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Xo. 1795 
 
 INSTRUCTIONS 
 
 FOR THE CARE, PRESERVATION, REPAIR 
 AND ADJUSTMENT OF 
 
 INSTRUMENTS FOR THE 
 FIRE-CONTROL SYSTEMS 
 
 FOR COAST AND FIELD ARTILLERY 
 
 (TWELVE PLATES) 
 
 DECEMBER 18, 1906 
 i^EVISED NOVEMBER J, J909 
 REVISED OCTOBER 9, I9I2 i^ 
 REVISED JANUARY 4, J9I6 
 
 WASHINGTON 
 
 GOVERNMENT PRINTING OFFICE 
 
 1917 
 
No. 1795 
 
 INSTRUCTIONS 
 
 FOR THE CARE, PRESERVATION, REPAIR 
 AND ADJUSTMENT OF 
 
 INSTRUMENTS FOR THE 
 FIRE-CONTROL SYSTEMS 
 
 FOR COAST AND FIELD ARTILLERY 
 
 (TWELVE PLATES) 
 
 DECEMBER 18, 1906 
 REVISED NOVEMBER J, 1909 
 REVISED OCTOBER 9, I9I2 
 REVISED JANUARY 4, I9I6 
 
 WASHINGTON 
 
 GOVERNMENT PRINTING OFFICE 
 
 1917 
 


 War Department, 
 Office of the Chief of Ordnance, 
 
 Washington, January 4, 1916. 
 This manual is published for the information and government of the Regular Army 
 and Organized Militia of the United States. 
 By order of the Secretary of War: 
 
 William Crozier, 
 Brigadier General, Chief of Ordnance, 
 (3) 
 
 365255 
 
INSTRUCTIONS FOR THE CARE, PRESERVATION, REPAIR, AND 
 
 ADJUSTMENT OF INSTRUMENTS FOR THE FIRE-CONTROL 
 
 SYSTEMS FOR COAST AND FIELD ARTILLERY. 
 
 INSTRUMENTS. 
 
 1. The instruments used in the fire-control and direction system 
 of the Coast Artillery include the following: 
 
 Swasey depression position finder, types A and All. 
 
 Lewis depression position finder, types A and B. 
 
 Lewis depression position finder, model of 1907. 
 
 Eafferty depression position finder, type B. 
 
 Barr and Stroud horizontal base range finder. 
 
 Azimuth instrument, models of 1900, 1900 Mi, and 1910. 
 
 Telescopic sight, models of 1896 M, 1897, 1898, 1898 M, 1899, 1902, 
 and for 14-inch gun turret. 
 
 Two-inch telescopic sight, models of 1906 and 1909. 
 
 Three-inch telescopic sight, models of 1904, 1910, and 1912, 
 
 Observation telescope, seacoast, model of 1908. 
 
 Periscope for 14-inch gim turret. 
 
 Gunner's quadrant, model of 1898. 
 
 Elevation quadrant, model of 1906. 
 
 Elevation quadrant for 12-inch mortar carriages, models of 1891 
 and 1908. 
 
 Fire commander's plotting board, model of 1906. 
 
 Whistler-Hearn plotting board, model of 1904. 
 
 Mortar plottihg board, models of 1906 and 1906 Mi. 
 
 Three hundred and sixty degree mortar plotting board, model of 
 1911. 
 
 Submarine plotting board, model of 1906. 
 
 Pratt range board, model of 1905. 
 
 Range board, model of 1909. 
 
 Deflection board, model of 1905, for guns. 
 
 Deflection board, model of 1906, for 12-inch mortar. 
 
 Wind-component indicator. 
 
 Set-forward ruler. 
 
 Prediction scale. 
 
 Predicter. 
 
 Mine-prediction ruler. 
 
 Time-interval recorder. 
 
 (5) 
 
Drawing boards, battle charts, harbor charts, and difference 
 boards. 
 
 Scale arms for harbor charts, and for difference boards. 
 
 2. The instruments used in the fire-control and direction system 
 for the Field Artillery include the following: 
 
 Weldon range finder. 
 
 Field Artillery range finder, 1 meter base. 
 
 Aiming circle, model of 1916. 
 
 Sextant telemeter, type A, model of 1911. 
 
 Battery commander's telesco'pe, models of 1904, 1905, and 1915. 
 
 Panoramic sight, models of 1904 and 1915. 
 
 Telescopic sight, models of 1896, 1896 M, and 1897. 
 
 Rear sight of various designs for different carriages. 
 
 Front sight of various designs for different carriages. 
 
 Observation telescope, field, model of 1908. 
 
 Range quadrant of various designs for different carriages. 
 
 Gunner's quadrant, models of 1892, 1897, and 1898. 
 
 Plotting board for mobile artillery, models of 1905 and 1906. 
 
 Field Artniery plotter, model of 1907. 
 
 Battery commander's ruler. 
 
 One-hundred-foot steel measuring tape. 
 
 3. Other instruments include: 
 
 Telescopic musket sight, models of 1908 and 1913. 
 Sixty-foot steel measuring tape for Weldon range finders. 
 
 4. In preparing instructions for the care, preservation, repair, 
 and adjustment of the above instruments, it is found most con- 
 venient to group the instruments in the following general classes: 
 
 (a) Optical instruments proper, including the telescopes of the 
 various depression position finders, azimuth instruments, 
 telescopic sights, panoramic sights, observation instruments, 
 etc., and Weldon range finders. 
 
 (6) Geared instruments, including the mechanical features of aU 
 instriunents, designed to measure accurately angles of azi- 
 muth, of elevation, or of depression, as the azimuth and the 
 elevation and depression gears of the various depression 
 position finders and the azimuth gears and features of the 
 various plotting boards. 
 
 (c) Scale arms, including all parts of instruments provided with 
 
 scales and straight fiducial edges. 
 
 (d) Wooden parts of instruments, as the board proper of the plot- 
 
 ting boards, of the Pratt range boards, of the time range 
 board, of the deflection boards, of the drawing board, etc. 
 ie) Special parts of instruments, not falling in any of the above 
 groups, as the canvas chart of the Pratt range board, the 
 rubber covering of the mobile artillery plotting board, etc. 
 
5. All persons using any of the instruments referred to above 
 should be thoroughly familiar with the various descriptive pamphlets 
 issued by the Ordnance Department relating to these instruments. 
 In addition thereto, all persons, including especially armament fore- 
 men and machinists, called upon to inspect, repair, or adjust any of 
 the above instruments should provide themselves with the working 
 drawings of the instruments in question by application through the 
 proper channels, if not already supplied with the drawings by arma- 
 ment officers. Before attempting to disassemble, adjust, or repair 
 instruments, the drawings should be carefuUy studied and a thorough 
 familiarity thus obtained with the component parts of any mecha- 
 nism and with the function of each part in the train of" movements 
 producing any given result. Complicated groups of gear wheels, for 
 instance, should never be separated without special attention to the 
 arrangement of the group and to the sequence of the varipus disas- 
 sembling operations with a view to reversing the .above operations in 
 proper order in reassembling. No forcing of parts together should 
 ever be tolerated. When such forcing seems necessary, the indication 
 is that the parts already assembled are incorrectly put together. 
 
 CARE AND PRESERVATION OF INSTRUMENTS. 
 
 6. The care and preservation of instruments is properly the func- 
 tion of those who use the instruments. Cleanliness, freedom from 
 moisture, dust, dirt, and grit, and proper oiling are of first impor- 
 tance. By proper oiling is meant the supply of the lubricating oil 
 specified in the pamphlets in proper amounts and at proper times. 
 For instance, heavy oil, as the vaseline used in the azimuth-circle 
 gear of the panoramic sight, should last 12 months after a proper 
 application. Machine oil used on the panoramic-sight stem needs 
 frequent renewal, with the cleaning of the parts daily or oftener. 
 Clock oil used on the finer gears of the gun center of the Whistler- 
 Hearn board will last ordinarily from four to six months without 
 renewing, depending on the amount of use received by the board. 
 In this latter case, frequent or excessive oiling actually will do harm, 
 as the excess amount will flow away from the bearings to the sur- 
 rounding parts and serve to catch dust and ultimately to clog up the 
 parts concerned. 
 
 When special chests or cases are issued with instruments, the 
 instruments should habitually be placed in them when not in use; 
 where chests or cases are not issued, as, for instance, in the case of 
 the wind-component indicator, the removal of dust, excess oil, or of 
 the moisture which collects on metal surfaces during high humidity, 
 should be daily attended to by the regular caretaker. 
 
HUMIDITY. 
 
 7. One of the most important points to be observed with reference 
 to the care and preservation of all classes of instruments is the pre- 
 vention as much as possible of the deposit of moisture from the atmos- 
 phere. The humidity of the atmosphere is one of the most potent 
 agents in producing the patina or film on the lenses and prisms of 
 optical instruments, and its continuous presence on the surfaces of 
 the optical glass will render them unfit for use; its action in warping 
 the wooden base of the Whistler-Hearn and other plotting boards, 
 drawing boards, deflection boards, and Pratt range boards is pro- 
 ductive of trouble and frequently necessitates a readjustment of 
 parts, as, for instance, by means of the slotted screw holes in the 
 scales of the gun deflection board; its action on steel parts is to 
 accelerate rusting, and thus not only to mar the appearance of instru- 
 ments, but also, in the case of gears, pinions, racks, etc., to destroy 
 accuracy and prevent easy functioning. It is not always possible 
 absolutely to avoid difficulty from this source, but careful covering 
 and oiling, the selection where possible of warm, dry places for the 
 storage of optical and other instruments when not in use, and the 
 prompt removal of deposited moisture wherever discovered will 
 reduce the effect of humidity. Especially telescopic sights and optical 
 parts of instruments should be stored in warm, dry places. 
 
 The condensation of atmospheric moisture on the lenses or prisms 
 occurs when the temperature of these parts is lower than the dew 
 point. The evaporation of this moisture may be hastened by turn- 
 ing on the lights mounted in telescopes. Heat from other sources 
 should not be applied directly, as it may result in unequal expansion 
 of the metal parts or of the optical parts of the instrument and 
 cause considerable errors of observation. 
 
 REPAIR AND ADJUSTMENT OF INSTRUMENTS. 
 
 8. Whenever from wear due to long service, from accident, or from 
 any other cause, an instrument is rendered unfit for service, a report 
 of the case, as directed in the following extract from General Orders, 
 No. 47, War Department, March 24, 1905, should be received by the 
 armament officer. 
 
 (1) The prisms and lenses in the telescopes of position finders, 
 azimuth instruments, and sights are not arranged for ad- 
 justment by those using them. The taking apart of tele- 
 scopes for any purpose and the making of any adjustments 
 other than those provided for in their construction and 
 described in the pamphlets issued by the Ordnance Depart- 
 ment, except under the supervision of district armament 
 officers, are therefore forbidden. 
 
(2) When telescopes or any instruments of the range-finding and 
 fire-control system for mobile and coast artillery issued by 
 the Ordnance Department require repair, a report describing 
 the character and extent of the injuries or defects will be 
 made to the armament officer of the district. In case the 
 repairs or adjustment required by telescopes and other deli- 
 cate instruments of precision are of such a nature that they 
 can not be made at the post, as above specified,, the instru- 
 ments will be shipped by express to such arsenal as may be 
 designated by the district armament-officer. 
 
 9. The armament officer of the district in which the repair is called 
 for will, either personally or through his proper ordnance foreman or 
 machinist, make an inspection of the instrument reported in need of 
 repair or adjustment. From the inspection he will decide whether 
 the telescope or other delicate instrument of precision can be repaired 
 at the post, by instrument makers or watchmakers in the vicinity, or 
 must be shippped by express to such arsenal as he may designate. In 
 general, in shipping instruments away from posts for repair, only 
 such parts should be shipped as are absolutely necessary to a proper 
 repair. Thus, frequently only the telescope of depression position 
 finders, azimuth instruments, etc., need be shipped when they only 
 are in need of repair; but, on the other hand, if, for instance, tide- 
 scale or height-scale parts of depression position finders are in need 
 of repair or regraduation, the entire instrument must be shipped, as 
 aU parts, including base and telescope, will then be required for the 
 final adjustment after regraduation. 
 
 10. The regraduation of instruments should be done only at an 
 arsenal or at a manufacturing plant equipped with accurate graduat- 
 ing machines. All other repairs of an extensive nature involving a 
 considerable outlay of money, including the obtaining of new prisms 
 and lenses or of new castings to replace broken parts, should be made 
 at an arsenal. 
 
 11. Who may disassemble and repair instruments. — Paragraphs 
 marked with an asterisk (*) are added for the use of instrument 
 makers in the adjustment of instruments or parts of instruments. 
 It is not intended that these adjustments shall be made at the forts, 
 but only at those places such as arsenals where special facilities are 
 provided. 
 
 12. The parts of sights and fire control instruments for the 3-inch 
 Field Artillery which may be disassembled by the battery, are speci- 
 fied in the Handbook for 3-inch Field Artillery Materiel. The dis- 
 assembling of other parts will be performed by skilled workmen only. 
 
 Prisms of sights and other telescopes will not be removed from 
 their holders except by skilled workmen. As a general rule the dis- 
 assembling and adjustment of sights and instruments requiring tools 
 
10 
 
 other than those issued with each instrument will be performed only 
 by skilled mechanics. 
 
 13. Screw threads. — ^A number of different standards of screw- 
 threads below ^-inch diameter have been used on sights and fire 
 control instruments. They are: the F. A., the V thread, the U. S., 
 the A. S. M. E., and the British Association. The F. A. standard 
 thread is a round 60° thread. Taps and dies for this standard are 
 made at the Frankford Arsenal only. This standard is used on 
 instrument of modelg dated prior to 1905, when it was superseded 
 for new design by the V thread standard. The V thread is a sharp 
 60° thread. Taps and dies of this standard are procured by Frank- 
 ford Arselial to special gauges. The V thread standard was super- 
 seded for new design in September, 1909, by the A. S. M. E. standard 
 thread which was recommended for adoption in 1907 by the American 
 Society of Mechanical Engineers. This thread is now the standard 
 thread for new designs for all screws below J-inch diameter. The 
 U. S. standard form of thread is on screws of cap screw sizes (varying 
 in diameter by -^ inch) used in the manufacture of the azimuth 
 instrument, model of 1900, and the Swasey depression position 
 finder. An independent system of screws with U. S. standard form 
 of threads is used on the Lewis depression position finder, model of 
 1907. Special screws with U. S. standard threads are found in other 
 instances. The British Association screw thread, a round thread 
 with a thread angle of 47^°, is used on Barr and Stroud range finders. 
 
 No holes should be retapped without first consulting the detailed 
 drawing to ascertain the diameter, pitch and type of screw thread 
 used. In case the proper taps are not on hand, they should be 
 requisitioned for. Screws for the various instruments are kept in 
 stock at Frankford Arsenal, Benicia Arsenal, and Manila Ordnance 
 Depot. In ordering screws, use the nomenclature given in the 
 pamphlet descriptive of the instruments or on the detailed drawings. 
 In ordering taps state the standard, the diameter, and the pitch. 
 
 14. In describing the method of repair and adjustment of the 
 instrmnents already listed in paragraphs 1 and 2 of this pamphlet, 
 repairs or adjustments of instruments will be taken up in proper 
 order, according as they may faU under one or more of the five 
 groups mentioned in paragraph 4. 
 
 TOOLS AND FIXTURES FOR OPTICAL REPAIR WORK. 
 
 (See Plates F, G, and H herewith and drawings 15-17-1 to 11, inclusive.) 
 
 15. A kit of tools for use in connection with optical repair work is 
 furnished for both Coast and Field Artillery. The list of tools and 
 fixtures comprising these sets will be found on Plate H herewith. 
 Only a few of these tools wiU require description. The use of several 
 
11 
 
 tools and fixtures will be described below under the instructions for 
 repair of various models of instruments. Before using pedestal No. 
 85, carefully level it so that its axis is vertical. 
 
 16. Collimating telescope for Field Artillery. — The collimating tele- 
 scope (No. 90) furnished with tools for Field Artillery work, is an 
 ordinary nonerecting type. It is adjusted for parallax by the usual 
 means of focusing the eyepiece on the cross wires and then removing 
 parallax by focusing the objective. To collimate the telescope use 
 the horizontal fixture (No. 86) mounted in pedestal (No. 85), holding 
 the telescope against the guide on the side of the fixture and sight on 
 a target having both horizontal and vertical lines. Rotate the tele- 
 scope on its axis 180° and if the cross wires do not coincide with the 
 target, correct half the error by adjusting the reticule by the reticule 
 screws and half the error by shifting the telescope. Repeat until the 
 adjustment is found to be correct. Whenever other telescopes can 
 be collimated in this manner, it should be done. 
 
 17. Collimating telescope for Seacoast Artillery. — The collimating 
 telescope (No. 98) furnished with tools for Seacoast Artillery work is 
 the ordinary nonerecting (astronomical) type with Ramsden eye- 
 piece. The aperture of its objective is 1 inch. The power is 8 and 
 the field of view is 3°. The draw tube, operated by a focusing ring, 
 provides for the removal of parallax between the image and the 
 reticule. The eyepiece is adjustable for focusing on the reticule. 
 The cross-wire ring is held in position by four screws and washers. 
 The collimation adjustment for this telescope is similar to that 
 described above in paragraph 16. 
 
 To disassemble the draw tube, remove the screw holding the focus- 
 ing ring cap to the focusing ring (see drawing 15-17-10), unscrew the 
 cap and pull out the draw tube. The eyepiece is retained in the draw 
 tube by a retaining screw. The objective cell is also locked in the 
 tube by a retaining screw. 
 
 With the telescope is a bracket for use in collimating telescopic 
 sight, model of 1899, and rings which fit the outside bearing, surfaces 
 of the tube and which adapt the collimating telescope for use in the 
 telescope seats of the telescopic sight, model of 1902, the 3-inch 
 telescopic sight, model of 1904, and the 2-inch telescopic sight, modal 
 of 1906. 
 
 CLINOMETER, MODEL OF 1909. 
 
 18. Use. — This instrument is provided for the checking of elevation 
 scales. To use it, set up the clinometer on a clinometer rest. Level 
 the cross level using the adjusting screw. Do not clamp the adjusting 
 screws too tightly. Level the elevation level by means of the eleva- 
 tion mechanism of the gun or mortar on which the clinometer is used. 
 Reverse the clinometer and relevel the cross level, if necessary. In 
 
12 
 
 case the elevation level vial bubble is not central as before, correct 
 half the error by adjusting the vernier by means of the vernier adjust- 
 ing screw and half the error by means of the elevating mechanism of 
 the gun or mortar. Repeat the operation to verify the adjustment. 
 Care should be taken to loosen the vernier clamping screw before 
 adjusting the vernier and to tighten it after adjusting it. 
 
 To set the clinometer to a given elevation, imclamp the slow-motion 
 clamp, grasp the carriage on a surface as near as possible to the T 
 guide surface of the support and slide the carriage to the approximate 
 position desired. Then clamp the slow-motion clamp and make final 
 adjustment by means of the slow-motion screw. 
 
 The least reading of the clinometer is 1 minute. A movement of 
 the bubble of the elevation level of 0.1 inch corresponds to 30 seconds 
 of arc. 
 
 19. Adjustment. — The elevation level is adjusted by means of the 
 horizontal adjusting screws so that if the elevation level is set level, 
 the clinometer may be rotated several degrees on the clinometer rest 
 without being moved out of its level position. The elevation level is 
 adjusted by means of the vertical adjusting screws to allow for setting 
 the mark of the vernier correctly. 
 
 The cross-level bubble should be central when the support is ver- 
 tical, and it should remain central while the gim or mortar is elevated 
 a few degrees, or the carriage is sUd over the support a few degrees. 
 A test of the correctness of the adjustment of the cross level should 
 preferably be made when the elevation level is approximately level. 
 The vertical adjusting screws are adjusted so that the cross level 
 indicates level when an accurate machinist's level laid across the top 
 surface of the support at right angles to it indicates level. The 
 horizontal adjusting screws are adjusted so that the bubble of the 
 cross level remains central as the gun or mortar is elevated. 
 
 OPTICAL. INSTRUMENTS (Group a). 
 GENERAL CONSTRUCTION. 
 
 20. The construction of optical systems of service instruments 
 vary from that of the simple GalUlean and astronomical telescopes 
 to the intricate systems of the periscope and the horizontal base 
 range finders. The larger number of telescope systems, however, 
 consist of an objective, an erecting system, and an eyepiece. In 
 some telescopes, as the battery commander's telescope, for example, 
 additional prisms are used for the deflection of the entrance pencil 
 90°, in order that the axis of the telescope may be made vertical. 
 The periscope systems include a combination of prisms so mounted 
 that the image remains erect and the eyepiece in a fixed position 
 during the rotation of the periscope head through a complete circle. 
 
13 
 
 In horizontal base range finders special prism systems for accomplish- 
 ing a sharp division of the field as well as the erection of the image 
 are employed. 
 
 21. Objectives. — The objectives of service telescopes consist of 
 combinations of two or three lenses which are, with few exceptions, 
 combined to prevent spherical aberration and are, with the exception 
 of the larger objectives, cemented. When two lenses or a doublet 
 is used it consists of a crown-glass convergent lens and a flint-glass 
 divergent lens. The crown or the flint may be in front; depending 
 upon the optical characteristics of the glass. When three lenses or 
 a triplet is used it consists either of two collective crown-glass 
 lenses and a flint-glass dispersive lens, the fhnt being the central 
 lens, or of two flints and a crown, the crown being on the inside. 
 In some telescopes, as that for the Swasey depression position finder, 
 the objective is centered in the tube by means of coUimating screws, 
 but ordinarily the optical axis of an objective is not adjustable 
 in respect to the axis of the tube. In the latter class of instruments 
 the telescope is collimated by adjusting the cross wires to bring their 
 intersection into the optical axis of the objective. 
 
 22. Erecting systems .^-Erecting systems are of various types con- 
 sisting of lenses or of prisms. The lens-erecting system consists 
 of two or more lenses inserted in the telescope system in the rear 
 of the focal plane of the objective, usually in the eyepiece, and so 
 constructed as to form a positive image of the image formed by 
 the objective. By it the inverted image of the objective is rein- 
 verted. In the simpler form the system, together with the, eye- 
 piece, is known as the Fraunhofer eyepiece or terrestrial eyepiece. 
 This system is used in the telescopic sight, model of 1899. In a 
 modified form of this system, such as used in the telescopic sight 
 for 14-inch turret mount, the simple lenses are replaced by cemented 
 combinations in order to secure improved optical qualities. 
 
 23. The earher prism-erecting system used in service telescopes 
 is the Brashear Hastings erecting prism shown on Plate A. This 
 prism consists of two 30° triangular prisms cemented to the base 
 of a prism of pentagonal section with 90° roof angle. The path of 
 the axial ray is shown on Plate A. The efficacy of this group of 
 prisms depends not only on the correct angular relation of the various 
 surfaces but also upon the proper assembMng of the components. 
 In it the roof angle is required to be ground within an extremely 
 smaU angular error. 
 
 The Porro system of erecting prisms is shown in Plate C. The 
 system consists of two right-angled triangular prisms mounted with 
 their axes at right angles to each other and with the half of the 
 hypothenuse faces of each overlapping. The path of the rays being 
 bent back upon itself permits a shortening of the telescope. For 
 
14 
 
 these reasons the Porro system has superseded the Brashear Hastings 
 system in sei-vice telescope construction. 
 
 A Porro erecting system, modified for a telescope with a vertical 
 axis, is shown in Plate E. 
 
 24. The periscope prism system consists of three prisms. See 
 Plate E. The right-angled deflecting prism is connected with the 
 erecting prism so that during the revolution of the former through 
 a complete circle the latter rotates with half the angular velocity 
 of the former. The optical effect of the system is the inversion of 
 the image and the nonrotation of the image during the rotation 
 of the system. The image which, however, is reversed right for 
 left is corrected by means of an additional prism. 
 
