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 DESCRIPTION 
 
 OF THE 
 
 GALVANIC CHRONOGRAPHIC 
 
 APPARATUS 
 
 OF THE 
 
 ROYAL OBSERVATORY, GREENWICH. 
 
 [Foi'ming the Appendix to the Greemmch Observations^ 1856 . ) 
 
 LONDON; 
 
 PRINTED BY GEORGE EDWARD EYRE AND WILLIAM SPOTTISWOODE, 
 PRINTERS TO THE QUEEn’s MOST EXCELLENT MAJESTY. 
 
 FOR HER MAJESTY’S STATIONERY OFFICE. 
 
 1857 . 
 

 DESCRIPTION 
 
 01<' THE 
 
 GALVANIC CHRONOGRAPHIC APPARATUS 
 
 OT* THE 
 
 ROYAL OBSERVATORY, GREENWICH. 
 
 The practical introduction of Galvanic Chronographic Apparatus, in a form available 
 for the purposes of an Observatory, is entirely due (so far as I am aware) to American 
 Astronomers. The history of its successive steps of advance in the United States is 
 given, with due reference to official documents, in the Annals of the Astronomical 
 Observatory of Harvard College, Vol. I. Part I. It was from a letter of Dr. Locke to 
 myself, dated 1849 , January 13 , that I first became acquainted with the system pro- 
 posed by that gentleman ; and from a letter of Professor Mitchel, dated 1849 , July 10, 
 that I received details of Professor Mitchel’s method, though I was aware that his 
 attention had been for some time directed to the subject. 
 
 The method of Dr. Locke contemplated the keeping a galvanic battery in constant 
 action during those portions of time in which no signals (whether for clock-seconds or 
 for moments of observation) were exhibited ; the battery-action being suspended for 
 the instant in which the signal is given. Professor Mitchel’s method employed the 
 battery only for giving the signal. This appeared to me preferable, both for diminution 
 of the consumption of battery-elements, and for the superior distinctness of the signal. 
 The fillets employed by Dr. Locke appeared to me entirely inapplicable to the uses of 
 an Observatory, where more than 500 feet would be required for a single evening ; they 
 are not, however, essential to his principle. Professor Mitchel’s specimens exhibited 
 the second-signals as dots in a radial arrangement, the measures of time being taken 
 along the circumferences of successive circles, and thus representing equal portions of 
 time by different measures of space, according to the radius of the circle on which they 
 fell. This appeared to me likely to lead to inconvenience ; it is not, however, necessarily 
 connected with the system. 
 
 B 2 
 
[iv] Description of the Galvanic Chronographic Apparatus 
 
 On reviewing these matters, it appeared to me that the objeets to be obtained, in 
 order to make tlie principle of chronographic registration useful at the Royal Observa- 
 tory, must be the following : — 
 
 1 . The record must be made by dots or punctures, following each other in a spiral 
 line upon a sheet of paper wrapped round a cylinder, which revolves, nearly or exactly^ 
 in a definite time of convenient period as referred to sidereal reckoning. 
 
 2. jSIeans must be provided for interrupting at pleasure that movement upon which 
 the sequence of spirals depends, and at the same time interrupting the action of the 
 galvanic battery, in order that paper may not be unnecessarily consumed Mhen obser- 
 vations are discontinued. 
 
 3. Means must be provided for distinctlj’- separating the records of observations made 
 before and after such discontinuance. 
 
 4. An important result would be attained if the regulation of the movement could 
 be made so perfect, that the instrument itself, while maintaining the motion of the 
 barrel, could itself be used as transit-clock, 
 
 5. Supposing this object to be not attained, it is still very desirable that the barrel 
 revolve with great uniformity, in order that the punctures of different turns of the 
 spiral corresponding to the same second of transit-clock-time but in different minutes, 
 should be arranged in a straight line as nearly as possible parallel to the barrel-axis, for 
 the sake of focility of reading. 
 
 With these guiding principles, the apparatus was arranged in the form which I now 
 proceed to describe. 
 
 Figure 1 is a view of the whole apparatus from the south. (The dial-plate of the 
 clock faces the east.) It is to be remarked that the barrel is protected by a jointed 
 case of plate-glass, and that the clock and the pendulum are inclosed in boxes whose 
 sides consist of glass pannels, and thus the whole which is represented in Figure 1 is 
 actually at once visible to the eye, except only a part of the pendulum-suspension, 
 which is indicated by dots. 
 
 A is the cast-iron platform which supports the whole of the apparatus except the 
 pendulum. It is an inverted tray, strongly ribbed ; its upper surface was planed by 
 the planing-engine. The height of the upper surface above the floor of the room is 
 3 ft. 4 in. 
 
 B,B, are two of the four posts which support A. They are connected by diagonal 
 braces below the range of this view; 
 
 C is a box, through MRich the clock-weight descends. 
 
 D, D, two standards, whose pedestals arc screwed upon A, which support the anti- 
 friction wheels on which the pivots of the barrel rest. 
 
 E, the Great Barrel, revolving in 2 minutes of sidereal time. It is of brass, and is 
 covered with a layer of woollen cloth. A sheet of paper is wetted, and in this state is 
 
OF THE Royal Observatory, Greenwich, 
 
 [v} 
 
 wrapped round the cloth, and its folding edges are united by cement ; when the paper 
 becomes dry, its surface is tight and smooth. To remove the paper, the cemented 
 edges are wetted. Six similar barrels are provided, in order that when one is fully 
 charged, another may be substituted for it without delay. 
 
 F is the toothed wheel of 300 teeth upon the eastern end of the barrel. 
 
 G, G, two standards which carry the support of the pinion that drives F, the two 
 guides of the sliding pricker-frame, the two long screws which give motion to the 
 piicker-frame, and the apparatus for ungearing the long screws, and for suspending the 
 galvanic action. 
 
 H, the pinion of 30 teeth, revolving in 12 seconds, which drives the wheel F. It 
 receives motion from the clock. 
 
 I, the spindle of H. It is not a spindle of a wheel of the clock, but is connected 
 with a spindle of a wheel of the clock in the same line by a clutch, which acts at the 
 beginning of the connexion by friction, and finally makes a firm union. 
 
 J, J, the two guides of the sliding pricker-frame. 
 
 K, the upper of the two long screws by which the pricker-frame is made to travel. 
 The screw-thread is removed from a few inches of that end of the screw which is visible 
 in this view, in order that, if from inadvertence the revolution of the screw should be 
 permitted to continue after the arrival of the pricker-frame at the west end of the 
 screw, the power of the screw to continue its longitudinal motion should cease, and 
 there should be no danger of breaking the frame of the instrument. 
 
