloon does not come directly between the observer and the sun. If the latter condition obtains, the light then passes through the balloon, rendering it invisible. On days of few and very light clouds a balloon of translucent coloring may be used with equal success; but on days with appreciable cloudiness or haze a balloon of opaque coloring must be used to obtain the best results. In general — Uncolored balloons will be used upon clear days, or when there is an assurance that the sun will shine on the balloon throughout the flight, and Colored balloons will be used upon days when clouds, haze, or mist cause the sky to present a white or grayish appearance. Occasions will arise when the supply of colored balloons will become eixhausted, and a satisfactory run can not be made without one. One of the uncolored type may then be satisfactorily colored by the following method: The materials needed are some raw linseed oil and a small quantity of printer's ink. It is well to have two or three colors such as red, blue or black, and yellow. Add sufficient linseed oil to each can of ink to make a thick syrup or paste. There will be little difficulty in this since the ink is so readily soluble in the oil. To color the balloon successfully and conveniently, and without damage to the clothing, requires a little special manipulation, which is accomplished as follows: Place the thumbs of each hand within the neck of the balloon and allow the fingers to extend down the outside. Slightly distend the neck and bend the extended fingers in toward the palm of the hand at the same time pushing the walls of the balloon up to the region of the neck. Then by exerting a double Imeading movement, by rolling the back of the hands over each other, the walls of the balloon will be passed through the small passage of the neck, exposing the greater portion of the interior surface of the balloon. However, the balloon is not to be turned inside out completely, but the apex is left protruding from the underside, sufficiently to allow a finger hold for turn- ing the balloon back to the initial position. The balloon thus prepared will appear with the greater portion of the interior surface exposed above and outside the neck, and forming a depression at the point where it passes through the appendix of the balloon to the remaining portion of the unturned balloon on the underside of the hand. Now, in this depression, place a small quantity of the ink and oil mixture to the amount of about 2 or 3 grams. After the ink has been so placed, turn the balloon to the initial position by pulling on the lower protruding portion. This will close the surplus walls of the balloon over the ink mixture, thus preventing it from coming in contact with the neck or exterior surface of the balloon. When completely turned, proceed with the kneading until the color is evenly distributed. The kneading is quite de- sirable in itself and provides for maximum inflation of balloon, as will be explained later. Patching leaky halloona. — Occasionally balloons, when received from the manufacturers, will be found to have small "pinholes." In some cases such holes may develop during inflation due to small "air bubbles" or other defects. These defective balloons should not be dis- carded, but can and should be patched and made ready for use by the following method: Procure a piece of very fine emery paper, an ounce or two of benzine, a small tube of Goodyear rubber cement, and a piece of" a previously burst balloon. Turn the defective balloon inside out and lay it upon a flat surface, with the portion to be patched uppermost. Slightly roughen the rubber around the pinhole, also the piece of "patch" rubber, with the emery paper, wash each with a little benzine, and then apply to each a thin layer of the cement. The cement should be allowed to dry for about five minutes, when another layer should be applied. Place the patch on the prepared surface of the balloon, press it firmly down and then lay a small weight upon it, in order to insure even and complete coherence. The balloon should remain thus for 12 to 24 hours, after which it is turned back so that the patch is on the inside. The balloon is now ready for use, but should not be 68 INSTEUCTIONS FOE AEEOLOGICAL OBSEEVEES. inflated to give a rate of ascent greater than 180 m/m (preferably 160). During inflation the patch should be closely watched; if it curls up at the edges appreciably, the balloon should be laid aside and the patch later recemented. The size of the patch to be used will vary somewhat with the size of the hole, but in general a diameter of 1^ to 2 inches is recommended. Experience has shown that it is well to inspect each lot of balloons as soon as received and to patch all defec- tive ones at one time. Size. — ^At present the balloons in use for pilot balloon work are 6 and 9 inches in diameter uninflated. In prac- tically all single-theodolite observations 6-incli balloons will be used, while the 9-inch will be reserved for double theodolite work. The 9-inch are sometimes used in single- theodolite work when it is observed that an extremely high wind velocity obtains either aloft or at the surface. But a 6-inch balloon filled to a high ascensional rate is recommended in preference to a 9-inch for single-theodo- lite work. In double-theodolite work either 6-inch or 9-inch balloons may be used, depending upon the sky conditions at the time of observation. On hazy days or when low clouds predominate, or when the velocities at the surface and lower levels are low, 6-inch balloons should be used, thus leaving the 9-inch for days when there is an assurance of a fairly long flight. WeigJiing. — The weight of the empty balloon varies widely for both the 6-inch and the 9-inch sizes. The weight of the 6-inch will range from 15 grams to 50 grams, with a mean weight of about 25 grams, while the 9-inch wiU range from 30 grams to 75 grams, with a mean weight around 52 grams. In determining the weight of a bal- loon, a balance like that shown in figure 44 is used, and the accuracy is carried to the nearest whole gram. Before weighing the balloon, it is noted that the beam of the balance is in true equilibrium when both pans are free from load and the rider is in position at the zei'o point on the scale. The balloon is then folded two or three times along the major axis to form a long narrow strip, which i-i then firmly rolled into a ball, commencing at the apex of balloon, that all air may be expelled through the neck in the process of rolling. If the balloon is prepared in this manner, the weight obtained will for the most part be the actual weight of the empty envelope. If a filling apparatus such as that shown in figure 44 is used, the procedure will vary but little. Equilibrium will be estab- lished as with the free balance, the balloon likewise rolled and expelled of air, will be placed over the nozzle and weighed to the nearest whole gram. Inflation. — Inflation may be classed as "indefinite" and "definite." By indefinite inflation the balloon is filled to a convenient size, and the resulting ascensional rate interpolated from Table 26 (section 8), or computed from the formvda. First, the balloon is selected as to size and color, then it is vigorously worked and laieaded in the hands until it becomes warm and flexible. Stretch- ing and kneading it well before attaching it to the nozzle eliminate much bursting during inflation. A mild kneading is not sufficient; it should be pulled and stretched until there is a sensibility of heat when pulled over the hands. The balloon is then carefully folded, rolled, and weighed on a free balance as described above. With the balloon still rolled tightly, it is placed in the palm of the hand with about 1^ or 2 inches of the neck free and protruding from between the fingers and thumb. It is then brought near the nozzle of the filler pipe where it is held until the gas has been turned on at the hydrogen tank. A quick spurt of the gas will drive the air from the tube and this operation is quickly followed by the placing of the balloon over the nozzle. Thus the system is practically free of air and gas. The balloon is then securely wrapped and tied to the nozzle with tape and the gas is allowed to enter the balloon, slowly at first, until the rubber begins to stretch in all directions when the flow may be increased and carried to full inflation. Full inflation should not be accomplished in less than 40 to 50 seconds. Much of the bursting during inflation is due to too rapid filling. The size to which inflation can be carried will depend upon the convenience of the sta- tion, that is, the size of passages and openings through which the inflated balloon must be transported to the free air. Balloons should always be inflated inside a building or in a place well sheltered from drafts and cur- rents. The presence of these disturbances, though small in themselves, materially affects the ascensional rate of the balloon. It is necessary that this rate of ascent be measured in still air, free from such gusts. Since the filling will be done inside, the width or size of the open- ing through which the balloon must be passed to the free air will generally limit the diameters of the inflated bal- loon. An opening 29 inches wide, the average ^vidth of a common door, is equivalent to about 74 cm. and the balloon to be passed through this opening should not be inflated much beyond tliis diameter, for compression of the balloon to allow passage, and contact with the sharp edges and corners of casings mil often result in the puncture of an inflated balloon. Much care must be given to the handling of the in- flated balloon until it is released, for the tightly stretched rubber becomes quite delicate and is easily punctured by contact with relatively blunt corners or rough sur- faces. For this reason it is best to set the movable arm of the calipers at the width of the smallest opening tln-ough which a successful passage must be made, and then fill the balloon to that diameter. Thus, for an open- ing of 74 cm. in width, the calipers should be set for not more than 75 cm., and as the inflated balloon approaches this diameter, place the calipers in a horizontal position about the balloon so that one arm of the calipers is in contact with the surface of the balloon. As the increasing size of the balloon reaches the setting of the calipers, shut off the gas by closing the valve on the hydrogen tank. INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. 69 Sealing. — The balloon is now ready to be sealed and this is accomplished in the following manner: Prepare two No. 16 rubber bands for the tie, by placing them together over the fingers. The two bands are then given a half twist and doubled over to make a 4-stranded ring or loop. With a finger of each hand in this 4- stranded loop, the bands are slightly stretched and the fingers meanwhile twirled a few times so that the strands of the loop may be made even in tension, or the stress on the various strands equalized. The bands will now un- dergo considerable stress before any one of the strands will break. When this is completed the tie so prepared is slipped half way over the thumb and fingers of one hand, leaving the other entirely free. To apply the tie to the balloon, firmly grasp the neck of the balloon with the free hand about the nozzle and untie the tape. Place the other hand on the under side of the balloon with palm upward and fingers extended to form a shallow cup, and while the inflated balloon is held on the nozzle, it is raised or stretched vertically at the neck, and turned about until the neck is twisted upon itself. Care should be exercised that long or sharp finger nails do not punc- ture the balloon. By lessening the grip upon the nozzle, the balloon is allowed to slip therefrom and the neck is twisted further to insure a close hard roll or stem. With the free hand the band prepared for sealing is removed from about the fingers and slipped over the twisted por- tion of the neck where it is tightly wrapped by a series of alternating half twists and loopings accompanied by a firm tension on the bands to insure a tight joint. The balloon is now inflated and, if the foregoing directions have been closely followed, is properly sealed. The next procedure is to measure the free lift or the mass in whole grams which the inflated balloon will just lift from a horizontal plane. The free lift of a balloon is measured by attaching it to the left-hand pan of the free balance and placing weights thereon sufficient to bring the beam system of balance into equilibrium. In the event that the balloon can not be attached to the scale pan, it may be attached to a 200-gram, or any other kno^vn weight greater than the free lift, by means of a rubber band looped at each end as a slip noose. One end of the band is drawn over the neck of the balloon and the other is drawn over the knob of the weight. A weight of 200 grams will ordinarily be greater than the free lift of the balloons inflated to a maximum diameter of 74 cm. When the free lift is greater than 200 grams, the balloon may be attached to a larger weight. The weight with the balloon attached is then placed on the left-hand pan of the free balance which it will depress to the stop. SmaUer weights are then applied to the right-hand pan of the balance until equilibrium of the beam system is reestablished. The difference between this weight and that to which the balloon is attached will give the free lift of the balloon. As an example, suppose the weight attached is a 200- gram weight, and the weight applied to the opposite side of the free balance amounts to 19 grams, then the free lift {I) is equal to 200 grams - 19 grams or 181 grams. With the weight of the balloon {w), and the amount of the free lift (Z), as factors, the ascensional rate of the inflated balloon is computed from the f onnula : T/=72(^y.or (1) F=72U. (I.)