 25. Eyepieces. — ^Among the numerous types of eyepieces foimd in 
 service telescopes are: 
 
 The negative, consisting of a divergent lens as used in the tele- 
 scope of the sextant telemeter. 
 
 The Ramsden, consisting of two simple convergent lenses of 
 equal focal length and separated by a distance equal to two -thirds of 
 the focal length of a lens. 
 
 The Kellner, a modified form of the Ramsden eyepiece, in which 
 a single eye lens is replaced by a cemented doublet with plane face; 
 for example see Plate A. This class is largely used. 
 
 The Steinheil, consisting of a cemented triplet with the crown col- 
 lective element inside. This, for example, is found in the musket 
 sight. 
 
 A special development of the Ramsden, the orthoscopic in which 
 the field lens consists of a triplet and the eye lens of a plano-convex 
 lens with small separation. For example, that used with the obser- 
 vation telescope, seacoast, model of 1908. 
 
 The terrestrial or Fraxmhofer eyepiece, in which an erecting system 
 is combined with the eyepiece proper. 
 
 With the exception of the telescope in which the first-mentioned 
 divergent class of eyepieces is used all have fields in which a reticule 
 may be placed. 
 
 26. Adjustment. — Each lens of an optical system is designed to 
 reduce the aberrations of the system to a minimum. This design is 
 based upon calculations in which is considered, among other things, 
 the optical qualities of the glass used, the direction in which fight 
 traverses the system, the separation of lenses and the curvature of 
 each surface. Due to the nimierous conditions involved, the curva- 
 ture of each surface is special. After test of the elements of a system 
 they are assembled and the system is adjusted for the best results. 
 Thus for the proper performance of an optical system there is but one 
 way in which the components of a compound lens or system may be 
 assembled, and but one distance at which the elements of a system 
 
15 
 
 may be spaced. Thus the importance of the instruc,tions given below 
 to mark each element to indicate the direction in which Ught traverses 
 the system and the relation of components to each other. Failure 
 to observe these instructions will cause imperfect definition by an 
 increase in the spherical aberrations and in many cases increased 
 errors in curvature of the field and distortion. In some cases the 
 impairment in definition may not be noted except by an experienced 
 observer, but it will be sufficient to cause eye strains. 
 
 OPTICAL DEFECTS. 
 
 27. Chemical disintegration of optical glass is caused by the action 
 of moisture, dust, and acid. Water is taken into composition in the 
 surface layers of the glass and the alkahne contents of the glass set 
 free. The resistance of glass to decomposition depends upon its 
 chemical composition. Dust causes what is known as lead spotting — 
 the formation of brown spots of irregular outlines or, in the more 
 advanced stages, the covering of the whole surface with a brown film. 
 Flint glasses used in the divergent elements of lenses are especially 
 sensitive to attacks of this nature. The decomposition is due to the 
 action of the weak organic acids present in dust. Among acids which 
 decompose optical glass is acetic acid, which is present in the per- 
 spiration of the body. Thus the caution against the leaving of finger- 
 marks on optical surfaces. 
 
 The decomposition of optical glass by weathering is due to the 
 action of both water and acids present in dust or elsewhere. The 
 form of decomposition ordinarily observed is lead spotting. The rate 
 of decomposition increases with the temperature. It is especially 
 rapid in the warm moist cHmate of the Tropics. Thus greater pre- 
 cautions are required in warm climates than in the cooler regions. 
 
 Decomposition first appears ordinarily on the flint of objectives 
 and the exposed plane surface of the flint of the eye lens. The crowns 
 of some objectives are also subject to attack. The glass used in 
 prisms is comparatively not subject to decomposition 
 
 To examine an optical surface for evidences of decomposition 
 hold the piece so that the Ught of bright daylight is reflected by it 
 nto the eye. Focus the eye on the glass surface. It is seldom that 
 any surface defects will be apparent in light transmitted by the 
 piece. 
 
 The surface decomposition detracts from the efficiency of any 
 optical element by reducing the amount of Ught transmitted by the 
 system. To remove the affected surface repoHshing is necessary. 
 This work should be done only at an arsenal or a properly equipped 
 optical shop. 
 
 28. The balsam used in cementing compound lenses or prisms 
 sometimes dries and cracks, the effect being observed in a delicately 
 
16 
 
 formed tracery somewhat resembling frost markings in shape in the 
 case of prisms, and small bright disks in the case of achromatic 
 lenses. Whenever this becomes sufficiently pronounced to observe 
 the image, the telescope of the instrument affected should be sent to an 
 arsenal for overhauling. In no case should the recementing of 
 prisms and lenses be attempted at posts. 
 
 CLEANING AND KEADJUSTING. 
 
 ■ 29. Cleaning. — For cleaning optical surfaces use the cloth and the 
 special lens paper furnished for that purpose. An old soft linen 
 handkerchief is also good. Under no circumstances use dirty cloths, 
 dirty chamois skins, cotton waste, or similar materials. A camel 
 hair brush is excellent for removing dust or lint. In case a solvent is 
 required in cleaning, alcohol should be used. It is permissible to 
 breathe upon the surface, but not to spit upon it. Saliva causes 
 deterioration of lenses. Water, as explained above, is also harmful. 
 It is preferable that it be not used except in very small quantities, as 
 from the condensation of the breath. 
 
 In cleaning take care to remove with a brush all particles which 
 might scratch the surface. Then moisten the surface with alcohol 
 or the breath and wipe it carefully. Then dry it with a clean cloth or 
 paper and wipe off any remaining lint with a soft brush. While 
 cleaning take care that the fingers do not come in contact with a 
 polished surface. Also do not allow any oil to reach the glass. 
 
 30. Cleaning lenses. — In disassembling compound objectives for 
 cleaning, unscrew the cell retaining ring and carefully push the 
 objective from its ceU, noting which surface is the front surface and 
 without disturbing the relative position of the component lenses. 
 Mark an arrow (A ) across the, periphery of the lens, the point of the 
 arrow toward the front surface. While cleaning do not wipe off the 
 marks. With the aid of the arrow in reassembling, preserve the 
 original relation of all the optical surfaces. The elements of a com- 
 poimd lens should be separated by a ring of thin, preferably black, 
 paper. In case a ring is not available stick three small narrow pieces 
 of paper near the edge of each surface to prevent the glass surfaces 
 from coming into contact with each other. Reassemble the compound 
 lens in its cell with the same surface to the front as originally found. 
 
 In removing lenses from their cells and in inserting them do not 
 bring too much pressure to bear upon them. The flint element is 
 especially liable to be broken. The cells are made of slightly larger 
 diameter than the lens and if not wedged by tilting the lens should 
 freely seat itself. Chipping the edges should be avoided. 
 
 A compound lens should not be removed from its ceU unless, after 
 cleaning the exposed surfaces, it is found that the interior surfaces 
 
17 
 
 also require cleaning. This will be seldom. Under no circumstances 
 attempt to remove a lens that is burnished or crimped in its cell. 
 Such lenses are cemented. 
 
 The lenses of eyepieces are ordinarily burnished in cells which are 
 screwed into an eyepiece tube. For cleaning, unscrew the cells but 
 do not remove the lens from its cell. If the cells are of the same 
 diameter note before disassembling the order in which the lenses are 
 assembled and reassemble in the same order. 
 
 31. Cleaning Br asJiear- Hastings prisms. — ^The Brashear-Hastings 
 erecting prism is supported in a metal holder by a crossbar and two 
 screws (see Plate B) for adjustment of the line of collimation. The 
 prism may be rocked on the cross bar by means of the screws. In 
 adjusting care should be taken to bring a slight pressure to bear on 
 each screw but not to strain the prism. On gun sights after adjust- 
 ment the space between the prism and its holder is fiUed in with 
 plaster of paris. In tiftie the plaster will crumble and require replace- 
 ment. Examine the plaster of paris once a year and without straining 
 them test the prism adjusting screws to see that they have not 
 loosened. Do not remove the prism from its holder for cleaning. All 
 surfaces may readily be cleaned without removal. Take especial 
 care not to chip the edge of the roof of the prism. After cleaning 
 look through the prism to detect any trace of the deterioration of the 
 balsam. 
 
 When reassembling the prism holder in its seat take especial care 
 to seat properly the dowel pins and to screw up tightly the prism 
 holder screws. 
 
 32. Cleaning Porro prisms. — Porro prisms are ordinarily held in 
 milled seats by springs as shown in Plate C. Generally it wiU be 
 sufficient to clean only the exposed surfaces, in which case do not re- 
 move the prisms from their seats. In case it is necessary to remove 
 the prisms, carefully mark each prism so that it may be assembled in 
 the same seat and without turning it end for end. Sometimes notches 
 are cut in prisms as an aid in assembling, but this is not always the 
 case. To avoid interchanging it is advisable to disassemble but one 
 prism at a time. These precautions are necessary, as it is imprac- 
 ticable to grind the angles of a prism without appreciable error, and 
 interchange or reversal when assembling will change the position of 
 the opticle axis of the instrument. 
 
 33. Tests. — The correctness of assembling and the accuracy of ad- 
 justment of an optical system may be tested by noting its definition 
 and its freedom from errors. Ordinarily a test for definitioil, or the 
 cleanliBSS and distinctness with which objects appear, is sufficient. 
 Make the test on clearly defined, distinct, distant objects, preferably 
 on objects which stand out in sharp relief against a light background, 
 
 9950—17 2 
 
18 
 
 such as lighthouses, stacks, poles, etc. Observe the sharpness with 
 which the details of the objects are brought out in all parts of the 
 field of view. The quality of a telescope may best be determined by 
 comparison with other telescopes, preferably with those of the same 
 power. 
 
 No telescope image is entirely free from errors, but in all systems 
 the residual errors should not be sufficient to impair good definition 
 or to interfere with the efficient use of the telescope. 
 
 In all telescope images it will be observed that a color fringe borders 
 the outlines of well-defined objects. If the fringes are of yellow or 
 purple color they are due to a residual chromatic aberration which 
 it is not practicable to remove in manufacture. If, however, a fringe 
 of a distinct red or blue color is visible in the center of the field some 
 part of the optical system is out of adjustment or the elements are 
 not properly corrected. Faults of this nature will most likely be 
 found in terrestrial eyepieces. 
 
 Practically all objectives contain small errors known as spherical 
 aberration, but in no objective should the amount be large. It 
 may be increased by the reversal of lenses, especially of objectives. 
 An appreciable increase will impair the definition of the telescope. 
 To measure the spherical aberration, cover aU of the objective except 
 a small circle about i inch diameter at its center. Remove parallax 
 from the telescope and note the position of the draw tube. Then 
 cover all the objective except a narrow ring near its periphery and 
 again remove parallax. Measure the difference in the position of the 
 reticule under the two conditions named. This is the spherical 
 aberration. 
 
 The images of straight lines in the central and outer zones of the 
 field are sometimes curved either inward or outward. This error, 
 known as distortion, should be smaU in any service telescope. It 
 may, however, be greatly increased, especially by the reversal of an 
 objective or of a field lens of an eyepiece. 
 
 Poorness of illumination may be due to dirt or moisture on the 
 surfaces of some optical element or in rarer cases to the surface 
 decomposition of the glass or to the breaking away of the cement. 
 
 The condition of the interior surfaces of a telescope may be exam- 
 ined without removing the eyepiece by a magnifying glass held in 
 rear of the eyepiece and moved to bring the desired surfaces into view. 
 
 If double images of well-defined lines near the center of the field 
 appear the fault is probably due to errors in the roof angle of the 
 prisms. 
 
 Errors in the adjustment of prisms may be detected by testing the 
 coUimation ot the telescope, 
 
 34. Mounting of cross wires. — Wires are mounted on a frame or 
 holder in shallow grooves. Before assembling see that the ends of 
 
19 
 
 these grooves are free from sharp edges. Especially see that the end 
 of the groove from which the wire emerges before passing imder a 
 clamp is slightly rounded. The lower surface of the clamp or clip 
 should be smooth and its edges slightly rounded to avoid cutting the 
 wire. Unless these precautions are observed in mounting cross wires 
 in gun sights, the wire may be broken by the shock of firing. 
 
 In moimting platinum wire 0.001 inch in diameter, clamp the free 
 end of the wire under the clamp of the holder in line with the slot. 
 Place a weight on the other end of wire, grasp the holder with one 
 hand, slide the wire under the clamp, guide it into the groove, use a 
 slight pressure on the holder to draw the wire taut, and then clamp the 
 wire. 
 
 35. Platinum wire 0.0005 inch in diameter is silver coated. To 
 remove the silver coating, bend a U-shaped frame of wire, preferably 
 aluminum, of y^ inch or smaller diameter. The length of the U should 
 be about 3 inches and the distance between prongs J inch to } inch 
 greater than the length of cross wire required. Cover the frame 
 with beeswax for a distance of 1 inch from the open end. Mount 
 the wire loosely on the frame, protecting the ends by the wax. Then 
 hold the wire mounted on the frame in a concentrated solution of 
 nitric acid for 5 or 10 minutes. Examine it carefully with a magnify- 
 ing glass to see that all silver has been removed. Then wash by 
 gently moving the wire through water. 
 
 The wire, still mounted on the frame, should be slipped under the 
 clamps and guided into the grooves of the holder. Before clamping 
 bring the wire taut by permitting the U frame to be supported by 
 the wire. After clamping cut the wire from the frame. 
 
 36. In mounting wire 0.0005 inch in diameter or finer without 
 clamps, use a solution of ordinary brown shellac dissolved in alcohol 
 to the consistency of cream. FoUow the same method as described 
 above except that after the wire is located in its groove apply a drop 
 of shellac with a sharp pointed piece of wood or other sharp tool. 
 Allow the shellac to dry from 1 to 2 hours before cutting the wire from 
 the frame. 
 
 37. Plastering 'prisms in their holders. — ^After adjusting the prism 
 in its holder for collimation of the horizontal cross wire, set up the 
 prism adjusting screws lightly and set the lock nut for the prism 
 adjusting screw against the holder. Then remove the holder with 
 the prism from the telescope and fiU the space between the prism and 
 the holder with plaster of paris and water mixed to the consistency of 
 thick paste. Work the plaster in the space between the prism and 
 holder, using a knife, piece of wood, or any other instrument, pack 
 the plaster tightly and completely fiU the space. Remove the sur- 
 plus plaster and set aside to harden for two or three hours. 
 
20 
 
 Use a good grade of dental plaster of paris, which will set in from 
 5 to 10 minutes. ^ 
 
 38. Directions for preparing a silvering paste and for applying it. — 
 In case the silvering on metallic parts of instruments becomes worn 
 and unsightly, a moderately thin paste should be made by mixing 
 1 part of silver chloride, 15 parts of cream of tartar, and 5 parts of 
 salt (NaCl) and enough water added to the mixture to form a paste. 
 Let the silver stand over night to remove impurities. 
 
 Clean the surface to be silvered with fine emery or crocus cloth. 
 All grease, dirt, etc., should be relnoved in order to get good results. 
 Then rub the surface thoroughly with salt and a little water. Apply 
 the paste with the finger, rubbing until a good white surface appears, 
 then wash over the surface with cream of tartar and water. Wipe 
 the surface and allow to stand until thoroughly dry. It wiU be 
 preferable if the silvered surface is warmed before lacquering, but this 
 may be found impracticable in many cases. The paste should be 
 used shortly after preparation. - 
 
 Then lacquer with white lacquer, using two coats. The white 
 lacquer is prepared as follows: Dissolve 1 pound of kiln-dried white 
 shellac in one-half gallon of alcohol, allow it to stand 24 hours, then 
 run it twice through filter paper. It may be obtained ready for use 
 by requisition in the usual manner. 
 
 39. LitJiarge cement — The litharge cement used in sealing pano- 
 ramic sights is manufactured as follows : Boil raw linseed oil in a pan 
 imtil it smokes. Then set it on fire and let it burn for a few minutes. 
 Cover the pan to extinguish the blaze and pour while warm into a 
 receptacle containing red lead and Mtharge in the proportions of 1 
 oimce of each to a quart of oil. Keep at a temperature of 70° F. for 
 10 days and agitate once a day. Apply the cement in a thin coating 
 to the parts to be cemented and aUow it to dry at the ordinary tem- 
 perature. Only a very small quantity of cement is required. It 
 dries very slowly. It is not affected by either water or alcohol. 
 
 This cement is used for sealing the interior chambers of instru- 
 ments. To obtain a sealed joint, careful fitting of plane surfaces is 
 required. The cement wiU not compensate for poor fitting. Litharge 
 cement may be dissolved by turpentine. 
 
 40. Silvering of mirrors. — A silvering solution may be prepared as 
 follows: Make separately two solutions — one to be designated solu- 
 tion No. 1 and the other solution No. 2. 
 
 Solution No. 1. Mix 49.6 grams of nitrate of silver (dry in crystals) 
 and 113.4 cubic centimeters of distilled water. After the silver 
 nitrate has been dissolved, add ammonia drop by drop until the 
 brown precipitate falls. Stop adding ammonia just before the solu- 
 tion clears. 
 
21 
 
 Solution No. 2. Mix 35.43 grams of Rochelle salts (dry in crystal) 
 and 85.05 cubic centimeters of distilled water. 
 
 Take one part of solution No. 1, one part solution No. 2, and two 
 parts distilled water in a small vessel just large enough to hold the 
 piece to be silvered. First carefully clean the surfaces to be silvered 
 with grain alcohol. Suspend the piece in the vessel with the face to 
 be silvered downward and immersed a httle below the surface of the 
 solution. 
 
 Place the vessel with suspended piece on a receptacle containing 
 white sand and heat over a gas flame until the temperature of the 
 solution is brought nearly to the boiling point. Extinguish the 
 flame and allow to cool. When cold remove the silvered piece and 
 wash with distilled water. Remove any superfluous silvering by 
 rubbing with a small pine stick previously wet with 50 per cent 
 solution of nitric acid. Wash the piece in water and then in alcohol 
 and allow to dry for two or three hours, when it wiU be ready for a 
 protecting cover, preferably two coats of shellac varnish. 
 
 For large mirrors use a covering of paraflin backed with tin foil. 
 The mirror is gently heated and the melted paraffin is poured in a thin 
 film over the entire silvered surface. For large mirrors great care 
 must be taken in heating the mirror and in applying the hot paraffin, 
 as extremes of temperature may cause the glass to crack after the 
 paraffin has flowed evenly over the entire silvered surface and the tin- 
 foil backing is applied. The paraffin prevents the action of the 
 atmosphere on the silvered surfaces and the tin-foil backing prevents 
 the paraffin from being rubbed or scratched off. For small work, as, 
 for instance, the prisms of the Weldon range finders, however, either 
 of the following mixtures may be used: 
 
 (a) A mixture of beeswax and resin — equal parts. The beeswax 
 is sliced in small pieces and boiled so as to get rid of aU free acid, 
 and the resin is selected as pure as possible. The mixture is put on 
 quite hot. It is well to have the prisms warm before applying the 
 mixture. 
 
 (h) The method given in (a) may be improved upon by uging the 
 best shellac, if this can be obtained free from impurities. Shellac 
 may be prepared by dissolving out the impurities in absolute alcohol, 
 which should not contain more than 0.2 per cent of water. After 
 dissolving, filter the varnish through three thicknesses of cheese- 
 cloth. After silvering, heat the prisms to about 160° F. and apply 
 two coats of varnish. 
 
 41. Cementing of optical elements. — When the conditions described 
 in paragraph 28 become sufficiently pronoimced to obscure the image, 
 the lenses of prisms affected should be removed and placed in an 
 alcohol bath to dissolve out the balsam. It frequently takes from 
 two days to two weeks, or over, to separate the parts of lenses. In 
 
22 
 
 refractory cases the alcohol may be heated gradually over a water 
 bath at 150° F. to accelerate the operation. The parts should not 
 be removed from a hot bath, but should be left to cool off gradually. 
 After separating the parts, remove all trace of the old balsam and clean 
 and dry thoroughly preparatory to recementing. Absolute cleanli- 
 ness of the surface is necessary. The room in which the operation is 
 conducted should be as free from dust as possible. The balsam should 
 always be the best obtainable quality of paper-filtered Canada 
 balsam. In cementing, spread a thin film of balsam over the sur- 
 faces to be cemented; be sure that the film entirely covers each 
 surface and that no air bubbles occur, then bring the parts carefully 
 together and place in a receptacle free from dust for the preliminary 
 setting. By the preliminary setting is meant the first stage of the 
 cementing process, in which the balsam gradually draws the two sur- 
 faces closer and closer together and holds them fairly tight, but still 
 adjustable. The time for the preliminary setting varies from one to 
 two days, the interval being less as the temperature increases. When 
 it is found by actual trying that the surfaces are held fairly tight 
 together, the final close adjustment by hand should be made. For 
 lenses, this consists in getting the mechanical and optical axes of the 
 group into coincidence. 
 
 42. Cementing lenses. — Compound lenses when issueil in instru- 
 ments have already been properly assembled. Before separating 
 such lenses, therefore, a soft-pencil arrow (y\) should be placed across 
 the circumferential rim of the lenses, crossing aU in the direction of 
 the optical axis. This pencil arrow should be carefully preserved, for 
 in reassembling these same lenses, if the pencil mark on each letis is 
 brought into proper relation with the marks on the other lenses, the 
 original relative position will be exactly reproduced. If for any 
 reason one part of the group has had to be changed the entire group 
 will have to be tested again for correct relation and then assembled. 
 
 To determine whether the lenses of a group are properly ground 
 for assembhng, take them carefully by the rims and assemble 
 them without balsam in the position which they should occupy. 
 For properly ground surfaces, a series of color rings symmetrically 
 placed about the optical axis will be observed when two adjoining 
 lenses of a group are brought together. Should the surfaces, how- 
 ever, be too high or too low in spots, then at these spots either absence 
 of color rings, or color rings appearing which have their center out 
 of the optical axis of the group, will be observed, depending on the 
 extent of the incorrect surface. When this color test shows the sur- 
 faces are not in proper contact, the parts should be returned for 
 regrinding and repolishing. Where good results are obtained, the 
 best position should be marked with an arrow (y\) across the rim 
 and the group then assembled with balsam. 
 
23 
 
 43. Cementing prisms. — Compound prisms are more difficult to 
 cement than lenses. For prisms a target must be constructed and a 
 fixture for holding the prisms during adjustment must be arranged, 
 depending on the shapes of the prisms. In preparing fixtures or in 
 inserting prisms into the fixtures do not scratch the glass. All grit, 
 chips, and dirt must be carefully avoided. 
 