 L is a balanced winch for occasionally turning the screw K by hand, when it is not 
 connected with the clock. 
 
 M, M, is a spindle of a wheel of the clock, connected with K, when necessary, by a 
 clutch. It revolves in ten minutes. 
 
 N is the lower of the two long screws. It is connected (as regards rotatory motion) 
 with K by toothed wheels on the outside of the vrestern standard G, so that it necessa- 
 rily revolves in the same time as K. 
 
 0, O, is the wooden frame of the box of plate-glass which covers the barrel. 
 
 1 , P, &c. aie brass hinge-pieces screwed to the plate-glass with intervening layers of 
 vulcanized caoutchouc. 
 
 Q, Q, two handles fixed in the bottom of the lower piece of plate-glass. To open the 
 box, the lower plate is turned upwards and over till its handles Q rest upon the upper 
 plate, and then the two plates are turned up together into a vertical position, in which 
 they are retained by a wooden hook, omitted in this Figure, but shown in Figure 2. 
 
 R is a system of four galvanic wires, by which power is given to the two galvanic 
 magnets wdiieh drive the two prickers that make the punctures on the barrel. Two of 
 the wires with one magnet have relation to the circuit which is completed at every 
 second b}'- the action of the transit-clock, and thus, by means of one of the prickers, 
 impress on the barrel a puncture at every second ; the other two are in the eircuit which 
 is completed by the touch of the observer’s finger, and thus, by means of the other 
 
[vi} Description of the Galvanic Chronographic Apparatus 
 
 pricker, impress on the barrel a puncture at the instant of each observation. (It will 
 be mentioned below that two wires, acting by one galvanic magnet and one pricker, are 
 sufficient for both those offices, but that four wires and two prickers are convenient.) 
 The wires pass over fixed bearers near the ceiling of the room, while their lower ends 
 partake of the motion of the frame carrying the galvanic magnets and prickers, as it 
 slides from one end of the barrel to the other. The descriptions attached to the four 
 wires correspond to the nomenclature of attachments in the map of wires, &c. preserved 
 in the Observatory. 
 
 S, a piece of wood attached to the ceilmg of the room, with four rounded openings 
 through which the wires pass. 
 
 T, a wooden case inclosing the four wires in their descent to the floor, on their way 
 to the batteries in the basement, and to the subterraneous passage to the transit-room. 
 One of them rises again to the gearing-rheotome X, and again descends through the 
 |loor. 
 
 V, the observation-rheotome, or small apparatus for interrupting or completing the 
 circuit of the observation-current. There is a similar apparatus, the transit-clock- 
 rheotome, beneath the platform A (not shown in the plates), for interrupting or com- 
 pleting the circuit of the current produced by the beats of the transit-clock ; this is 
 employed in the operation of ruling lines upon the barrel E. 
 
 W is one of the transit-clock- wires, which, having been led from the contact-spring 
 in the transit-clock, rises up through the floor to the gearing-rheotome X. 
 
 X is the gearing-rheotome. It is so connected with apparatus, to be described below, 
 that the same movement which puts the long screw K in connexion with the clock- 
 spindle M, does at the same time complete the circuit through X ; and when the con- 
 nexion of K and M is broken, the circuit through X is also broken. The other wire 
 which descends from X through the floor is not seen in this view. 
 
 The details of the clock will be described in the explanation of subsequent figures, 
 
 Y is the wooden frame of the glass case of the clock. 
 
 Z is the vertical spindle which is put in motion by the clock and revolves in two 
 seconds. 
 
 a is the radial arm carried by Z, moving in a horizontal plane and acting on the 
 pendulum-spike h. 
 
 b is the stone pillar which rises through the room to support the northern pivot of 
 the polar axis of Shuckburgh’s equatoreal in the room above. 
 
 c is the large cast-iron bracket which carries the suspension-piece of the clock- 
 pendulum. It embraces two sides of the pier b, and is fixed to each side by a single 
 strong screw. 
 
 d is a flat iron plate sliding upon the top of c, and adjusted horizontally by three 
 screws, of which two are seen in the view. The suspension-piece of the pendulum is 
 attached to its lower surface, and passes downwards through a large opening in the 
 horizontal part of the bracket c. 
 
OP THE Royal Observatory, Greenwich. 
 
 {vii} 
 
 e, a case inclosing the pendulum-suspension. 
 
 f, the suspension arches of the pendulum, to be described hereafter. The suspension- 
 apparatus permits the pendulum to move in every direction. 
 
 g, the pendulum ; it is a compensation pendulum, with steel rod and quicksilver in 
 an iron cistern. Upon the steel rod there is a small sliding weight, for adjustment of 
 rate. 
 
 h, the spike at the bottom of the pendulum cistern, on which the radial arm a of the 
 clock acts ; by this action the circular motion of h or the conical motion of g is main- 
 tained. 
 
 i, the wooden frame of the glass case which incloses the pendulum. 
 
 Figure 2 is a view of the apparatus from the east side. 
 
 k shows the position of the plate-glass-covering of the Barrel, when it is opened. 
 
 1, a wooden hook, for retaining the plate-glass in a safe position. 
 
 in, the dial-plate of the clock ; it shows hours to 24, minutes to 60, and seconds to 
 60. The seconds-hand travels with a uniform smooth motion. 
 
 n, a small slider guided by two screws, partly hidden in Figure 2 by the dial-plate, 
 but exhibited completely, and on a larger scale, in Figure 2 Its explanation will 
 
 be best understood from the following : — 
 
 Figuie 2 (^), the slider n as seen from above. In the process of ruling lines on 
 the bairel, it is necessary to slide one of the clock-spindles lengthways, so as to ungear or 
 detach its wheel from the pinion in which it acts. By withdrawing a locking-lever at 
 the distant end of the spindle, the separation is permitted 5 and by pushing forward the 
 slider n or o, whose inclined end acts on the near end of the spindle, the spindle is forced 
 endways, and is letained in the position to which it is so forced ; and the separation of 
 the wheels is thus effected. 
 
 ^ p, a lever, by pushing which in the longitudinal direction of the barrel-axis, the 
 circuit is completed at the rheotome X, and at the same time K is put in connexion 
 with M ; or, by pushing in the opposite direction, the galvanic circuit and the spindle 
 connexion are both broken. The lever is seen more completely in Figures 12 and 14. 
 
 q, a small piece of wood, attached by a hinge to the wooden frame of the cover of 
 the barrel. When it is lifted, the lever p can be moved from one position (as that of 
 completing circuit, &c.) to the other position (as that of breaking circuit, &c.), or mce 
 versa ; but when q is dropped, the lever p is retained immoveably in the position (which 
 ever it may be) in which it is placed. It is seen more clearly in Figures 3 and 12. 
 
 r, s, two brass cylinders attached to the clock frame, carrying two glass cylindrical 
 vessels nearly filled with water. 
 
 t, V, two silken cords, passing over pullies. Their upper ends are fastened so as to 
 act horizontally on the frame of the “ intermediate wheel ” in the chronometric 
 governor, and their lower ends sustain weights in the water (conical cups carrying 
 
{viii} Description op the Galvanic Chronographic Apparatus 
 
 shot), the preponderance of one of which over the other defines, in the chronometric 
 governor, the power which maintains the conical movement of the pendulum g. 
 