- (2) wherein F= ascensional rate, or vertical velocity of balloon, Z = the free lift, representing the actual lifting force in grams, of the inflated balloon, L = the total lift, or the free lift plus the weight of the balloon expelled of air. Formula (1) may be further simplified to the following working form, without alteration of the resulting values: F=72 (log Z- 1 log i)- (3) Example: Let the weight (w) be 29 grams, and the free lift (Z) be 181 grams, then the total lift (i), will be w-\-l, or 210 grams (29 grams -I- 181 grams = 210 grams). Substituting these values in formula (3) and solving, we have : log Z = 2. 25768 -log i = 2. 32222 X ? = 1. 54815 0. 70953 X . 625 = log 0. 44346 = antilog 2. 7762 X 72 = 199. 89 Thus the ascensional rate for the balloon inflated under these conditions is 200 meters per minute. This opera- tion is greatly simplified by referring to table 26 (sec- tion 8), in which the ascensional rate may be found at the intersection of weight column and free-lift line. Reference to table 27 (section 8), "Altitude time-tables for various rates of ascent," for the ascensional rates foimd will give the height of the balloon for the end of any particular minute during which the balloon may be in the air. In this table it wiU be observed that the values for the first five minutes do not increase regularly by multiples of the ascensional rates given in the head- ings of the columns, but that they are in each case slightly larger than the values indicated by those rates. These increased values have been obtained by applying certain additive corrections, viz., 20 per cent for the first minute, 10 per cent for each of the second and third minutes, and 5 per cent for each of the fourth and fifth minutes. For a discussion of the necessity of applying these corrections, see paper by Capt. B. J. Sherry on "The Rate of Ascent of Pilot Balloons," Mo^'THLT Weather Review, December, 1920, pp. 692-694. In case any ascensional rate is used other than those given in table 27, it will be necessary to apply the additive corrections at the time of observation. The computed altitude of the balloon at the end of the first minute will then be 120 per cent of the ascensional rate; at the end 70 INSTKUCTIONS FOE AEROLOGICAL OBSERVERS. of the second minute it will be tliis value plus 110 per cent of the ascensional rate; and so on. To eliminate this inconvenience it is urged that the "definite inflation" method be employed whenever possible. Measuring. — Two diameters of the balloon are then measured: The vertical diameter or that along the major axis from the neck to the apex; and the horizontal diam- eter, or that in a plane perpendicular to the vertical diameter. In making these measurements of balloon diameters, with the balloon calipers, it has been found best to lay the calipers alongside the balloon with the graduated bar about parallel with the diameter to be measured, and the arms well opened and extending to one side disengaging the balloon. Upon the bar as an axis, turn the calipers to engage the balloon at the great- est width and move the sliding arm until the opening between the two arms just contains the balloon. The reading on the main bar at inside edge of the movable arm will be the desired diameter in centimeters. Manipu- lation of the calipers after this fashion will eliminate much of the bursting during inflation. The balloon is now ready for release. By "definite inflation," the ascensional rate to be used is decided upon, and the balloon inflated to meet those requirements. Inflation of this nature can be accom- plished only with the aid of some filling apparatus, which should be sufficiently sensitive to register the weight of the balloon and the free lift to the nearest whole gram. Figure 44 shows a simple arrangement of such apparatus and works very well when carefully assembled. The balance regularly supplied for balloon work is fitted up as follows : A wooden nozzle, N, figure 44, about 2 inches long by 2 inches in diameter, is turned from a piece of compact wood. The circular surface is corrugated in rings about one-fourth inch apart, which will assist in retaining the neck of the balloon and generally eliminate the need for tying. Through the center of the cylindrical block is bored a hole sufficiently large to receive the end of an elbow or right-angle bend of piping. This com- pleted nozzle is securely fastened to the right-hand side of the balance, centrally over the pan, and with the free end of the elbow extending in a horizontal direction and perpendicular to the line of the beam system. A piece of lead tubing, T, about 20 to 24 inches in length, is passed through the round hole in the base of the balance and thence between the scale bar and fulcrum support until about 6 inches of tubing extend above this point. Note that there is sufficient space between the lead tubing and scale bar to allow the passage of rider on the scale bar. This will necessitate the bending and slight flattening of the tubing at that point. When the lead tubing is all placed, the sot screw in the base of balance is turned in to hold the tubing in place, and the remainder of the tubing extending below the base is bent at right angles to pass out at the back of the balance. A short length of rubber tubing is here attached to connect the lead tubing with a three-way stopcock, C. The remainder of hydrogen line, L, is identical with that supphed for indefinite inflation. About 2 inches of the lead tubing extending above the balance is bent through a right-angle bend toward the front of the balance or in the same general direction as that of the free end of nozzle elbow, N, and the two ends connected with a rub- ber U-tube, U, of very fight flexible material. Tare, or counterweight, W, is then added to the left-hand pan of the balance to bring the beam system into equilibrium, and the apparatus is then complete. The procedure for definite inflation is as follows: Decide upon the rate of ascent to be used, 160, 180, or 200, etc., meters per minute. Table 28 (sec. 8); see that filling apparatus is in equilibrium; select color and size of baUoon, knead, fold, roll, and weigh as above stated. While still firmly rolled, stretch the neck of the balloon over the filler nozzle in a manner similar to that described under indefinite inflation, and turn on the gas slowly. In some instances it will be necessary to tie the balloon on the nozzle, in which case the string is placed on the nozzle side of the balance and the whole system adjusted for equilibrium before the baUoon is w^eighed. While the balloon is being filled, determine the amount of free lift to be given to it by referring to Table 28, imder the colunan head of selected ascensional rate and opposite to the weight of the balloon. As an example, suppose the ascensional rate selected is 200 m/m, and the weight of the baUoon is 34 grams. Then in Table 28, under 200 and opposite 34, it is found that the necessary free lift to which this particular balloon must be inflated is 188.0 grams. Had the ending of free lift been in tenths of grams, it would have been reduced to nearest whole grams. Weights equivalent to that mass are placed on the pan of balance under the baUoon. This end of the beam system will then be depressed to the stop. When sufficient gas has been admitted to raise the beam system to the point of equUibrium the valve at the tank is closed. The final adjustment is made by means of the three-way stopcock. GeneraUy the baUoon is filled to a point just beyond equilibrium and the surplus of gas allowed to escape through the three-way cock. When the balance is brought to equilibriiun mider these condi- tions this particular balloon is properly inflated to give an ascensional rate of 200 m/m. It is now sealed and measured as in indefinite inflation. If the foregoing instructions have been closely fol- lowed, everything is in readiness for an actual observation. Cavtion. — Never aUow the presence of lighted cigars, pipes, cigarettes, lamps, or lanterns in or near the buUd- ings during the process of inflation. Hydrogen gas when mixed with the air in correct proportions forms a very powerful explosive. Even glowing coals and cinders are sufficient to ignite the gas. 4. MAKING AN OBSERVATION. Regularly, at all stations unless otherwise specified, observations wiU be taken at 8 a. m. and 4 p. m., seventy- Fig. 44.— Balloon-filling apparatus used for ''definite" inflation ( C, threeway stopcock; i, hydrogen line; A', filler nozzle; T, lead tubing; U, rubber U-tube; W, counterweight). INSTRUCTIONS FOB AEROLOGICAL OBSERVERS. fifth meridian time. Occasionally special observations will be requested, and these will be made at the times indi- cated. But whether morning, evening, or special, the procedure will be identically the same. Not all stations will telegraph both morning and evening observations, but each station will be instructed separately with respect to the observations that are to be telegraphed. A pilot-balloon observation may be divided into three parts, (1) collection of data, (2) computation and plot- ting, and (3) reduction and tabulation. The first part, the collection of data, is the making of the observation itself, and involves the taking and the recording of balloon data, meteorological data, and ob- served readings of azimuth and elevation angles. Computation and plotting, the second part, is a con- necting link between (1) and (3). It includes the work necessary to prepare the observed data for reduction and tabulation. There are various methods by which this may be accomplished, viz., the slide-rule method; the graphical method, and the logarithmic method. The last part (3), covers the major portion of the work connected with the average pilot-balloon observation, namely, plotting the flight, determining the direction and velocity at the end of each minute, plotting the velocity- ♦azimuth graph, and reading off and tabulating the values for the specified levels. The single-theodolite observation requires the services of two men, the observer and the recorder. The mate- rials necessary are the theodolite, balloons, balance and weights, supply of hydrogen, tape or string, rubber bands, measuring calipers, watch or timing apparatus, slide rule, plotting board, graphing board, clip board, ascensional rate tables, conversion tables, forms, art gum, and pencils, both hard and soft. The observer is responsible for the setting of the theodo- lite, and the orientation on north or south, the meteor- ological data, and the proper placement of cross hairs over the balloon during the observation. The recorder is responsible for the preparation of the balloon, reading of angles at theodoUte, recording of all data on Form No. 1110-Aer., Table 19, and the computations so far as possible dm'ing the observation. The theodolite, balloons, balance, and weights have been already discussed. The hydrogen used for inflation is supplied, under considerable pressure, in strong steel cylinders. These cylinders when charged should be stored in a cool or at least well-shaded place, and entirely free from exposure to flame or glowing coals and embers. The watch is generally used for marking the time, though there are a few cases in which an idle "triple register" clock has been arranged as a time-interval clock. The slide rule, plotting board, etc., will be discussed in their turn. To arrange the time-interval clock as mentioned above, run a wire through the binding post of both wind direc- tion and sunshine brush and thence to the battery. From there it is carried to the place of observation, where it is connected to a buzzer, or bell, and passed through a switch, thence back to the ground post of the clock. By this arrangement the clock will give a double signal at the end of each minute. The signals, or the two buzzes, will be about five seconds apart. It should be so arranged that the first buzz will be a little long and quite loud, and the second buzz much shorter and as definitely short as can be successfully arranged. The first buzz will be known as the "warning" signal and the second buzz as the "read" signal. This "warning" signal will give ample time for the observer to center the balloon and the recorder to prepare for the reading of the angles. Without the interval clock it will be necessary to keep close watch of the time, in which case the "warning" signal will be called by the recorder about five seconds before the expiration of the minute, or the "read," signal. Generally the balloon is released on the full minute, therefore the "read" signal would occur at the sixtieth second and the "warning" signal on the fifty-fifth second. Since the observer is entirely responsible for the data obtained by theodolite when the angles are carefully and accurately read, he will set up the instrument over the observation point, level, and orient as described in earlier paragraphs under "The Theodolite," section 2. Suppose this setting to be with an elevation angle of 1 °.3 and the azimuth angle of the 45° horizontal vernier to be 345°. 