 The following method should be followed in adjusting and as- 
 sembling the parts of a Brashear-Hastings erecting prism, assum- 
 ing that each of the parts is correct in itself: Consult first the draw- 
 ings of the instrument to which the prism belongs, and determine 
 from them the amount of overhang each of the 30° prisms has over 
 the ends of the 90° prism. Cement the two 30° prisms to the 90° 
 prism with balsam, taking care to get each in the proper relation as 
 to overhang, parallelism of sides, etc. Then put the group aside for 
 the balsam to set. As the balsam sets it gradually draws the prism 
 surfaces closer and closer together. After a few days (one or two 
 if the process is aided by gentle baking in a properly constructed 
 oven) it will be foimd that the prisms require a little effort to'move 
 them from one position to another. This is the time for final adjust- 
 ment. Place the prisms, 90° prism down, in a previously prepared 
 Y-shaped steel block, of which the sides of the Y make an exact 
 right angle, carefully cut and ground to receive the 90° prism. The 
 lowest element of the Y in the block should be so placed as to make 
 the upper plane surface of the 90° prism, on which the two 30° 
 prisms are assembled, horizontal when the block is placed in a hori- 
 zontal position. Place a target containing fine vertical and hori- 
 zontal axes at a convenient distance (20 to 30 feet) and at a height 
 corresponding to the height of the center of the 30° prisms, when 
 the entire group is placed in the Y block. Adjust a coUimating 
 telescope or some proper mount behind the Y block, so that when 
 the telescope is horizontal in looking through the telescope at the 
 axes of the target, the prism being temporarily removed from the 
 Y block, the cross hairs of the telescope shall coincide with the axes 
 of the target. Now place the Brashear-Hastings prism in the Y 
 block and look through the telescope at the axes of the target. In 
 the general case the cross hairs of the telescope and the axes of the 
 target will not coincide. To bring about coincidence move the Y 
 block carefully on its horizontal plate until the axes of the target as 
 seen through the prism coincide with the cross hairs of the telescope. 
 Having attained this position, be sure that the Y block and the 
 telescope are not altered in position during the subsequent opera- 
 tions. Now lift the Brashear-Hastings prism out of the Y block and 
 tiu-n it 180° in a horizontal plane and replace in the Y block. This 
 wiU result in bringing what originally had been the far 30° prism 
 
24 
 
 next to the telescope and in moving the 30° prism that had been 
 next to the telescope to the target side. Again look through the 
 telescope. If the prisms are correctly adjusted the axes of the 
 target as seen through the prisms in their new position will still 
 coincide with the cross hairs of the telescope. If the axes and cross 
 hairs do not coincide, correct for half the error by moving each of the 
 30° prisms equal amounts. Correct for the remaining half error by 
 moving the block. Note that in moving the 30° prisms the position 
 of these prisms, overhang, parallelism of sides, central distance, etc., 
 remain as laid down in the drawings. Having obtained coincidence 
 by the methods just outlined, reverse the prism again .and continue 
 correcting for half the observed error by moving the prisms and for 
 the other half by moving the block, until the axes and cross hairs do 
 not lose coincidence after reversing the prisms. The prisms are now 
 adjusted and should be put aside to allow the balsam fully to set. 
 After the balsam has fully set, the small end pieces should be cemented 
 to the group and the group then assembled in the prism holder and 
 then in the optical tube, as described in connection with special 
 instruments, the adjustments of which are given in this pamphlet. 
 
 44. Illumination of reticule. — The intensity of illumination of 
 reticides is varied by withdrawing the lamp from the aperture which 
 admits the entrance cone of rays to the reticule chamber, as in the case 
 of the azimuth instrument models of 1900 and 1900 Mi, or by varying 
 the diameter of the entrance cone of rays by means of a fixed and 
 movable diaphragm, as in the case of the telescope for all models of 
 depression position finders and 2-inch and 3-inch telescopic sights. 
 In order not to obscure the field of view the intensity of illumi- 
 nation of the reticule should be reduced as much as possible on both 
 the horizontal and vertical wires. For the 2-inch and 3-inch tele- 
 scopes but one lamp is provided, and in order to reduce the amount 
 of light entering the reticule chamber, the lower mirror on the lamp 
 bracket (see paragraph 10, pamphlets Nos. 1955 and 1956) should be 
 rotated to secure the maximum intensity of illumination and the 
 upper mirror should be rotated to secure an equal degree of illumina- 
 tion. The intensity of illumination of both wires should then be 
 reduced as much as possible by turning the finger grip which operates 
 the moving diaphragm. 
 
 Mirrors are used in the reticule illumination devices of the tele- 
 scopes of the Lewis depression position finder Type A and the 2 -inch 
 and 3-inch telescopic sights. In case the necessary intensity of 
 illumination can not be secured, the mirror holders should be removed 
 and the mirrors polished with a dry cloth. 
 
 For night observation the best results will be obtained by the 
 use of the low-power eyepiece furnished with instruments. The 
 
25 
 
 diameter of the eye ring is greater with the low-power eyepieces 
 and more nearly equals that of the pupil of the eye. Hence the 
 field of view is better illuminated. 
 
 45. The following examples are given as directions for removal of 
 optical parts, for cleaning, and for readjusting. The methods of 
 making adjustments, etc., will not be described for all instruments, 
 but only for the various types of instruments. 
 
 TELESCOPIC SIGHT, MODEL OF 1899. 
 (See Handbook of Sights for Cannon and Drawings 15-2A22, 1, 2, and 3.) 
 
 46. To remove the erecting system. — Remove the objective and cell, 
 the erecting system clamp ring screw, the tube cap, deflection slide, 
 and lower deflection scale. Enter teat wrench No. 29 through the 
 objective end of telescope, engage it in the teat holes in the first 
 diaphragm and screw the erecting system completely out through 
 the eyepiece end of telescope. 
 
 Scratch a short line across all joints as an aid in assembling each 
 piece in the correct order and in tightening up screw threads. Some 
 of the parts have similar threads on both ends and care must be taken 
 not to reverse the piece end for end. Do not remove any lens from 
 its cell. 
 
 Unscrew the first lens cell. Do not remove the first diaphragm. 
 Grasp the erecting system in a chuck and unscrew the second lens 
 cell. Clean and replace both cells. Remove the third lens cell, 
 clean, and reassemble. 
 
 47. To assemble the erecting system. — Insert the erecting system 
 threaded and rearmost, through the reticule chamber and screw into 
 place, using teat wrench No. 29. Align the hole in the wall of the 
 front erecting system tube with the seat of erecting^ system clamp 
 ring screw. Assemble the objective, the reticule, and the eyepiece 
 and test to determine whether parallax can be removed from the 
 cross wires. If not, remove the objective and revolve the erecting 
 system tube in the proper direction until parallax may be removed 
 and the clamp ring screw assembled. Replace erecting system 
 clamp ring screw. 
 
 Little dirt works into the erecting system of this telescope. It will 
 not therefore be necessary to remove the erecting system except at 
 long intervals. 
 
 48. To collimate the telescope. — ^Mount bracket No. 102 of optical 
 repair kit on fixture No. 86, and pedestal No. 85. Level the pedestal. 
 Insert collimating telescope No. 98 in bracket No. 102 and bring the 
 image of the crosslines of a target into coincidence with the reticule 
 to collimating telescope. Test the collimation of the collimating 
 telescope and correct it if necessary. Then remove bracket No. 102 
 
26 
 
 and collimatijig telescope from fixture No. 86 and place the telescope 
 to be coUimated upon the fixture without changing the position or 
 adjustment of fixture. Loosen the four reticule holder screws and 
 adjust reticule holder so that the horizontal wire coincides with 
 horizontal wire of target and so that the vertical wire is plumb. 
 Turn the deflection kaob until vertical wire coincides with vertical 
 line of target. Loosen the upper deflection scale screw^s and reset 
 the upper deflection scale if necessary. Loosen the two deflection 
 knob screws and set the deflection micrometer to 0. Reset the 
 lower deflection scale and test adjustment by the eyepiece. 
 
 This telescope may also be collimated by using bracket No. 102 
 on the telescope seat of the gun carriage. The method of adjusting 
 is the same as described above. Collimating the telescope on the 
 gun carriage will probably be found preferable. 
 
 TELESCOPES WITH BRASHEAR-HASTINGS ERECTING PRISMS. 
 
 49. The telescopes of the following instruments are equipped with 
 this kind of prisms: 
 
 Telescopic sight, models of 1896 Mi, 1897, 1898, 1898 M, and 1902. 
 Lewis depression position finder, types A and B. 
 Swasey depression position finder, type A. t 
 
 Azimuth instrument, model of 1900. *■ 
 
 Three-inch telescopic sight, model of 1904, Nos. 1-26, inclusive. 
 
 TELESCOPIC SIGHTS, MODELS OF 1896 MI, 1897, 1898, AND 1899 M. 
 (See Handbook of Sights for Cannon and Drawings 15-2A19, 1 to 4, inclusive.) 
 
 50. For adjusting telescopic sights, models of 1896 Mi, 1897, 
 1898, and 1898 M, a trunnion bracket (No. 87) is furnished with the 
 optical repair kit. The following examples of its use will be given, 
 which is applicable to either of these models of sights. Attention is 
 also invited to ' ' Handbook of Sights for Field and Seacoast Carriages 
 not covered by other Pamphlets" (Form No. 1952). The fixtures 
 and tools mentioned by numbers pertain to the optical repair kit. 
 
 51. Prepare a target on which is one horizontal line and two ver- 
 tical lines, the distance between which is equal to twice the horizontal 
 distance from the axis of the telescope to the axis of the telescope 
 trunnions. The horizontal line of target should lie as near as prac- 
 ticable to the horizontal plane which includes the optical axis of the 
 telescope. One leveling screw of the pedestal should lie in the ver- 
 tical plane of the trunnions of the sight. 
 
 Level the trunnion bracket (Fixture No. 87) in the pedestal (Fix- 
 ture No. 85) with a striding level (No. 74). Set the telescope without 
 the prisms assembled in the trunnion bracket; adjust the telescope 
 level to make the bubble central in level vial by changing the elevation 
 
27 
 
 of the telescope. Set the micrometer elevation dial and vernier to 
 read 0. (The setting of level should be tested in the usual way.) 
 Insert the cross-wire frame (if not already assembled) and adjust 
 the horizontal wire to coincide with the horizontal line on the target. 
 Remove the telescope from the fixture. Rotate the swivel of trun- 
 nion bracket 180° from its former position against the stop. Replace 
 the telescope in the bracket bottom side up. If the horizontal cross 
 wire is not in the plane of the optical axis, correct for half the error 
 by moving the cross-wire frame by the small adjusting screws in the 
 top of the frame, and for half the error by moving that leveling screw 
 of the pedestal which lies in the same vertical plane as the axis of the 
 trunnions of the sight; without changing the level of the pedestal, 
 reverse the telescope and recorrect if necessary. 
 
 52. If the horizontal cross wire can not be adjusted due to error 
 in adjustment of the telescope level,^ the cross-wire frame should be 
 left in an intermediate position and the adjustment for coUimation 
 made as closely as practicable by adjusting the prisms (see below) 
 and corrected as described above after the prisms are adjusted. 
 
 53. For adjusting the vertical cross wire move the vertical wire" 
 to near the center of the diaphragm and the micrometer deflection 
 dial to zero for trial. (It is assumed that the prisms are disassembled.) 
 Put the telescope in the bracket. First adjust the cross level so that 
 the bubble of level vial remains central throughout the entire arc 
 of elevation of the telescope (for the models of 1898 and 1898 M 
 sights). If adjustment of the level vial is necessary, remove the cap 
 from cross level and adjust it by the internal adjusting screws (see 
 paragraph 172). If the adjustment is made correctly, the vertical 
 cross wire should foUow a plumb line during elevation of the telescope. 
 
 54. In adjusting the cross levels of the models of 1896 Mi and 
 1897 sights, set the telescopic sight tnmnions approximately level in 
 the trunnion bracket and the cross wire at 0° deflection and level the 
 cross level. Align the vertical wire on a plumb line without changing 
 the deflection setting. Then elevate the telescope through the great- 
 est possible range of elevation scale. If the vertical wire does not 
 follow the plumb line, correct the error by the adjusting screw of the 
 telescopic sight holder to bring the vertical wire into coincidence with 
 the plumb line. Then adjust the cross level by moving its axis in a 
 plane perpendicular to the surface of the base of the level case imtil 
 the bubble is central. Repeat the test to verify the setting. 
 
 Then put the sight in the trunnion bracket of gun at 0° elevation 
 and level the cross level. Elevate the gun through as great an arc as 
 possible. If the bubble of cross level does not remain central, slightly 
 loosen the screws of the level case and adjust the level so that the 
 bubble is central at this position. In this adjustment the axis of the 
 
28 
 
 level is moved in a plane parallel to the base of the level case. Kepeat 
 test and after adjustment is satisfactory, readjust the level for move- 
 ment of telescope in elevation as directed in preceding paragraph. 
 
 55. After the cross level is adjusted' ahgn the telescope on the 
 right-hand vertical line of target. Take out the telescope and replace 
 it bottom side up, turning the swivel of bracket as before. If the 
 vertical wire does not coincide with the left-hand vertical line of 
 target, determine the amount of the error by means of the microme- 
 ter deflection dial, and turn back the micrometer toward the first 
 position by one-half of the measured error. Reset the telescope on 
 the target, with the vertical wire in this new position. Reverse the 
 telescope and proceed as before to correct the adjustment of the 
 vertical wire. The micrometer deflection dial should be set at 
 and the internal scale adjusted for this position. 
 
 56. CoUimate the prisms as described below for 3-inch telescopic 
 sights, model of 1904, Nos. 1-26, inclusive. Then remove prism and 
 holder from the telescope tube, fill the space around the two adjust- 
 ing screws between the prism and the holder with plaster of paris 
 and allow the plaster to set. Carefully clean the prisms and replace 
 them and the holder in the telescope. Set the telescope with the ver- 
 tical cross wire on a vertical fine of target. Insert the holder screws 
 into the telescope body and align the prism holder so that the coin- 
 cidence of the vertical cross wire with a line on the target is not dis- 
 turbed. Test the adjustment by reversing the telescope as described 
 above. Then tighten the prism holder screws and replace the prism 
 box cover. The horizontal and vertical axis should then be tested 
 for collimation and coUimated if necessary, as described above. 
 
 57. After a workman has become famihar with the adjustment 
 of sights in the manner described above, it will be sufficient if prisms 
 are located centrally in telescope tube before the cross wires are 
 collimated. Then set the horizontal cross wire in an intermediate 
 position and coUimate by adjusting the screws between the prism 
 and holder, moving the axis of the prisms in a vertical plane only. 
 Remove the prism and the holder and fill the space between them 
 with plaster of paris. Then complete the coUimation of the hori- 
 zontal wire by adjusting the cross-wire frame. Adjust the vertical 
 wire as described above. In this case, test the location of prisms in 
 the tube by looking through the telescope and observing that neither 
 edge of prism is seen within the diaphragm or that both edges are 
 seen equally spaced from the sides of diaphragm. 
 
 58. After a telescopic sight is adjusted in this manner, it should 
 be tested for parallelism with the axis of the bore of the gun. If the 
 line of coUimation of the sight is not parallel with the axis of the bore 
 at 0° deflection and 0° elevation, the sight brackets on the gun car- 
 
29 
 
 riage should be adjusted, or tlie V's of the trunnion bracket should be 
 filed or scraped to make the line of collimation parallel to the axis of 
 the bore under the conditions stated. 
 
 TELLESCOPIC SIGHT, MODEL OF 1902. 
 (See Drawings 15-2A18, 1, 2, and 3.) 
 
 59. To collimate this telescope, use collimating telescope No. 98 
 with rings Nos. 101, pertaining to the optical repair kit, in the cradle 
 of sight. Point the gun at a given object and adjust the prisms by 
 the prism-adjusting screws so that the line of collimation of sight 
 agrees with that of coUimating telescope. The erecting prism holder 
 is located in the telescope tube by dowel pins. Relocation of these 
 pins will not be required except to compensate for errors in cementing 
 the elements of the erecting prism. After adjustment of the hori- 
 zontal plane containing the line of collimation, set up the prism- 
 adjusting screws so that they just come in contact with the glass 
 surface, set the lock nuts and fill in with plaster of paris as described 
 in paragraph 37 above. 
 
 3-INCH TELESCOPIC SIGHTS, MODEL 1904, NOS. 1-26, INCLUSIVE. 
 
 (See Plate A.) 
 
 60. To dismount the eyepiece and prism. — To remove the prism 
 holder, unscrew the four screws (1) on cover (2); unscrew (3) and 
 lay aside with washer (4); unscrew (5), and the whole prism, with 
 holder, can be taken from the telescope body. To remove the prism 
 from its holder, unscrew (6), take out piece (7), and the whole prism 
 is now ready to be removed. Great care must be taken to replace 
 the prism in exactly the same position in the holder. Plate A shows 
 clearly the method of dismounting the eyepiece. No attempt should 
 be made to remove the lenses of the eyepiece from their cells. 
 
 61. The lenses of the objective of this telescope are secured in the 
 holder by crimping, and should not be removed for cleaning or any 
 other purpose, except by an expert instnunent maker. 
 
 62. To assemble and adjust the telescope. — ^Assemble and insert the 
 eyepiece, but not the prism, as the telescope must be adjusted without 
 the latter. Place the coUimating telescope No. 98, using rings 
 No. 103 in the telescope bearings of the sight cradle. Select a target 
 at least 300 yards' distance and bisect it with the cross wire. Then 
 revolve the collimating telescope 180°, and if the cross wires bisect 
 the same target exactly then the adjustment of the coUimating tele- 
 scope is correct. , Remove the coUimating telescope and without 
 changing the pointing of the sight, insert the 3'' telescope in its bear- 
 ing in the cradle. If the cross wires are to one side, or up or down 
 
30 
 
 from the target selected, then the whole error must be corrected with 
 the cross-wire adjusting screws (9). Check the correctness of the 
 adjustment. Then with the telescope in position and carefully 
 ahgned on the target, insert the prism and screw down tight screw 
 (5) and also screw (3). If the telescope does not bisect the target 
 exactly as before, then the correction up or down must be made 
 wholly with the screws (3) and (10); (3) holds the prism holder to 
 the telescope body, and (10) are pushing screws, which raise and lower 
 the image of the objective in relation to the cross wires. The adjust- 
 ing sideways is done by screws (11), and to do this the screw (3) 
 must be unscrewed and the whole prism holder, with the prism hinged 
 on screw (5), raised enough to reach the screws (11) and then dropped. 
 
 Great care must be taken that both the screws (10) are turned 
 exactly the same amount and touch the telescope body at the same 
 time, otherwise, by screwing down the screw (3), the whole holder 
 will be twisted and the prism may be broken or strained sufficiently 
 to destroy good definition. 
 
 After inserting and adjusting the prism, the telescope should point 
 to exactly the same point as without the prism. All adjusting with 
 screws must be done carefully and in such a way as not to put any 
 strain on the metal, because if the screws are too tight the adjustment 
 wiU change rapidly. As a general rule, it is always advisable to 
 tighten each screw just enough to secure a firm contact between 
 the two parts without any strain whatever. 
 
 SWASEY DEPRESSION POSITION FINDER, TYPE A. 
 (See Plates B and C.) 
 
 63. To dismount the eyepiece. — Plate C indicates clearly the con- 
 struction and method of dismounting the eyepiece. No attempt 
 should be made to remove the lenses of the eyepiece from their rings. 
 
 64. To dismount the objective (Plate C). — Unscrew objective shade 
 (45-46), then unscrew the objective cell (91), unscrew the ring (93) 
 which holds the objective in the cell, and put a clean piece of hnen 
 on a table and take out the objective (92) from the cell (91). To 
 do this it is best to unscrew first ring (93) and lay the cell of the 
 table with the ring (93) end up. Then put a clean piece of linen 
 over the left hand; put left hand covered with hnen on top of cell 
 and lenses, and reverse, so that the left hand is on the bottom and the 
 right hand on the top. Now raise the cell slowly and both lenses will 
 come out of the cell easily. Should the lenses fit a httle snugly, es- 
 pecially in cold weather, bring the whole cell into a warm room and let 
 it stand for about one hour; the lenses should then be readily removed 
 from the cell. Before separating the lenses, place a soft-pencil arrow 
 (^) across the circumference. Clean carefully and put back in the 
 
31 
 
 same position. There are three small pieces of paper pasted on one 
 of the lenses of the objective, exactly 120° apart and at the egde, to 
 separate the two lenses. 
 
 65. To dismount, re'place, and readjust 'prism (Plate B). — Remove 
 cover by unscrewing the screws. 
 
 Unscrew the two screws (1) and take out the prism with its holder, 
 loosen (4) a trifle, take out screws (2), and remove crossbar (3). 
 Then the prisms will come off from the holder easily. 
 
 Clean prisms carefully, insert in holder, put in place piece (3); put 
 in screw (2) and tighten screws (3); then slowly tighten screws (4). 
 
 This telescope, with the Brashear-Hastings prism removed, is ad- 
 justed exactly as described for the telescope of Type Ai below. 
 After this is done, the Brashear-Hastings prism must be inserted with 
 screws (1), Plate B, and if the image now on the target is too high or 
 too low, then this must be corrected with screws (4) by loosening one 
 screw a trifle and tightening the other one. If the image is to one 
 side, loosen slightly one of the screws (1) and move prism holder in 
 desired direction. This is best done by wedging a screw driver be- 
 tween the opening of the telescope body and the prism frame. In 
 case the prism holder can not be moved to one side correct the error 
 by changing the collimation of the objective. After adjusting, put 
 the cover on top of the telescope and secure with screws (5). 
 
 In this telescope no adjustment of the reticule is provided. 
 
 ADJUSTMENT OF PRISMS OF LEWIS DEPRESSION POSITION FINDER, 
 
 TYPE A. 
 
 (See Pamphlet No. 1873.) 
 
 66. The vertical adjustment of the prisms of the Type A position 
 finder should be made in reference to the tide scale in order to mini- 
 mize, the error of the range scale for various heights of tide. In 
 making this adjustment, set the range scale at infinity (if not prac- 
 ticable set at maximum range on scale) and the tide slide at either 
 extreme of the scale. Set up a target with horizontal line in the 
 horizontal plane of the axis of the trunnions of telescope. Direct the 
 telescope on the target and by turning the refraction screw bring the 
 horizontal cross wire of the telescope to coincide with the horizontal 
 line of the target. Then translate the tide slide to the other extreme 
 end of the scale. If the horizontal cross wire stiU remains on the 
 horizontal fine of the target, the prism is correctly adjusted vertically. 
 If the coincidence of the cross wire and the horizontal fine is disturbed, 
 correct half the error by rotating the prisms in a vertical plane by 
 means of the prism holder screws and half the error by rotating the 
 telescope on the trunnions by the refraction screw. Repeat until the 
 adjustment is found to be correct. 
 
32 
 
 67. In the telescopes for the followmg instruments Porro prisms 
 are used for erecting the image : 
 
 Swasey depression position finder, type All. 
 
 Lewis depression position finder, model of 1907. 
 
 Azimuth instrument, models of 1900 Mi and 1910. 
 
 Three-inch telescopic sight, models of 1904 (after No. 26) and 1910. 
 
 Two-inch telescopic sight, models of 1906 and 1909. 
 
 Observation telescope, seacoast, model of 1908. 
 
 Observation telescope, field, model of 1908. 
 
 Battery commander's telescope, models of 1904, 1905, and 1915. 
 
 Telescopic musket sight, models of 1908 and 1913. 
 - 68. Porro prisms of all telescopes mentioned above are fixed in 
 position in a holder and do not permit of adjustment as in the case 
 of Brashear-Hastings prisms. Each telescope is tested for adjust- 
 ment of prisms before it leaves the manufacturer and no change 
 should be found necessary. Telescopes with Porro prisms are ordi- 
 narily collimated by moving the cross-wire holder. In a few tele- 
 scopes the objective can be adjusted as in the case of the telescope 
 for the Swasey depression position finder, types AI and All. 
 
 3-INCH TELESCOPIC SIGHT, MODEL OF 1904 AFTER NO. 26. 
 (See Plate III, Pamphlet No. 1955.) 
 
 69. To dismount eyepiece. — Plate III, Form No. 1955, indicates 
 clearly the construction and method of dismoimting the eyepiece. 
 No attempt should be made to remove the lenses of the eyepiece 
 from their cells. 
 
 70. To dismount the prisms. — To take off the prism holder, unscrew 
 aU screws and remove the holder from the telescope body by simply 
 raising the holder from the telescope body; push down one end of the 
 prism spring to disengage the recess or receiver and pull or turn the 
 spring sideways. If this is done, and the spring removed, the prism 
 is ready to be taken out. Care must be taken after cleaning the 
 prism that it is mounted in the same position as before. 
 