 Figure 3 is a representation of the apparatus as viewed from above. 
 
 w is a piece of plate-glass covering the greater part of the large opening in the back 
 part of the roof of the box covering the Barrel. 
 
 X is a narrow opening which is left for the system of wires R to travel along, as the 
 pricker-frame travels from one end of the barrel to the other. 
 
 A portion of the pricker-frame is seen imperfectly through w and x. 
 
 y, y, two screws acting in the plate d, and supporting the two primary suspension- 
 springs of the pendulum. They are visible in this view through holes in the plate 
 which covers d. 
 
 z, a small piece of wood attached to the box by hinges, by lifting which the gearing- 
 rheotome X is discovered. 
 
 Figure 4 represents the principal train of the clock, as viewed from the east. 
 
 a is the wcight-line-barrel. 
 
 h is the weight-line (a wire-rope). It supports the weight by a sheaf of two pullies 
 (a single pully also being attached to the lower side oi the platform A), and lises into 
 the clock at c. The tension upon b is about 21 lbs., and it descends 8-4; inches in 
 one hour. 
 
 c is the rising part or return of the weight-line. It is attached to the going-lever m, 
 on which it acts with a tensile force as nearly as possible equal to that with which h 
 acts upon a. 
 
 d is the barrel-ratchet of 48 teeth. 
 
 e, e, the barrel-clicks, their centers of motion being on the wheel h. 
 
 f the going-ratchet of 80 teeth, forming part of the wheel h. 
 
 g, the going-click, whose center of motion is in the fixed clock-plate. 
 
 h, the barrel wheel of 96 teeth, revolving in 2 hours. 
 
 i, the pinion of 32 teeth, in which it works. 
 
 ;, the second wheel of 48 teeth revolving in 40 minutes. 
 
 k, the lantern pinion of 12 teeth in which it works. 
 
 /, the sliding-frame which carries the center of motion of i andy. 
 
 m, the going-lever, on which the tension of the return of the weight-line c acts. 
 
 71 , the center of motion of 711 , fixed in the clock-plate. 
 
 0, the guide fixed to the clock-plate, in which the end-rod of I slides ; the other end 
 of / being jointed to the lever m, and therefore requiring no guide. 
 
 The action of the lever in, slider I, and click g, is the following. As the clock con- 
 tinues going in the ordinary Avay, successive teeth of the ratchet pass undei the click g*. 
 The slider t is kept in position by three forces, namely, the pressure of the teeth of 
 
OF THE Royal Observatory, Greenwich. 
 
 i" ix 
 
 1i against the teeth of i (as produced immediately by the weight-line (5»), the reaction of 
 the teeth of k against those of /, and the pressure of the lever m (produced by the 
 return of the weight-line c), acting to thrust the slider endways. The position taken 
 by the slider under this action is definite ; as, if it slide too far to the left, the moment 
 of the action of c upon the lever m is increased, and tends to bring it to the right ; or 
 the contrary, if it is too far to the right. But when the winch is applied to Avind up 
 the cord, the pressure of h upon the wheel h ceases entirely. The pressure of c and m 
 continue, and the portion of this pressure which is throAvn upon the teeth of i pushes 
 the wheel Jb backwards, till a tooth of f lodges against g. Then the rotation of k is 
 kept up by the action of the teeth of /, in the movement which is caused by the pressure 
 of m upon the slider /, and which carries I towards the right, the wheels i and j at the 
 same time revolving in the bush which is fixed in 1. The effect of this movement 
 is that the Avheel j does for the time revolve round that tooth which is in bearing on 
 the teeth of the Avhecl h (iioav firmly fixed) ; and thus revolving, it maintains the 
 motion of k as in the ordinary state. The line c during this time is descending. As 
 soon as the pressure of the hand on the Avinch is relieved, h presses i and I to the left ; 
 and, as the moment of the action of c cn m has been diminished by the change of 
 position of m, the pressure of h on I overcomes it and forces the lever m to the left, 
 raising the cord c, and restoring all to their original state. 
 
 It Avas intended at first to use a smaller pinion for ^ and a larger Avheel fory, Avith the 
 purpose of making the barrel a go for 8 days ; and the lever ?)i and guide o Avere accom- 
 modated to this. But it AVRS found that an inconveniently heavy Aveight Avould be 
 required, and the Avheels Avere so changed as to make the barrel go 2 days only. 
 
 pis a wheel of 70 teeth revolving in 10 minutes. The spindle of this Avheel is M, 
 which is connected bv a clutch Avith the lonq- screw K. 
 
 7, the pinion of 7 teeth in Avhich p acts. 
 
 r, a wheel of 40 teeth, revolving in one minute. This Avheel carries the seconds- 
 hand. 
 
 s, the pinion of 8 teeth in Avhich it acts. 
 
 if, a contrate Avheel of 48 teeth, revolving in 12 seconds. The spindle of this wheel 
 is connected by a friction-clutch Avith I, the spindle of the large pinion H, Avhich acts 
 in F to drive the Barrel E. It is upon the near end of the spindle of t that the slider 
 n or o acts. When the locking lever at the distant end of the spindle (to be hereafter 
 described) is removed, and the slider n or o is forced, the contrate wheel t is pushed 
 out of its gearing with the pinion u, but s is not detached from gearing with r, nor H 
 from F, and thus the Barrel can be turned with great rapidity without any interference 
 with the movement of the pendulum or the wheels immediately connected with it. 
 
 «, a pinion of 8 teeth with vertical spindle, revolving in 2 seconds, 
 a fly attached to u, consisting of a bar loaded at its extremities, 
 a bevelled wheel of 50 teeth on the same spindle. 
 
 Gueenwicii Obsek\wtion.s, 1856 . — Appendix. ^ 
 
{xj Description of the Galvanic Chronographic Apparatus 
 
 the flat friction-plate on the same spindle. It receives the friction which, in a 
 modification of the chronometric-governor, regulates the expenditure of power, and 
 leaves a uniform force to act on the wheels that maintain the rotation of the pendulum. 
 
 y, the bevelled “ intermediate wheel” of 50 teeth. Its center of motion is carried by 
 the moveable frame on which the fine cords t and v act. In rotation round its center, 
 it is driven by w. 
 
 z, a bevelled wheel of 50 teeth attached to the vertical spindle Z. It is driven hjy. 
 