6 with zero of the base plate on north. (See Table 19.) After setting of the theodolite is completed, the ob server will note and record the current meteorological data comprising the amount, kind, and direction of movement of the clouds, the direction and velocity of movement of the surface wind, the current temperature and the wet bulb temperature, the pressure, and the rela- tive humidity. Where a regular meteorological observa- tion has been taken within 15 minutes of the actual start- ing time of the balloon ascension (time of balloon release) that meteorological observation may be used instead of taking another. But in the event that a period of more than 15 minutes of time has elapsed, a separate and com- plete meteorological observation will be made. The results of this meteorological observation and the settings of the theodolite will be entered in the respective spaces upon the work sheet, or Form No. 1110-Aer. In the meantime the recorder will select the size and color of balloon to be used, weigh, inflate, and measure the free lift and ascertain the ascensional rate as in- structed under "Inflation," section 3. Suppose the balloon selected is a 6-inch red, and it is to be given a definite inflation to attain an ascensional rate of 200 m/m. The weight of the balloon is found to be 38 grams. When referring to Table 28, we find that a free lift of 193.1 grams is required to give the inflated balloon an upward velocity of 200 m/m. Since the free lift of infla- tion is measured only in whole grams, this will be re- duced to 193 grams and balloon inflated to that point. All of these data will be recorded in the proper spaces on Form No. 1110-Aer. as soon as they are determined. i2 INSTRUCTIONS FOE AEROLOGICAL OBSEIIVEES. [Form No. lllO-Acr.; Station (place of observation). Ascension number, 2136. Table 19. u. s. department of aqeicultuee, weather bureau. Pilot Balloon Ascension Report. Date, July 10, 1920. Number of theodolites used, 1. Starting time, 8:26 a. m. 75th meridian time, Observation point, A. Altitude, 55.3 m. Observation point, Altitude, m. Miuute. Elevation angle. Azimuth angle. o Distance from observar tion point. m. Altitude. ■m. Wind direction. Wind velocity. m.'p.s. Minute. Elevation angle. Azimuth angle. Distance from observa- tion point. m. Altitude. Wind direction. Wind velocity. m. p. s. 1.3 345.6 Zero setting on north. Zero setting on ; \ 16.7 2.5.6 21.35 21.35 21.2 21.05 20.7 20.65 21.9 23.95 25.95 27.9 29.2 33.3 35.1 35.6 35.85 35.5 34.3 32.65 29.2 27.95 1.3 203.4 221.7 225. 1 222.6 217.2 213.8 210.2 209.5 208.5 205.9 199.2 190.3 183.0 169.5 155.7 144.7 137.3 127.4 120.0 111.3 108.6 103.3 345.6 800 960 1,736 2,272 2,840 3,380 3,968 4,508 4,728 4,732 4,724 4,720 4,832 4,420 4,408 4,612 4,840 6,180 5,720 6,400 7,680 8,480 240 460 680 890 1,100 1,300 1,500 1,700 1,900 2,100 2,300 2,600 2,700 2,900 3,100 3,300 ,3,500 3,700 3,900 4,100 4,300 4,500 222 242 233 205 195 194 196 206 156 114 108 106 80 68 72 73 67 67 66 80 81 63 8.0 8.6 11.3 9.6 10.0 10.0 9.8 6.2 3.0 7.1 10.8 12.0 14.0 17.8 16.2 12.8 13.2 15.2 16.8 19.6 19.3 18.4 2 1 1 ■ g 1 \\ 13 1 1 :::;:: ::::.. :..i 16 18 - -- 19 20 21 22 Checked. Theodolite number, Observer, Recorder, Disappearance due to ."■.■.".".■.■.■pat 17396 rick Henry John Doe haze Theodolite number, ... Observer, Recorder, Disappearance due to . . Diameter at full lift — Vertical, 80.0; hor. 74.C cm. 38 gm. 193 gm. 231 gm. 200 m. p.m. Clouds. Amt. Kind. Dir. Baseline, : length, Azimuth, Visibility, Sun, Notes, No ascensiou Xor— a. m. Date p. m. Weight, Free lift, TotalUft, Upper Inter 1 Ci wsw. Good. .... Bright. Lower.... 1 Cu NNE. Tables, low clouds. 9. rain. T-A curve, m. p. m. .6" Red. Type of balloon,. Surface wind direction, NNE. velocity, 10 m/h. 4.5 m/s. Temperature, 23°. 3-18° .5 C. Pressure, 1,017.9-1,021.7 mb. Humidity, 62%. Now that all is in readiness for the observation, the ascension will he started, or the balloon will be released. The recorder will be provided with Forms No. 1110-Aer. on a clip board, hard pencil, slide rule, and watch. The observer will hold the inflated balloon near to and about level v.dth the theodolite head, until the signal of "read" (or reh'n^f) is pronounced by reforder or is given by the time-interval clock. If the time-interval clock is used the balloon will be held in readiness at the first buzz, and released on the second buzz. The exact time of release to the nearest minu'te is noted and recorded in the proper space at the top of Form No. 1110-Aer. If the watch alone is depended upon for time, then the recorder wUl bo forced to v/at''lj the time and call out the signals "warning" and "read" as they occur. By the latter system of time marking the balloon will be placed in readiness at the si:j;nfi.l "warning" from the recorder at the fifty-fifth second, and released at the following signal of "read," at the sixtieth second. Also the exact time of release is noted and entered upon Form No. 1110-Aer, Suppose the starting time to be 8:26 a. m. As the bal- loon rises and moves out from the station the observer will determine the direction of -wind movement to the nearest of the 16 compass points, which he will call to the recorder, who will enter the same on Form No. 1110- Aer. Suppose this to be NNE. Note that the vsdnd direction will be just opposite to that toward which the balloon moves. As soon as the btiUoon has moved away from the obser- vation point sufficiently, the observer will sight the main tube of the telescope upon the balloon, by means of ball and V sight, then throwing in both tangent screws VT and HT, figure 35, continue to sight balloon over the main tube while turning the tangent screws to keep the theodolite trained upon the balloon. Note that object end of telescope is alwnys inclined toward the left as the observer looks through the front; that is, the eleva- tion angle at VV, figure 35, must never be greater than 00 degrees. Wlien the rate and character of motion to keep the balloon in line of sight have been attained, con- INSTEUCTIONS FOE AEROLOGICAL OBSERVERS. 73 tinue the movement, and quickly change the position of the eye to look through the telescope at front or eyepiece. If the rate of movement has been properly judged, the balloon will appear in the field near the intersection of the cross hairs. Thereafter the observer will keep the balloon in the field by suitable movement of the tangent screws. When the surface wind velocity is low, oftentimes there will be much difhculty experienced in placing the balloon in the field of the theodolite. Under such con- ditions much assistance can be given by the recorder. The observer posts himseK at the front of the telescope with hands placed on the respective disengaged tangent screws. The recorder, with one hand on the telescope standard and the other on the main tube of the telescope, will turn the telescope until the vertical plane of move- ment is in line with the balloon, and, holding in this position, will slowly turn the telescope over its vertical axis until the balloon comes into the field of the tele- scope. '^Vhen this occurs, the observer will throw in the tangent screws and proceed as directed above. Fifty-five seconds after the release of the balloon, a signal of "warning" will be given, either by the recorder or by the time interval clock. When this signal is given, the observer will bring the intersection of the cross hairs directly over the balloon and keep it there until the second signal of "read" is given, when the motion will be stopped to allow the reading of the angles. The recorder, at the "warning" signal, will post himself just behind the observer and a little to the right, so that he can easily see both elevation and azimuth verniers, and make a mental note of the degrees of each. Then at the signal "read," as quickly as possible after the motion of tangent screws has been stopped, the angles of elevation and azimuth Yv^ill be read and recorded on Form No. 1110-Aer. Always read the azimuth angle from the same horizontal vernier by which the theodolite has been oriented. Ordinarily the observer will read one angle and the recorder will read the other. Whether the observer reads the elevation angle or the azimuth angle depends largely upon the way the base plate is oriented. If the orienta- tion setting is on the right horizontal vernier HV, figure 35, it is better for the observer to read the azimuth angle and the recorder the elevation angle, but if the orienta- tion setting is on the 45° horizontal vernier Jiv, figure 35, then it is better for the observer to read the elevation angle and the recorder the azimuth angle. In any event, the observer should not attempt to read either angle dur- ing the first five minutes or more, for during this time the lateral movement of the balloon is so great in com- parison with the field of the telescope that it is easily lost from the field, and this often results in the entire loss of time and material. The data for a minute or so might better be lost than to lose the balloon at this early stage. The recorder has nothing else to do at that time but read the angles. To read either of the angles it is not necessary for the observer to remove his eye from the telescope tube, and thereby lose the focus of balloon, but he may read either angle with the other eye. To read, retain the eye in the position as though peering through telescope and cast the other eye upon the vernier to be read. A little practice will prove this to be as simple and easy as though reading with both eyes. The observer will find that much relief is obtained, and much eye strain eliminated, by observing with both eyes open. Do not squint, or close the unused eye. A little practice will enable the observer to keep one eye at the instrument and read one angle with the other eye without difficulty. When he becomes proficient, even though the gaze of the one eye may be directed upon one or the other of the verniers, the other eye will gain and register an impression of the movement of the balloon, and should the balloon pass a little from the field during the reading, it may be regained readily by aid of the movement just mentally registered. Many instances will arise, however, wherein the ob- server will be unable to read either angle due to the fact that the balloon movement is so rapid as to require his full attention. In such cases, the recorder will read both angles, reading that first which the observer indicates is changing the more rapidly. A reading should be missed rather than be the means of losing the balloon. During the first 2 to 4 minutes the balloon can generally be seen by the naked eye, and thus easily placed in the field again. In a few instances, principally when the balloon turns and comes back directly over the station, the balloon move- ment will be more rapid than can be followed by tiu-ning of the tangent screws. However, loss of the balloon can be prevented without much difficulty if the following instructions are closely followed. While grasping the horizontal tangent screws, HT, figure 35, between the thumb and forefimger of the right hand, extend the middle finger past the 45° horizontal vernier, Tiv, figure 35, to rest upon the threaded groove of the baseplate, BP, figure 35, just below the edge of the revolving plate of the telescope standard. Letting this act as a brake, carefully throw out the tangent screw and retain the finger so placed. It is unnecessary to release the hand- hold upon the knurled head of the tangent screw. It acts as a rest for the hand. In a similar manner the middle finger of the left hand is extended until the ball of the finger is placed over the small space between the back edge of the vertical circle, VO, figure 35, and the pivot bearing near the middle of vertical tangent screw. Exercise a firm pressure here, then throw out vertical tangent screw and shift the thumb and forefinger to grip the edge of vertical circle, VO, figure 35. The middle finger in each case acts as a brake, steadying the move- ment of the telescope through the respective planes. With the fingers so placed and a httle careful judgment on the part of the observer, it is an easy matter to follow a balloon going overhead at a good rate of speed. When 74 INSTEUCTIONS FOE AEEOLOGICAL OBSEEVEES. the rate of movement has diminished sufficiently, the tangent screws are gradually thrown in again and the ordinary procedure followed. In single-theodolite observations the angles will be read to the nearest tenth of a degree (see description of vernier and figs. 36 and 37), and only at the completion of the minute as signaled by the time interval clock or the recorder. At the signal "warning" it is well to read the angles to the point of ascertaining the whole degrees, then the final reading or the reading to tenths of degrees can be made in much less time and directly at the "read" signal. It is practically necessary that the angles be read quickly and accurately. Comparatively small errors in reading angles can be detected when, the run is carefully plotted. Thus the necessity for quick and accurate work. As soon as the angles are read, the observer will bring the balloon near the center of the field by means of the tangent screws, where he will keep it until the following "warning" signal is given. In the meantime the recorder will enter the reading that he has made in the proper column on Form No. 1110-Aer., and opposite the corresponding minute. Suppose the azimuth angle for the first minute, read by the recorder from the 45° horizontal azimuth vernier, is 203°. 4; this he will record in the column under azimuth angle and opposite 1 in the minute column. The observer then calls out the angle which he has read and the recorder enters this; e. g., 16°. 