 71. The prism holders on sights after No. 297 differ somewhat 
 from those that preceded. The holder is separate from the cover 
 and is secured to the tube by five screws, three entered from the 
 outside of the tube on the right hand and two entered inside the cover 
 through a shoulder on the prism holder. The cover is in two pieces, 
 the smaller of which is secured to the right-hand side of the prism 
 holder by three screws. The larger is secured to the smaller by 
 three screws and to the prism holder on the left side by two screws ; in 
 addition, one screw secures it to the rear flange of the prism-holder 
 seat and one to the front flange. In dismounting, first remove the 
 larger piece of the cover and then the smaller, w^hen the prism holder 
 
may be taken out. The parts should be assembled in reverse order. 
 The method of removing the prisms from the holder, cleaning, and 
 reassembling is the same as that described in preceding paragraph. 
 
 72. To dismount the objective. — Unscrew the objective holder and 
 lay it on a clean table covered with fine white paper. Then unscrew 
 the ring securing the three lenses (56) in the holder. Be careful that 
 the two black paper rings which separate the lenses are not lost. 
 Before taking the lenses apart, put a soft-pencil arrow (>) across the 
 periphery and in line with the optical axis of the objective, the point 
 of, the > toward the outside surface of the objective. This will serve 
 to indicate that the three lenses must be put in the same position as 
 before cleaning; with the indicated arrow lines, the position of the 
 lenses can not be changed, because there is only one position where 
 the lines of the arrow will match. 
 
 73. To adjust the telescope. — Place the collimating telescope No. 98 
 with rings No. 99 in the cradle bearing and sight on an object. Test 
 and adjust collimating telescope if necessary. . Remove the collimat- 
 ing telescope, and without disturbing the position of the bearings 
 insert the telescope to be adjusted, and by means of the cross-wire 
 holder screw collimate it to agree with collimating telescope. (See 
 paragraph 62.) 
 
 74. Make the vertical wire parallel with a plumb line. The holes 
 through the focusing sleeve and draw tube for reaching the cross-wire 
 ring screws are slotted for this purpose. Before this adjustment 
 make sure that the focusing sleeve (51) is screwed tightly into the 
 tube. If the focusing sleeve can be screwed in too far, its flange 
 should be packed up with a thin piece of metal, paper, or other suit- 
 able material. 
 
 SWASEY DEPRESSION POSITION FINDER, TYPE All. 
 
 (See Plate C herewith and Plates I and II, Form No. 1875.) 
 
 75. The eyepiece and objective of this telescope are the same as in 
 the type A instrument and should be dismounted as described in para- 
 graphs 29 and 30. 
 
 76. To dismount and replace the prism (Plate C). — Take off screw 
 (81) and turn focusing nut (50), holding the eye end (53) until the 
 thread of the focusmg nut is disengaged with the thread of the eye 
 end, and then slide out the whole eye end. Remove screw (86) and 
 sprmg (87) and the prism (88) can be hfted out, cleaned, and replaced 
 in position. Take off eyepiece and micrometer box by imscrewing 
 screws (82), then unscrew (83), remove the spring (84), and the 
 prism (85) can be removed, cleaned, and placed in position as before. 
 Insert spring (84) and screw in screw (83), assemble micrometer box 
 and eyepiece to prism holder with screws (82), put into telescope, and 
 see that screw (81) fits in the slot of the prism holder. 
 
 9950—17 3 
 
34 
 
 77. To adjust the telescope for level and collimation (Plates I and 
 II, Form No. 1875). — Set the striding level on top of the telescope, 
 turn the range crank on range drum, and bring the level bubble in the 
 center of the glass scale; then reverse the striding level, and if the 
 bubble is not exactly in the center of the divided glass scale, correct 
 half the error with the adjusting screws of the striding level, and the 
 other half with the range crank (71). Repeat this several times until 
 the level bubble remains in the center. 
 
 78. Set the azimuth index at and bring the striding level bubble 
 to the center of the glass scale by turning the range crank, then revolve 
 the whole telescope and cradle 180° on the vertical spindle, so that 
 the azimuth index reads 180°. If the level bubble should happen to 
 be in the center of the glass scale, the axis is perfectly plumb in 
 this position ; but if the level bubble is not in the center then half of 
 this error must be corrected on the leveling screws (47) and the other 
 half by turning the range crank (71). Repeat these readings several 
 times and at the end set in azimuth every 90° — first 0°— 180° and 
 180° -0°, and then 90° -270° and 270° -90°. If the level bubble 
 remains exactly in the center, then the instrument is correctly leveled 
 and all that is necessary is to open the door (74) in front of the 
 range-drum cover, loosen a trifle the three screws on the range drum 
 and set the range drum so that telescope level on the drum corre- 
 sponds with the index line of the range pointer (78). Next point 
 the telescope to some distant object and find some point or target 
 bisected by the cross wires. Then take off the striding level (46) , open 
 the two caps (66) on the telescope trunnion, take the telescope out of 
 the bearings and reverse the trunnion axis with the whole telescope, 
 close the two trunnion caps, set the striding level .on top of the tele- 
 scope, and turn the range crank so that the level bubble is again in 
 the center of the glass scale. The cross wires should exactly bisect 
 the same target as before; if they do not they are either too high or 
 too low or to the right or to the left. In eiiher case only half the 
 amount of this error is to be corrected by shifting the objective. 
 Loosen sUghtly the screws (89), Plate C, and by using the screws (90), 
 Plate C, always in opposite directions, loosen one and tighten the 
 other either up or down or sideways until the telescope is adjusted 
 correctly. This Operation must be repeated several times to insure 
 correct adjustment. Note that the horizontal wire may be moved 
 in a vertical plane and that before coUimating the horizontal wire 
 should be moved to bisect the field of view. 
 
 79. To adjust the vertical wire, type All, serial numbers'^ after No. 
 219 only. — In case the vertical wire is not parallel to a plumb line 
 loosen the four screws holding the wire ring in the micrometer slide 
 and rotate the wire ring in the micrometer slide until- wire is plumb. 
 Then set up screws. 
 
35 
 
 LEWIS DEPRESSION POSITION FINDER, MODEL OF 1907. 
 (See pamphlet No. 1876, Description of Lewis D. P. F., Model of 1907.) 
 
 80. To replace and to adjust the cross wires of telescope. — Remove 
 the eyepiece adapter (21) from the prism case back. Unscrew the 
 cross-wire adjusting screws (15) and remove the cell for spider lines. 
 Insert the cross wires (platinum wire 0.0005 inch diameter or spider 
 web) and replace the cell for spider Une in the eyepiece adapter, 
 taking care that the cell for spider lines is concentric with the bore 
 of the eyepiece adapter. Replace the eyepiece adapter and in case 
 the vertical cross wire does not appear to bisect the field of view 
 adjust the position of the cell for spider lines by means of the two 
 cross-wire adjusting screws (15) on the sides of the eyepiece 
 adapter. 
 
 Make the vertical wire parallel with a plumb line set up at a dis- 
 tance for which parallax may be removed from the telescope. It will 
 be noted that the holes through which the cross-wire adjusting screws 
 (15) pass are slotted to permit this adjustment. This operation may 
 well be combined with the next, the target described being made of 
 suflB.cient length for making the vertical Une plumb. 
 
 81. Use fixture No. 86, or any other surface plate, on pedestal No, 
 85, and level with bench level No. 73. Using collimating telescope 
 No. 98, with a convenient set of rings or guides, lay off on a target a 
 horizontal line whose image is coincident with the horizontal cross 
 wire. If the target is near, make the necessary allowance for the 
 difference in heights of the Center of the coUimating telescope and of 
 the objective of the Lewis depression position finder and lay off a 
 second line to represent the height of center of Lewis depression 
 position-finder telescope. Screw the counterweight of telescope to 
 be coUimated to a position nearest the center of the trunnion yoke 
 (53). Clamp the telescope to the surface plate so that the bar (51) 
 bears uniformly on it, or lay the telescope on the surface plate with 
 the bar in uniform contact and support the outer end of the telescope. 
 Adjust the two cross-wire adjusting screws (15) on the top and 
 bottom of the eyepiece adapter (21) so that the horizontal cross wire 
 coincides with the image of the horizontal line of target. Verify the 
 adjustment of the vertical wire. Assemble the telescope. 
 
 On instruments Nos. 154 and higher, remove the angles piece at- 
 tached to the side of bar (51) before placing the telescope on a surface 
 plate. 
 
 82. On instruments of serial numbers 154 and above the objective 
 is mounted in an adjustable collar, the axis of which is adjustable 
 in respect to the axis of the tube of the telescope. This adjustment 
 is to compensate errors in manufacture and should not need be made 
 in the field. If the parts are disassembled, center the adjustable 
 collar in the tube so that about equal movement of the objective 
 
36 
 
 may be made in any direction. Make the coUimation adjustment by 
 the cross-wire adjusting screws. If the collimation adjustment can 
 not be made correctly by those screws, loosen the four screws 
 clamping the adjustable collar to the flange of the tube and by 
 means of the radial screws in the adjustable collar make the 
 necessary correction of the line of sight. Kepeat the test and tighten 
 all screws. 
 
 83. Alternate method. — Set up a transit or level so that the center 
 of the telescope of transit or level is in the same horizontal plane as 
 the center of the telescope of the Lewis depression position finder 
 (or make the necessary allowance for difference in height). Before 
 measuring to obtain the center of the telescope make the bar (51) 
 parallel to the tangent screw rail as described in succeeding para- 
 graph. Lay off a permanent target to indicate the position of the 
 horizontal plane through the axis of the objective of the position 
 finder. 
 
 Level the position finder. Set the range dial at some range, 
 greater than 1,500 yards but less than the maximum range, for which 
 the compensating bar (14) and the tangent screw rail (46) are parallel. 
 (After releasing the clamp screw (12), no movement of the compen- 
 sating screw (11) should occur during translation of the slide block 
 (42) even if the compensating bar and tangent screw rail are not par- 
 allel. The setting of the bar and rail, however, guards against 
 accidental disturbance of the compensating screw.) Release the 
 ijlamp screw (12). Adjust the compensating screw (11) so that 
 AS the slide block (42) is moved along the tangent screw rail (46), the 
 horizontal cross wire remains ahgned on the same external object. 
 Then adjust the horizontal cross wire to bisect the line previously 
 laid off. 
 
 In case a permanent target for telescope level is laid off, measure 
 the distance between body (8) and pedestal cap (33) and when col- 
 limating the telescope see that the distance between these parts is 
 not appreciably changed. In case the target is at least 100 feet dis- 
 tant, a variation of one thirty-second of an inch in the distance be- 
 tween body and pedestal cap may be neglected. 
 
 84. To lay off a target at the height of the axis of telescope without 
 the aid of a transit coUimate the telescope on a surface plate as de- 
 scribed above, and mount the telescope in its yoke and level the table. 
 Set the range dial at some range greater than 1,500 yards and less 
 than the maximum reading for which the compensating bar (14) and 
 the tangent screw rail (46) are parallel. Release the clamp screw 
 (12). Adjust the compensating screw (11) so that, after unclamping 
 the nut block (30), as the sUde block (42) is moved along the tangent 
 screw rail (46), the horizontal cross wire remains ahgned on the same 
 internal object. Then lay off a target whose image coincides with 
 
37 
 
 the cross wires and use this target for future coUimation of the 
 instrument. 
 
 85. The telescope may be collimated approximately by adjusting 
 the horizontal wire in the same manner as described in paragraph 80 
 for the vertical wire — that is, to bisect the field of view. 
 
 BATTERY COMMANDER' S TELESCOPE, MODELS OF 1904 AND 1905. 
 
 (See Plate E, herewith, pamphlet No. 1796, and drawings 22-17-1 to 6, inclusive, 
 for model of 1905, and drawings, 22-2-1,, 6, 7, 8, 9, and 10 for model of 1904 instru- 
 ment.) 
 
 (The symbols given apply to the model of 1905 instruments only.) 
 
 86. For a description of the operations of disassembling and clean- 
 ing the battery commander's telescope which are permitted in the 
 field, see pamphlet No. 1796 (Handbook of Battalion and Regi- 
 mental Equipment of Field Artillery and of Fire Control Equipment 
 of Field Artillery Batteries, with instructions for its care). A 
 description of the operations of disassembling the base of the instru- 
 ment will be found in paragraphs 174-176 below. 
 
 87. To clean the objective prism (6V). — Remove the telescope from 
 the mount, take out the four objective prism box cover screws (5P) 
 from the front face of the objective prism box cover (5J), remove the 
 cover (5J), turn the telescope over, and gently tap against the hand 
 and withdraw the objective prism (6V). Before removing the prism 
 mark the top, in order that it may be reassembled in the same 
 manner as originally adjusted. The three polished surfaces of the 
 prism should be carefully cleaned. Reassemble parts in the reversed 
 order. 
 
 The objective prism base (5G) should not be removed from the 
 objective prism box (5H). 
 
 88. To remove the objective. — Unscrew the four objective prism base 
 screws (5M) on the circumferential surface of the objective prism 
 base (5G) and draw off the objective prism box (5H) and the ob- 
 jective prism base (5G) together. Do not separate the base from 
 the box. Unscrew the objective cell (5E), clean the objective lens 
 (6W), and replace. Do not attempt to remove the objective from 
 its cell. 
 
 89. To clean the focusing mechanism. — The objective prism and box 
 and the objective cell should be removed. Then take out the focus- 
 ing pinion sleeve screw (5DA) and pull out the focusing pinion (5U) 
 and the focusing pinion sleeve (5CA). The draw tube (5B) may now 
 be removed. Carefully clean all parts, put a little vaseline on the 
 focusing rack (5S), and lightly oil the draw tube (5B) with clock oil. 
 Insert the draw tube with a downward spiral motion, align the focus- 
 ing rack, and assemble the focusing pinion (5U). The objective cell 
 holder (5D) is soldered to the draw tube and should not be removed. 
 
38 
 
 90. To disassemhle the focusing pinion (5U). — Loosen the focusing 
 pinion nut screw (5AA), unscrew, gently tap to allow the focusing 
 pinion knob washer (5X) to drop out, pull off the focusing pinion 
 knob (5W), noting that it is keyed to the shaft, and take off the 
 focusing pinion sleeve (5CA). Clean, lightly oil with clock oil, and 
 assemble in the reversed manner. 
 
 91. For cleaning the Porro lyrisms. — It will be necessary to take 
 out the three prism cover screws (2KA) in the axis prism cover 
 (2LA) and to remove the cover. Then unscrew the four prism 
 holder screws (2FA) and remove the axis prism holder (2MA). 
 Loosen the prism holder spring screw (2GA) and take out the upper 
 (small) prism. The lower prism may be taken out as soon as the 
 prism holder is removed. Carefully mark the prisms before removal, 
 in order to reassemble them in the position for which they were 
 originally adjusted. If these precautions are taken, no difficulty 
 should be experienced in reassembling. 
 
 92. To disassemhle the eyepiece. — ^Take out the eyepiece screw 
 (5GA) and pull the eyepiece from the eyepiece adapter (5EA). The 
 field lens ceU (5HA) and the eye lens cell (5JA) may be unscrewed 
 from the eyepiece tube (5FA). Do not attempt to remove the lenses 
 from their cells. 
 
 93. To remove the reticule (6H). — For cleaning, it will be necessary 
 to unscrew the eyepiece adapter (SEA) from the axis (2PA). But 
 first mark the position of the eyepiece adapter (SEA) as assembled 
 in the axis (2PA) by drawing or scratching a line across the top 
 surface of the eyepiece end of the axis and the end of the adapter. 
 Then unscrew the eyepiece adapter (SEA), take out three of the 
 reticule holder screws (6C), hold the reticule holder (6A) by the 
 finger, and remove the fourth reticule holder screw and allow the 
 reticule holder to drop out onto the palm of the hand. Keep the 
 reticule holder screws (6C) and washers (6B) together, and reassemble 
 them in the same hole from which removed. Also note the position 
 of the reticule before disassembling, in order to put it back in the 
 same position. 
 
 In reassembling, place the reticule holder (6A) in the eyepiece 
 adapter (SEA) in the proper position, insert the reticule holder screws 
 (6C) in the same holes from which removed. Tighten opposite screws 
 and adjust the reticule holder concentric with the bore of the adapter. 
 Test this position with inside cahpers. Reassemble the eyepiece 
 adapter (SEA) in the axis (2PA), so that the marks made on the 
 adapter and the axis come opposite each other. Then assemble the 
 Porro prisms (if not in place), the eyepiece, and the objective (if 
 not already in place). 
 
39 
 
 94. Adjustment. — ^After assembling all the parts except the objec- 
 tive prism and prism box, the telescope will now be adjusted. For 
 this purpose carefully level the base of the instrument on a stable 
 mount or plate. Put the telescope in the trunnion bearings so that 
 the axis of the objective lies in a horizontal plane. Adjust the reti- 
 cule holder (6A) by the reticule holder screws (6C) so that the vertical 
 line on the reticule is parallel to a plumb line. In making this 
 adjustment do not disturb the concentricity of the reticule holder 
 and the eyepiece adapter. 
 
 95. To more perfectly coUimate the telescope, set the azimuth 
 scale at and accurately align the vertical line of reticide on a plumb 
 line. Keverse the base 180° so that the azimuth scale reads 32. 
 Take out the telescope from its bearing, turn it around, and replace it 
 in the trunnion bearing. Correct half the error of the vertical line of 
 reticule from the plumb line by readjusting the reticule holder, 
 taking care to keep the vertical line parallel to the plumb line. Cor- 
 rect the remainder of the error by rotating the platen (4R) by the 
 slow motion screw. Repeat until the adjustment of the reticule is 
 made satisfactory. 
 
 96. Then assemble the telescope in its normal position, ahgn the 
 vertical line of reticule on a plumb line, and rotate the telescope on 
 its trunnions until the axis of the telescope tube is vertical. Carefully 
 maintain the position of the telescope for direction. Assemble the 
 objective prism box (5H) with prism mounted therein, and tighten 
 the four objective prism base screws (5M) for the position of the 
 prism box in which the vertical wire is aligned on the plumb line. 
 Note that the prism box can be rotated slightly to secure this ad- 
 justment. 
 
 97. Lay off on a target a horizontal line in the same horizontal 
 plane as the axis of the objective prism. Release the platen, so that 
 it can revolve freely. Set the telescope by turning the elevation 
 micrometer head (4WA) so that the telescope will rotate on a fixed 
 vertical axis. Change the adjustment of the reticule, if necessary, to 
 bring the horizontal line of reticule onto the horizontal hne of target. 
 Repeat to test adjustment. Set the elevation dial (4HA) and the 
 elevation scale (2S) to read for this position of telescope. In case 
 the horizontal line of reticide can not be ahgned on the target in this 
 manner, it will be necessary to change shghtly the elevation of the 
 telescope by turning the elevation micrometer head. 
 
 98. Ordinarily the reticule of the telescope may be adjusted satis- 
 factorily by carrying out the instructions of paragraphs 95 and 97 
 above. The elevation scale and the elevation dial should then be 
 set to read when the horizontal line of the reticule is aligned on a 
 line in the same horizontal plane as the axis of the objective prism. 
 
40 
 
 BATTERY COMMANDER' S TELESCOPE, MODEL OF 1915. 
 (See Plate J herewith, pamphlet No. 1796, and drawings 22-39-1 to 13, inclusive.) 
 
 99. To clean the objective prism. — Take out the prism shield cell 
 screws, unscrew the prism shield cell, release lock nuts, and with- 
 draw objective prism. The three polished surfaces of the prism 
 should be carefully cleaned. Reassemble parts in the reversed 
 order. The prism adjusting ring should not be disturbed. 
 
 100. To remove the objective. — ^Take out the telescope tube screw 
 (upper), remove the objective prism holder, take out objective cell 
 retaining screws, and withdraw the objective in its cell. Do not 
 attempt to remove the objective from its cell. Clean the objective 
 and replace. 
 
 101. To remove the eye lens. — ^Take out hood retaining screw, re- 
 move the hood, take off the focusing nut sleeve, take out the three 
 focusing nut retaining screws, then remove the focusing nut; the 
 eye lens and its cell may now be unscrewed. Do not remove the 
 eye lens from its cell. 
 
 102. To disassemble the eyepiece. — Take out reticule adjusting ring 
 screw, remove the reticule adjusting ring, take out eyepiece tube 
 retaining screw, and unscrew the eyepiece. The reticule may now 
 be removed for cleaning Reassemble the parts in the reversed order. 
 
 103. To disassemble the elevation worm mechanism,. — Take out the 
 two eye distance scale screws, remove the eye distance scale, un- 
 screw end bearing lock nut, and remove the elevation worm end 
 bearing and elevation worm washer. By next driving out steel 
 pin the elevation worm knob can be removed and the elevation 
 worm withdrawn. 
 
 OBSERVATION TELESCOPE, FIELD, MODEL OF 1908. 
 (See Pamphlet No. 1796.) 
 
 104. The lenses forming the objective of this telescope are cemented 
 and the objective should not be removed from its cell for cleaning. 
 
 105. To clean the prisms. — ^Remove the cover; but unless after 
 cleaning the exposed surfaces dirt or moisture is seen on the unex- 
 posed surfaces, the holder shoidd not be removed from the cover nor 
 the prisms from the holder. If it is found necessary to clean the un- 
 exposed surfaces, remove the screws which hold the holder to the 
 cover and then pull the holder and cover apart. Then remove a 
 prism-retaining spring and take out one prism. Only one prism 
 need be removed from the holder. The prism should be marked 
 before disassembling, in order that it may be replaced in exactly the 
 same manner. Do not reverse the prism, as it has been adjusted by 
 
41 
 
 the manufacturer and tested for the adjustment in which it is issued 
 to the service. In reassembling, note that the prism holder is located 
 on the cover by two dowel pins. 
 
 TELESCOPIC MUSKET SIGHT, MODEL OF 1908. 
 (See Pamphlet No. 1957.) 
 
 106. As stated in pamphlet No. 1957, the body of this telescope and 
 its objective must remain intact and the prism holder should never 
 be opened except by a competent person. In case moisture collects 
 on the interior optical surfaces, it may be evaporated by imparting 
 a gentle warmth to the telescope. 
 
 107. Removal of prisms. — The prism holder is tightly fitted to the 
 body to prevent the access of dust, moisture, etc., into the interior 
 and is held to the body by five body screws. After removal of these 
 screws the prism holder may be withdrawn from the body. Care- 
 fully clean the polished surfaces of the prisms without removing them 
 from their holder. The prisms should be withdrawTi from their 
 holder for repairs or for adjustment of the telescope by an instrument 
 maker only. Replace the holder so that the prisms are in the same 
 relation to the lenses as before removed. 
 
 108. Removal of lenses. — The objective and cell may be removed for 
 cleaning by unscrewing, the cell being held only by the screw thread 
 on its periphery. The reticule holder is adjusted by special tests by 
 the manufacturer and should not be disturbed. The objective, reti- 
 cule, and eyepiece are crimped in their ceUs and should never be re- 
 moved. 
 
 109. If the objective cell is removed, care should be taken to screw 
 it in tightly when assembling, as in this sight the location of the 
 objective in respect to the reticule is made for a medium range and 
 should not be varied. Aside from the adjustment permitted for 
 focusing the eyepiece, the construction of the telescope admits of no 
 adjustment except by an experienced instrument maker. In case 
 parallax can not be removed for medium ranges the sight should be 
 shipped to an arsenal for overhauling. 
 
 TELESCOPIC MUSKET SIGHT, MODEL OF 1913. 
 (See Pamphlet No. 1957.) 
 
 110. This instrument is identical with the model of 1908, except 
 that the objective is mounted in the objective cell and held in place 
 by the objective retaining nut. 
 
42 
 
 PANORAMIC SIGHT, MODEL OF 1904. 
 (See Plate D herewith, Pamphlet No. 1659, and Drawings 15-2AII-1 to 6, inclusive.) 
 
