348 REPORT — 1851. 



A®, a brass plate, capable of sliding freely in a groove in H and over y. 

 Its left end is cut (in the manner shown) to form a hook, which may be made 

 o fit (or rest upon) alittle peg projecting from the back of F. 



h'', a plate of ground glass fixed in H opposite to the narrow aperture in 

 /j*, with its ground surface exactly in the upper plane oi y. Upon this plate 

 a scale divided to -^(h of an inch is etched. 



When both h^ and H are placed in F, h^, before the commencement of the 

 registration, covers y entirely, and the position of h^ is such, that its right 

 end stands at about jJ^th of an inch to the left of e'. The imacre of 6' is 

 visible on the scale etched on A' through the aperture of h*. 



I is the pulley on the barrel arbor of the time-piece. 



JS a small gut cord passing through F and attached to I and to one of 

 the studs h^. 



i", a cord passing over 



i', a pulley, and suspending a weight (not shown). 



i^, a cord attached to I, and sustaining 



j^, which is a counteracting weight rather heavier than the weight (not 

 shown) suspended by i". 



i^, a clamping milled-headed nut, screwed on the barrel arbor of I. When 

 it is relaxed I can revolve freely on the arbor. 



K, the case of the time-piece. 



AS a pointed index fixed on K (and serving the purpose of a hand). 



k\ a milled-headed nut attached to an arbor passing through the clock- 

 plates, and connected with a lever and fork, &c. behind, whicli can be made 

 to stop or release the pendulum at any given moment (by turning A^)*. 



As, tiie support of K, and adjustable for height. 



P P, bearers supporting A, AS A% B, &c. {vide fig. 2). 



Q, a cross bearer supporting F, &c. (y'tde fig. 3). 



All these bearers are of well-seasoned and straight-grained deal, and bolted 

 together accurately. 



R is a case, supported by rabbeted pieces under P P, and capable of being 

 slid to and fro. It protects the lower part of B from dust, &c. 



The manipulation and action of that part of the instrument, &c. which has 

 now been described is (shortly) as follows: — 



1st. Y having been rfti^T/ polished (in the board, fig. 3, Plate XVIII., Report 

 for 1850), is placed in H, and coated by placing H in the coating boxes (fig. 

 5. Plate XVllI. of same Report). — 2nd. A^ is slid over Y (still in the coating 

 box). — 3rd. H, &c. is placed on the carriage A^ A' (fig. 3, Plate XXII. of this 

 Report), resting at the left end of_/' ; and, at the same time, the hook of A* 

 is fitted on a pin projecting from the back of F. — 4th. The door of F is 

 closed ; thereby causing the spring f^ to press upon A*, and to cause A^ to 

 press upon the left lip ate' of the mouth-piece E (t)jc?e fig. 2, Plate XXI. &c.). — 

 5th. The image of b^ox\ the ground-glass scale li' may then be observed through 

 the narrow apertures in the doors of F and H, in order to verify focus, &c. — 

 Cth. The time-piece in K is started, at the proper moment, by means of A\ 

 The revolution of I now causes H, &c. to move, at the rate of half an inch 

 per hour, to the right, carrying Y with it, but leaving A* at rest. Successive 

 portions of V are therefore exposed to the action of light passing from D, or 

 from a window, through C, through c^, through the tube and vacant part of 

 B above 6S through G and through e' ; and if 6' varies its height, during 

 the motion of H, &c., unequal portions of Y are acted upon by the light. — 



* Vide fig. 7, Plate I., Report for 1850. 