7 in the column headed "Elevation angle." During the time that is left between the readings the recorder will compute the values for the -column headed "Distance from observation point" with the slide rule. Explanation of this process will be taken up in following sections. By doing the computation at this time fully 25 per cent of the working time of an observation will be saved, and permit an earlier filing of the coded mes- sage in the telegraph office. At the recurrence of the "warning" signal all other duties will be suspended and the full attention of both men given to the placing of balloon on cross hairs and the accurate determination of the angles. This same procedure obtains so long as the balloon can be kept in sight. When the balloon disappears, the observer will call out the reason for such disappearance and then check the setting and orientation of the theodolite. This reason of disappearance and the results of rechecking will be entered on Form No. 1110- Aer. in the proper spaces. Let Table 19 be the Form No. 1110-Aer. of an observation containing the above mentioned data. When the orientation setting is checked there is seldom any change necessary to be made. When the change amounts to a few tenths of a degree there is little that can be done in the way of correction, unless it is evident that the setting has been in error throughout the ffight. Corrections should be made to the azimuth angles when there is reason to believe that such corrections should be made. This will emphasize the need of care and atten- tion to the minutest detail throughout the whole of the observational work. The cause of disappearance will be recorded according to the following reasons. They stand in their order of frequency and relative importance. 1. Clouds: Against. In base of. Obscured by. 2. Burst. .3. Distance. 4. Haze. 5. Sun. 6. Obscured by — Tower. Chimney. Etc. 7. Overhead: High elevation angle. Kapid change of angles. 8. Accident: Kicking of theodolite. Allowed to pass off field. Vibration of theodolite, etc. 9. Abandoned. When the disappearance is due to clouds, it will be specifically stated whether against, in, or behind clouds. If this is not known, a statement to that effect should be made. If the balloon is seen to enter the base of clouds, particular attention will be given to the azimuth and elevation angles of the balloon, and the fractional part of the minute of the balloon's disappearance after the last minute reading. The product of this fraction of a minute into the rate of ascent, when added to the altitude of balloon for the last minute observed, will give the altitude of the cloud base. The direction and velocity of clouds is then computed in the same manner as for any other specific point of the projection. (See section 5.) Disappearance due to distance will not occur during a short ffight, except in rare cases where there is a very strong wind at the surface and aloft. A distance of 10 kilometers is the minimum value for this entry. Hori- zontal distances of less than that amount are due to other causes, possibly haze, fog, etc. Occasionally the balloon will run across the sun's disk, making observation impossible; however, such instances should be rare, since the theodoHtes now in use have a special eyepiece with pivoted disc of colored glass, permitting observation until the balloon actually begins to cross the sun. Other instances will occur when the balloon will be lost behind the anemometer tower, chinaney, or other obstruction. At a properly selected station possessing low angle of obstructions this reason will be of small frequency. The entry will be made, "obscured by - - " During periods of low surface wind veloc- ity, the elevation angles for the first few minutes will be relatively high. In fact, the balloon may be directly overhead. The balloon may change its course and come back directly over the observation station. The change of the angles, especially the azimuth angle, will then be INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. 75 rapid. In case of disappearance due to either of these causes an explanatory note should be entered after the en- try "Overhead." There will be a certain amount of loss due to accident, which is caused by the kicking or knocking of theodolite sufficiently to throw the balloon out of the field. This disappearance is due to carelessness, and with due attention to the work at hand will be eliminated altogether. Strong surface winds will sometimes throw the theodolite into such a state of vibration that the balloon can not be accurately placed at the cross hairs, and this will finally result in the loss of balloon altogether. An explanatory note must also accompany the entry of accident. There are but few cases when the balloon will be abandoned, principally to permit the early file of a coded message containing the observed data. The checking of the setting and orientation is accom- plished by setting the telescope of the theodolite upon the orientation point and noting the readings at the same verniers by which the theodolite was originally oriented. If there is no change within a few tenths of a degree, the readings will be entered in the proper columns on the second line under the last entry of observed angles, as "check." Otherwise, corrections will be made on the observed data. In this instance the setting at the end - of the observation was identical with that of the initial orientation, 1°.3 elevation, and 345°. 6, azimuth angle. Double-theodolite observations require the cooperation of three, four, and sometimes more men, all depending upon the arrangement of station and scope of work at hand. The prevailing arrangement of double theodolite station requires four men for the observation work, an observer and a recorder posted at each station. Their respective duties are nearly identical with those in a single-theodolite observation. Little or no slide-rule computation work is done while the observation is in progress. During the time that the primary station is preparing the balloon and setting the theodolite, those detailed for duty at the secondary station will have arrived at that station, set, and oriented their theodolite according to one of the methods set fprth in "Orientation of theodolite," section 2. Each station will be provided with a signal flag about 3 feet square, and attached to a short pole, or staff, to facilitate signaling to the other station. When all is ready at either station the signal flag will be exposed so that the men at the other station can see it. When both preparation signals are posted, all is in readiness for the ascent. The actual mode of signaling of the balloon release should be adopted and understood by all of the observers. Two methods are here given, both of which have been found to be very satisfactory. In the first, when the preparation signal at the primary station is answered by that of the secondary station, the recorder at the primary station, commencing one minute before the balloon is to be released, will wave the flag vigor- ously and in plain view of the observer at the secondary station for a period of 55 seconds. At the end of this time the flag is poised high above the head for the succeeding interval of five seconds, at the expiration of which the flag is brought down with a decided stroke. At the final downward stroke, the observer, who has been holding the balloon near the head of the instru- ment, will release it. The time of release will be noted and recorded at both stations, their time pieces having been compared before the flight. When the time pieces are not compared and set together previous to the flight, there is likely to be much inconvenience at the secondary station in regard to the watch time of warn- ing and read signals. They may come at 21, 29, 51, or any other odd second. Another method of signaling the release of the balloon is to expose the inflated balloon at arms' length above the head in full view of the observer at the secondary station. When all is in readiness for the release, the observer at the primary station will lower the balloon to the ground about 10 seconds before the time of release, where he will hold it for five seconds, at which time he will raise it to the initial position above the head. On the expiration of the minute, or on the sixtieth second, he will release the balloon. The recorder at each station will note and record the time of release as in the pre- ceding method. As soon as the balloon is released, the sign;il flags will be taken down at both stations by the recorder. The observers at both stations will immediately sight their theodolite upon the balloon and follow closely as in- structed under single-theodolite observation. The ob- server at the secondary station will have little difficulty in this matter, since his theodolite is already trained upon the balloon at the primary station. When the balloon is released he has only to follow it by manipu- lation of the tangent screws. Location of the balloon at the primary station will be identical with that during a single-theodolite observation. At each station the recorder will have to note the time and call signals for the readings which will be taken at the end of each successive minute from the time the balloon is released. The data at primary station will be entered on left-hand half of Form No. 1110-Aer., Table 20, and when that half of the sheet is filled up, a second sheet will be used. In single-theodolite work the second or right-hand half of the sheet would be used for the con- tinuation of the data, but with the double-theodolite work the second half of the sheet is reserved for the entry of the data of the other station. Thus we have all the observed data for any one minute at both stations, on the same sheet and in the same lines. The data at the secondary station will be entered on the right-hand side of the sheet only. Form No. 1110-Aer. will provide for a single-theodolite run of 60 minutes, but only for a run of 30 minutes for double-theodolite work. Table 20. At the completion of the observation the data from the one station will be copied on the Form No. 1110-Aer. of the other. 76 INSTEUCTIONS FOR AEROLOGICAL OBSERVEES. [Form No. 1110-Aer.] Station (place of observation). Ascension number, 1111. Table 20. u. -■. department of ageicultube, weather bueead. Pilot Balloon Ascension Report. Date, July 14, 1920. Number of theodolites used, 2. Starting time,7 :25 a. 90tli meridian time,. . . Observation point, A of A B. Altitude, 228.14 m. Observation point, B of A B . Altitude, 230.33 m. Minute. Elevation angle. Azimuth angle. o Distance from observa- tion point. TO. Altitude. TO. Wind direction. Wind velocity. m. p. s. Minute. Elevation angle. o Azimuth angle. Distance from observa- tion point, m. Altitude. TO. Wind direction. Wind velocity. TO. p. s. n 0.0 0.0 Zero setting on north. 0.0 0.0 Zero setting on north. I 31.1 28.2 26.4 21.4 19.6 19.2 19.0 18.2 17.6 16.9 16.3 43.5 66.5 72.0 79.3 81.6 83.1 83.8 86.2 88.3 88.9 88.7 400 840 1,320 2,160 2,930 3,535 4,160 4,975 5,650 6,510 7,600 212 450 656 850 1,044 1,240 1,435 1,635 1,795 2,005 2,225 56 82 93 89 89 89 94 101 97 90 87 6.9 8.4 11.9 13.7 11.7 10.4 11.7 12.9 13.3 16.1 18.0 1 2 3 4 6 6 7 8 9 10 11 12 13 14 7.1 15.6 25.3 29.7 28.0 26.8 25.1 24.2 22.8 21.2 19.8 18.9 18.3 18.0 314.3 330.4 .349.4 24.9 45.1 55.8 62.0 69.5 74.9 77.9 79.4 81.2 83.8 85.2 Check. 1 _ 3 1 4 5 j 1 — 6 7 1 8 9 10 11 Check 13394. John Doe. Patrick Henry. Obscured by St. Cu. cloud. TheodoUte m 12348. Jam es L. Jones. I. S. Smith. . Cu. cloud. i Disappearance due to: ... Disappearance due to: . . ....Enters Diameter at lull lift- )cm. 37.5sm. Clouds. 1 Amt. Kind. Dir. Baseline, Azimuth, ... Visibility, Sun, . . .A. B.; length, 1781.86. Vertical, 75.5; bor., 71.( In Lo 122°.55. Weight, 2 A.St St. Cu. W. W. Fair. rreeUft, 172.0 gm. gm. wer Obscured. 209.5 Total lift, ... Notes Weather cloudy. Rate of ascent from — Tables, 191 m. p. m. T-A curve, 202 m. p. m. Type of baUoou, C.-R.-6" Surface wind, direction, SW . velocity, 4.5 m/s. Temperature, 22°. 5 C. Presstire, 989. 2 mb. Humidity, 89%. The balloon will be followed as long as it can be kept in sight. Never should it be abandoned at either station before disappearance, without strong reasons for doing so. However, as soon as the balloon is lost at either station the flag will be raised as a signal to the other station. In cases where the balloon is lost sight of at one station for an appreciably longer period than at the other, the remainder of the flight beyond the time of disappearance at the one station may be computed by the single- theodolite method. Follov/ing the disappearance of the balloon, and before the theodolite is disturbed from its setting, a check of the levels and orientation will be made. Note that the azi- muth bearing is read from the same vernier by which the theodolite was oriented. If there are no corrections to be made the "check" will follow in the second line after the last line of observed data. The data will then be plotted and reduced in the same way as in the making of a single-theodolite observation. The methods of plotting vary to some extent, however, and will be taken up in regular order in subsequent p.nragraphs. In but few cases will slide-rule computations be per- formed during the double-theodolite observation. In many cases, however, it may be possible to do the com- putation and plotting while the flight is in progress. In such instances the computing work is generally carried on at a third poiat, which has telephonic communication with both observation stations. All three terminals of the line end in a head set, wliich allows free use of hands, and yet provides for the immediate use of the telephone. A time-interval system is easily installed in the telephone line, and will serve to mark the release of the balloon and the observation signals for each of the successive min- utes, making it possible to read the angles at both stations at the same instant. Communication from the primar}" station will prepare the secondary station for the time of balloon release. Wlien the observing stations are connected by tele- phone, then an observation can be carried on with only three men. But if computation and plotting are carried on during the flight, then four or more men will be needed. The regular force of two men obtains at the primary sta- tion, where they perform their regular duties much the same as in a single-theodolite observation, with the ex- ception that the recorder, speaking plainly, calls the ob- served data to the third party in the computing room. At the secondary station one man can easily observe the balloon and read the azimuth angle, which he calls to the computer over the telephone. Where this practice is carried on it is best to orient the theodolite by the right azimuth vernier. The computer, or the party in the computing room, receives and records all data from both INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. 