 111. Sealing of sights. — In all panoramic sights in which the shutter 
 window (5K) is inserted in the eyepiece elbow (6E) and in those 
 sights having the shutter window burnished in the shutter, which 
 have been issued from Frankford Arsenal later than May 1, 1912, all 
 exposed optical elements and machined joints leading to the interior 
 chambers of the sight which contain optical elements, are sealed with 
 litharge cement. No parts of such sights except the worm box 
 mechanism and the movable index cover will be removed except at 
 an arsenal or other establishment equipped for repairing panoramic 
 sights. The parts of the sight which may be removed in the field 
 are specified by pamphlet No. 1659 (Handbook of the 3-inch Field 
 Artillery Materiel). 
 
 112. The optical parts of the panoramic sight should be removed 
 only in case of necessity. This sight is a delicate instrument and is 
 difficult to adjust accurately. In case moisture condenses on the 
 optical parts of unsealed sights it may be evaporated by allowing the 
 sight to stand in a warm, dry room. No part of the sight should be 
 disassembled for which specific directions are not given below, and 
 then only after careful study of the following paragraphs and the 
 pamphlet referred to above. In case the method of reassembhng is 
 not given it should be done in the reversed order to which the parts 
 are disassembled. 
 
 113. To clean the rotating head window (5D). — Unscrew the window 
 ceU in rotating head (2P). Do not remove the window from the cell. 
 
 114. To disassemble the eyepiece. — ^Remove the set screw from the 
 underside of the eyepiece elbow (6E) and unscrew the field lens cell 
 (6N). For cleaning the lenses, remove the set screw (3Z) on underside 
 of field lens cell (6N) and unscrew the eye lens cell (6L). The field 
 lens (5M) is held in place by the field lens retaining spring (6R) 
 both of which may drop out as soon as the eye lens cell is disas- 
 sembled. In reassembhng note that the field lens should be assem- 
 bled with its flat surface toward the reticule (5K). 
 
 115. Disassembling of azimuth circle mechanism. — If it is necessary 
 to disassemble the azimuth circle mechanism, throw out the worm- 
 box eccentric lever (4A), disengaging the worm (4 J) from the worm 
 gear on the azimuth circle (2E). Insert a pin in the radial hole in the 
 spring-box pin for worm box (4B). Throw the eccentric lever (4A) 
 back and engage the worm in the azimuth circle (2E). Push the 
 spring box (411) toward the worm knob (4N) about J inch and then 
 pull the spring box straight out. Take out the stud (3M) from worm- 
 box eccentric lever (4A) and remove the worm-box eccentric lever 
 (4A). ' Pull out the dowel for worm-box pin (4G) with a pair of 
 
43 • 
 
 pliers and drive out the worm-box pin (4F). Then pull out the 
 worm box (4B) and the worm (4J) complete. 
 
 116. To clean the worm (4J) remove the worm knob (4N) and 
 draw the worm (4J) from the worm box (4B). Do not remove the 
 worm index (4E) from the worm (4J), in order not to change the 
 adjustment of the azimuth mechanism. 
 
 117. To disassemble the azimuth circle, etc. — Remove the five radial 
 screws from the hood for azimuth circle (2F) and unscrew it from 
 the azimuth-circle support (5C). Remove the window cell in totat- 
 ing head (2N) if it is not already disassembled. Then lift the hood 
 for azimuth circle (2F) from the sight. 
 
 118. Before removing the azimuth circle (2E), the rotating head 
 (2N), etc., turn those parts until the on the azimuth circle (2E) is 
 opposite the center of the supporting lug on the eyepiece end of the 
 shank. Then pull the azimuth circle (2E) and the rotating head (2N) 
 straight off without rotating the gears by the least amount. Mark 
 the tooth on the large pinion (2LA) which is opposite the nearest 
 corner of the rotating prism (5B) . Then make a mark on the rotating 
 prism holder (4Q) directly opposite the marked tooth of the pinion. 
 Drive out the pinion shaft (2MA) from the underside of the azimuth- 
 circle support (5C). Move the pinions opposite the opening in the 
 azimuth-circle support (5C) and withdraw by inverting the sight. 
 Grasp the rotating prism holder (4Q) and withdraw the rotating 
 prism (5B) and the rotating prism holder (4Q) and the supporting 
 sleeve for rotating prism (5A) from their seat in the shank (5L). 
 
 119. Do not remove the covers for rotating head (2M) and do not 
 disassemble the rotating head (2N) and the azimuth circle (2E) from 
 the azimuth-circle hub and gear (2D) ; also do not remove the rotat- 
 ing prism (5B) from the rotating prism holder (4Q) nor the rotating 
 prism holder (4Q) from the supporting sleeve for rotating prism (5A). 
 Also do not disturb the adjustment of the lower reflecting prism (5J). 
 These parts may be disassembled only by an expert instrument 
 maker with proper facilities for readjusting, etc. 
 
 120. Cleaning and oiling. — Carefully clean all gears and exposed 
 surfaces of metal parts. Benzine may be used in cleaning the worm 
 and gear teeth. Apply it with a toothbrush or similar brush. After 
 thoroughly cleaning, put a little vaseline on the worm and gear teeth 
 and a little clock oil on the inside circiunferential and lower surfaces 
 of the azimuth circle (2E) and the' outside surface of the supporting 
 sleeve for rotating prism (5A). Two drops of clock oil on each of 
 the parts is sufficient for proper lubrication. Never use emery cloth, 
 crocus cloth, or any abrasive on any part of the panoramic sight. 
 Be careful not to allow any oil to drop on the glass surfaces. Leave 
 no free oil to run down onto glass surfaces after reassembling. 
 
44 
 
 121. Clean the exposed surfaces of the rotating head prism (5E) 
 and the rotating prism (5B). Use a soft cloth free from lint on a 
 stick to reach such surfaces as can not be otherwise reached for 
 cleaning. After carefully wiping the optical surfaces, brush them 
 with a camel hair brush. Do not in any manner change the adjust- 
 ment of these prisms. 
 
 122. In reassemhling, insert the rotating prism holder (4Q) and the 
 parts assembled thereto and bring the mark made on the rotating 
 prism holder (4Q) opposite the pinion shaft (2MA) seat. Insert the 
 pinions for rotating prism (2LA) and rotating head (2N) through 
 the opening in the azimuth-circle support (5C) and engage the teeth 
 of pinion and gear so that the mark made on a tooth of the pinion 
 comes opposite the mark made on the holder. Insert the pinion 
 shaft (2MA). Place the azimuth circle (2E) and the attached parts 
 over the azimuth-circle support (5C) without engaging any teeth, and 
 rotate the azimuth circle (2E) so that the of scale comes opposite 
 the supporting lug on the front face of the shank (5L). Then drop 
 the azimuth circle (2E) in place and reassemble other parts. 
 
 123. To remove the objective lens (5H). — Special tools not furnished 
 with sights are required. For this purpose take out the four radial 
 screws in the lower part of the shank (5L). First note whether 
 opposing marks are on the upper surface of the eyepiece elbow (6E) 
 and the lower surface of the shank. If not, scratch a light mark on 
 these two surfaces, in order that the parts may be reassembled in 
 exactly the same position as originally adjusted. Then put the eye- 
 piece elbow (6E) in a vise. Use spanner wrench and block No. 34 
 (furnished with tools and fixtures for optical repair work) and unscrew 
 the elbow from the shank (5L). Remove the set screw in the upper 
 end of the eyepiece elbow (6E). Use spanner wrench No. 32 and 
 unscrew the objective lens cell (6A). Do not remove the lens from 
 its cell. 
 
 124. To disassemble the reticule (5K). — Remove the two screws in 
 the adjusting block for reticule cell (6H) and gently shake out the 
 reticule cell (6G). The reticule should not be disturbed in its cell. 
 In cleaning the reticule (6G), use cloth as free as possible from lint. 
 After cleaning it, examine its surface with a magnifier (the eyepiece 
 may be used for this purpose), and if not perfectly clean reclean it. 
 Use a camel hair brush for wiping off dust and lint. This special 
 precaution is necessary, as the reticule is in the focal plane of the 
 eyepiece and any dust thereon wiU be magnified. 
 
 125. Lower reflecting prism. — With the objective lens cell (6 A) and 
 the reticule cell (6H) removed, the lower reflecting prism (5J) may 
 be cleaned. For this purpose remove also the eyepiece elbow covers 
 (6B) and clean the back surfaces as well as the faces of this prism. 
 In this connection note paragraphs 119 and 121 above. 
 
45 
 
 126. Adjustment of reticule. — When reassembling the reticule cell 
 (6G), insert the adjustable block for reticule cell (6H), but do not 
 tighten the screws. After all other parts of the sight are assembled 
 adjust the reticule ceU (6G) so that the vertical line is parallel to a 
 plumb line. The reticule ceU (6G) and the adjustable block for 
 reticule cell (6H) may be slightly rotated for this purpose. Also 
 adjust the reticule cell (6G) by translating it longitudinally until it 
 is in the focal plane of the eyepiece and there is no parallax when 
 observing objects at least 1 mile distant. To secure this adjustment, 
 the objective lens cell (6 A) must have been replaced in exactly the 
 same position as before disassembling. In order that the field may 
 be vertical, the eyepiece elbow (6E) must be screwed up so that the 
 marks on it and the shank (5L) come opposite each other and the 
 eyepiece elbow (6E) is entered by the same number of threads. 
 Great care must be taken in reassembling the sight. 
 
 127. If the field is not vertical, either the rotating prism (5B) has 
 been wrongly assembled or the eyepiece elbow (6E) has not been prop- 
 erly screwed up. If parallax can not be removed, either the objective 
 lens cell (6A) or the field lens cell (6N) or the reticule cell (6G) has 
 been incorrectly assembled. For adjusting the reticule cell (6G) the 
 panoramic sight may be mounted in its seat on the rear sight or it 
 may be mounted in vertical fixture No. 89 (furnished with tools and 
 fixtures for optical repair work). Fixture No. 89 is used on round 
 surface plate No. 88, which should be centered and leveled on pedestal 
 No. 85. 
 
 128. Adjustment of azimuth circle. — Ordinarily the azimuth circle 
 (2E) will be set with the panoramic sight in its seat on the rear 
 sight as described in pamphlet No. 1659. It will be corrected 
 for errors in the rear sight or its support. It may, however, be ad- 
 justed independently of the rear sight as follows: Mount hori- 
 zontal fixture No. 86 in pedestal No. 85 and carefuUy level. Screw 
 guide for coUimating telescope No. 90 in horizontal fixture No. 86 
 and align collimating telescope No. 90 on a plumb line. Clamp the 
 fixture in place, remove the collimating telescope and guides, and 
 secure the panoramic sight shank clamp to the horizontal fix:ture. 
 Set panoramic sight at the azimuth of 48 and insert it in the seat 
 prepared for it on the horizontal fixture, turn the worm knob (4N), 
 and align the line on the reticule with a plumb line without changing 
 the setting of the fixture. Then adjust the azimuth circle to read 
 48 when the line on the reticule (5K) coincides with a plumb line. 
 For adjusting the azimuth circle, note that the movable index cover 
 (2UA) may be moved and that the worm index (4E) on the worm 
 (4 J) may be adjusted. 
 
 129. The azimuth circle of a panoramic sight must be adjusted 
 for a particular gun and for a particular rear sight. The adjustment 
 
46 
 
 of the worm index (4E), the movable index cover (2UA), and the 
 worm (4J), as made by the manufacturer of the panoramic sight, 
 will probably not be found correct for a particular gun. It is intended 
 that the final adjustment of the azimuth circle (2E) of a panoramic 
 sight be made by the battery commander by making the line of sight 
 of the panoramic sight parallel to the axis of the bore of the gun 
 and setting the scales accordingly. 
 
 130.* Special notes on adjusting panoramic sights. — The larger rec~ 
 tangular surface of the rotating prism is polished and is known as the 
 ''base." 
 
 To adjust the rotating prism in its holder, put shank with elbow 
 and eyepiece assembled in horizontal fixture No. 86 with eyepiece up. 
 Direct telescope at a plumb hne. Insert the rotating prism wrapped 
 with paper as described below into the holder and the holder into the 
 supporting sleeve for rotating prism and assemble them in the shank 
 without the gearing. Turn the prism so that the end surfaces lie in 
 vertical planes and a plumb line appears parallel to the vertical line 
 of the reticule. Move the fixture if necessary to make the image of 
 the plumb line coincide with the vertical line of reticule. Then turn 
 the rotating prism 180° until plumb line again appears parallel to the 
 vertical line of the reticule. Correct half the error of deviation of the 
 vertical" line on the reticule from a plumb line by slightly fihng off and 
 slightly bending over the supporting walls of the upper and lower 
 ends of the prism holders. Note that if the upper surface is bent 
 toward the axis of the holder the lower surface on the same side of 
 holder should be filed by an equal amount, as the prism should be 
 rotated on one of its shorter axes. The filing or bending of holder 
 should be only on the surface prepared for the base of the prism and 
 the opposite surface. Do not touch the other two surfaces of the 
 prism holder. The amount of metal to be taken off will be only a few 
 thousandths of an inch. Then rotate the fixture to again bring the 
 vertical line of the reticule on the plumb line and repeat the test. 
 Before assembling the prism in its holder for test or final adjustment 
 partially wrap the prism with a sheet of dull black paper 0.005 inch 
 thick of the length of the bearing surface of the holder. For this 
 purpose turn back one edge of the paper ^ inch against the polished 
 surface of the base, then wrap the paper over the three unpolished 
 surfaces and turn it over the other edge of the base and cut so that 
 it extends -^ inch beyond the edge of the base. After final adjust- 
 ment of rotating prism insert the set screw in prism holder. Note that 
 the set screw should not bottom in the notch in the rotating prism. 
 
 131.* In adjusting the prisms of this sight the following intruc- 
 tions should be followed : It is assumed that the lenses and mountings, 
 the rotatingiprism, the pinions and pinion shaft, the azimuth circle,. 
 
 * See paragraph 11. 
 
47 
 
 and the rotating head are assembled. Use vertical fixture No. 89 on 
 pedestal No. 85, with round surface plate No. 88. Carefully level 
 and place the panoramic sight in the socket of vertical fixture No. 89. 
 Now look through the eyepiece. If the field of view seems to incline 
 either to the right or left, it will be necessary to remove the rotating 
 head and the azimuth circle and change the relation of the prism to 
 the larger gears. This change is made by removing the pinion shaft 
 and turning the pinion until those teeth are in mesh, which bring 
 the field of view into a vertical position. This operation usually 
 requires much care and time. If it be found after long trial that one 
 position of the teeth gives better results than any other position, but 
 that the results are not yet satisfactory as to verticality of the field,, 
 it wiU then be necessary, having determined this best position of the 
 teeth, to make the ultimate adjustment for verticality of the field 
 on the rotating prism and rotating prism holder. To do this, unscrew 
 the rotating prism holder screw, securing the rotating prism holder 
 to the supporting sleeve for rotating prism. The rotating prism 
 holder with rotating prism may then be revolved in the supporting 
 sleeve by hand until the field assumes the correct vertical position. 
 Having obtained the position, clamp the rotating prism holder and 
 the supporting sleeve carefully together and driU and tap a new hole 
 for the set screw. The field adjustment should now be satisfactory. 
 The pinion and gear teeth which are in mesh to give verticality of 
 field should be spot marked for future adjustment. These marks, 
 are readily recognized by any machinist or instrument maker and 
 no difficulty should be experienced in at once bringing the field into 
 proper adjustment. Also note that the portion of the above descrip- 
 tion relating to the removal of the set screw securing rotating prism 
 holder and supporting sleeve together is intended to be applied only in 
 extreme cases, when from violent accident great injury to the parts 
 of the panoramic sight has been produced. In such cases the adjust- 
 ment must, of course, proceed on the same lines as if the parts had 
 never been assembled together. In the general case, however, na 
 need will be found for removing the set screw and redriUing. It 
 may occasionally be necessary to loosen the set screw slightly, and 
 then push, by the merest hair the rotating prism holder in one direc- 
 tion or the other, again tightening the screw. But caution is enjoined 
 for any such operation. 
 
 132.* Replace rotating head, azimuth circle, etc. The sight still 
 mounted in the vertical fixture is then directed toward a target at 
 the same height as the center of the window ceU. Such a target 
 should be laid out carefully, using an accurate transit or Y leveL 
 Now look through the eyepiece of the panoramic sight. The hori- 
 zontal line of the reticule from end to end should appear at the same 
 
 ♦See paragraph 11. 
 
4M 
 
 height as the fixed target selected. If the cross line appears above 
 or below the target, correction should be made on the lower reflecting 
 prism and not on the reticule. The necessary correction shoidd be 
 made by fihng carefnUy the brass bearings of the seat for the lower 
 reflecting prism in such a way as to make the prism lean forward or 
 backward, as the case may be, an amount sufl3.cient to correct for 
 the full error. This operation is extremely dehcate, and the fihng or 
 scraping should be proceeded with most carefully. The bearing 
 surfaces of the prism seat must be cut away to produce a change in 
 the position of the prism from front to rear, or the reverse only, 
 but lateral tilting produced by leaving the seat higher on one side 
 than the other must be avoided. 
 
 PANORAMIC SIGHT, MODEL OF 1915. 
 (See Plate K herewith, Pamphlet No. 1659, and Drawings 15-15G-1 to 10, inclusive.) 
 
 133. The optical parts of the panoramic sight should be removed 
 only in case of necessity and then by order of an officer of the Ord- 
 nance Department. All the joints are sealed when they leave the 
 manufacturer and any disassembhng wiU break this seal and allow 
 dust and moisture to enter. In case moisture condenses on the 
 optical parts of unsealed sights, it may be evaporated by allowing 
 the sight to stand in a warm, dry room. This sight is a dehcate 
 instrument and is difficult to adjust accurately. Reassembling 
 should be done in the reversed order to which the parts were disas- 
 sembled. 
 
 134. To disdssemhle the eyepiece. — Take out the eye lens ceU retain- 
 ing screw, remove the eye lens cell and reticule cell. To clear the 
 lenses, take out the reticule cell rietaining screw, unscrew reticule 
 cell in which the reticule is permanently fastened, take out field lens 
 retaining ring screw and unscrew the field lens retaining ring which 
 permits the field lens and eye lens to be removed. In reassembhng 
 note that the eye lens and field lens be assembled with their curved 
 surfaces toward each other. 
 
 135. To disassemble the rotating head mechanism with the elevation 
 device from the instrument. — Remove the four azimuth scale retain- 
 ing ring screws and unscrew the rotating head from the upper end 
 of the azimuth worm wheel. The azimuth scale with azimuth scale 
 retaining ring can now be removed. To disassemble the elevation 
 device, loosen the locking screw, remove the elevation worm microme- 
 ter head, loosen the elevation worm retaining nut screw, and then 
 remove the elevation worm retaining nut. The elevation worm can 
 now be removed by turning. To unscrew the rotating head cover, 
 remove the rotating head cover screw. Remove the prism holder 
 cover screw and unscrew the prism holder screw. Remove the two 
 elevation index retaining screws and then elevation index can be 
 
49 
 
 lifted from the elevation index support. Remove the support 
 retaining ring screw and unscrew the support retaining ring. Remove 
 the elevation index support screw and unscrew the elevation index 
 support. Drive out the segment lock pin and the elevation segment 
 will drop from its seat to the interior of the head. Unscrew the 
 rotating head prism holder stop screw and then withdraw the rotating 
 head prism holder. The elevation segment can now be removed by 
 using the fingers. To remove the elevation worm bushing loosen the 
 bushing clamp plug screw which releases the elevation worm bushing 
 clamp plug. Remove the rotating head spring which releases the 
 prism support back, and then remove the rotating head prism. The 
 prism shield can be removed by unscrewing the two prism shield 
 retaining piece screws and removing the prism shield retaining piece. 
 
 136. To disassemble the azimuth mechanism. — Loosen the locking 
 screw, remove the azimuth micrometer, drive out the taper pin from 
 the worm knob, unscrew the worm knob and remove the lever spring, 
 take out azimuth worm lever screw and remove the azimuth worm 
 lever. The azimuth worm may now be withdrawn by turning and 
 the azimuth worm bushing and bushing spring can now be removed. 
 Remove the three deflection worm wheel and support ring screws, 
 then unscrew and dismount the azimuth worm wheel cover. Re- 
 move the azimuth worm wheel support spring and azimuth worm 
 wheel. Disassemble the azimuth worm wheel support with interior 
 mechanism. Drive out the pinion shaft which will allow the rotating 
 head pinion to slide into the slot in the azimuth worm wheel support 
 in such a manner that the rotating prism supporting sleeve with 
 rotating holder can be removed. The rotating prism pinion with 
 rotating head pinion can now be removed. Do not remove the 
 rotating prism from the rotating prism holder. 
 
 137. To disassemble the deflection mechanism. — Remove the de- 
 flection dial by loosening the locking screw, drive out the taper pin 
 from the worm knob, unscrew the worm knob from the end of the 
 deflection worm; the compensating spring can now be removed. 
 The deflection worm can be withdrawn by turning. Remove the 
 two deflection worm wheel support screws which release the deflection 
 worm-wheel support, remove the deflection worm-wheel and sup- 
 porting ring and deflection worm-wheel support from the upper end 
 of the shank, loosen the deflection worm bushing clamp plug screw 
 which releases the deflection worm bushing ^lamp plug, and re- 
 move the deflection worm bushing. 
 
 138. To remove the objective lens. — Take out four elbow retaining 
 screws, unscrew the elbow from the shank, take out two objective 
 ceU retaining screws, and unscrew the objective lens cell. Do not 
 attempt to remove the lens from its cell. With the objective lens 
 
 9950—17 i 
 
50 
 
 cell and the eyepiece removed, the lower reflecting prism may be 
 cleaned. For this purpose the elbow covers should be removed and 
 the back surfaces as well as the faces of this prism should be cleaned. 
 
 WELDON RANGE FINDERS. 
 (See Pamphlet No. 1908 and Drawing 22-1-41.) 
 
 139. In the Weldon range finder, accurately ground and polished 
 prisms are held in a metal frame. The prisms should not be removed 
 for any purpose, and care should be taken not to disturb them in their 
 mounting, as with the range finder rigidly held vertical the prisms 
 are so located by optical tests as not to displace the image from the 
 horizontal plane of the object. In case adjustment of prisms is 
 required, it should be done only by an experienced workman with 
 a complete set of working fixtures and tools. 
 
 140. In order to secure the maximum intensity of illumination, the 
 refracting surfaces should be kept clean and free from moisture, 
 finger prints, etc. The silvered surface of a prism requires no atten- 
 tion. In case after careful cleaning the image is poorly illuminated, 
 the range finder should be sent to an arsenal for resilvering the prisms 
 or for other repairs. 
 
 141.* Methods of assembling prisms. — The Weldon range finders at 
 present in the service have been obtained from various sources and at 
 different times, and they differ sUghtly in dimensions, means of 
 securing prisms, and in other minor p)oints. There have been used 
 three general methods of securing prisms in place: 
 
 (a) By cement. 
 
 (6) By pins or plugs let into the prisms. 
 
 (c) By clips bent over edges of the prisms when their presence does 
 not affect the field of view. 
 
 (a) Where cement has been used, as for instance, either sodium 
 silicate or sealing wax, immersing the range finder complete in cold 
 water and gradually raising the temperature to the boiling point will 
 ultimately loosen the cement and allow removal of the prism. The 
 time required by this process depends upon the quality and condi- 
 tion of the cement used. Frequently an hour or more is required to 
 loosen the prisms. 
 
 (b) Where pins or screws have been let into the prisms, cement 
 may also have been used to aid in securing these. When screws have 
 been used it will frequently be found that the screw head has been 
 filed away. It will, therefore, be necessary in this case to make a 
 new slot in the remaining part of the screw. Then loosen all cement 
 as above described and, using a small screw driver, turn the screw 
 out. This sometimes proves to be a very difficult operation. 
 
 ♦ See paragraph 11. 
 