 «, «, a, three anti-friction wheels which support the upper part of Z. One of them 
 
 is carried by a spring. 
 
 i6, the cock which carries the upper pivot of u, a:, and w, the lower pivot of Z, and 
 the center of motion of the moveable frame that carries the center of motion of y. It 
 will be remarked that there is no connexion between w and except by the action of 
 the “ intermediate wheel ” y ; and that iv and 2 ; revolve in opposite directions. 
 
 y, the arch-head of the moveable frame, with a groove in which the cords t and v act. 
 A hole which is seen in /3 is made for the purpose of allowing the end of the arch- 
 head to pass freely through (3. 
 
 £, a cup loaded with a piece of lead, connected with the arch-head by a flexible 
 spring, and travelling by means of a wheel upon the curved lever. 
 
 e, the curved lever, to be described hereafter. 
 
 K, the near or eastern pivot of the curved lever. The axis of the curved lever is in 
 the direction perpendicular to the clock-face. 
 
 is used in other figures to denote the distant or western pivot of the curved lever, 
 a counterpoise for the curved lever. 
 
 0, the pressure-pin fixed in the lower side of the curved lever. This pin presses 
 upon the friction-plate .r. The amount of its friction depends on the position of the 
 arch-head y and the weight S. When S has travelled so far upon the curved lever as to 
 be far removed from the axis of which '( is the pivot, the pressure of S upon the friction- 
 plate, and the consequent friction, are so great as to stop the clock. When 8 is nearly 
 above the axis, as in the view, the pressure and friction are insignificant. 
 
 1 , I, the tAvo brass cups in water, partly loaded with shot, suspended from t and v. 
 
 Figure 5 is the dial-train. 
 
 X, a pinion of 12 teeth, on the same spindle as /r, p, and M, revolving in 10 
 minutes. 
 
 A a wheel of 72 teeth, revolving in one hour and carrying the minute hand. 
 
 jj. a wheel revolving in 24 hours and carrying the hour hand. 
 
 No further explanation is necessary. 
 
 Figure 6 is a view of the upper or regulating part of the clock, from the south. 
 
 V is an index, pointing to a graduation upon the arch-head, which gives a measure of 
 
OF THE Royal Observatory, Greenwich. 
 
 (xi] 
 
 the position of the arch-head, and of the consequent position of the weight S, and of the 
 friction which the pressure-pin 0 produces on the revolving friction-plate x. 
 
 Figure 7 is a horizontal plan of the regulating part of the clock, 
 
 ^ is the western pivot of the curved lever. 
 
 Figure 8 is a horizontal plan of the friction-plate and curved lever only. 
 
 Figure 9 is a horizontal plan of the arch-head and parts connected with it only. 
 
 The action of the regulating-part may now be explained. It must be understood 
 that the weight hanging on the cord v is greater than that hanging on the cord t. Let 
 the excess be W. This will have the elfect of pushing the center of the intermediate 
 wheel y towards the south with a force n x W, where n is the proportion of the radius 
 of the arch-head to the distance oiy from the center of the arch-head. In the ordinary 
 
 state of things, with the arch-head resting tranquil, there must be a pressure — 
 
 exerted by the teeth of w upon those of y, and a pressure — g — exerted in the opposite 
 
 direction by the teeth ofy upon those of which implies a pressure of ” exerted by 
 
 the teeth of 2 ; upon those of^ in the same direction as the first ; and thus all the forces 
 sustained hyy balance. But as we cannot assert that the magnitude of the weight acting 
 
 upon the barrel a is such as to produce exactly the pressure — 2 — the teeth of w, 
 we must apply a Aveight to the barrel which will, unless it is reduced, produce a force 
 greater than - 2 — the teeth of w, and we must have some means of reducing that 
 
 91 X 
 
 force on the teeth of iv to the value — 2 “’ '^'he means of reducing is given in the 
 
 friction of the presure-pin 0 upon the friction-plate x, produced by the weight S. The 
 arch-head therefore w^hen tranquil must rest in one certain definite position, which draws 
 the weight S to such a position upon the curved lever, that the pressure of the pressure- 
 pin 0 upon the friction-plate x exactly consumes the excess of force derived from the 
 
 t X W 
 
 weight-barrel, and leaves the due pressure — 2 — 3,ct on the teeth of y. 
 
 Suppose now, from inequality in action of the weight-line on the weight-barrel, 
 friction in the train, resistance of the Great Barrel, or any other cause not higher in the 
 wheel-work than w, the force which acts on w; is suddenly increased, so as to accelerate 
 the revolution of v, ?x, and x. The rotation of 2 ^ will not be immediately affected, for 
 it is connected by the arm a with the heavy pendulum, whose inertia is very great. 
 Consequently the acceleration of the rotation of v, w, and 2 ;, will carry the wheel y and 
 its center towards the north, or the arch-head towards the south ; it will therefore 
 draw the weight 8 further along the curved lever so as to be farther from the axis ? ; 
 
 it will therefore increase the pressure of S upon x, and the consequent friction ; and will 
 
 UNIVErtSiTY OF C 2 
 
 ILLINOIS LIBRARY 
 
[xii] Description of the Galvanic Chronographic Apparatus 
 
 thus reduce the power derived from the train of wheels till the remainder which acts 
 
 • • • • • 7?- X W t • 
 
 upon ?/ is diminished to its proper value —2 — 5 which the arch-head will be 
 
 tranquil. 
 
 It is easy to observe this effect by any arrangement which impresses either greater 
 foj'ce or greater resistance on the wheel-train or Great Barrel. If the Barrel is put out 
 of balance, by altering one of the adjusting-weights to be hereafter mentioned, the 
 arch-head y is seen to slide backwards and forwards under the index v, the period of its 
 oscillation coinciding exactly with the time of rotation of the Barrel. 
 
 By this arrangement, therefore, the maintaining power upon the wheel y is sensibly 
 constant, and that upon the arm a, which immediately maintains the motion of the 
 pendulum, is affected by the friction, &c., only of the wheels y, z, and of the anti- 
 friction wheels « « «. The only resistance to the motion of the pendulum arises from 
 the resistance of the air and the friction of the suspension. The inclination of the 
 pendulum-rod to the vertical soon becomes such that these forces balance ; and will 
 frequently remain sensibly unaltered during many hours or days. It is, however, much 
 affected by small irregularities in the friction of y, 0, &c. 
 