77 stations, placing that of primary station on the left-hand to forbid the making of an ascension. It is recognized half of sheet and that of the secondary station on the that there are times when it would be a waste of balloon right-hand half of the sheet. He then immediately plots and gas to attempt an ascension; but, on the other hand, the data, or constructs the horizontal projection, before conditions must not be too easily and quickly dismissed the lapse of the whole minute. The recorder at the pri- as belonging to this class. In general, it may be said mary station will receive and record the angle or angles that an ascension should be made under all conditions reported by tlie secondary station. This will be the except those which incur danger to the instrument, original record and sliould be rendered in carbon with marked discomfort and possible injury to the health of data from both stations and on the same sheet or sheets. the observers, or a loss of the balloon below 250 meters. At any convenient time during the ascension the visi- If such conditions disappear within 30 minutes of the bility and condition of the sun will be noted and recorded time of the scheduled observation the ascension should according to the following scales: • be made; and if it is judged that such conditions may T-r. •i-,-^ 7 . occur at the time of observation, the ascension should be Vmbility scale. Liimtmg i i u- i distance bcgun early, possibly as much as a halt hour. Scale. Descriptive term. (meters). ° . ■ j i • i i i • xi, Dense fog— prominent objects not visible at 50 It is recognized that, m the last analysis, the question 1 Very bad— proHiinent objects not visible at 200 of omitting an ascension is one that must be decided 2 Bad— prominent object? Bot visible at 500 locally, and that no ironclad rules can be set down in 3 Very poor-promineut objects not visible at 1,000 jj^gtructions. But it is a question that has a strong 4 Poor — prominent objects not visible at 2,000 i-xix j.t_ j 5 Indifferent-Drominent objects not visible at 4,000 personal element, and IS one that must be answered c Fair— prominent objects not visible at 7, 000 conscientiously by those concerned. Times when ascen- 7 Good— prominent objects not visible at 12,000 sions are likely to be omitted owing to unfavorable 8 Very good— prominent objects not visible at 30,000 -weather conditions are often those which would be of 9 Excellent-prominent objects visible beyond 30,000 ^^^^^^^ scientific value. The observer should bear m This scale is nearly self-explanatory. The distances mind at all times the value of the data he is securing can be laid off on a map of the section of the country, and and the many uses to which they may be put, and he prominent objects selected as the points of reference. should try to cultivate such a spirit of sincerity. This, Sim bnghtness scale. coupled with good judgment, is certain to result in the , „ .„. , ^, . -L. ^ ^ *,• n satisfactory collection of aerological data. 1. Brilliant — Of rare occurrence; atmosphere must be exceptionally •' ° clear; smooth surfaces and shiny objects glisten. 5_ COMPUTATION. 2. Bright — As in a normal clear sky. . i, ■ ii, 3. Intermittent— Alternate sun and shadow; sky containing clouds of The second part in makmg an observation, or the the bunch formation. computation, may be accomplished by either one of 4. Through clouds— Sim quite dimmed by continuous clouds; grayish three methods; that is, by slide-rule method, graphical ^PP®^Z,^^f ®- ^ , ..,,., 1, 1 A f V, + f J, f method, or by logarithmic computation. The computa- 5. Faint— Disk of sun barely visible through clouds of sheet formation, "^^" '.,-,-,■.■, , ^- • i i as (li. St. A. St., or St. tion of smgle-theodohte observations is nearly always G. Obscured— Sun completely hidden by any dense cloud layer. done by means of the slide-rule method, though the This scale is also seK-explanatory. In each case the sun graphical method is frequently used when men doing brightness and the visibility will be entered on the Form, observation work are not proficient m manipulation of using for this purpose the appropriate terms rather than the slide rule. The slide-rule method ^aves much time the numbers; e. g., "brilliant," "faint," "dense fog," etc. when there is a Imuted period durmg which the observa- Omission of an A3cension.-It sometimes happens tion must be completed, and for the same amount of that at the time of the scheduled pilot-balloon observa- time expended on either method will give results more tion the weather conditions are such that an observer closely comparable with the results by logarithms, might carelessly or indifferently call off an ascension The logarithmic method is seldom used msmgle-theodolite when it is really possible to make a satisfactory observa- computation because of the time mvolvpd m the work, tion. For example, a light sprmkle of ram might be Practically the only use made of it is as a means of check- sufficient to give the observer the excuse for calling off the ing the computation by either of the other methods, ascension, even when the drops are so few as to cause The shde-rule method provides a means whereby the neither injury to the theodolite, discomfort to the ob- observed data can be reduced durmg the observation server, the early disappearance of the baUoon, nor appre- itseH for the construction of the horizontal projection ciable retardation in the ascensional rate of the balloon, immediately after he completion of the ascension. Snow flumes of short duration often preclude an ascen- whereas by either of the other two methods the computa- sion at the scheduled time, when a very few minutes tion must be suspended until the inakmg « the obser- later an ascension would be easily possible and worth nation is complete, and by one of these until after the while It is expected that an ascension will be made horizontal projection is made. By the graphical method within 30 minutes of the scheduled time, either before more than the observed data is not determmed until or after, if weather conditions are such as not positively after the horizontal projection has been made. 78 INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. Double-theodolite computation is generally accom- plished either by the graphical method or by the loga- rithmic method. The slide rule is frequently used for the solving of the trigonometric formulse when immediate general results are desired. The greatest accuracy is attained by the logarithmic method, though it involves considerably more time than the graphical method. Computation by logarithmic method is preferred, though the graphical method will be used frequently. All methods will be given full discussion in the following paragraphs. Method I. {!).. Single-theodolite computation, slide-rule method. — The slide rule used by the Weather Bureau for the computation of pilot-balloon observations is the K. & E. polyphase duplex slide rule. It is a 10-inch rule of mahogany, with the scales graduated upon a white celluloid base. The principle of the slide rule is purely logarithmic, and each scale is graduated after that prin- ciple, but the manipulation of it and the work done with it are purely mechanical and can be readily taken up without the slightest knowledge of logarithms. The scales of the slide rule in general use for pilot- balloon computation are the tangent scale T, the sine scale S, and the associate scales of D and A. For single- theodolite computation, little but the T and the D scales will be used, and these in conjunction with the formula tan e =-5, will be sufficient. e = the observed elevation angle for any one minute, which is found on T scale of central slide of rule. A = the theoretical altitude or elevation of balloon at end of each minute. It is the product of ascen- sional rate into time in minutes from release of balloon. This value is found on the lower or D scale of the slide rule. (Z = the horizontal distance from the observation point to a point directly underneath the balloon. A complete manual of instructions is furnished with each slide rule, and for that reason but little attention need be given here to the manipulation of the slide rule. Therefore, special reference is made to sections 3 and 7, and to pages 2 and 16 of the "Mannheim and Polyphase Slide Rule Manual." The supplement at the end of the manual will give much information of practical interest. Slide-rule computation for pilot-balloon work is af- fected to some extent by the elevation angle, which separates the work into two phases, namely, elevation angles less than 45° and elevation angles greater than 45°. While an explanation of computation involving an elevation angle of more than 45° is given early in section 7 of the manual, the direct application to pilot-balloon computation can be stated in simpler form, and will follow later. In ordinary computation, the elevation angle is less than 45°, and in such cases the procedure is simple enough. To compute the value d from the formula, tan e = -,> where e is less than 45°, the runner of the slide rule is set at h, in meters, on the D scale of shde rule, and then central shde is moved until the elevation angle e (for the same minute) on scale T is brought under the hair line of runner. The value of d is then read from the D scale of shde rule under the index of the central shde. In some instances this will be the right index and at other times it will be the left index. With reference to data sheet for single-theodolite observation. Table 19, to com- pute the distance out for the first minute, set the runner of shde rule on 240 of the D scale, then adjust the central shde until 16°. 7 (the elevation angle for the same minute) on the tangent scale is placed under the hair line of runner and coincident with 240 on the D scale. Under the right index of shde and on the D scale read 800 meters. Notice that the subdivisions on the T scale for angles less than 20° are equivalent to 5 minutes of arc and those subdivisions from 20° to 45° are equivalent to 10 min- utes of arc, while the divisions of angles as read from the theodolite are in degrees and tenths of degrees. There- fore, it will be necessary to convert the tenths of degrees to lainutes in order to make the settings of T scale ac- curate. This is a simple mental operation accomphshed by multiplying the tenths of the angle by 6, the resulting product being the fractional part of the angle converted to minutes. This value found will be recorded on the Form No. 1110-Aer., in the column headed "Distance from observation point." Proceed with the remainder of the flight in the same way, making sure that each computation is made only on altitude and corresponding elevation angle. When the elevation angle is above 45°, set the index of the T scale over h found on D scale, set the hair line of the runner over the elevation angle found on T scale, and read the value d under the hair line of runner on D scale. This value is the quantity sought, and is to be recorded in the corresponding space onForm No. 1110-Aer. As an example, suppose the elevation angle is 54°.9 and the altitude of the baUoon is 600 meters. To compute the value of d for this case we would set the index of central shde over 600 on the D scale, then on the T scale of the central shde we would find the angle 54°.9 and place the hair line of the runner thereon. Under the hair line and on the D scale we would read off the value of d, or 422 meters. It will be noticed that the T scale provided only for angles of 45° or less, and since the func- tion of an angle is equal to the cofunction of the comple- mentary angle, the operation involves a reversal of the method when an acQgle of more than 45° is recorded. To simplify the settings when the angles are greater than 45°, let the 5° divisions of the tangent scale be re-marked beginning at the 40° division which will be designated as 50° ; 30° will be 60°, etc. If these divisions are marked upon the celluloid surface of the rule in red ink, it will be found to assist greatly in the settings for angles greater than 45°. Let it be noticed and used as a check that the results of all slide-rule computations made on angles of elevation less than 45° will be greater than the h value on which the computation was made. Similarly, the results INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. 