51 
 
 (c) Where clips are used the screws seeming the lower clips should 
 be removed. The prisms may then be removed from their seats 
 without trouble. The upper clips, soldered to the projecting rings, 
 need not be removed. 
 
 142. No special tools, other than small screw drivers, pinchers, etc., 
 are needed. The prisms should be handled carefully and inserted 
 and removed by the fingers, except in extreme cases, when a wooden 
 wedge or stick, carefully used, may be needed to remove tightly fitted 
 prisms. 
 
 143. The latest method adopted for securing prisms in the Weldon 
 range finder is by clips and is shown in the plate. This method is 
 believed superior to any other yet devised and is simple in application. 
 Cement is no longer used, as it is liable to deterioration, with loss of 
 prism. 
 
 144.* Having removed the prisms from the case for resilvering or 
 other repair, to reassemble, proceed as follows: Prepare the prism 
 seat so that it will receive the prism snugly. Three small steel 
 blocks, cut accurately to the dimensions of the prism, should be 
 prepared. These small steel blocks are used in adjusting the clips, 
 as they will sustain the pressure required in bending or otherwise 
 fitting the chps, whereas the prisms would crack or chip under this 
 pressure. The upper clips shown on the plate are fu^t soldered to the 
 case. They should then be bent over the steel blocks to give a snug fit. 
 The lower chps shown are secured by screws after the upper clips 
 have been adjusted and the prisms seated. A thin piece of paper 
 under each prism will be found useful as a buffer for the silvered face 
 in fitting the prism securely in its seat. 
 
 By a snug fit is meant a fit so close that any looseness or shaking 
 is prevented, and yet not so close that undue pressure is brought to 
 bear on the prism by the chps. If undue pressure is brought to bear 
 on the prism, the effect will be to warp the transmitted rays slightly 
 and thus shghtly blur the target seen through the prism. 
 
 145.* The tolerance permitted in the angles of prisms for Weldon 
 range finders is ± three minutes measured as the error of the angle 
 through which a ray is deflected from the specified angle. By careful 
 grouping of such prisms, range finders are made in which the range 
 error for either the first two prisms grouped together, or the last two 
 grouped, does not exceed ± 1 per cent of the range. In testing and 
 adjusting, a prism must be held or located so as not to displace the 
 image from the horizontal plane of the object. 
 
 xllthough of apparently simple construction great care is required 
 in the testing and adjusting of prisms of this range finder. If prisms 
 are removed for resilvering or other repairs, a fixture should be pro- 
 vided to hold the range finder vertically, and a telescope should bo 
 
 * See paragraph 11. 
 
52 
 
 used in locating the prisms. Each prism should be so adjusted that 
 for the range finder held vertically the object and image are in the 
 same horizontal plane. Care should be taken not to mix the prisms 
 originally assembled in a given range finder, as they are not inter- 
 changeable with similar prisms from other range finders. 
 
 FIELD ARTILLERY RANGE FINDER, 1-METER BASE. 
 
 (See pamphlet No. 1796.) 
 
 146. Under no circumstances shall this instrument be disassembled 
 or adjusted except by the manufacturer or by an arsenal especially 
 equipped for instrument work. 
 
 AIMING CIRCLE, MODEL OF 1916. 
 (See Plate L herewith, Pamphlet No. 1796 and Drawings 22-41-1 to 7, inclusive.) 
 
 147. The optical parts of the aiming circle should not be removed 
 unless it is absolutely necessary. When the instrument leaves the 
 manufacturer all the joints are sealed, and the breaking of this seal 
 allows dust and moisture to enter. In case disassembling is neces- 
 sary, reassembling should be done in the reversed order. 
 
 148. To disassemble the eyepiece. — Take out the eyepiece retaining 
 screw, unscrew the eyepiece, which carries with it when assembled 
 the eye lens, the field lens, and the reticule. Unscrew the reticule 
 cell but do not disturb the reticule. Unscrew the eyepiece cell 
 which contains the eye lens and the field lens. To remove the lenses 
 from the cell, unscrew the lens nut, remove the field lens, take out 
 the lens separator, and remove the eye lens. 
 
 149. To dean the elbow prism and erecting prism. — Take out the 
 elbow cover retaining screw, unscrew the elbow cover, take out the 
 two erecting prism holder screws, and withdraw the erecting prism 
 holder. Care should be taken not to disturb the prisms when 
 cleaning. 
 
 150. To clean the objective prism or the objective. — ^The telescope 
 must be dismantled. 
 
 151. To disassemble the elevation mechanism. — Drive out taper pin 
 from worm knob, remove worm knob and take out bearing cap 
 retaining screw, unscrew bearing cap, and withdraw elevation worm 
 by turning. This allows the telescope elbow to be removed after 
 the five objective prism housing screws have been unscrewed. Take 
 out the six shutter guide screws, slide the shutter guides with the 
 shutter to the left-hand side and take out five objective prism hous- 
 ing screws; withdraw the angle of site mechanism which allows the 
 objective prism housing to be removed. Do not attempt to remove 
 the prism from the housing. 
 
53 
 
 152. To remove the objective. — Unscrew the objective lens cell nut. 
 Scratch a line on the eccentric washer and objective lens ceU before 
 removing them. Do not remove the objective from its cell. 
 
 153. To disassemhle the angle of site mechanism. — Loosen angle of 
 site dial locking screw, drive out taper pin from worm knob, remove 
 worm knob and take out bearing cap retaining screw, unscrew bear- 
 ing cap, and withdraw the angle of site worm by turning. Take out 
 the three level vial holder screws, remove the level vial holder, take 
 out the three worm wheel holding disk screws, and remove the worm 
 wheel holding disk and angle of site worm wheel. 
 
 154. To disassemhle the azimuth worm mechanism. — Loosen the azi- 
 muth worm knob locking screw and remove the azimuth worm knob 
 and the lever spring; take out the azimuth worm lever screw and 
 remove the azimuth worm lever. The azimuth worm may now be 
 withdrawn by turning, then remove the azimuth worm bushing and 
 bushing spring. 
 
 155. To disassemhle the compass inechanism. — Unscrew the cover 
 ring and hft the glass cover with parts assembled thereto from the 
 instrument. Take out the three level housing screws and remove 
 the level housing. Take out the three needle release guide plate 
 screws and remove the needle release guide plate (lower), unscrew 
 the needle release button and remove the spring. The needle release 
 guide plate (upper) and the needle release guide plate (lower) may 
 now be separated and removed from the glass cover. Do not attempt 
 to disassemble the level unless the fluid has leaked out to such an 
 extent as to require refilling. 
 
 156. To remove the compass needle from the needle release guide 
 plate (lower). — L^nscrew the needle release collar. 
 
 SEXTANT TELEMETER, MODEL OF 1911, TYPE A. 
 
 (See pamphlet No. 1796.) 
 
 (See Plate I.) 
 
 157. To disassemhle the worm. — If for any purpose it is necessary to 
 remove the worm, rotate the worm until the worm wheel is brought 
 up to the stop plunger, draw back the stop plunger, and continue 
 rotation of the worm wheel until it and the movable mirror are clear 
 of the worm box. Then unscrew the four worm-box cap screws and 
 draw out the worm-box cap with worm, etc. To disassemble, loosen 
 the worm locking screw, unscrew the retaining nut, using teat wrench 
 No. 105, and draw off the micrometer head and worm box cap. To 
 remove the worm from the worm box, first remove the worm plunger 
 screw and then the worm plunger and worm plunger spring. Then 
 push the worm and worm bearing out of the worm box, applying slight 
 pressure on the end from which the micrometer was removed, clean. 
 
54 
 
 lightly oil with clock oil all bearing surfaces, except the worm teeth, 
 which should be lightly coated with vaseline. Reassemble in the 
 reversed order. Take special care that no dirt or grit remaias en 
 any bearing surface. Adjust the retaining nut to remove all longi- 
 tudinal play and readjust the niicrometer scale of the micrometer. 
 
 158. To disassemble tlie cover. — Remove the two fixed mirror-holder 
 screws holding the fixed mirror holder to the cover. Rotate the worm 
 imtU the clinometer scale registers 6, draw back the stop plunger and 
 continue rotation of the worm wheel a few revolutions in the same 
 direction. Remove the optical square body from its seat in the 
 cover. Move the pendulum until its toe is about } inch from the 
 post opposite the pendulum lock. Unscrew the four cover screws 
 and lift the cover. Revolve the worm wheel until disengaged 
 from the worm and remove worm wheel and pendulum assembled. 
 Then slip the pendulum arms over the worm wheel and remove the 
 index dial. 
 
 1 59. To disassemble the pendulum. — Bend the pendulum arm inward 
 to release the spring lock and push the arm through the undercut 
 groove of pendulum weight. After removal of both arms the pen- 
 dulum prism and prism spring may be pushed from their seat. To 
 remove the pendulum lens cell, take out the pendulum lens screw and 
 unscrew the cell. As all its joints are sealed with litharge cement 
 the pendulimi weight should be disassembled only when repairs are 
 required. 
 
 160.* Notes on adjustment. — The pendulum lens is adjusted so that 
 its focal plane lies in the exposed surface of the pendulum prism on 
 which is etched a reference line. The telescope, which is focused for 
 an object about a mile distant, is placed in the axes of the pendulum 
 lens and the lens cell is screwed in or out until the reference line on 
 the prism is seen sharply defined by the telescope. This position is 
 noted and a ring is made to fit* between the upper surface of the pen- 
 dulum weight and the flange of eye lens cell. A set screw is also 
 inserted in the cell. In final assembling all exposed joints of the 
 parts are lightly coated with htharge cement for sealing. 
 
 Before assembling in the instrument the pendulum is suspended 
 by its arms and the position of the balancing screw in the pendulum 
 weight is adjusted until the front face of the pendulum is inchned 
 11° 15' from the plumb. 
 
 161.* A coating of htharge cement is placed on the back of the 
 movable mirror after silvering. The mirror is then placed in the 
 movable mirror holder and the ends of the holder are burnished over 
 the mirror. The mirror and the holder are assembled in the worm 
 wheel and secured by burnishing the worm wheel lightly over the 
 sides of the mirror. In this operation care must be taken not to 
 
 * See paragraph 11. 
 
strain the mirror, otherwise the definition of the optical system will 
 be impaired. The space between the mirror holder and the worm 
 wheel is then filled with a mixture of litharge cement, whiting, and 
 lamp black mixed to the consistency of soft putty. 
 
 162.* After the optical systems are assembled the telemeter is 
 placed on a plane horizontal surface, cover up, the movable mirror 
 is set for vertical coincidence of the images formed by direct and 
 reflected pencils, and the fixed mirror holder is rocked on a hori- 
 zontal axis by means of the four fixed mirror screws which enter 
 the frame and the two fixed mirror adjusting screws which bear 
 against the frame imtil horizontal lines of the two images are coinci- 
 dent. Either the upper or the lower bearing surface of the mirror 
 holder should be in contact throughout its length with the fixed 
 mirror seat of the frame. The index is then adjusted so that while 
 the two images of objects about a mile distant are in coincidence, the 
 reference line on the index is opposite the graduation of the index 
 dial. The micrometer scale is then set to register 0. The telemeter 
 is then placed on end on a horizontal surface with the microm- 
 eter above, the movable mirror is rotated to register 3 centitoes 
 elevation, and the telescope is directed on a target at any distance 
 in the same horizontal plane as the axis of the telescope. The pen- 
 dulum is then released by throwing the pendulum lock, and the 
 adjusting screw in the pendulum weight is adjusted so that the 
 image of the reference line is superposed upon the image of a hori- 
 zontal line i mil above the target. The telemeter is then disas- 
 sembled, a dowel pin is added to hold the index in its proper place, 
 and a hole is drilled and a pin driven through the adjusting screw 
 and pendulum weight. The allowance made in the adjustment of 
 the pendulum weight compensates for the loss of weight resulting 
 from the insertion of the pin. The telemeter is then, reassembled for 
 final adjustment of the fixed mirror for coincidence of horizontal 
 lines and for the setting of the scale at when the images formed by 
 the direct and the reflected pencils from distant objects are coincident. 
 
 163. In subsequent adjustments after repairs the fixed mirror may 
 be rotated on its vertical axis to bring the images of a distant object 
 into coincidence when the index registers on the index dial. After 
 setting the fixed mirror the final adjustment for coincidence of vertical 
 lines of images is made by rotating the movable mirror for coincidence 
 of images and then adjusting the micrometer scale to register 0. In 
 this case a rebalancing of the pendulum will be required. The 
 accuracy of both the telemeter and the clinometer systems are tested 
 by comparisons with graduated circles. 
 
 * See paragraph 11. 
 
56 
 GEARED INSTRUMENTS (Group b). 
 
 164. Gearing. — Loss of adjustment and lack of accuracy due to 
 gearing is ordinarily made apparent by what is known as backlash, 
 lost motion, or looseness. This looseness develops either from the 
 actual wear of the parts which mesh together or from the loss of posi- 
 tion and looseness of surrounding parts, which should keep the gears 
 in close contact. Thus, taking the range quadrant and rear sight of 
 the 8-inch field materiel as examples, the pinions, quadrant-arm 
 racks, and scroll gear, worms, etc., are from the very nature of their 
 service subjected not only to constant wear, but to constant wear 
 under the severest conditions of weather, dust, grit, etc. The close 
 mesh and fit of these parts will deteriorate, and this deterioration 
 sometimes proceeds very rapidly. When possible, if new parts are 
 not available and the demands of the service prevent the return of 
 the part affected for repair, a thin washer, an added bushing, or otheif 
 similar slight repair wiU tide over the difficulty. But when th6 
 looseness developed is so great as to destroy the value of the instru- 
 ment, new gears, worms, etc., must be cut, and the parts refitted 
 and adjusted. For service in the field it should be remembered that 
 instruments issued from the Frankford Arsenal have corresponding 
 parts of the same model interchangeable. Thus a good part of one 
 otherwise unserviceable instrument may be taken and used for 
 another instrument, when such exchange is necessary. Rear-sight 
 brackets, shank sockets, shank, etc., may thus be interchanged. 
 
 165. Where the looseness has developed from the loss of position 
 of surrounding parts which should keep the gears in close contact, 
 as, for instance, in the case of the gun azimuth subdial mechanism 
 in the Whistler-Hearn plotting board, the dial box in which the 
 mechanism is housed should be moved closer up to the movable limb 
 and resecured by the screws provided. If backlash exceeding 0.03° 
 is still found, the gears themselves or their bearings should be exam- 
 ined for dust or dirt. Careful cleaning of such parts will frequently 
 remove a cause of error in the readings obtained. The worm stand 
 of plotting boards may be similarly adjusted. 
 
 166. On those instruments in which a worm and worm gear are 
 employed to obtain rotation in horizontal or vertical planes, adjust- 
 ments are provided to remove longitudinal play between the worm 
 and worm bearing and to remove backlash between the worm and 
 worm gear. To remove longitudinal play, turn up the screw or nut 
 on the end of the worm until there is no longitudinal shake of the 
 worm, but the worm should revolve freely when disengaged from the 
 worm gear. The worm is ordinarily held in mesh with the gear by a 
 flat spring. The pressure of the worm on the gear is regulated by 
 an adjusting screw. This adjusting screw should be set at the critical 
 
57 
 
 position at which there is no backlash between worm and gear and 
 the pressure of the worm against the spindle is a minimum for no 
 backlash. 
 
 167. Care should be taken to keep the gears of instruments clean 
 and lightly oiled. The cutting of worms and gear sufficiently accurate 
 for instrument use is a difficult machine operation, and the accuracy 
 of such parts can be preserved only by careful handling, cleaning, 
 and adjusting these parts in service. 
 
 168. Test of levels. — Levels furnished with instruments are ordi- 
 narily adjustable, although the open sights and range quadrants for 
 mobile artillery and the mortar quadrants contain nonadjustable 
 levels, which are rigidly held in a metal casing or tube and are accu- 
 rately adjusted and tested by the manufacturer and do not require 
 adjustment by the service. Adjustable levels are of two types — one 
 adjusted by exposed adjusting screws as the levels on the base of an 
 azimuth instrument or of a battery commander's telescope; the other 
 adjusted by internal screws, to reach which a cap must be removed 
 from the level box, as in the case of the cross level on the range quad- 
 rant and the elevation level on the rear sight for 3-inch field materiel. 
 Both types of adjustable levels are accurately adjusted and tested by 
 the manufacturer, but these levels are designed for and will require 
 adjustment by the service. 
 
 169. In case of breakage or looseness of level vials belonging to 
 instruments, the metal case surrounding the level vial must be 
 opened, and in case of a broken vial the broken parts and old packing 
 must be removed. A level of the same degree of sensitiveness as 
 that originally in the instrument should be obtained. The level 
 vial mixture should be specified as 60 per cent alcohol and 40 per 
 cent ether. Levels differ in sensitiveness, depending upon the accu- 
 racy demanded in the instruments with which they are used. Thus 
 the large striding level for the Swasey depression position finders 
 shows a movement of the bubble of -^ inch for a variation in level 
 of 15 seconds of arc; the level for the gunner's quadrant shows a 
 movement of the bubble of y? inch for a variation in level of 5 minutes 
 of arc; the Weldon range-finder level is simply a general leveling 
 device for an instrument held in the hand, subject to constant vibra- 
 tion, and hence is not sensitive; any good commercial vial of the size 
 needed, not specially ground, but in which the highest point for 
 bubbles is easily determined and symmetrically placed, will do for 
 this use. Levels in which the ^^^-inch graduation is to show a 
 certain variation in minutes or seconds of arc must have the interior 
 surface of the vial specially ground to the correct radius of curvature 
 Such levels before acceptance should be tested on a regular level-test- 
 ing machine. If one of them is not available, a Y block properly 
 mounted to receive the level, terminating in standards which can h( 
 
58 
 
 raised or lowered definite amounts by screw action, and from which, 
 knowing the pitch of the screw, etc., the angle to which the Y block 
 is tilted ma}' be determined, can be used in ascertaining the move- 
 ment of level bubbles corresponding to a certain angular displace- 
 ment. Levels must be ground so that the movement of the bubble 
 over the length of the graduations on the vial is uniform. 
 
 170. Adjustment of levels. — Having tested the level vial for sensi- 
 tiveness and uniformity, place paper or cotton packing in the bottom 
 of the metal level holder, so that the level will fit snugly. Care must 
 be taken not to pack the level too tightly, as a very tightly packed 
 level vial, exposed to extreme variations of temperature, will probably 
 crack. On the other" hand, when the level is not packed sufficiently, 
 it will readily change in position and thus not remain true. Having 
 determined the proper amount of packing, by inserting and removing 
 the level frequently until the right fit is found, pack the ends of the 
 level to prevent longitudinal motion in the case, using cotton or a 
 slight amount of plaster of paris (dental plaster which will set in 
 from 5 to 10 minutes), then screw on the level holder end caps or top, 
 as the case may be. As an example illustrating the principles of level 
 adjustment, take the striding level of the Swasey depression-position 
 finder, Type Al. Prepare a carefully turned cylindrical block, 
 mounted on a small pedestal or base provided with a leveling attach- 
 ment, as three screws at the vertices of an isosceles triangle. Place 
 the striding level on the cylindrical block and bring the bubble to the 
 center of the scale by means of the leveling screws of the pedes taj of 
 the cylindrical block. Then lift the level from the cylindrical block 
 and turn it around so that the former right end will become the left 
 end, and place again on the cylindrical block. If the level is properly 
 adjusted, the bubble will still be in the center of the scale. If the 
 level is not properly adjusted, correct for half of the bubble error by 
 the small screws at either end of the level vial case, and for the other 
 half of the error by the leveling screws of the pedestal. Then reverse 
 the striding level as before, and continue this process until the bubble 
 shows no variation after reversal, when the striding level will be 
 properly adjusted. 
 
 171. The following additional examples of specif cases are given 
 as containing such remaining information on the principles of level 
 adjustment as may be necessary. The adjustment of the elevation 
 or angle of site level for the range quadrant of the 3-inch field materiel 
 is made as follows: After carefully packing the level and closing 
 vial holder, the zero mark on the holder is brought opposite the 
 reference number (3) on the level scale by means of the clinometer 
 level screw. (See plate and description of ''Range quadrant" in 
 pamphlet No. 1659, ''Handbook of the 3-inch Field Artillery 
 Materiel.") The micrometer disk is then loosened, by releasing its 
 
59 
 
 retaining screw, and is turned until the zero mark on the scale is 
 brought opposite the zero or index mark on the quadrant body. 
 The retaining screw is then tightened, when these parts will be in 
 adjustment for range. 
 
 172. The transverse or cross level of the range quadrant is adjusted 
 as follows: The cross-level vial is first secured in its tube and then 
 inserted in the level holder. One end of the tube containing the 
 level vial fits snugly in the level holder. The other end of the tube 
 is somewhat smaller and contains four radial adjusting screws. The 
 verticality of the rocker arm should be determined by the testing 
 level or by a steel square projecting from a horizontal plate in such 
 manner that the base of the square will rest on the plate when the 
 vertical edge is in contact with the planed surface of the rocker arm 
 or parallel to it. The level should be adjusted by means of the 
 upper and lower radial screws for this position of the rocker arm. 
 Then by means of the two side radial screws the level vial and tube 
 should be adjusted in the level holder, so that the bubble remains 
 central, while either the quadrant or the body is moved in a vertical 
 plane. 
 
 173. The following detailed instructions for the disassembling of 
 bases of some of the more complex instruments are given below. No 
 instrument should be disassembled except when required. 
 
 BATTERY COMMANDER'S TELESCOPE, MODEL OF 1905. 
 (See Plate E.) 
 
 174. To disassemhle the center and the worm mecMnism. — Remove 
 the platen caps (4DA) and lift out the telescope. Do not remove the 
 four spindle screws (2B). The spindle should not he removed from the 
 platen. Remove the one spindle-nut screw (2C) and the spindle nut 
 (2J), using teat wrench. No. 41. 'Throw the azimuth worm out of 
 mesh, loosen the slow-motion screw, and lift the platen (4R) with 
 spindle (2A) and the horizontal hmb (4B) from the fixed limb (2W) 
 carefully, to avoid bruising. Unclamp the slow motion clamp screw 
 and remove the slow-motion arm (3E). Remove the platen cover 
 (4FA) . After taking off the worm box stud nut (4AA) and unscrew- 
 ing the azimuth worm box stud (4M) , lift the azimuth worm mechan- 
 ism from the platen (4R). Remove the azimuth worm adjusting 
 screw (4U) , loosen the dial nut screw (4 JA) , and remove the dial nut 
 (4Y), the two azimuth dial screws (4SA), and washers (4UA). 
 Remove the azimuth micrometer head (4K) and the azimuth dial 
 (4NA) and push the azimuth worm from its bearing. 
 
 Drive out the eccentric crank pin (2V) and drive iii eccentric (2T) . 
 The eccentric crank (2U) will then drop off. Reassemble all parts in 
 the reversed order. Use clock oil on the spindle bearing. 
 
GO 
 
 175. To disassemble the leveling screws, etc. — Screw the four leveling 
 screws (3CA) into the fixed limb to remove friction between the level- 
 ing plate (3 A) and the fixed limb nut (2X). Take out the fixed limb- 
 nut screw (2M), unscrew the fixed limb nut (2X), using adjustable 
 key wrench No. 37. Lift off the leveling plate (3A) and the screw 
 collar (3D). The four leveling screws (3CA) may then be removed 
 from the fixed limb (2W) and the shoes driven off with a light blow 
 of a maUet. 
 
 Remove the plunger sleeve screw (3S), unscrew the slow-motion 
 plunger sleeve (3L) from the fixed limb. The slow-motion plunger 
 (3K) and slow-motion plunger spring (3M) may then be separated 
 from the slow-motion plunger sleeve. 
 