 When we wish to increase the inclination of the pendulum, which is to be done by 
 increasing the maintaining power upon the wheel y, the process is, not to alter the 
 weight upon the barrel-line (supposed to be great enough or greater than is absolutely 
 necessary), but to put a small shot into the northern cup i. This overcomes the force 
 actually exerted by w upon y, draws the arch-head towards the north, and causes S to 
 travel along the curved lever so as to diminish the pressure of fl upon x, and the con- 
 sequent friction ; and the force exerted by w upon y gradually increases till it becomes 
 equal to the new or increased value of — after which the arch-head remains quiet, 
 as before. 
 
 The object of suspending the cups 1, 1, in water, is to impede the sudden movement 
 of the arch-head (which implies an irregular motion cither of the pendulum or of the 
 Great Barrel) without offering the slightest impediment to its slow movement. 
 
 Figure 10 is a horizontal plan of the upper part of the clock, showing the radial 
 arms, &c. 
 
 Four arms are represented, of which two are mere counterpoises to the others. They 
 have been planned with different intentions. The straighter arms, whose concave sides 
 precede in the ordinary motion, were so shaped in order that the action of the pressing 
 surface of a upon the spike of the pendulum, friction included, might be truly in the 
 direction of a tangent to the circle described. The more curved arms, whose convex 
 sides precede, were so shaped in order that, when the inclination of the pendulum is 
 large, the friction might have some effect in diminishing the resolved part of the force 
 
OF THE Royal Observatory, Greenwich. 
 
 {xiii} 
 
 of gravity on the pendulum (which, at large inclinations, is too great for isochronism) ; 
 the arrangement has not been sensibly beneficial. 
 
 The small projections from the sides of a are lumps of solder which have been affixed 
 for the purpose of measuring degrees of inclination of the pendulum-rod. The inclina- 
 tion usually maintained is about 3.^-°. 
 
 Figure 1 1 is a perspective view from below of the suspension of the pendulum. 
 
 arc two pieces of split metal, connected with the suspension plate d, through 
 Avhich the primary suspension-springs pass. These springs, however, are not supported 
 by 0, but by two screws y y, represented in Figure 3. 
 
 TT, TT, the two primary suspension springs. 
 
 p is an arched piece of brass suspended by v, tt. 
 
 0 - is a piece of brass arched in the opposite direction, and, as regards its horizontal 
 plan, at right angles to p. It is firmly connected with p, and is in fact cast with it. It 
 supports the secondary suspension-springs. 
 
 T, r, the two secondary suspension-springs. 
 
 u, an arched piece of brass, suspended by r, t, in which the pendulum rod g is fixed. 
 
 The attachments of the springs are so adjusted that the top and bottom of the 
 secondary springs are at precisely the same height as the top and bottom of the primary 
 springs. It is evident that, by the combination of the flexures of the two pairs of 
 springs, the pendulum is free to move in all directions, exactly as if it were suspended 
 from the point -which is the intersection of the line joining the top of tt tt, with the line 
 joining the top of r t. The pendulum, in its motion, always turns the same side 
 towards the north. 
 
 Figure 12 is a view, from the south, of the mechanism between the clock and the 
 Great Barrel. 
 
 <p is the locking-lever to wdiich allusion was made in the description of f, Figure 4. 
 The end of the pivot of I rests against it. 4 ) wdll be seen better in subsequent Figures. 
 
 % is the center upon which turns. 
 
 4/, is a notched circular plate or rude toothed wheel firmly fixed to I. The notches 
 have no purpose but to receive the pins of the piece (2). 
 
 wis a tube, sliding freely upon the spindle of the 12-second contrate-weeel if, but 
 compelled by a pin in a slot to receive its rotatory motion. 
 
 It must be remarked that the end of the axis of the contrate-wheel abuts firmly 
 against the end of I. 
 
 ( 1 ) is a long plate of brass firmly fixed to w. 
 
 (2) is a plate in the transverse direction, firmly fixed to w, carrying two pins at its 
 ends which may fall into the notches of 4/. It will be seen better in Figure 13. 
 
 (3) , (3), are long pins firmly fixed to (1). 
 
{xiv} Description of the Galvanic Chronographic Apparatus 
 
 (4) , (4), are two screws, which have double-shoulder-bearing in (1). 
 
 (5) is a loose plate of metal similar to (1), but connected with nothing. It passes 
 loosely over I, and over (3), (3); but the screws (4), (4), are tapped into it. 
 
 (6) , (6), (6), (6), are four steel springs, to press the circular plate \I/. Two of them 
 are fixed to (1), and two are fixed to (5). 
 
 The action of the friction-clutch may now be explained. If the screws (4), (4), be 
 relaxed to the utmost, the plates (1) and (5) will be widely separated, and the action of 
 the two springs (6), 6), attached to (1) will push the slider w back, so that the pins of 
 (2) will be withdrawn from the notches of 4. In this state, there is no connexion 
 between the slider co or the spindle of the contrate-wheel on the one hand, and the 
 spindle I on the other hand. The clock therefore will continue to go (without any sen- 
 sible alteration of the inclination of pendulum and the rate, by virtue of the regulating 
 apparatus) without giving motion to I, H, F, and the Great Barrel ; or the Barrel may be 
 lifted from its bearings, and another barrel may be substituted for it, (which operation 
 will infallibly give motion to H and I,) without disturbing the wheels of the clock. 
 
 It is now required to put the Barrel in connexion with the clock. The attendant 
 drives the screws (4) (4) alternately, as the motion of the clock brings them within 
 his reach, driving them as nearly as possible by equal degrees. The four springs 
 (6) (6) (6) (6) begin to embrace the plate 4/. Their friction at length becomes so great, 
 that they gradually give motion to the Barrel. After a short time it is found that the 
 hold is so complete, that there is no discoverable slip of the springs upon the plate \J/. 
 Still, as accident might cause a slip, it is not proper to trust entirely to this frictional 
 connexion. The screws (4) (4) are therefore driven still further, till the pins of (2) enter 
 the notches of 4/, and then the connexion is perfectly secure. It is necessary to make 
 the connexion in this cautious manner, on account of the great weight of the Barrel and 
 Pendulum, the delicacy of the intervening wheels, and the probability that some would 
 be broken if any sudden connexion were attempted. 
 
 The Barrel is always kept in motion and ready for use, except at the times of 
 adjusting or changing the Barrel, &c. 
 
 (7) is the sliding clutch-piece for connecting M, the spindle of the 10-minute wheel 
 p of the clock, with the long screw K. The pin which compels (7) to receive the 
 rotatory motion of M is not shown in the Figure, but it is to be understood as similar 
 to that by which rotatory motion is given to w. For making connexion with (8), (7) 
 has a center-pin and a pin at the extremity of an arm. 
 