79 of all slide-rule computations made on angles of elevation greater than 45° will be Zessjtliat the corresponding h factor. Some difficulty is had in making the final close adjust- ments of the central slide during the computation. The following method, when closely followed, will eliminate any such trouble: Hold the rule between the thimib and first finger with one hand at either end of the slide rule so that the ball of the thumb and the tip of the first finger are placed over the seam of the slide rule between the rule itself and the central slide. Now, to make the setting, apply the principle of the parallel rule; that is, while firmly holding the rule as directed, extend one hand and arm while the other is drawn backward. This motion will cause the slide in the rule to move gradually and smoothly toward the end of rule which is being extended. Reversing the operation will drive it to the other end. By performing this movement slowly, the setting can be made as close as the eye is able to deter- mine. Plotting, or the construction of the horizontal j)rojection. — Immediately after the observation is taken and com- putation is completed, the data will be plotted and re- duced. The process of plotting is slightly different for the two methods, slide-rule computation and graphical method. As a matter of fact, the computation in the graphical method is preceded by the plotting or the con- struction of the horizontal projection. Plotting from logarithmic computation is identical with plotting from slide-rule computation, though more accurate, and also a much longer operation. The plotting board in use throughout the service is the most practical apparatus of its kind which has yet come to our knowledge. After prolonged study of vari- ous methods this board was selected for its simplicity and accuracy. It consists of a drafting board about 42 inches square. Over the central area is glued a circular sheet of millimeter cross-section paper. At the center of the area, and set into the board, is a brass bearing and pin A, figure 45. From the center of this pin or post three distance scales are drawn: Scale AC is a single scale and so constructed that 1 cm. = 100 m.; AD is a double scale in black and red. The divisions on the black scale, or the right side of the scale base, are such that 1 cm. = 200 m., and the red scale, or that on the left side of the scale base, is equal to 1 cm. = 400 m. Let these scales be designated as 1, 2, and 4. The num- ber of the scale will correspond to the number of hundred meters which 1 centimeter will equal. Let the lines on which the scales are graduated be known as the indices of the d scales, and let the scales themselves be Imown as d-1, d-2, and (?-4. At a convenient distance from the center, and extending perpendicularly toward the rio'ht from each of the scale bases, are drawn altitude scales EF and GH. These scales are so constructed that they are homologous to the respective distance scales; that is, 1 cm. = 100 m., 1 cm. = 200 m., and 1 cm. =400 m. Let these scales be known as l-h, 2-h, and 4-h, respectively, to agree with the distance scales so designated. In the quadrant to the right of the scale base, and near the edge of the circular sheet of millimeter paper, is drawn a 90-degree ai'c, graduated in half degrees. This arc is to be used for the elevation setting when the projection is constructed by the graphical method. Over the cir- cular area of paper and fastened to the brass pin as a center is placed a disk of frosted celluloid with the cir- cumference graduated in half degrees. The subdi\risions of half degrees are made to aid in determining settings of azimuth angles when projection is being made. A brass arm, AX, plays about the central pin and on the grad- uated 90-degree arc for the graphical computation, but is not used when the flight is plotted after the slide-rule computation. Its main use is in graphical projections of double-theodolite work. To plot, or construct, the horizontal projection of the computed flight, the plotting board will be arranged with the scale selected, 1-d, 2-d, or 4-(Z, directly in front of the operator. The celluloid on plotting board is then cleared of ail previous records by erasing the pencil marks with a piece of soft eraser or art gum. Note tha-t only soft erasers are used for this purpose. The celluloid protractor is then revolved about the center until the observed azimuth angle for the minute to be plotted is found on the edge of the disk and placed over the index of the scale selected. Then taking the computed dis- tance out for the same minute as a second factor, a point is plotted on the celluloid surface directly over this value found on the scale selected. The point is set off, or made more prominent, to distinguish it from any other point that may have been left upon the board, by en- circling, or by marking with a small cross, letting the intersection come at the position of the point. The method of encircling is recommended. Only very soft and well-sharpened pencils will be used on the celluloid protractor. It is difficult to place a point accurately with a dull point, and a hard, or even a medium soft, pencil will not make a mark easily distinguished. The average scale selected will be 2--d of the double scale AD, figure 45, or that in which 1 cm. = 200 m. Scale 1-d, AC, figure 45, will be chosen only when the wind movement for the first few minutes is compara- tively small, the observation a short one, or the maxi- mum distance out less than 5,000 meters. Observations of another character than these ■will be started upon the larger of the double scale, 2-d, and if necessary trans- ferred to the smaller scale 4,-d. As an example see horizontal projection for single-theodohte observation onfigm:e45. A, 1, 2, 3 .... 21, 22, designated by points inclosed with small circles. This is the horizontal pro- jection for sample flight recorded on Form No. 1110- Aer., Table 19. The plot is to the scale 1 cm. = 200 m., or scale 2-d. The board is arranged so that this scale is directly in front of the operator, then the azimuth angle for the first minute 203°. 4, is foimd on circum- ference of the celluloid disk which is revolved until this 80 INSTEUCTIONS FOE AEEOLOGICAL OBSEEVEES. angle is placed over the scale base or index of scale AD, and point 3 is placed over the scale base on scale used, AD, figure 45. The distance from the observation 2-d at a scale distance of 1,736 meters from the observa- point for the same minute, 800, is then found on the tion point. The point is inclosed by a circle and marked scale 2-d and a point placed there directly over the scale 3. Had the flight extended over a greater length of base, with a soft pencil. Set off by marking with cross or time, such that the maximum distance out would have Pig. 45.— Singlo-theodolite plotting board. encircling with a small circle, and number the point as 1. exceeded 10,000 meters, the last two minutes on scale Proceed in the same manner with succeeding minutes 2-d would have been plotted on scale A-d with the same 2, 3, 4, etc. Note that the setting of plotting board in azimuth setting. The reason for this will be explained this figure is for the third minute of the tabulated data; later. From the repetition of the two points the hori- that is, the azimuth angle 225°. 1 is set over the line zontal projection will be continued on 4-(Z. Had the INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. 81 flight been started on scale 1-d, the double plot would have taken in the last two points before 5,000 meters distance out, or points 16 and 17. That is, point 16 would have been plotted on both scale 1-d, and scale 2-d, the azimuth setting of 144°. 7 obtaining on both scales. Likewise, point 17 would be repeated. Method I. {2). Sincfle-theodolite, grafhical method. — If the graphical method is substituted for the slide-rule com- putation, then the plotting of the horizontal projection will be somewhat different, and will in truth precede the actual derivation of distance from observation point. Slide-rule computation during the observation will not be necessary. The only duties of the recorder will be to read and record any data pertaining to the observation. Directly after completion of the ascension, a horizontal projection of observed data will be made on the plotting board. By this method, the plotting board will be equipped with the brass arm, and arranged with a selected distance scale directly m front of the operator, as though plotting from sHde-rule computation. To plot or construct the horizontal projection for any minute, find the observed azimuth angle on edge of celluloid protractor and set this over the scale base selected, then set the beveled edge of the brass arm . AX, at the observed elevation angle on the 90-degree arc in the quadrant of the circle, to the right of the azimuth index. Then, with the altitude of the balloon as the third factor, find this value on the altitude scale agree- ing with the distance scale on which the horizontal pro- jection is being made, and foUow line through this point parallel to the scale base until it intersects the edge of the brass rale. From this point drop a line perpen- dicular to the line just run through the point on the elevation scale, to the scale base or index where a point will be placed, set off by circle or cross and numbered. Horizontal projection A, 1, 2, 3 ... . 21, 22, figure 45, shows the setting for plotting of the third minute. Scale 2-d was selected for the plot. The azimuth setting of 225°. 1, and elevation setting 21°.4, obtain, as may be seen from figure. Now on elevation scale corresponding to distance scale, in this case 2-h, the altitude for the same minute is found and a line run through this point parallel to distance scale index. Careful attention given to the millimeter lines of millimeter paper base wiU aid in running the parallels and perpendiculars in the plot- ting operation. The altitude for the third minute is 680 meters. Note that KL, figure 45, runs through 680 on scale 2-h and parallel to the scale base or index of scale 2-d. At the point of intersection, L, between this line KL and edge of brass arm, drop a perpendicular to the index of scale 2-d, and place the point 3. Note that L 3 is perpendicular to index 2-d. The points A, L and 3 determine a right triangle, and with reference to formula tan e = ^, the base A 3 is equivalent to dis- tance out, since 3 L is the altitude of balloon and angle 3 A L, the angular elevation. 46329—21 6 When the observation is plotted by the graphical method three unknown values are to be determined from the horizontal projection instead of two as in the method by slide-rule computation. From the method under present discussion, distance from observation point, wind direction, and wind velocity must be determined, while by the slide-rule method only wind direction and wind velocity need be determined from the horizontal projec- tion. To determine the distance from observation point of points plotted by the graphical method, revolve the protractor or celluloid disk xintil the point in question comes directly over the index of distance scale upon which horizontal projection is made, then read off the distance from the same scale. For example, to find the distance out for the third minute in plot A, 1, 2, 3 ... . 21, 22, figure 45, bring the third point over the index scale 2-d and read the position of point 3 on scale 2-d. By this method the distance out seems to be about 1,725 meters against 1,736 by the slide-rule method. The general average of results obtained by the slide-rule method com- pares more closely with results obtained by logarithmic computation than do the results from the graphical method. Therefore, the slide-ride method should be used in preference to the graphical method. Not only is it more accurate but it is a much quicker method. Method I. (S). Single-theodolite, slide-rule computation, graphical cosine plotting. — A third method of graphical plotting, convenient, speedy, and very accurate, if worked out carefully, is based upon the use of the natural cosine value of 0.6000, which reduces, graphically, the resulting horizontal distances to velocities in meters per second. The protractor is prepared for this method of plotting by drawing a line, as AT or AV, figure 45, on the milli- meter paper in the quadrant to the right of the index of each distance-out scale, so that it will make an angle with the scale base equal to 53°. 