 176. To remove the elvation worm mechanism. — Remove the two 
 elevation worm-box studs (4GA) and lift off the worm box. Loosen 
 the dial-nut screw (4JA), remove the dial nut (4Y), the two elevation- 
 dial screws (4TA) and the screw washers (4UA). Lift off the eleva- 
 tion dial (4HA), drive out the elevation worm (4Z) by tapping 
 ligh tly on the threaded end of the worm, thereby forcing out the plug 
 (4X) and releasing the elevation micrometer head (4WA). 
 
 AZIMUTH INSTRUMENT, MODEL OF 1910. ^ 
 
 (See Pamphlet No. 1656 and drawings 22-30-1 to 14, inclusive.) 
 
 177.^ To disassemble the base. — Remove the azimuth stop (llT), 
 unscrew the spindle-washer screw (9F) and lift off the spindle washer 
 (1 ID). Lift off the body (9A) and yoke (lOA) assembled from the 
 azimuth circle (9B). Remove the spindle-nut lock screw (llAA) 
 an d, using adjustable key wrench No. 36, unscrew the spindle nut 
 (1 IC). The azimuth circle may then be lifted from the leveling 
 plate (lOP). 
 
 To remove yoke (lOA) from body (9A) take out the yoke-washer 
 screws (lOT), draw off yoke washer (llK) and separate yoke from 
 body and azimuth slow-motion arm (9D). 
 
 178. To disassemble worm. — Remove the yoke and the body from 
 th e azimuth circle. Take off the worm-box cover (9C). Remove the 
 worm-shaft screw (lOV). Draw off the drum crank (lOL), the azi- 
 muth drum (lOG), the drum adjusting clamp (lOJ), and drum 
 adjusting sleeve (lOK) assembled. Loosen the azimuth-drum cover, 
 set screw (lOY) and pull off the azimuth drum cover (lOB). 
 Unscrew partially the worm-box adjusting screw (8AC). Remove 
 the worm-box support screws (lOZ) and draw out the worm-box 
 support (lOR). Unscrew the worm-box pivot (8X) and draw out 
 the worm screw (lOF) and the worm box (lOH) assembled. Unscrew 
 
 1 These instructions also apply to the azimuth instruments, models of 1900 and 1900 Mi. 
 
(Jl 
 
 the worm-screw bearing screw (lOAA), pull out the worm-screw 
 bearing (lOQ) and shp out the worm screw (lOF). 
 
 Use clock oil on all internal bearing surfaces. Assemble all parts 
 in the reversed order. In case the felt strip (IF) becomes unservice- 
 able replace it by a good grade of soft felt J inch thick. 
 
 SWASEY DEPRESSION POSITION FINDER.^ 
 
 (See pamphlet No. 1875 and drawings 22-22-1 to 15, inclusive.) 
 
 179. To disassemble the azimuth worm mechanism.. — Loosen the 
 azimuth drum lamp-bracket screw (14FB) and rotate the azimuth- 
 drum lamp bracket slightly. Loosen the worm-box pivot screw 
 (14YA) and unscrew the worm-box pivot (8Z). Throw the worm 
 out of mesh and pull the worm box assembled down out of its seat. 
 Remove the azimuth-drum screw (14M) and pull off the azimuth 
 drum (8S). Loosen the azimuth drum-cover screw (14P) and remove 
 the azimuth drum cover (8Q). The azimuth drum lamp bracket may 
 also be disassembled. Take out the worm-box adjusting screw (14U) 
 and the worm-box oil tube (8DA). Push out the worm screw (8B) 
 and the worm-box bush (8C). 
 
 In assembling, tighten the azimuth drum screw (14M) so that the 
 worm screw may revolve in the worm box without great friction and 
 without longitudinal play. Adjust the worm-box adjusting screw 
 (14U) so that the worm screw comes just to bearing with the azimuth 
 circle and operates without appreciable backlash. 
 
 180. To remove the range yointer arm (9T). — Remove the range 
 pointer cover (6P) and the curvature attachment guard (6F). Un- 
 screw the two range pointer screws (14GA) in the forks of the range 
 pointer arm (9T) . Remove the screws from the range pointer guides 
 (9W) and (9X). Pull out the range pointer (9U) and the range 
 pointer guides (9W) and (9X). Take out the four pointer bracket 
 cap screws (14AB) and remove the range pointer bracket (9N). 
 Loosen the pointer arm screw (14B) and push out the range pointer- 
 arm shaft (9Y). When reassembling, note that a flat is machined 
 on the range pointer-arm shaft (9Y) for the set screw. 
 
 181. To remove the hell cranlc lever (6D). — Remove the curvature 
 attachment guard (6F). Scribe a line across the rack on the beU 
 crank lever and the worm sleeve (4AA) for reference in assembling. 
 If no other parts are to be disassembled, take care that the range 
 drum is not moved while the bell crank lever is disassembled. If 
 other parts are to be disassembled, the instrument should be set for 
 telescope level and the range drum removed before the bell crank 
 lever is taken off. Remove the lever post caps (7B). Lift off bell 
 crank lever assembled. 
 
 1 The nomenclature given is for the type All instrument. The parts of this instrument will be disas- 
 sembled only in case of necessity for making repairs or correcting errors, etc. 
 
(ili 
 
 182. To remove the range drum. — If the range pointer arm (9T) is 
 to be removed, set the instrument at a short range and remove the 
 pointer arm screw (14B) from the hub of the arm (9T). Then revolve 
 the drum until it indicates telescope level. Note that in this position 
 the cam crank pin (6E) bears on the flat of the cam (6T). Remove 
 the range pointer cover (6P). Take out the two range pointer screws 
 (14GA) from the fork of the range pointer arm (9T) and the screws 
 from the range pointer guides (9W) and (9X). Pull out the range 
 pointer (9U) and the range pointer guides. Remove the screws hold- 
 ing together the two sections of the range drum cover (lOD) and (lOE). 
 Remove from the cradle the range crank (9K), the oiler for oiling the 
 range crank shaft (9H), and the oiler for lubrication of the azimuth 
 circle. Take out the large drum-cover screws (14S) holding the drum 
 covers to the cradle (7D). Pull off the drum covers. Take out the 
 three screws from the slotted holes in the range drum (9L) and remove 
 the range drum (9L). Unscrew the drum gear screw (14A) and pull 
 off the range drum gear (9E). The range crank pinion (9D) and 
 range crank shaft (9H) may now bfe removed. No attempt, how- 
 ever, should be made to remove these parts until after the range 
 drum gear is removed. 
 
 183. To remove the cam of the curvature attachment. — Remove the 
 range drum and gear complete. Note instructions in paragraph 159 
 above regarding setting of range drum before it is removed. Mark 
 the opposite teeth of the worm shaft pinion (5T) and the cam shaft 
 gear (5U). These teeth may already be spot marked. Remove the 
 cam bracket caps (5Q) and pull out the cam shaft (4V), cam (6T), 
 and cam shaft gear (5U) assembled. The cam and cam shaft gear 
 are located on the cam shaft (4V) by paper pins. The cam, cam 
 shaft, and cam shaft gear may be removed after the curvature 
 attachment guard (6F) is taken off, provided that a bent wire is used 
 in removing the. capstan head screws holding the cam bracket caps 
 (5Q). If, however, other parts are to be disassembled, it wiU be 
 preferable to remove the range drum, etc., first. 
 
 184. To remove the range drum shaft. — Remove the range drum 
 (9L), the range pointer arm (9T), the range pointer bracket (9N), 
 the bell crank lever (6D), and cam shaft with cam and gear. Note 
 instructions above for setting of the range drum before its removal 
 and for marking the opposite teeth of the worm shaft pinion (oT) 
 and the cam shaft gear (5U), and for marking the bell crank lever 
 and the worm sleeve. Drive out the taper pin and remove the worm 
 shaft pinion (5T). Loosen the cam bracket screw (5N). Remove 
 the two capstan head screws holding the worm sleeve (4AA) in the 
 cam bracket (5L), the filister head screw holding the cam bracket 
 (5L) to the cradle (7D), the one headless locating screw locating the 
 worm sleeve (4AA) in the cradle (7D), and the clamp screw (14BB) 
 
63 
 
 from the cradle. Pull worm sleeve (4A*A) to the rear, slipping from 
 it the cam bracket (5L). Loosen the set screw holding the worm 
 sleeve bush (6C) in the worm sleeve (4AA), pull out the range drum 
 shaft (4Q), and remove the worm sleeve bush (6C). 
 
 Reassemble in reversed order, taking care to mesh gearing to the 
 teeth previously marked, to locate the flat on the smaller end of the 
 cam uppermost, and to assemble the bell crank lever according to the 
 mark previously scribed. 
 
 185. To remove the cradle, etc., from the base, — Take out the oil cup 
 from spindle washer. Remove the brush block (ISW). Use teat 
 wrench No. 43 and unscrew spindle washer (USA). Then lift off 
 the cradle (7D). Four men are required for this work. The cradle 
 must be lifted directly up about 12 inches. The vertical spindle 
 (llJA) is driven in the azimuth circle (8F) and should not be removed. 
 To remove the azimuth circle (8F) and the azimuth plate (7C) loosen 
 the azimuth drum set screws (14CB) and lift the two parts off the 
 base (7E). Remove the spindle nut screw (14ZA) from the spindle 
 nut, unscrew the spindle nut (llRA) and lift the azimuth circle from 
 the azimuth plate (7C). 
 
 One leveling shoe (8K) is made with a tongue. The position of this 
 shoe may be changed without disassembling the azimuth circle (8F) 
 from the azimuth plate (7C). 
 
 186. Notes on assembling. — Assemble the range drum shaft and 
 the worm sleeve bush, etc., in the worm sleeve (4AA). Slide the 
 worm sleeve and cam bracket (5L) in their seats, locating the worm 
 sleeve by the headless locating screw, and put in the screws which hold 
 the cam bracket and clamp the worm sleeve. Assemble in the cam 
 bracket (5L) with flat of cam uppermost, the cam shaft (4V) with cam 
 (6T) and cam shaft gear (5U) assembled. Place in position the 
 crank lever noting the marks previously scribed. If no marks are 
 scribed on it, assemble it so that its rear end just clears the rear lug 
 of cradle. While placing the bell crank lever in its bearing hold up 
 the cam crank (5V) so that the cam crank pin (6E) does not touch the 
 cam. In this position of the cam and the bell crank lever, the cam 
 crank pi'i (6E) should rest on Ihe flat of the cam. Assemble the 
 range crank pinion (9D) and range crank shaft (9H) . 
 
 Then assemble the range drum gear, the range drum at telescope 
 level, and the pointer mechanism. The range pointer arm (9T) 
 should be meshed in the range drum shaft so that the pointer indicates 
 telescope level. Assemble the worm shaft pinion as marked (if not 
 marked assemble for trial) . Rotate parts by the range crank to prove 
 that the range drum may be revolved from telescope level to the 
 shortest range. If the full movement can not be obtained, loosen 
 the four pointer bracket cap screws (14AB) and shift the pointer 
 
"64 
 
 bracket on the worm sleeve to obtain it. Assemble the pointer arm 
 screw (14B) with the range drum set for a short range. 
 
 187. To test adjustment} — Level the cradle, set the range drum at 
 telescope level, assemble the telescope and the striding level. Adjust 
 the striding level. Set the telescope level. Adjust the cam crank 
 screw (5W) if necessary so that the top surface of the carriage crank 
 (5P) is perpendicular to the height scale. Slide the height slide (4E) 
 assembled along the rail and by the telescope observe any external 
 object. If, during movement of the height slide, the image shifts 
 in respect to the cross wires, remove the plunger (4P) and adjust the 
 plunger screw (4U) in the plunger. Replace the plunger for trial and 
 readjust it until the image remains stationary. Level the telescope 
 by the range crank. If the cam crank pin (6E) does not rest on the 
 flat of the cam (6T) , remove the worm shaft pinion (5T) , turn the cam 
 shaft until the pin rests there and reassemble the pinion. Now the 
 movement of the range crank has thrown the guide (12G) out of 
 parallelism with the rail of the bell crank lever. Readjust the 
 plunger (4P) until there is no movement of the image over the cross 
 wires when the height slide is moved, readjust the level of the tele- 
 scope by the range crank until the striding level indicates level. 
 Repeat until when the telescope is level and the height slide may be 
 moved without changing its level. Then set the range drum to 
 indicate telescope level. 
 
 This adjustment may be made with the use of the Testing Instru- 
 ment described in Pamphlet No. 1875. In this case observe the 
 rotation of the telescope by means of the testing instrument instead 
 of by the telescope. 
 
 188. To set the height scale. — After adjusting the telescope, the 
 height slide, the curvature mechanism, and the range drum, set the 
 drum at telescope level (the telescope being level) and adjust the 
 testing instrmnent ^ to register 0. With the height scale set for the 
 proper height, measure the angular rotation of the telescope for 
 various setting of the range drum. In case the angles measured are 
 greater than the calculated angles, move the height slide to register 
 a slightly smaller height of site. Repeat the readings and readjust 
 until the measured angles agree with the calculated angles. Then 
 adjust the height scale pointer screw (6V) until the height scale 
 pointer (llN) registers the correct height. Loosen the screws in the 
 pointer stop (IIP) and set the index line of the pointer strip opposite 
 the line on the height scale pointer. Make this adjustment for the 
 mean height at which the instrument is to be used. 
 
 1 For instructions for collimation and leveling by means of the striding level see paragraph 78, 
 « For description of the testing instrument and instructions for its use see Pamphlet No. 1875 (Descrip* 
 tton of the Swasey Depression Position Finders). 
 
65 
 
 189. To determine the angular error of the instrument, bring the 
 range drum to register the specified range and read the angle of rota- 
 tion by the testing instrument. Subtract the observed reading from 
 the calcidated angle to obtain the error. If it is desired to obtain 
 the error in yards, set the testing instrument to the calculated angle 
 and read the range from the drum. The range error is the meas- 
 ured range subtracted from the calculated r|inge. The following are 
 calculated values of the angular rotation of the telescope from tele- 
 scope level to the range specified for the stated heights of site : 
 
 
 Angle of rotation in minutes for height of instrument of— 
 
 Range. 
 
 60 feet. 
 
 81 feet. 
 
 126 feet. 
 
 210 feet. 
 
 282 feet. 
 
 396 feet. 
 
 Telescope level 
 
 
 
 8.576 
 9.W2 
 10.286 
 12. 727 
 18.034 
 23.552 
 34.799 
 
 
 
 10.764 
 12.216 
 13.294 
 16.738 
 24.501 
 31.573 
 46.830 
 
 
 
 15.451 
 17.945 
 19.739 
 25.332 
 39. 582 
 48.760 
 72.605 
 . 
 
 
 
 24.202 
 28.640 
 31. 771 
 41.374 
 61.000 
 80.833 
 120.694 
 
 
 31.702 
 
 37.806 
 42.083 
 55.122 
 81.617 
 108.314 
 161. 877 
 
 
 
 11,000 
 
 43. 576 
 
 9.000 
 
 52. 319 
 
 8000 - 
 
 58.409 
 
 6,000 
 
 76.886 
 
 4,000 
 
 114.249 
 
 3,000 
 
 151. 796 
 
 2,000 
 
 226.984 
 
 
 
 LEWIS DEPRESSION POSITION FINDER, MODEL OF 1907. 
 
 (See drawings Class 22, Division 21, drawings 1 to 10, inclusive, and pamphlet No. 
 
 1876.) 
 
 190. To disassemhle the internal mechanism. — Take off the tele- 
 scope by loosening the trunnion center screws (4E) and pidling 
 trunnion centers (4T) out gradually to prevent the telescope from 
 jarring. Remove the table clamp (4C) by driving out the taper 
 pin (4P) and unscrewing the head (4Q) and taking out the clamp 
 screw (4R) (left hand thread). Take off the gear guard ring (5D), 
 first removing the 12 screws holding same to table. Remove the 
 5 screws holding the gear case (5M) to the table (5A), being careful 
 to note position of long and short screws and take off the gear casie 
 (5M). Unscrew the small headless screw in the gear (5H) and drive 
 out the pinion (5J) from the gear (5H) with a small stick and hammer. 
 Loosen the three table center screws (4L) and (4Z) in the body 
 about U turns and lift off the table (5 A) (2 men required), by raising 
 on opposite sides with equal force, taking care not to force parts or to 
 injure the center. Mark one s^ot of table center (4G) and one table 
 center screw so that the table may be put back in same position. 
 
 191. To dismantle the range gearing. — Set the range scale at 1,500 
 yards and mark the position of the range dial gear (3Q), the rack gear 
 (3S), and the lower worm shaft gear (2W). Remove the range dial 
 gear plate (3E). Mark the position of the range pointer (3TA). 
 Remove the lower worm shaft gear (2W), holding the rack gear (3S) 
 9950—17 5 
 
G6 
 
 to prevent its rotation. Remove the rack gear plate (3F) and the 
 rack gear (3S). Assemble in the reversed order. 
 
 192. To disassemble the azimuth gearing. — Remove the trunnion 
 yoke screw (4B) and pull out the trunnion yoke (4F). Unscrew the 
 screw located directly under the trunnion yoke screw which holds 
 the table (5A) to the tabel center (4G). Drive out the table center 
 (4G) by tapping lightly, on the head of the center screw (4H). Do 
 not remove the azimuth circle (6P) and holder (6Q) unless it is 
 necessary. Never attempt to remove these parts until after the 
 table has been removed from the body (6B). 
 
 Remove the screw for table (6G) and the small headless screw in the 
 screw for azimuth dial pinion (4M) and unscrew the screw for azimuth 
 dial pinion (4M). The azimuth dial assembled (4X) will then drop 
 out. Remove the screws for azimuth dial block (6E) [these are the 
 first and fourth screws in the table extending in a line outward from 
 the azimuth circle window (5B)] and slide out the azimuth dial 
 block (6R) and ^oiy degree scale (6S) assembled. The screw for 
 azimuth dial pinion (4M) and the eccentric for azimuth dial block 
 (6D) may now fall out. Assemble in the reversed order. Make 
 sure that the pin which is located half in the azimuth dial pinion (4D) 
 and half in the azimuth dial center (4N) is driven home. Otherwise 
 backlash may be found in the ^hj degree scale (6S). 
 
 193. To remove the compensating mechanism. — Set the range scale 
 at 1,500 yards and note the position of the cam (2Z) and the pin for 
 bar (3D). Take off the worm shaft nut (2P). Mark the position of 
 the lower worm shaft gear (2W) in reference to the range dial gear 
 (3Q). Remove the lower worm shaft gear (2W). Take out the 
 four screws holding the screw and gear case (2A) and lift it from the 
 table. 
 
 194. To change the class of an instrument. — Remove the com- 
 pensating mechanism and the range dial as described above. The 
 range dial gear and the compensating mechanism of class required 
 may then be assembled in the reversed order specified above. Take 
 care to set all parts in the same manner in respect to each other as 
 those removed; that is, the range dial and the range pointer should be 
 at 1,500 yards, the rack gear (3S) at the position marked and the 
 cam (2Z) and pin for bar (3D) should be in same position as on com- 
 pensating mechanism taken off. (The position of the cam and pin 
 for bar is that shown on Plate IV of pamphlet No. 1876 — Description 
 of the Lewis Depression Position Finder, Model of 1907.) 
 
 It is possible that the hole through the center of trunnion yoke (4F ) 
 will needs be elongated to obtain short-range readings at the extreme 
 readings on the tide scale. Test to see that the lug on the trunnion 
 of the telescope tube does not come in contact with the sides of this 
 clearance hole. 
 
67 
 
 195.* To disassemble the compensating mechanism. — After removal 
 of the compensating mechanism which has previously been set at 
 1,500 yards, remove the two intermediate gear plates (2BA). Take 
 out the two screws holding the worm wheel shaft bracket (2B) to 
 the screw and gear case (2A). Unscrew the screws holding the 
 worm shaft plate (2R) and draw out the worm shaft plate (2R) 
 the worm shaft (2X) and the upper worm shaft gear (2G) assembled. 
 To disassemble the upper worm shaft gear (2G) remove the set 
 screw from it and draw off the gear from the worm shaft. If the 
 bevel gear (2D) and the worm wheel (2C) are to be disassembled, 
 first drive out the taper pins (2E) and (2YA) from the bevel gear 
 (2D) and the collar (2ZA). Remove the set screw from the cam 
 and drive out the taper pin (2J) from the cam (2Z). Then drive 
 the cam shaft (2L) into the screw and gear case (2A). If the cam 
 is to be removed loosen the screw holding the pin for bar (3D) and 
 push out the pin for bar (3D). The cam may then be slipped out. 
 Note that the tangent screw gears (2HA) are marked for assembling 
 in a particular position on the inner sleeve nut (2EB) and the outer 
 sleeve nut (2DB). If removed, these geare should be carefully 
 assembled in the same manner. The parts disassembled may 
 then be assembled without readjustment of the compensating 
 mechanism, provided that the outer sleeve nut and the inner sleeve 
 nut have not been changed in position. 
 
 196.* If the tangent screw rail is to be removed, measure and 
 record the distance from the bottom of the screw and gear case (2 A) 
 to the top of tangent screw rail (3UA). After the removal of screws 
 holding the tangent screw gear (2HA) to the inner sleeve nut (2EB) 
 and the outer sleeve nut (2DB), the tangent screw rail (3UA) with 
 sleeve nuts assembled may be withdrawn from the screw and gear 
 case (2A). The inner sleeve nut (2EB) and the outer sleeve nut 
 (2DB) may then be removed and later the tangent screws (2AA). 
 Clean all gears and all bearing surfaces before assembling and oil all 
 parts. Examine small pieces for burrs and remove them if found on 
 bearing surfaces. Be exceedingly careful in cleaning the threads of 
 tangent screw and sleeve nut Oil these threads with clock oil. In 
 instruments of classes A and AA the screws have 210 threads per 
 inch, and any dirt or grit in the threads will interfere with the smooth- 
 ness of operation and the accuracy of these parts. 
 
 197.* Assembly of compensating mechanism. — Reassemble in the 
 reverse order, noting that the lower numbers on the tide scale on 
 the tangent screw rail (3UA) should be over the outside end af the 
 screw and gear case. Adjust the inner and outer sleeve nuts on the 
 tangent screws until the tangent screw rail is exactly parallel with the 
 
 * See paragraph 11. 
 
.68 
 
 bottom surface of the screw and gear case. Locate the cam (2Z) so 
 that the pin for bar (3D) is in the left end of cam groove (see note 
 on drawing 22-21-8). Locate the intermediate gear plates (2BA) so 
 that the intermediate gears (2U) mesh the pinion and tangent 
 screw gears (2HA) without backlash and so that the outer sleeve nut 
 (2DB) operates smoothly and without backlash. The assembled 
 height from the surface of the tangent screw rail to the axis of the 
 telescope (axis of trunnion centers) is specified on drawing 22-21-8. 
 If the height of rail from base of screw and gear case is made the 
 same as measured before disassembling, the rail should be located 
 correctly from the axis of the telescope. It may be noted that the 
 surface of the table to which the compensating mechanism is fitted 
 is accurately scraped in reference to the lower surface of the inner 
 hub of the table. 
 
 198. To test correctness of assembly} — ^After assembling the table 
 test by operating the outer sleeve nut to see that the range scale may 
 be operated throughout the limits of range. In case the range 
 pointer is not correctly set, keep the range scale at 1,500 yards, 
 remove the table, take off the lower worm shaft gear (2W) and 
 move the rack gear and pinion (3U) to the desired position, and 
 reassemble. If the range dial gear (3Q) is limited in movement, lift 
 and block up the table, and, if the desired additional movement is 
 small, spring the range dial gear (3Q) sufficiently to throw it out of 
 mesh with the lower worm shaft gear (2W) and move it in the desired 
 direction. If the required additional movement is considerable, dis- 
 assemble and reassemble all parts, setting the range dial gear (3Q) 
 and the range pointer (3TA) at 1,500 yards and the cam (2Z) so that 
 the pin for bar (3D) is in the left end of slot. 
 