 (8) is the mushroom-head of the long screw K. It has a hole in the center, and a 
 series of holes round the circumference (enlarged on the east side to a conical shape), 
 better seen in a subsequent drawing (Figure 14). When the clutch-piece (7) is pushed 
 towards (8), its pin engages in one of the conical holes, and thereby giving a small 
 motion to the screw, if necessary, it soon enters the cylindrical part of the hole, and 
 the long screw and the 10-minute spindle then revolve together. 
 
OF THE Royal Observatory, Greenwich. [xv] 
 
 (9) is a flat circular disk carried by the clutch-piece, on which the lever p acts to 
 slide the clutch-piece. 
 
 (10) is a hook attached to the lever p for acting on (9), so as to withdraw the 
 clutch-piece. The lever p itself makes the pressure on (9)} which is required for 
 thrusting the clutch-piece into connexion with (8). 
 
 ( 1 1 ) is a brass spring, forming the connecting part of the gearing-rheotome. It 
 springs upwards, except when it is forced down by (14). 
 
 (12) , a galvanic wire passing down through the floor, Avhence it rises under cover of. 
 the case T, passes through S, and descends (forming one of the collection of wires R) 
 to the “ Barrel Magnet A, which drives the Transit-Clock-pricker. It is connected 
 with (11) by an ordinary terminal screw. 
 
 (13) , a brass pin connected with the wire W. 
 
 (14) , a block of wood carried by the lever p. 
 
 When the lever p is pressed towards the west, the block (14) forces (11) into contact 
 with (13), and thus completes the communication between (12) and W. There is 
 then no interruption of the galvanic circuit, of which (12) and W form part, except in 
 the transit-clock, and there it is completed at every second of the transit-clock. It 
 will be remarked that the same motion of the lever p, which forces X into contact 
 with (13), does also establish the connexion between (7) and (8), or between M and 
 K ; so that, at the same instant at which the transit-clock begins its punctures, the 
 screw K begins to revolve, carrying longitudinally the pricker-frame (to be described 
 hereafter). 
 
 (15) , three antifriction wheels carrying the axis of the 12-second wheel. 
 
 (16) , two antifriction wheels carrying the pivot of the Great Barrel. 
 
 (17) , the pivot of the Great Barrel. 
 
 Figure 13 is a perspective view of the friction-clutch, requiring no explanation 
 beyond that which has been given above. 
 
 Figure 14 is a view, from the east, of the eastern standards, &c. 
 
 (18) is the head of the pin on which the lever p turns. 
 
 Figure 15 is a view, from the west, of the western standards, &c. 
 
 ( 19 ) is a toothed wheel attached to the upper long screw K. 
 
 (20) is a similar toothed wheel upon a fixed center. 
 
 (21) is a similar toothed wheel upon the lower long screw N. 
 
 By this arrangement, the two long screws turn in the same direction and with the 
 same velocity. 
 
 (22) is one of the adjusting- weights upon a spoke of the Great Barrel. 
 
Description of the Galvanic Chronographic Apparatus 
 
 {xvi} 
 
 Figure 16 is an end view of the Barrel from the east. 
 
 (22) (22) are the two adjusting weights at the opposite ends of the Barrel. 
 
 (23) (23) are the two fixed weights at the opposite ends of the Barrel. 
 
 For putting the Barrel in balance, there is provided a support, unconnected with this 
 machinery, but bearing antifriction wheels exactly similar to those in this machinery, so 
 that the movement of the Barrel Avhen placed upon it is extremely delicate. The 
 Barrel is turned till one of the weights (22) is in the vertical ; and the other weight (22) 
 is slid till the Barrel does not tend to move, and is then fixed ; then the Barrel is turned 
 till the second weight (22) is in the vertical, and the first weight (22) is adjusted in 
 like manner. The barrel is then perfectly in balance in all positions. 
 
 Figure 17 is a view from the west (partly sectional) of the Pricker-Frame. 
 
 (24) is the foundation-plate of the Travelling Pricker-Frame. A large portion of 
 its central part is cut away, to allow the two Barrel Magnets to project downwaids 
 through it. Near its upper and lower edges it is made thicker, to admit of its being 
 bored and cut with internal screw-threads for the action of the screws K and N. The 
 interval between successive folds of the same thread on either of these screws is 0’5 inch ; 
 and as the screw occupies ten minutes in turning, in which time the great barrel has 
 made five revolutions; it follows that, in one revolution of the barrel, the flicker 
 Frame advances OT inch. There are on each screw three parallel sciew-thieads. The 
 extreme edges of the travelling plate are adapted to slide in chases in the long guides 
 J and J. 
 
 (25) is a brass plate forming the upper portion of the bridge-piece, of which the side 
 is not represented in this view, as it would in great measure conceal the Barrel Magnets. 
 The feet of the bridge-piece are fixed by screws to (24). 
 
 (26) a piece of wood attached to (25), for insulating the connecting brass plates and 
 terminals to which are attached the wires of R and the wires of the coils of the 
 “ Barrel Magnets A and B.” 
 
 (271, (27), one part of the iron core of “ Barrel Magnet A.” The other part of the 
 core is concealed by (27), and the other bobbin of “Barrel Magnet A is concealed 
 by the bobbin in sight. (27) is connected by a screw with (25). 
 
 (28) , (28), similar parts of the core of “ Barrel Magnet B.” 
 
 (29) , (30), (31), three brass cocks attached to (24), in which the pivots of the 
 pricker-levers turn. 
 
 (32) , the piece of iron carried by the “ Pricker-Lever A,” which is attracted by the 
 core (27)- It is represented in the Figure as if at this moment attracted by the effect 
 of a galvanic current passing through the coils of “ Barrel Magnet A.” 
 
 (33) , the pricker or conical point carried by the same lever as (32), which, in con- 
 sequence of (32) being raised, is driven downwards so as to make a puncture upon the 
 paper of the Great Barrel. The punctures given by (33) are those which correspond 
 
OF THE Royal Observatory, Greenwich. 
 
 (xvii) 
 
 to seconds of the Transit-Clock, a current being sent through the coils of “A” bj the 
 completion of circuit, which is effected by a 60-tooth wheel on the arbor of the seconds- 
 hand, forcing two slender springs into contact at every start of the seconds-hand. 
 
 (34) the piece of iron carried by the “ Pricker -Lever B,” which is attracted by the 
 core (28). It is represented in the figure as not attracted at this moment. 
 
 (35) , the pricker carried by the lever of (34), at present withdrawn from the Barrel. 
 The punctures given by (35) are those Avhich correspond to observations ; a current 
 being sent through the coils of “ B ” by the completion of circuit, which is made by 
 the observer’s touch either of a spring on the Transit-Circle, or of a spring on the 
 Altazimuth. 
 