13, or the angle whose natural cosine is 0.6000. To construct the horizontal projection by this method, rotate the celluloid disk until the observed azimuth angle, on the edge of the disk, is set over the outer end of AT or AV, figure 45. Then, finding the distance from observa- tion point on the d scale that has been selected, drop a perpendicular from this point and produce until it inter- sects the line AT or AV, where a point is placed and set off as described in the foregoing methods. Successive points for the remainder of the ascension are plotted in the same manner. The horizontal projection by this method is automatically reduced so that the straight-hne distance between alternating points is divided by 12, which operation converts the horizontal distance trav- ersed during a two-minute interval to velocities of wind movement in meters per second. The observer should have some practice with this method and should become thoroughly familiar with i t before attempting to make the projection of an actual observation. Much care must be taken in running the 82 INSTEUCTIONS FOR AEEOLOGICAL OBSERVERS. perpendiculars from the distance scale to the line AT or AV, figure 46. It will be noticed that the range of dis- tance scale by this method is about 30 per cent less than the range of the distance scale of the two preceding methods. The particular advantage of this method lies in the speed with which the direction and velocity may be determined, as will be shown under determination of direction in "Reduction of data," section 6. Method I. H),. Single-theodolite, logarithmic computa- tion. — This form of computation for single-theodolite work involves the use of the same formula as that used in slide-rule computation, namely, tan c = -^, or d= Any convenient table of logarithms to the fifth place may be used. As an example, suppose the balloon to be at an altitude h, of 400 meters, and the observed elevation angle (e) 34°. 6, then the distance out, d, is found by sub- tracting log tan e from log 400 ; log 400 =2.60206 — log tan34°.6 = 9. 83876 logd d = 2.76330 =.579.83 and since we use the distance to the nearest whole meter, this is reduced to 580 meters, the distance out for that reading. Double-theodolite computation. — While there are nu- merous methods of graphical computation for double- theodohte observations, the basic principle of all is the same. A series of triangles is formed and projected upon a horizontal plane where the required parts can be conveniently measured by the use of a properly divided scale. Some methods are simpler than others and still may be retained within the same limits of accuracy. Three graphical methods have been carefully studied out and favorably accepted for their accuracy, simpHcity, and speed. Any complete graphical method necessitates the use of a graduated circle or protractor at either end of a scaled base line. Two of the graphical methods are adaptations of the single-theodolite plotting board, one of which involves the permanent alteration of plotting board, while the other, and that favored most, brings about only a temporary alteration of the board. Method II. (1). Double-theodolite, graphical method. — The first of the above-mentioned schemes has been explained fully in the Monthly Weather Review for April, 1919, page 222. Where all double-theodolite work is over one base line, or all base lines of a station are of the same length, this scheme is very satisfactory, but it is not well adapted to stations having a system of base lines of varied lengths, for, as the length of the base line varies, so must the scaled distance AB vary in proportion, and this variation is difficult to accomplish on a single- theodolite plotting board as it is now arranged, with its fixed center. However, the radial lines from station B might be drawn upon tracing paper, and a slot prepared along the 0°-180° fine to receive the protractor pin and allow for adjustment of base-line length, but this is un- satisfactory, since much difficulty will be experienced m placing the auxiliary sheet and keeping it in place over the fixed millimeter paper. Unless the base line is laid off to comparatively small scale, the method will not pro- vide for long runs, since it is difficult to alter the scale distance of the base Ime. Again, if the base-line scale is small, there will be considerable difficulty in plotting points and measuring velocities and directions for- ascen- sions during periods of little wind movement. For the above reasons the following method is given as the simplest and most applicable graphical method to be used with the single-theodolite plotting board. This method can be used for a base line of any bearing and any length within the limits of the distance scale on the protractor. The length of the base line may be changed or the scale of the same base line may be increased or decreased at will. Method II. {2) . Double-theodolite, graphical method. — The preparation of the single-theodolite plotting board for double-theodolite observations necessitates the use of a brass arm, and a point so placed as to represent the location of secondary station with reference to bearing and distance from primary station. To accomplish the location of this point, revolve the celluloid disk until the azimuth bearing of base line is placed over the index of the scale selected, then on that scale set a point at a distance from the center that will have a proper ratio to the distance from the secondary to the primary station. This point will mark the position of the secondary sta- tion, or station B. Place the brass arm over the central pivot, and the preparation is complete. As an example, let the horizontal projection. A, 1, 2 . . . . 10, 11, figiu-e 45, be the representation of data for double-theodolite observation on Form No. 1110-Aer., Table 20. Note that the line AB is in the direction from A, of 122°. 55, and that B is a point on that line a scale distance of 1,781.86 meters from A. For purposes of explanation, let N-S be the north-south line through the secondary station, or that just located. To use the protractor, and to plot these data, let the center of the celluloid disk, figure 45, be the primary sta- tion, or station A, and the auxihary point be the second- ary station, or station B. The data from both stations must be reduced to the same origin of orientation points. For graphical plotting, both theodohtes should be ori- ented with the zeros of base plates on north. Keep in mind the fact that all azimuth settings for station B will be made by rotating the celluloid disk until that setting, on its edge, is placed over the index of the scale selected. For a direction of north, south, or any other direction at station B, will be parallel, so far as this work is con- cerned, to the same direction at station A. Therefore the point A with its circumscribed arc of 360° may be used for setting any direction at station B. All azimuth settings at station A will be made with the beveled edge of the brass arm pivoted at the center of protractor. To construct the horizontal projection for the data recorded on Form No. 1110-Aer., Table 20, rotate the INSTEUCTIONS FOR AEROLOGICAL OBSERVERS. 83 celluloid disk until the azimuth reading at B, 314°.3, is set oyer the index of scale 2-// 1 > 1 1 1 1 > 1 1 d .§ P 1 > n t > 1 S t 5 1 1 > ■■§ > a 1 > 1 1 -3 > 1 > 1 £ 3 1 > 1 nnw. s. wnw. wnw. wnw. ssw. 3 4 4 7 3 1 nne. sse. wnw. nw. nw. sw. 4 7 8 8 5 S nne. sse. wnw. nw. n. ssw. low clo nw. nw. ene. sse. sw. n. sw. w. ■ nw. ne. 4 10 11 9 9 10 lids 9 6 9 5 5 4 8 6 7 5 nne. s. nw. wnw. nne. s. wnw. nw. ne. sse. nne. sw. w. nw. 5 10 14 10 10 9 10 ll 7 3 7 7 6 5 n. nw. wnw. n. s. wnw. nw. nne. sse. n. sw. w. nw. wnw. 5 16 11 9 8 11 7 10 8 2 8 9 6 7 nnw. nw. wnw. n. sw. wsw. wnw. nne. ese. wnw. wsw. w. nw. wnw. 6 13 12 g 7 8 9 10 7 4 8 8 5 11 wnw. wnw. nw. wsw. wsw. wnw. nw. ese. wnw. w. ndligh w. w. wnw. wnw. n. nne. ene. e. w. wsw. 7 22 11 8 17 10 4 3 4 9 ;. 3 8 18 11 11 8 7 2 5 8 wnw. nw. wnw. wsw. w. wnw. wnw. w. w. w. w. nnw. nne. ne. e. wnw. sw. 9 15 7 18 12 12 5 U 'e 9 10 9 8 7 2 5 7 wnw. nw. w. wsw. wnw. w. nw. ,w. nw. nne. ene. ese. w. sw. 14 16 15 18 7 14 2 8 8 8 6 1 7 6 w. nw. wsw. wsw. w. nnw. w. wnw. n. ene. nnw. wnw. sw. 14 18 20 13 8 3 9 9 9 3 1 9 9 w. nw. wsw. wsw. w. wnw. w. wnw. nnw, nw. n. wnw. w. 11 19 22 19 9 7 11 11 8 3 2 10 10 w. wsw. wsw. w. wnw. wnw. nnw. nw. n. wnw. w. 14 20 18 7 9 11 10 4 3 13 9 w. wnw. wnw. nw. nw. wnw. wnw. 9 8 12 10 4 5 15 w. w. wnw. nnw. wnw. nw. w. 3 8 16 10 8 2 17 nw. wnw. w. 2 3 4 5 6 7 8 nnw. nw. nne. sse. ssw. nnw. s. Calm. w. ne. se. ssw. nw. Gahu. sw. ssw. sw. ne. n. n. ne. sw. ssw. sw. 4 1 4 1 3 1 2 "3" 4

196 194 194 194 193 193 192 192 191 191 190 190 190 189 189 188 ISS 188 187 1S7 INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. Table 26^.— Rate of ascent, in meters per minute, far weight (w) and free lift (i)— Continued. 113 I. w. 15 16 17 18 19 196 197 197 197 197 198 198 198 199 199 199 200 200 200 20O 201 201 201 202 202 202 203 203 203 203 204 204 204 205 205 205 205 206 206 206 206 207 207 207 207 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 36 36 37 188 189 189 189 190 190 190 191 191 191 192 192 192 193 193 193 194 194 194 195 195 195 196 198 196 197 .197 .197 .197 198 198 .198 .199 199 199 199 200 200 200 201 38 39 40 155 198 198 199 109 199 200 200 200 201 201 201 202 202 202 202 203 203 203 204 204 204 204 205 205 205 206 206 206 206 207 207 207 207 208 208 208 208 209 209 209 198 198 198 199 199 199 199 200 200 200 201 201 201 202 202 202 203 203 203 203 204 204 204 204 205 205 105 206 206 206 206 207 207 207 207 208 208 208 208 209 197 197 198 108 198 199 199 199 200 200 200 200 201 201 202 202 202 202 203 203 20.3 204 204 204 204 205 205 205 205 206 206 206 206 207 207 207 208 208 208 208 197 197 197 198 198 198 199 199 199 199 200 200 200 201 201 201 202 202 202 202 203 203 203 204 204 204 104 205 205 205 206 ,206 206 206 207 207 207 207 208 2D8 196 196 196 197 197 197 198 198 198 199 199 199 199 200 200 200 201 201 201 202 202 202 203 203 203 203 204 204 204 204 205 205 205 205 206 206 206 207 207 207 195 196 196 196 197 197 197 198 198 198 198 199 199 199 200 200 200 200 201 201 201 202 202 202 203 203 203 203 204 204 204 205 205 205 205 206 206 206 206 207 195 195 195 196 196 196 197 197 197 198 198 198 199 199 199 199 200 200 200 201 201 201 202 202 202 202 203 203 203 204 204 204 204 205 205 205 206 206 206 206 194 195 195 195 196 196 198 197 197 197 198 198 198 198 199 199 199 200 200 200 201 201 201 201 202 202 202 203 203 203 203 204 204 204 205 205 205 205 206 208 194 194 194 195 195 196 196 198 197 197 197 197 198 198 198 199 199 199 200 200 200 200 201 201 201 202 202 202 202 203 203 203 204 204 204 204 205 205 205 205 193 104 104 194 195 195 195 196 196 198 197 197 197 198 198 198 199 199 199 199 200 200 200 201 201 201 202 ,202 202 202 203 203. 203 203 204 204 204 205 205 205 193 193 194 194 194 195 195 195 198 198 196 197 197 197 198 198 198 198 199 199 199 200 .200 200 200 201 201 201 202 202 202 203 203 ,203 203 204 204 204 204 205 193 193 193 194 194 194 195 195 196 196 196 196 190 197 197 197 198 19S 198 199 199 199 200 200 200 200 201 201 201 202 202 202 202 203 203 203 204 204 204 204 192 192 193 193 193 194 194 W4 195 195 196 196 196 196 197 197 197 198 198 198 198 199 199 199 200 200 200 201 201 201 201 202 202 202 203 203 203 203 204 204 192 192 192 193 193 193 194 194 194 195 196 196 196 196 196 197 197 197 198 198 19S 198 199 199 199 200 200 200 200 201 201 201 202 202 202 203' 203 203 203 204 191 192 192 192 193 193 193 194 194 194 195 195 195 186 196 196 196 197 197 197 198 198 198 199 199 199 199 200 200 200 201 201 201 202 202 202 202 203 203: 203 191 191 192 192 192 193 193 193 193 194 194 194 195 195 195 196 196 196 197 197 197 198 198 198 198 199 199 199 200 200 200 201 201 201 201 202 202 202 203 203 190 191 191 191 192 192 192 193 193 193 194 194 194 195 195 195 196 196 196 197 197 197 198 198 198 198 199 199 199 200 200 200 200 201 201 201 202 202 202 202 190 190 191 191 191 192 192 192 193 193 193 194 194 194 195 195 195 196 198 196 197 197 197 197 198 198 198 199 199 199 200 200 200 200 201 201 201 202 202 202 190 190 190 191 191 191 192 192 192 193 193 193 194 194 194 195 195 196 190 196 196 196 197 197 197 198 198 198 199 199 199 199 200 200 200 201 201 201 201 202 189 189 190 190 191 191 191 192 192 192 193 193 193 193 194 194 194 195 195 195 196 196 106 197 197 197 .198 198 198 198 199 199 .199 500 200 200 200 201 201 201 189 189 189 190 190 190 191 191 191 192 192 192 193 193 193 194 194 194 195 196 195 196 196 196 197 197 197 197 198 198 198 199 199 199 200 200 200 200 201 201 188 188 189 189 189 190 190 190 191 191 191 192 192 192 193 193 193 194 194 194 196 196 195 196 196 196 196 197 197 197 198 198 198 198 199 199 199 200 200 200 188 188 188 189 189 189 190 190 190 191 191 191 192 192 192 193 193 193 193 194 194 194 196 196 195 196 .196 196 197 197 197 .198 198 198 198 199 -199 .199 200 200 187 187 188 188 189 189 189 190 190 190 191 191 191 192 192 192 192 193 193 193 194 194 194 195 196 196 196 196 156 157 158 169 160 161 162 183 164 165 166 ,167.., 168 169 170 171 173 176 178 180 181 183 197 197 186 198 188 198 190 198 191 199 199 193 109 200 1. W. 