 199. Accuracy tests. — The accuracy of readings may be measured 
 by comparison with a bar scale graduated in inches and fractional 
 parts. Set the height for the given height of site and the range 
 scale at a range of about 8,000 yards for instruments whose range 
 scales are graduated to 12,000 yards and of about 4,500 yards for 
 other instruments. Set up the bar scale vertically at exactly 100 
 feet distance from the telescope (trunnion center) axis, so that the 
 bar scale reading given in table below for the range setting specified 
 is intersected by the horizontal cross wire. This is calculated so 
 that the of scale corresponds to the ''telescope level" position of 
 the telescope. Then by moving the range mechanism, without dis- 
 turbing the compensating screw, bring the telescope successively to 
 the bar scale readings and read the range registered on the range 
 scale. To obtain the range error, subtract the measured range from 
 the calculated range. 
 
 1 Collimate the telescope as described in paragraphs 80-85. 
 
C9 
 
 200. Data for accuracy tests. 
 
 Range. 
 
 Bar scale reading in inches for a height of instrument of — 
 
 24 feet. 
 
 60 feet. 
 
 81 feet. 
 
 126 feet. 
 
 210 feet. 
 
 282 feet. 
 
 396 feet. 
 
 8° 
 
 
 
 1.684 
 
 1.731 
 
 1.790 
 
 2.043 
 
 2.695 
 
 3.421 
 
 4.948 
 
 
 
 2.994. 
 3.331 
 3.590 
 4.443 
 6.295 
 8.221 
 12.148 
 
 
 
 3.757 
 4.264 
 4.640 
 5.843 
 8.395 
 11. 021 
 16.348 
 
 
 
 5.394 
 6.264 
 6.890 
 8.843 
 13.817 
 17. 021 
 25.348 
 
 
 
 8.448 
 9.997 
 11.090 
 14.443 
 21.295 
 28.221 
 42.148 
 
 
 
 11.066 
 13. 198 
 14.690 
 19.243 
 28.495 
 37. 822 
 56.548 
 
 
 
 11,000 
 
 15. 212 
 
 9,000 
 
 18.264 
 
 8,000 
 
 20 390 
 
 6,000 
 
 26.843 
 
 4,000 
 
 39. 895 
 
 3,000 
 
 53 021 
 
 2,000.. . 
 
 79 348 
 
 
 
 If desired, the target may be set up at a shorter distance, provided 
 that the bar scale readings are proportionally reduced. 
 
 SCALE ARMS (Group c). 
 
 201. Scale arms and all graduated surfaces give incorrect results 
 if their fiducial edges for any reason lose the form they properly 
 should have. Thus, the long plotting arms for a Whistler-Hearn 
 plotting board, if handled roughly, or if bent too much, become 
 warped in one direction or another, giving readings too great or too 
 small, depending on the direction of warping. Such arms must be 
 removed from the board, and by careful reverse, bending, peening, 
 and testing with a straightedge, returned to their original condition. 
 In tapping such arms, tap very lightly and carefully, for otherwise 
 the tapping will result in broadening out the distance between grad- 
 uations, and thus in destroying the accm-acy of the arm. Where 
 circular scales are bent out of shape and become eccentric, a gage 
 must be made for testing the edge after correction. Spoiled scales 
 may ordinarily be replaced by new ones obtainable from the Frank- 
 ford Arsenal. If time, cost of transportation, or other reason pre- 
 vents, new pieces must be prepared according to the drawings, and 
 graduated carefully. The index head of a milling machine may be 
 used if no circular graduating machine for circular scales is avail- 
 able. For straight scales, if no rectilinear graduating machine, 
 least reading 0.001 inch, is available, use the best vernier gage 
 obtainable for the purpose. Lettering, numbering, and index marks 
 wiU in such cases ordinarily have to be stamped in. The stamping 
 increases the length of the scales; hence the stamping must be done 
 before the final graduation, the position of the various numbers 
 being determined as closely as possible. If an engraving machine 
 is available, the graduating should be done first and the engraving 
 second. 
 
7.0 
 
 WOODEN PARTS (Group d). 
 
 202. Wooden parts of instruments, if destroyed or damaged so as 
 to interfere with the action of the other parts of the same instru- 
 ment, should be replaced when possible by the same material as 
 that originally used. The various drawings specify the material 
 and its method of preparation, including the linseed oil and varnish 
 treatment. Warping can only be provided for by increasing clear- 
 ances already uUowed. Slotted instead of round screw holes, etc., 
 are suggested as means of overcoming difficulties ii;i the adjustment 
 of metal parts to a wooden base which expands or shrinks unduly 
 with change of moisture in the air. No absolute method can be 
 given for such cases, and readjustment of all metal parts frequently 
 will be found necessary. 
 
 SPECIAL PARTS (Group e). 
 
 203. The canvas charts, with the blue-print chart attached, for 
 Pratt range board should be kept habitually flat when not stretched 
 in the board. If- it is desired to prepare new charts, obtain the 
 canvas of the size necessary and sew over a stretching form corre- 
 sponding to the frame of the board. While stretched tight paste 
 on the blue print in its proper position, giving careful attention to 
 the eyehole. Sew edges of blue print down after pasting, as they 
 will otherwise curl up and tear off. 
 
 204. The rubber covering of the mobile artillery board may be 
 rubbed up and in a measure improved as to elasticity by the use of 
 powdered sulphur. Keep the rubber out of the sun when practicable. 
 
 205. The steel tapes issued with Weldon range finders should be 
 kept clean and well oiled when not in use. When using, avoid get- 
 ting kinks in the steel ribbon. Never drag the tape over rough or 
 broken ground. Before winding up, clean the steel ribbon as it 
 comes in of all grit and dirt, for, if not, after once entering the case, 
 the parts will be rapidly clogged, scratched, and otherwise injured. 
 Should a tape break, repair the break by an extra piece soldered on, 
 or attached by suitable rivets, and of such length as to keep the 
 readings of the tape on either side of the break correct. 
 
 206. Time-interval recorders may be repaired and adjusted by 
 any competent watch repairer. 
 
 ADDITIONAL. TESTS. 
 
 207. For testing of plotting boards, if data for observation points 
 is not at hand, hypothetical points should be located in the field of 
 fire at long ranges, and the azimuth and distances of these points from 
 the primary and secondary stations and from the directing point of 
 the battery should be calculated. To test a plotting board, set the 
 primary and secondary arms at the calculated azimuths, note errors 
 
71 
 
 in the ranges from these stations and errors in gun arm range and 
 azimuth from the calculated values. 
 
 208. In case it is desired to report the condition of a plotting board 
 to an armament officer or to Frankford Arsenal, it will b(b of great 
 assistance if a complete test of the board be made and reported in 
 accordance with the following form, in each case reporting the model 
 
 and serial number: Tested for right (or left) base line yards 
 
 long with ranges from . yards to yards from the gun 
 
 center. The errors of readings were : Primary arms, maxi- 
 mum, yards; mean, yards. Secondary arm, maxi- 
 mum, yards; mean, yards. Gun arm, maximum, 
 
 yards; mean, yards. Gun arm azimuth circle, maxi- 
 mum, °; mean, °. The maximum error in gun 
 
 azimuth if the gun arm is moved from 1,500 through inter- 
 mediate positions to 2,500 is °. The gun arm set at the 
 
 azimuth of the normal is parallel to the primary arm set at the same 
 
 azimuth; error, °. The error in azimuth of the gun arm 
 
 due to moving the longitudinal slide through the full extent of its 
 
 movements is ° ; the error due to moving the lateral slide 
 
 similarly is °. The primary (or secondary) arm set at the 
 
 azimuth of the base line is parallel to the base line arm with an error 
 
 of °. The backlash of the gun azimuth mechanism is ° ; 
 
 that of the azimuth correction mechanism is ° ; that of the 
 
 primary index box is ° ; that of the secondary index box is 
 
 °. The base line arm vernier is located correctly; error, 
 
 °. With the gun arm center over the primary arm center the 
 
 maximum error of the gun arm azimuth circle compared with the 
 
 main azimuth circle is °. The fiducial edges of the arms 
 
 (naming them) vary from a straight edge by inches. 
 
 209. The following problems and results are furnished for testing 
 other instruments of the fire-control systems. The instrument should 
 be set at the given data of the problem and the results obtained on 
 the instrument compared with the calculated results. 
 
 Deflection hoard, model of 1905, for guns. 
 [For capped projectiles, short points.] 
 
 
 
 
 Service. 
 
 
 
 Subcaliber. 
 
 Given: 
 
 Interval — seconds . . . 
 
 15 
 
 10 
 
 16 
 
 10,000 
 
 
 30 
 
 90 
 
 11 
 
 6,000 
 
 
 15 
 
 35 
 
 16 
 
 2,000 
 
 30 
 
 Wind scale 
 
 65 
 
 Platen scale 
 
 11 
 
 jiaxige — yards 
 
 2,000 
 
 
 
 Gun. 
 
 8 in. 
 
 10 in. 
 
 12 in. 
 
 Sin. 
 
 10 in. 
 
 12 in. 
 
 Sub- 
 caliber. 
 
 Sub- 
 caliber. 
 
 Result: 
 
 Deflection scale 
 
 Azimuth correction scale 
 
 3.219 
 16. 219 
 
 3.323 
 16. 323 
 
 3.416 
 16.416 
 
 1. 834 
 9. 834 
 
 1.854 
 9. 854 
 
 1.847 
 9.847 
 
 2.643 
 15. 64.J 
 
 2.635 
 10.635 
 
 
 
72 
 
 Deflection board, model of 1906, for 12-inch mortars. 
 
 Given. 
 
 Result. 
 
 Azimuth 
 
 Elevation. 
 
 Deflection. 
 
 Model of 1890 M. 
 
 Model of 1886. 
 
 Subcaliber. 
 
 824 lbs. 
 
 1,046 1J>S. 
 
 824 lbs. 
 
 1,046 lbs. 
 
 10» 
 145» 
 271° 
 
 45° 
 55° 
 
 3 
 5.50 
 0.50 
 
 6.66 
 139.44 
 263.47 
 
 7.37 
 141. 15 
 264.54 
 
 7.33 
 141.06 
 264.47 
 
 7.90 
 142.42 
 265.34 
 
 8.88 
 144.75 
 266.79 
 
 Wind component indicator. 
 [Problem: Azimuth of wind, 135; azimuth of target arm, 190; velocity of wind, 50.] 
 
 Result: 
 Rai _ 
 Deflection component 9. 0425 
 
 fek RMge component 21. 321 
 
 Field-artillery plotter, model of 1907. 
 
 Observation of point settings. 
 
 Relocating readings. 
 
 Aiming point arm. 
 
 Target arm. 
 
 Gun arm. 
 
 Aiming point arm. 
 
 
 Target arm. 
 
 MUs. 
 
 Yards. 
 
 Mils. 
 
 Yards. 
 
 Yards. 
 
 MUs. 
 
 Yards. 
 
 Mils. 
 
 Yards. 
 
 56 
 56 
 
 2,000 ; 48 
 4,000 48 
 
 2,000 
 4,000 
 
 . 2,828 
 5,656 
 
 40 
 40 
 
 2,000 
 4,000 
 
 16 
 16 
 
 2,000 
 4,000 
 
 Battery commander's ruler, for 2.95-inch mountain gun. 
 
 
 12.5-pound 
 projectUe. 
 
 18-pound 
 projectile. 
 
 
 First 
 problem- 
 
 Second 
 probleuL 
 
 Third 
 problem. 
 
 Fourth 
 problem. 
 
 Given: 
 
 Angle of site of target 
 
 100 
 
 600 
 
 3,800 
 
 363.4 
 
 -20 
 1,000 
 3,400 
 
 177.3 
 
 100 
 
 600 
 
 3,800 
 
 493.8 
 
 -20 
 
 Range of obstacle 
 
 1,000 
 
 Range of target 
 
 3,400 
 
 Result: 
 
 Height of trajectorv, calculated 
 
 272.7 
 
 
 
 For 3-inch field gun. 
 
 
 First 
 problem. 
 
 Second 
 problem. 
 
 Third 
 problem. 
 
 Fourth 
 problem. 
 
 Given: 
 
 Angle of site of target 
 
 +130 
 1,000 
 4,600 
 
 282 
 
 -15 
 
 200 
 
 2,800 
 
 64 
 
 +20 
 2,400 
 5,200 
 
 164 
 
 +50 
 
 Range of obstacle 
 
 4,000 
 
 Range of target ... 
 
 5,600 
 
 Result: 
 
 Height of trajectorv. calculated 
 
 150 
 
 
 
73 
 
 For 4.7-inch gun. 
 
 
 First 
 problem. 
 
 Second 
 problem. 
 
 Third 
 problem. 
 
 Fourth 
 problem. 
 
 Given: 
 
 +1.% 
 1.000 
 6.O00 
 
 2S:!.2 
 
 -15 
 200 
 
 2,800 
 
 •12.2 
 
 + 20 
 3,800 
 6,700 
 
 137. 9 
 
 +50 
 
 Range of obstacle 
 
 Range of target . i 
 
 6.000 
 
 7 800 
 
 Result: 
 
 Height of trajectory, calculated 
 
 156.1 
 
 Sextant telemeter, Type A, model of 1911, slide ruler for solution of triangles. 
 
 
 First 
 problem. 
 
 Second 
 problem. 
 
 Third 
 problem. 
 
 Given: 
 
 Angle in mils 
 
 1.600 
 7 
 65 
 
 9,458 
 
 SOO 
 24 
 
 500 
 
 Difference in mils 
 
 3 9 
 
 Base 
 
 100 ! 36 
 
 Rcsnlt: 
 
 3,001 1 5,402 
 
 
 
INDEX 
 
 All numbers refer to paragraphs. 
 
 A. 
 
 Aiming circle, model of 1916: 
 
 Angle of sight mechanism, to disassemble 153 
 
 Azimuth worm mechanism, to disassemble 154 
 
 Compass mechanism, to disassemble 155 
 
 Compass needle, to remove 156 
 
 Elbow prism, to clean 149 
 
 Elevation mechanism, to disassemble 151 
 
 Erecting prism, to clean 149 
 
 Eyepiece, to disassemble 148 
 
 General information 147 
 
 Objective, to clean 150 
 
 Objective, to remove 152 
 
 Objective prism, to clean ! 150 
 
 Azimuth instrument, model of 1900 , • 177 
 
 Adjustment of worm .'J . .': .■'.■ 166 
 
 Azimuth instrument, model of 1910 , 177 
 
 Adjustment of worm , ..t^ , 166 
 
 Assembly of 178 
 
 Disassembly of 177, 178 
 
 B. 
 
 Balsam, application of 41 
 
 Deterioi-ation of 28 
 
 Battery commander 's ruler, test of 209 
 
 Battery commander's telescope, models of 1904 and 1905: 
 
 Adjustment of telescope 94, 98 
 
 Assembly of base 174 
 
 Assembly of telescope 87, 90, 91, 93 
 
 Cleaning of telescope 86, 87, 89, 91 
 
 Collimation of 95, 96 
 
 Disassembly of base 174-176 
 
 Disassembly of telescope 87-93 
 
 Battery commander's telescope, model of 1915: 
 
 Elevation worm mechanism, to disassemble 103 
 
 Eye lens, to remove 101 
 
 Eyepiece, to disassemble 102 
 
 Objective, to remove ^ 100 
 
 Objective pi-ism, to clean 99 
 
 C. 
 
 Cement, litharge 39, 161 
 
 Cementing of optical surfaces 41 
 
 Chart, canvas 203 
 
 (75) 
 
.76 
 
 Cheat, use of 6 
 
 Cleaning, instructions for 6, 29 
 
 Clinometer, adjustment of.* 19 
 
 Use of 18 
 
 Collimating telescope. See Telescope, collimating. 
 
 D. 
 
 Deflection board for guns, test of 209 
 
 Deflection board for mortars, test of 209 
 
 Depression position finder, Lewis, model of 1907: 
 
 Adjustment of cross wire 35, 80 
 
 Assembly of compensating mechanism 197 
 
 Assembly of range mechanism 196, 198 
 
 Change of class of 194 
 
 Collimation of telescope 81-85 
 
 Disassembly of azimuth mechanism 190, 192 
 
 Disassembly of compensating mechanism 193, 195 
 
 Disassembly of range mechanism. 190, 191 
 
 Test of \ 199, 200 
 
 Depression of position finder, Lewis, type A, adjustment of prism 66 
 
 Depression of position finder, Swasey, tyY>e A: 
 
 Adjustment of telescope 65 
 
 Disassembly of base 179 
 
 Disassembly of telescope 63, 64 
 
 Depression position finder, Swasey, types Al and All: 
 
 Adjustment of azimuth worm 166 
 
 Adjustment of height scale 188 
 
 Adjustment of range mechanism 187 
 
 Adjustment of telescope 78, 79 
 
 Adjustment of telescope level 77 
 
 Assembly of azimuth mechanism. 179, 185 
 
 , Assembly of range mechanism 186 
 
 Assembly of telescope 76 
 
 Collimation of telescope 78 
 
 Disassembly of azimuth mechanism .! 179 
 
 Disassembly of curvature mechanism 183 
 
 Disassembly of range mechanism 180-182, 184 
 
 Disassembly of telescope 75, 76 
 
 Test of 189 
 
 Disassembly, by whom 11, 12 
 
 E. 
 
 Erecting systems, construction of 22, 23 
 
 Eyepiece, adjustment of 26 
 
 Construction of , 25 
 
 F. 
 
 Field artillery range finder, general information 146 
 
 G. 
 
 Glass, decomposition of 27 
 
77 
 
 H. 
 
 Humidity, effects of 7, 27 
 
 L. 
 
 Lens, adjustment of 26 
 
 Cementing of 42 
 
 Cleaning of 30 
 
 Deterioration of 27, 28 
 
 Test of - 33 
 
 Level, adjustment of 53, 54, 170-172 
 
 Replacement of 169 
 
 Test of 168 
 
 M. 
 
 Mirror, silvering of 40 
 
 O. 
 
 Objective, construction of 20 
 
 Adjustment of 26 
 
 Test of 33 
 
 Observation telescope, field, disassembly of telescope 104, 105 
 
 Oiling 6 
 
 Optical repair kit 15 
 
 Tool No. 29 46 
 
 Tool No. 32 123 
 
 Tool No. 34 123 
 
 Tool No. 36 177 
 
 Tool No. 37 ; 175 
 
 Tool No. 41 : 174 
 
 Tool No. 43 185 
 
 Tool No. 73 81 
 
 Tool No. 85 16, 48, 51, 81, 127, 128 
 
 , Tool No. 86 16, 48, 81, 128 
 
 Tool No. 87 50, 51 
 
 Tool No. 88 127 
 
 Tool No. 89 127 
 
 Tool No. 90 16, 128 
 
 Tool No. 98 17, 48, 59, 62, 73, 81 
 
 Tool No. 99 73 
 
 Tool No. 101 59 
 
 Tool No. 102 48 
 
 Tool No. 103 62 
 
 Tool No. 104. ■ 157 
 
 9 
 P. 
 
 Panoramic sight, model of 1904 : 
 
 Adjustment of azimuth circle 128, 129 
 
 Adjustment of prisms. 127, 130-132 
 
 Adjustment of reticule 126, 127 
 
 Assembly of 122 
 
 Cleaning of - 111,120,121,124 
 
 Disassembly of Ill, 119, 123, 125 
 
 Sealing of Ill 
 
78 
 
 Panoramic sight, model of 1915 : 
 
 Azimuth mechanism, to disassemble 136 
 
 Deflection mechanism, to disassemble 137 
 
 Eye piece, to disassemble 134 
 
 General information 133 
 
 Objective lens, to remove 138 
 
 Rotating head mechanism, to disassemble 135 
 
 Plotting boards for mobile artillery 204 
 
 Test of • .• . . . 209 
 
 Plotting boards for seacoast artillery, backlash in 165 
 
 Form for report on 208 
 
 , Test of ; 207 
 
 Plaster, use of 37 
 
 Prism, adjustment of 68 
 
 By whom disassembled 12 
 
 Cementing of 43 
 
 Cleaning of : 31, 32 
 
 Construction of 18, 19, 23, 24 
 
 Deterioration of 22, 23, 27, 28 
 
 Plastering of 37 
 
 Silvering of 40 
 
 Test of ^ 33 
 
 Q. 
 
 Quadrant. (5ge Range quadrant.). 
 
 R. 
 
 Range board, Pratt, chart of 203 
 
 Test of 209 
 
 Range finder, Weldon: 
 
 Assembly of 141-143 
 
 Cleaning of < 140 
 
 Construction of. : 139 
 
 Prism for , 144, 145 
 
 Steel tape for 205 
 
 Range quadrant, adjustment of level 171, 172 
 
 Repairs, by whom made 8, 9, 11, 12 
 
 How made 5, 8, 164 
 
 Report, to whom made 8 
 
 Reticule, illumination of 44 
 
 Mounting of 34 
 
 {See also various telescopes.) 
 
 Rubber 204 
 
 Ruler, battery commander's. (See Battery commander's ruler.) 
 
 ,8. 
 
 Scale arms 201 
 
 Screw threads • 13 
 
 Sextant telemeter, type A: 
 
 Adjustment of..'.. .. .* 160, 162. 163 
 
 Assembly of 157, 161 
 
 Disassemblv of 157-159 
 
 Test of...- ^ 209 
 
 Silvering: 
 
 Mirrors 40 
 
 On metal 38 
 
79 
 
 T. 
 
 Tape, steel 205 
 
 Telescope, collimating 16, 17 
 
 Telescopic sight, models of 1896 Mi, 1897, 1898, and 1898 M: 
 
 Adjustment of 50-58 
 
 Collimation of 56, 57 
 
 Telescopic sight, model of 1899: 
 
 Assembly of 47 
 
 Collimation of 48 
 
 Disassembly of 46 
 
 Telescopic sight, model of 1902, collimation of 59 
 
 Telescopic sight, 3-inch, model of 1904, Nos. 1-26 inclusive: 
 
 Adjustment of : 62 
 
 Assembly of 62 
 
 Disassembly of 60, 61 
 
 Telescopic sight, 3-inch, model of 1904, after No. 26: 
 
 Adjustment of 73, 74 
 
 Assembly of 7, 72 
 
 Disassembly of 69-72 
 
 Telescopic musket sight, model of 1908: 
 
 Adjustment of 109 
 
 Disassembling of 106-108 
 
 Telescopic musket sight, model of 1913: 
 
 General information 110 
 
 Time-interval recorder 206 
 
 Tools. (See Optical repair kit.) 
 
 W. 
 
 Warping 202 
 
 Wind component indicator, test of 209 
 
 Wire, cross. (See Reticule.) 
 
 Wooden part 202 
 
 War Department, 
 
 Office of the Chief op Ordnance, 
 
 Washington, January 4, 1916. 
 
 December 18, 1906. 
 
 Revised November 1, 1909. 
 
 Revised October 9, 1912. 
 
 Revised January 4, 1916. 
 
 Form No. 1795. 
 
 Ed. Aug. 24-17—3000. 
 
 38025-2734-1. 
 

 
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 AIMING circle: 
 
 AIMING CIRCLE, MODEL OF 1916. 
 

 14 DAY USE 
 
 RETURN TO DESK FROM WHICH BORROWED 
 
 This book is due on the last date stamped below, or 
 
 on the date to which renewed. 
 
 Renewed books are subject to immediate recall. 
 
 L 
 
 ,.^o'5BWJ 
 
 ! 
 
 REC-D LD 
 
 
 AUG 14 19S8 
 
 
 
 i 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ! 
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 General Library 
 LD 21-50771-8, '57 University of California 
 (C8481sl0)476 Berkeley 
 
 ^ 
 
YC 64382 
 
 Syracuse. NJ 
 
 
 
 
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 UNIVERSITY OF CAUFORNIA UBRARY 
 
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