 (36) , a clamping-piece for carrying a glass pen for ruling lines on the barrel. It 
 is attached to the opposite side of the bridge-piece. It will be represented in another 
 Figure. - 
 
 (37) , a spring for forcing (36) into a position which causes the pen to press upon the 
 Barrel. 
 
 Figure 18 is a side view of “ Barrel Magnet B,” &c. 
 
 (38) is a weak spring, whose office is to separate (34) from (28), when the galvanic 
 current has ceased. There is a similar spring for (32). 
 
 Figure 19 is a view of the pricker-frame from below, the barrel being removed. 
 
 The prickers (33) and (35) are separated in the direction transverse to the length 
 of the screws, that is, in the direction of the Barrel’s rotation, by a space as nearly as 
 possible equal to the movement of the Barrel in one second of time (about 0-3 inch). 
 In consequence, the fractional parts of the second of time in an observation are always 
 accurately referred to the second of the transit-clock. The integer seconds also are 
 duly recorded, in consequence of the counting of the transit-clock seconds being 
 made to depend on the transmission of touch-signals through the pricker (35), as will 
 be explained below. 
 
 The prickers (33) and (35) are also separated in the direction of the Barrel’s axis, 
 by a much smaller quantity (about 0*02 inch) sufficient to keep the punctures quite 
 distinct. 
 
 Experiments have been made, on the advantage of dispensing entirely with one 
 pricker, or dispensing entirely with one battery. But it was found that when one 
 pricker only was used, there was risk of confusion of the transit-clock seconds with 
 the record of observations ; and when one battery only was used, the punctures, on 
 occasion of two falling together, were inconveniently feeble. 
 
 Figure 20 is a view ot the pricker-frame from the east, specially for the purpose of 
 showing the ruling-pen and the mounting of the prickers. 
 
 (39) is the center upon which the clamping-frame of the glass pen turns. It will 
 
 Greenwich Observations, 1856 . — Appendix. ^ 
 
{xviii} Description of the Galvanic Chronographic Apparatus 
 
 be seen that the action of the spring (37) tends to force the point of the pen into 
 contact with the Barrel. 
 
 The necessity for ruling the Barrel arises from this circumstance. When a sheet 
 is taken from the Barrel covered throughout with punctures corresponding to clock- 
 seconds, occasionally interspersed with punctures corresponding to observations, it 
 presents to the eye such a confusion of dots that without some leading lines it is nearly 
 impossible to interpret them. It was soon found desirable to rule lines which should 
 be parallel to the line of dots, as following each other in the rotation of the Barrel, and 
 affected by the slow motion of the pricker-frame. By the use of a pen carried by the 
 pricker- frame this will be effected, provided that by means of the clutch-piece (7) the 
 spindle M be put in connexion with K. Now in using fluid ink, it is convenient to 
 perform the operation of ruling rapidly, and therefore it is convenient to use the locking- 
 lever and the slider n or o in such a manner that the contrate-wheel t shall be 
 detached from u, which will allow the clock-weight to turn the Barrel with great velocity, 
 and will give the proportional speed of travelling to the pricker-frame which now 
 carries the pen. Thus the pen will with great rapidity describe a spiral exactly similar 
 to the spiral wdiich is traced by the line of transit-clock -punctures. 
 
 But there is yet an inconvenience to be overcome. When, by means of the lever p, 
 the spindle M is put in connexion with K, the galvanic circuit is at the same instant 
 completed at X ; and thus, during the rapid rotation of the Barrel, the pricker (33) 
 would at every second be forced down to the paper of the barrel, and the paper would 
 be torn and probably the pricker would be injured. To obviate this, the transit-clock- 
 rheotome is provided (to which allusion is made in the description of V), and, the 
 current being interrupted there, no injury arises from completing the circuit at X. 
 
 The material used for the lines is ink very much diluted with water. The entire 
 sheet upon a barrel (about 500 feet of line) is usually ruled at one charge of the pen, 
 and in a very few minutes. 
 
 In this view is exhibited the mounting of the prickers (33) and (35). They are 
 carried by long slender springs, whose upper ends are attached to pieces of brass fixed 
 to the pricker-levers. The springs, in both instances, are on that side of the pieces of 
 metal towards which the Barrel is moving, and they press with a slight pressure of 
 elasticity towards their respective pieces of metal. Although the springs are weak, 
 they very well sustain the endwise thrust which is necessary for making a puncture on 
 the paper. But when the point is lodged for a short time in the paper, the BaiTel still 
 moving drags the pricker with the paper (the flexure of the springs permitting it), and 
 there is no scratch or elongation of puncture. The punctures in fact are well-defined 
 round holes, in the position corresponding to the first blow of the pricker. 
 
 Figure 21 is a view of the 60-tooth wheel fixed upon the arbor of the seconds- 
 hand of the transit-clock, and of the springs which it forces into contact at every second. 
 
 The view requires little explanation. It will be easily understood that the springs 
 are attached to separate pieces of brass, insulated on dry wood, carrying separate 
 
OK THE Royal Observatory, Greenwich. 
 
 {xix} 
 
 terminal screws witii whieh two of the wires of il are connected ; and that there are 
 adjusting screws to determine the position of the springs when the wheel-tooth is not 
 acting on them. The parts forced into contact are a plate of platinum and a pin of 
 platinum. The spark which is formed at contact here, when the circuit is complete at 
 the transit-cloclc-rheotome and tlie gearing-rheotomc, slightly burns the plate and 
 transfers a small quantitj^ of metal from one of the springs to the other ; but several 
 months pass' before the galvanic communication is interrupted. The places of the two 
 springs ought to be so adjusted that the action of the tooth of the 60-tooth wheel 
 takes place after the action of the tooth of the 30-tooth escape-wheel upon the pallet 
 of the clock-pendulum has terminated ; then the resistance of the galvanic springs 
 does not sensibly affect the arc of the clock-pendulum or the maintenance of the pen- 
 dulum’s vibration. 
 
 One tooth of the 60-tooth wheel, namely, that which forces the springs together 
 when the second-hand starts to indicate 60“, is cut away ; and, therefore, one puncture 
 is lost in every sixty punctures upon the Barrel, or two punctures are lost in every 
 revolution of the Barrel ; and, in consequence of the great exactness with which the 
 l^arrcl perforins its revolution in two minutes of sidereal time, two entire columns of 
 punctures in the direction of the axis of the Barrel are suppressed. The method 
 of interpreting these will be understood from the following description of the method of 
 defining the zero of time which was used before the tooth of the 60-tooth wheel was 
 shortened. 
 