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 i 31 32 -33 34 36 36 37 38 39 40 209 210 210 210 210 211 211 211 211 212 212 212 212 213 213 213 213 214 214 214 214 215 215 215 215 215 216 216 216 216 217 217 217 217 218 218 218 218 218 219 209 209 210 210 210 210 211 211 211 211 2n 212 212 212 212 213 213 213 213 214 214 214 214 215 215 215 215 216 216 216 216 216 217 217 217 217 218 218 218 21S 209 209 209 209 210 210 210 210 211 211 211 211 212 212 212 212 213 213 213 213 214 214 214 214 215 215 215 215 215 216 216 216 216 217 217 217 217 217 218 218 208 208 209 209 209 210 ,210 210 ,210 210 .211 211 .211 211 212 212 212 .212 213 213 213 213 214 214 214 214 215 215 215 215 216 216 216 216 216 217 217 217 217 218 2081 208' 208 209 209 209 209 210 210 210 210 ' 211 211 211 211 212 212 212 212 213 213 213 213 213 214 214 214 214 215 215 215 215 216 216 216 216 216 217 217 217 207 208 208 208 208 209 209 209 210 210 210 210 211 211 211 211 212 212 212 212 213 213 213 213 214 214 214 214 215 215 215 215 216 216 216 216 216 217 217 207 207 207 208 208 208 208 209 209 209 210 210 i210 210 211 211 211 211 212 212 212 212 212 213 213 213 213 214 214 214 214 215 215 215 215 216 216 216 216 216 207 207 207 207 208 ,208 208 208 ,209 209 209 209 210 210 210 ,210 211 211 211 211 212 212 212 212 213 213 213 213 214 214 214 214 214 215 215 215 215 216 216 216 206 206 207 207 207 207 208 208 ,208 :208 209 209 209 ,210, ,210 210 ,210 211 211 211 211 212 212 212 212 213 213 213 213 214 214 214 214 214 215 215 215 215 216 216 208 206 206 207 207 207 207 208 ,208 208 208 209 ,209 209 209 210 210 210 210 211 211 211 211 212 212 212 212 213 213 213 213 214 214 214 214 214 215 215 215 216 205 208 206 206 206 207 207 207 207 208 208 208 208 209 209 209 210 210 210 210 211 211 211 211 212 212 212 212 212 213 213 213 213 214 214 214 214 215 216 215 205 205 206 ■206 206 206 207 207 •207 207 .208 208 208 208 209 209 209 209 210 210 210 210 211 211 211 211 212 212 212 212 213 213 213 213 214 214 214 214 214 216 205 205 205 205 206 206 206 206 207 207 207 207 208 208 208 208 200 209 209 210 210 210 210 211 211 211 211 212 212 212 212 213 213 213 213 213 214 214 214 214 204 205 205 205 206 206 206 206 206 207 207 207 207 208 208 208 208 209 209 209 210 210 210 210 211 211 211 211 211 212 212 212 212 213 213 213 213 214 214 214 204 204 204 205 205 205 205 206 206 206 206 207 207 207 208 208 208 208 209 209 209 209 210 210 210 210 211 211 211 211 212 212 212 212 213 213 213 213 213 214 204 204 204 204 205 205! 205, 205, 206 206 206 206 207 207 207 207 208 208 208 208 209 209 209 210 210 210 210 211 211 211 211 211 212 212 212 212 213 213 213 213 203 203 204 204 204 204 205 205 205 205 206' 206 206 207 207 ,207 207 208 208 208 208 209 209 209 209 210 210 210 210 211 211 211 211 212 212 212 212 213 213 213 203 203 203 204 204 204 204 205 205 205 205 206 206 206 206 207 207 207 208 208 208 208 209 209 209 209 210 210 210 210 211 211 211 211 212 212 212 212 212 213 202 203 203 203 204 204 204 204 205 205 206 205 206 206 206 206 207 207 207 207 208 208 208 208 209 209 209 209 210 210 210 210 211 211 211 211 212 212 212 212 202 202 203 203 203 203 204 204 204 204 206 206 205 205 206 206 206 207 207 207 207 208 208 208 208 209 209 209 209 210 210 210 210 211 211 211 211 212 212 212 .202 202 202 .202 203 203 .203 .204 204 204 .204 .206 205 .205 206 .206 .206 -206 .206 207 207 207 208 208 208 208 208 209 209 209 210 210 210 210 211 211 211 211 211 212 201 202 202 202 202 202 203 203 203 204 204 204 206 205 205 205 206 206 206 206 207 207 207 207 208 208 208 208 209 209 209 209 210 210 ,210 210 211 211 211 211 201 201 202 202 202 202 203 203 203 203 ,204 .204 .204 204 205 205 206 206 206. 206 206 207 207 207 207 208 208 208 208 209 209 209 209 210 210 210 210 211 211 211 201 .201 201 201 202 202 202 203 203 203 203 204 204 204 204 205 205 205 205 206 206 206 206 207 207 207 207 208 208 208 208 209 209 209 209 210 210 210 210 211 200 200 201 201 201 202 202 202 202 203 .203 .203 .204 204 204 ,204 .206 .205 206 205 206 206 206 206 207 207 207 207 208 208 208 208 209 209 209 209 210 210 210 210 200 196 200 200 198 201 201 201 201 202 202 203 202 204 202 203 206 203 203 208 203 204 204 ,211 204 204 213 21i 214 205 205 216 206 206 218 206 205 207 221 207 207 207 224 208 208 226 208 208 228 209 209 209 209 210 233 210 210 1 4632&— 21- 114 INSTRUCTION'S FOE AEROLOGICAL OBSERVERS. Table 26a. — Rate of ascent, in meters per minute, for weight (w) and free lift (l) — Continued. 235. 236. 237. 238. 239. 240. 241. 242. 243 244 245 246 247 248 249 250 15 )6 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 211 38 39 40 219 218 218 218 217 217 217 216 216 216 215 215 215 214 214 214 213 213 213 212 212 212 211 211 210 219 219 218 218 218 217 217 217 216 216 216 215 215 214 214 214 213 213 213 212 212 212 212 211 211 211 219 219 219 218 218 217 217 217 216 216 216 215 215 215 214 214 214 213 213 213 212 212 212 211 211 220 219 219 218 218 218 217 217 217 216 216 216 215 215 215 214 214 214 213 213 213 212 212 220 219 219 219 218 218 218 217 217 217 216 216 216 215 215 214 214 214 214 213 213 213 212 212 212 220 220 219 219 218 218 218 217 217 217 216 216 216 215 215 215 214 214 214 213 213 213 212 212 212 212 22U 229 219 219 219 218 218 218 217 217 217 216 216 216 215 215 215 214 214 214 2,13 213 213 212 220 22" 220 219 219 219 218 218 218 217 217 217 216 216 216 215 215 214 214 214 214 213 213 213 212 212 221 220 220 220 219 219 218 218 218 217 217 217 216 216 21B 215 215 215 214 214 214 213 213 213 213 221 220 220 220 219 219 219 218 218 218 217 217 217 216 216 216 215 216 215 214 214 214 213 213 213 212 221 221 220 220 220 219 219 219 218 218 218 V7 217 217 216 216 216 215 215 215 214 214 214 213 213 213 221 221 220 220 220 219 219 219 218 218 218 217 217 217 216 216 216 216 216 216 214 214 214 214 213 213 221 221 221 220 220 220 219 219 219 218 218 218 ?17 217 217 216 216 216 216 216 216 214 214 214 213 213 222 221 221 221 220 220 220 219 219 219 218 218 218 217 217 217 216 216 216 216 215 216 214 214 214 222 221 221 221 220 220 220 219 219 219 218 218 218 217 217 217 216 216 216 216 216 216 216 214 214 214 222 222 221 221 221 220 220 220 219 219 219 218 218 218 217 217 217 210 216 216 215 215 215 214 214 214 Table 27. — Altitude time tables for various rates of ascent. [Awensiona! rate in meters per minute.] Minutes. 190 210 220 240 260 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 2 J 24^ 25 23 27 28 29 30 31, 32 33 34, 35 33. 37 38 39, 40, 322 476 623 770 910 1, 050 1,190 1,330 1,470 1,610 1,7.50 1,890 2,030 2,170 2,310 2,450 2,590 2,730 2,870 3,010 3,150 3,290 3,430 3,570 3,710 3,8,50 3,990 4,130 4,270 4,410 4,550 4,690 4,830 4,970 6,110 5,250 5,390 6, 530 5,670 180 345 510 668 825 975 1,125 1,275 1,425 1,575 1,725 1,875 2,025 2,175 2,325 2,475 2,625 2,775 2,926 3,075 3,225 3,376 3,525 .3,675 S, 825 3,975 4,125 4,275 4,425 4, 675 4,725 4,875 5,025 5,175 6,325 5,475 5,625 5,775 5, 925 6,075 192 368 644 712 1,040 1,200 1,360 1,520 1,680 1,840 2,000 2,160 2,320 2,480 2,640 2,800 2,960 3,120 3,280 3,440 3,600 3,760 3,920 4,080 4,240 4,400 4,560 4,720 4,880 5,040 5,200 5,360 6,620 5,680 5,840 6,000 6,160 6,320 6,480 204 391 578 756 935 1,106 1,275 1,446 1,615 1,785 1,955 2,125 2,295 2, 465 2,635 2,805 2,975 3,145 3,315 3,485 3,665 3,826 3,995 4,166 4,336 4, 505 4,675 4,845 6,015 6,185 5,3.55 5,525 5,695 6,865 6,035 6,205 3, 375 6, 640 6,715 6,886 216 414 612 801 990 1,170 1,350 1,530 1,710 1,890 2,070 2,250 2,430 2,610 2,790 2,970 3,150 3,330 3,510 3,690 3,870 4,050 4,230 4,410 4,590 4,770 4,950 5,130 5,310 5,490 5,670 6,8.50 6,030 6,210 6,390 6,570 6,760 6,930 7,110 7,290 228 437 646 846 1,045 l,2i?5 1,425 1,615 1,805 1,995 2,185 2,375 2,665 2,755 2,945 3,1.35 3,325 3,615 3,705 3,895 4,085 4,275 4,466 4,656 4,846 5,035 5,226 5,416 6,006 5,795 5,985 6,175 6,365 6,665 6,745 6, 935 7, 125 7,316 7,506 7, 695 240 460 680 890 1,100 1,300 1,600 1,700 1,900 2,100 2,300 2,500 2,700 2,900 3,100 3,300 3,600 3,700 3,900 4,100 4,300 4,600 4,700 4,900 5,100 5,300 5,600 5,700 5,900 6,100 6,300 6,500 6,700 6,P0n 7,100 7,300 7, 600 7,700 7,900 8,100 252 483 714 934 1,155 1,365 1,676 1,785 1,995 2,205 2,416 2,625 2,8,35 3,046 3,255 3,465 3,675 3,886 4,096 4,205 4,515 4,726 4,935 5, 145 5, 365 6,566 5,775 6,985 6,195 6,405 6,615 6,825 7,036 7,246 7,455 7,6R6 7,875 8,085 8,296 8,505 264 506 748 979 1,210 1,430 1,650 1,870 2,090 2,310 2,530 2, 750 2,970 3,190 3,410 3,630 3,850 4,070 4,290 4,510 4,730 4,950 .5, 1 70 6,390 6,610 5,830 6,050 6,270 6,490 6,710 7,160 7,370 7,690 7,810 8.030 8,260 8, 470 8,690 8,910 1,495 1,725 1,955 2,185 2,415 2,645 2,875 3,105 3,335 3,565 3,795 4,025 4,255 4,485 4,715 4,946 5,175 5,405 5,635 5,865 6,095 6,326 6,556 6,785 7,015 7,245 7,475 7,705 7,935 8,165 S, .ffl.i 8, ('.2,=. .S, .>.,i5 9,0S5 9, .■515 288 552 816 1,068 1,320 1,560 1,800 2,040 2,280 2,520 2,760 3,000 3,240 3,480 3,720 3,960 4,200 4,4-10 4,680 4,920 5,160 5,400 5,640 5,880 6,120 6,360 6,600 6,840 7,080 7,320 7,560 7,800 8,040 8,280 8,520 8,760 9,000 9, 240 9,480 9,720 300 575 850 1,112 1,375 1,625 1,875 2,125 2,375 2,625 2,875 .3,125 3,375 3,625 3,875 4,125 4,375 4,625 4, 875 5,125 5,375 5,625 5,875 6,125 6,375 6,625 6,875 7,125 7,375 7,625 7,875 8,125 8,375 a, 62,5 8,876 9. 125 9; 37,1 9, 62,-. 9. &7.j 10; 126 312 598 884 1,157 1,4.30 1,690 1,950 2,210 2,470 2,730 2,990 3,250 3,510 3,770 4, 030 4,290 4,550 4,810 5,070 5,330 .5,590 6,860 6,110 6,370 6,630 6,890 7,150 7,410 7,670 7,930 8,190 8,450 8.710 8,970 9,230 9,490 9,750 10. 010 10,270 10, 530 324 621 918 1,202 1,485 1,75.5 2.025 2,295 2,665 2,836 3,105 3,375 3,645 3,915 4,185 4,455 4,725 4,995 5,265 5,535 5,805 6,075 6,345 6,615 6,885 7,155 7,425 7,695 7,%5 8,235 8,505 8,775 9,045 9,315 9,585 9,855 10,125 10,395 10,665 10, 935 INSTRUCTIONS FOR AEROLOGICAL OBSERVERS. 115 1 ABLE 28. — Free lift for definite inflation, for rates of ascent 140, 160, 180 ^00, no, 240, and 260 meters per minute. ' Rates ot ascent 140 160 180 200 220 240 260 w. 1. 1. 1. '■ 1. 1. 1. 15 43.8 44.8 46.7 46.7 47.6 48.5 49.4 50.3 51.2 52.0 52.8 53.6 54.4 .55.2 56.0 56. 8 .57. 6 58.3 .59.1 59.8 00.6 01.3 62.0 62.7 63.4 64.1 04.8 66.5 06.2 66.9 07.6 68.2 68.9 69.5 70.2 70.8 71.4 72.1 72.7 73.4 74.0 74.6 75.2 75.8 76.4 77.0 68.6 09.8 71.0 72.2 73.3 74.4 76.5 76.5 77.6 78.7 79.7 80.7 81.7 82.7 83. 7 84.7 85. ,■<«. 87.6 8S. '1 89.4 90.3 91.2 92.1 93.0 93.9 94.8 95.6 96.5 97.3 98.2 99.0 99.9 100.7 101.6 102.4 103.2 104.0 104.8 105.6 106.3 107.1 107.9 108.7 109.4 110.2 106.0 107.3 108.7 110.0 111.4 112.7 114.0 115.3 116.5 117.8 119.0 120.2 121.4 122.6 123.8 125.0 120.2 127.3 128.6 129.6 130.7 131.8 132.9 134. (1 135.0 136.1 137.1 138.2 139.2 140.3 141.3 142.3 143.3 144.3 145.4 146.4 147.4 148.3 149.3 150.2 151.2 152.1 153.1 154.0 156.0 165.9 161.1 162.6 164.2 166.7 167.2 168.7 170.1 171.6 173. 1 174.5 175. 9 177.3 178.7 180.0 181.4 182.7 184.0 185.4 186.7 188.0 189.3 190.0 191.9 193. 1 194.4 195.6 196.8 198.1 199.3 200.5 201.7 202.9 204.1 206.3 206.5 207.6 208,8 209.9 211.0 212.2 213.3 214.4 215.6 218.7 217.8 218.9 240.4 242.1 243.8 246.5 247.1 248.7 250.3 261.9 263.5 265.1 256.6 258.2 259.7 261.2 202.7 284. 2 286. 7 207.2 268.6 270.1 271.5 273.0 274.4 275.8 277.2 278.6 280.0 281.4 282.8 284.2 285.5 286.9 288.2 289.6 290.9 292.2 293.5 294.8 296.1 297.4 298.7 300.0 301.3 302.6 303.8 305.1 IB 17 IS 19 20 21 22 23 24 25 26 27 28 29 30 370. 9 378.5 380.1 .381.7 383.3 384.9 386.6 388.1 389.6 391.2 392.7 394. 2 396.8 397.3 398.8 400.3 401.8 403.3 404.8 406.2 407.7 409.2 410.6 412.1 413.5 414.9 416.3 417.7 419.1 420.6 421.9 31 32 33 36 37 38 647.0 548.6 550 3 41 42 43 563.5 555.1 46 556.7 658.3 48 559.9 561.5 563.1 51 564.7 52 566.3 53 567.8 569.4 570.9 56 572.4 574.0 58 575.5 577.0 (iO . . . . 678.6 Table 29. — Degrees Fahrenheit into degrees centigrade. "F •c. °F. »F. °C. °r. P P. 31 -0.66 33 66 18.89 -2 .1 0.06 32 .00 32 67 19.44 - 3 .2 .11 33 .56 31 68 20.00 - 4 .3 .17 34 1.11 30 69 20.66 - 5 .4 .22 36 1.67 29 70 21.11 - 6 .5 .28 3b 2.22 28 71 21.67 - 7 .6 .33 3V 2.78 27 72 22.22 - 8 .7 .39 38 3.33 28 73 22.78 - 9 .8 .44 39 3.89 25 74 23.33 -10 .9 .50 40 4.44 24 76 23.89 -11 1.0 .56 41 6.00 23 76 24.44 -12 1.1 .61 42 6.56 22 77 25.00 -13 1.2 .67 4;i 6.11 21 78 25.56 -14 1.3 .72 44 6.67 20 79 26.11 -16 1.4 .78 45 7.22 19 80 28.67 -16 1.6 .83 46 7.78 18 81 27.22 -17 1.6 .89 47 8.33 17 82 27.78 -18 1.7 .94 48 8.89 16 83 28.33 -19 1.8 1.00 49 9.44 16 84 28.89 -20 60 10.00 14 85 29.44 -21 61 10.56 13 86 .30. 00 -22 62 11.11 12 87 30.56 -23 53 11.07 11 88 31.11 -24 .54 12.22 10 89 31. 67 -25 65 12.78 9 90 32.22 -28 66 13.33 H 91 32.78 -27 67 13.89 7 92 33.33 -28 68 14.44 8 93 33. 89 -29 .59 15.00 5 94 34.44 -30 60 15.66 4 95 35.00 -31 61 16.11 :i 90 35.68 -32 62 16.67 2 97 36.11 -33 83 17.22 1 98 36.67 -34 64 17.78 99 37.22 -35 66 18.33 - 1 100 37.78 -36 TabI/35 30. — Miles per hour into meters per second. m. m. m. m. m. m. m. m. p.h. p. s. p.h. p.s. p.h. p.s. p.h. p.s. 1 .45 19 8.5 37 16.5 65 24.6 2 .89 20 8.9 38 17.0 58 25.0 3 1.3 21 9.4 39 17.4 57 25.5 4 1.8 22 9.8 40 17.9 58 25.9 5 2.2 23 10.3 41 18.3 59 26.4 6 2.7 24 10.7 42 18.8 60 26.8 7 3.1 25 11.2 43 19.2 61 27.3 8 3.6 26 11.6 44 19.7 62 27.7 9 4.0 27 12.1 45 20.1 63 28.2 10 4.6 28 12.5 46 20.6 64 28.6 11 4.9 29 13.0 47 21.0 65 29.1 12 5.4 30 13.4 48 21.5 66 29.5 13 5.8 31 13.9 49 21.9 67 30.0 14 6.3 32 14.3 60 22.4 68 30.4 15 6.7 33 14.8 51 22.8 69 30.8 16 7.2 34 15.2 52 23.2 70 31.3 17 7.6 35 15.6 53 23.7 18 8.0 36 16.1 54 24.1 Table 31. — Inches into millibars. Inches. 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 09 29.0 982.1 982.4 982.7 983.1 983.4 983.7 984.1 984.4 984.8 985.1 29.1 85.4 85.8 86.1 86.6 86.8 87.1 87.6 87.8 88.2 88.5 29.2 88.8 89.2 89.5 89.8 90.2 90.6 90.9 91.2 91.5 91.9 29.3 92.2 92.6 92.9 93.2 93.6 93.9 94.2 94.6 94.9 96.3 29.4 95.6 96.9 96.3 98.6 97.0 97.3 97.6 98.0 98.3 98.6 29.5 999.0 999.3 999.7 1,000.0 1,000.4 1,000.7 1,001.0 1,001.4 1,001.7 1,002.0 29.6 1,002.4 1,002.7 1,003.1 03.4 03.7 04.1 04.4 04.7 05.1 06.4 29.7 05.8 08.1 06.4 06.8 07.1 07.5 07.8 08.1 08.5 08.8 29.8 09.1 09.5 09.8 10.2 10.5 10.8 11.2 11.5 11.9 12.2 29.9 12.5 12.9 13.2 13.5 13.0 14.2 14.6 14.9 15.2 16.6 30.0 1,015.9 1,016.3 1,016.6 1,016.9 1,017.3 1,017.6 1,018.0 1,018.3 1,018.6 1,019.0 30.1 19.3 19.6 20.0 20.3 20.7 21.0 21.3 21.7 22.0 22.4 30.2 22.7 23.0 23.4 23.7 24.0 24.4 24.7 25.1 25.4 25.7 30.3 26.1 26.4 26.8 27.1 27.4 27.8 28.1 28.4 28.8 29.1 30.4 29.6 29.8 30.1 30.5 30.8 31.2 31.5 31.8 32.2 32.5 30.5 1,032.9 1,033.2 1,033.5 1,033.9 1,034.2 1,034.5 1,034.9 1,035.2 1,035.6 1,035.9 30.6 36.2 36.6 36.9 37.3 37.6 37.9 38.3 38.6 38.9 39.3 30.7 39.6 40.0 40.3 40.6 41.0 41.3 41.7 42.0 42.3 42.7 30.8 43.0 43.3 43.7 44.0 44.4 44.7 45.0 45.4 45.7 46.1 30.9 46.4 46.7 47.1 47.4 47.8 48.1 48.4 48. S 49.1 49.5 o ^mm^mw:mmmmm^