 It was an instruction to the observer that at the commencement of some convenient 
 decade of minutes, as for instance 15'\ 40™, he should by the touch-piece upon the 
 Transit-Circle give the following observation-punctures. The intervals were to be one 
 second. Remarking that 40™ contains four decades, he was to touch the touch-piece 
 at P, 2*^, 3 ^, 4^, then to wait for a few seconds, then to give fifteen touches for the 15'\ 
 In this manner a record of certain hours, minutes, and seconds, was made on the Barrel, 
 which left no difficulty in translating the record of every observation into hours, minutes, 
 seconds, and fractions of seconds. The only danger of failure was this, that an un- 
 skilful observer might inadvertently commence his touches at 0^ or 2“, instead of P, 
 and might thus vitiate every record to the amount of one second. 
 
 The risk of error of a second was entirely destroyed by the instrumental suppression 
 of the puncture of one of the seconds, and it only remained to ascertain what second is 
 suppressed. Upon performing the operation just described, it was found that the 
 second lost is 59^ This arises from the circumstance that the two prickers (as has 
 been mentioned) are separated by the space corresponding to one second of time, and, 
 therefore, the record of transit-clock-punctures is (in reference to the observation- 
 punctures) erroneous by one second. This seeming error is corrected by calling the 
 suppressed second 59" instead of 60\ 
 
 The operation for recording the decades of minutes and hours is still necessary as 
 before. 
 
 Greenwich Observations, 1856 .— Appendix. 
 
 E 
 
{xx} Description of the Galvanic Chronographic Apparatus 
 
 The battery for the Transit-Clock consists, at the present time, of fifteen cells, and 
 that for the Observations consists of seventeen cells. The plates are of zinc and 
 platinized silver, about four inches broad and seven inches deep ; the acid used is the 
 sulphuric acid of commerce diluted -with about twenty times its quantity of water. The 
 batteries are always charged and in connexion, and ready for use at any moment. 
 
 The two wires which communicate with “ Barrel Magnet A” are interrupted by the 
 battery and by the two rheotomes, and are then led in underground passages and along 
 the area wall of the dwelling-house to the Observatory, where they pass under the 
 floors to the slender springs in the Transit-Clock. 
 
 The two wires which communicate with “ Barrel Magnet B ” are interrupted by 
 their battery and by one rheotome, and are led to the Observatory, where each of them 
 bifurcates ; one branch from each is led, by contact-rings on the conical axis of the 
 Transit-Circle, to the touch-piece of the eye-end of the Transit-Circle telescope (as 
 is fully explained in the description of the Tran sit- Circle), and the other branch from 
 each is led into the South Dome, where the two branches are soldered to two insulated 
 rings fixed upon the fixed horizontal circle, which are touched by two insulated springs 
 carried by the revolving frame of the Altazimuth. Each of these springs communicates, 
 by bifurcating wires, with two touch-pieces fixed upon the lower horizontal plate of 
 the revolving frame, one adapted to use with Graduated Face of Vertical Circle Right, 
 the other with Graduated Face of Vertical Circle Left. 
 
 The following notice will perhaps give a sufficient idea of the routine of use of this 
 apparatus. 
 
 As the Barrel carries the record of observations made with two instruments (the 
 Transit-Circle and the Altazimuth) which are usually employed by two different 
 observers, there are prepared two cards, one inscribed, “ In use for the Transit-Circle,” 
 and the other “ In use for the Altazimuth.” These cards are loosely tied upon the 
 gearing lever p, and, when the apparatus is not in use, are thrown backwards out of 
 sight. When an observer comes to begin observations, suppose with the Transit- 
 Circle, he first turns the winch L about half a revolution, in order to separate the new 
 series of punctures from the last which was left on the Barrel ; then he presses the lever 
 p to the west, and locks it in that position by the piece q. The “ Barrel Magnet A ” 
 immediately begins to make the transit-clock-punctures. Then he places in front the 
 card “ In use for the Transit-Circle,” and he goes to the Transit- Circle and makes 
 observations by touch of the touch-piece, recording in a memorandum-book the name 
 of each object and its approximate time. At some convenient time, he records hours 
 and decades of minutes in the manner described above. 
 
 Suppose now that the Altazimuth Observer comes to commence his observations. He 
 finds that p is already locked to the gearing-position, and he has therefore no instru- 
 mental movement to make, but he places the card “ In use for the Altazimuth ” 
 
OF THE Royal Observatory, Greenwich. 
 
 [xxi} 
 
 also in front. He then goes to the Altazimuth and makes observations by toueh of 
 the toueh-piece, recording always the name of the object and its approximate time, but 
 he does not record hours, &c. (unless there be no observer at the Transit- Circle, in 
 which case the Altazimuth Observer must go to the Transit-Circle for that purpose.) 
 
 Suppose now that the rransit-Circle Observer has finished his observations. He comes 
 to the instrument, but finding the card “ In use for the Altazimuth,” he does not 
 disturb p, but merely places his own card out of sight. 
 
 Finally, the Altazimuth Observer terminates his observations. He comes to the 
 apparatus, and turns back his card “ In use for the Altazimuth. ’ There is then no 
 card in sight, and therefore it is his duty to press the lever p to the east, and to lock 
 it fast in that position by q. The transit-clock-punctures and the advance of the 
 pricker-frame cease immediately, and no unnecessary consumption of paper takes 
 place. 
 
 On the next morning, the superintendant of the Transit Department detaches the 
 friction-clutch by gradually unscrewing (4), (4), takes out the Barrel, and places it 
 upon a wooden stand in which its pivots are supported with the axis in an inclined 
 position, so that its rotation is like that of the Polar Axis of an Equatoreal. He sits 
 before this, and turns the Barrel to bring different punctures under his view ; the light 
 then falls upon all in the same way, and the reading is free from error as regards direc- 
 tion of illumination. First he identifies and marks in ink the time-zero signals, and 
 by means of these he writes the hours and minutes corresponding to each commence- 
 ment of a minute, as well as the seconds at the top of each column of seconds. Then 
 he identifies the first transit- wire-observation in each transit, and writes the name of the 
 object observed. Lastly, he reads off in hours, minutes, seconds, and tenths of seconds 
 (the latter being taken by means of a divided scale of paper) the time of every transit- 
 observation, which an assistant enters into the proper book for reduction. The Barrel 
 is then restored to its place, and, by driving the screws (4) (4), the friction clutch 
 connects the Barrel with the clock, and all is ready for new observations. 
 
 When several of the Barrels are fully charged with observations, the paper is wetted 
 at the overlapping edge at which the cement is applied, the edges are separated, each 
 sheet is taken off, the successive sheets are tied together in packets of a month each, 
 and these packets are preserved in drawers. 
 

 
 
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