721 



HOROLOGY. 



HOROLOGY. 



722 



fitting the hole in the ratchet. In this situation the wheel and ratchet 

 are ready to receive the fusee with its ratchet ; but it must be borne 

 in mind, that though the pin c fits exactly in the hole iu the auxiliary- 

 ratchet, and thereby prevents it from turning round, it does not pre- 

 vent its having as much motion as the spring itself has in the notch in 

 the fusee-wheel ; the spring must also be conceived to have been forced 

 into its place with the pin pressing strongly against the end of the 

 notch o. The fusee is now attached to the wheel by passing its arbor 

 through the hole in the centre of the wheel, and is secured in its place 

 by a pin and collet on the opposite side, which prevent their separa- 

 tion, at the same time allowing the fusee to turn with a moderate 

 degree of force. In this state the fusee, &<x, must be considered as 

 placed within the frames of the clock or watch in connection with the 

 other part of the train of wheels, &c. A click, or, as it is sometimes 

 called, a detent, is also placed between the frames, and by means of a 

 slight spring is made to act in the teeth of the auxiliary-ratchet. The 

 action of the whole apparatus will be understood by comparing the 

 relative positions of the several parts. The space through which the 

 spring a b c acts in the notch o p with sufficient force to maintain the 

 motion of the watch, is about equal to two teeth of the fusee-wheel ; 

 and the time in which the fusee-wheel goes through a distance equal 

 to two teeth varies in different watches from 10 to 12 minutes, a time 

 more than sufficient for the operation of winding. 



We must next describe the escapement, so important in horology. 

 This term is applied to a combination of parts in a clock or Watch, 

 which has for its object the conversion of the circular motion of the 

 wheels into a vibratory motion, as exhibited in the pendulum. In the 

 description we are about to give, the term will be made to include the 

 scape-wheel, the pallets with their arbor or axis, and a bent lever 

 attached thereto, called the crutch, which last piece maintains the 

 motion of the pendulum. In a watch this combination consists of the 

 scape- wheel, together with all those parts lying between it and the 

 balance, and which are concerned in converting the circular motion of 

 the wheels into the alternating one of the balance. In Graham's dead- 

 beat etcapement the distance between the centre of motion p of the 

 pallets and the centre of the scape-wheel is equal to one diameter of the 

 scape-wheel. In Jig. 11, the tooth i has just given impulse to the pallet 

 p and escaped from it ; the tooth o has in consequence fallen upon that 

 part of the pallet Q called its arc of rest, which, in both pallets, is 

 formed by a circle struck from the centre of motion p of the pallet*. 

 The impulse given by i causes the pendulum, and with it the pallets, 

 to vibrate some distance after i has left r and o has fallen on Q ; but 

 the arc of rest being concentric with the centre of motion of the pallets, 

 the wheel ceases to rotate, or remains dtad, until the pendulum by its 



Fig. 12. 



returning vibration lifts the pallet Q so high as to allow the tooth o to 

 get upon the face or inclined plane of the pallet, upon which it then 

 acts. The tooth drives up the pallet, and with it the pendulum, until 



.Fig. 11. 



Dead-Bcat Escapement. 



the tooth o escapes from the pallet Q ; when another tooth h, on the 

 opposite side of the wheel, falls on the arc of rest of the pallet p, which 

 arc is in this pallet on the outside, and on which the tooth rests until 

 by the return of the pendulum the pallet P is lifted so high as to allow 

 k to get on the inclined plane or face of the pallet p, upon which it 

 acts. The tooth raises the pallet and with it the pendulum, till it 

 escapes and gains the position , when the same process is repeated : 

 the wheel alternately giving impulse to one pallet and resting on tbe 

 circular part of the other, which we have denominated the arc of rest. 

 When the pendulum is in a state of rest, some one tooth is always 

 resting on one of the circular arcs ; the pendulum being put in motion 

 brings a pallet into a position to receive an impulse from the wheel- 

 tooth, when the process already described commences. 



Most of the great improvements in pocket watches have been made 

 in the horizontal or fat forms ; but the common vertical watch must 

 be first described. 



The annexed cut (Jig. 12) represents such a watch as it would appear 



It h 



Section of Vertical Watch. 



if the dial (which is here omitted) were turned downwards. A is the ' 

 barrel ; B, the fusee ; 6, the chain by which motion is communicated ] 

 from the barrel to the fusee, on which is the great or fusee wheel 

 acting on the centre-wheel pinion D, on which is riveted the centre- j 

 wheel : the arbor of the pinion D being prolonged through the plate 

 of the watch as far as I. The centre-wheel and its pinion revolve in 

 an hour. Upon that part of the arbor D which is on the outside of 

 the plate or frame is placed the cannon-pinion, which has a hole quite 

 through it for the reception of the centre-wheel arbor, on which it 

 turns spring-tight. The cannon-pinion is secured in its place by a 

 small pin through the end of the centre-wheel arbor /, the end of the 

 pinion being squared to receive the minute-hand h. The cannon-pinion 

 has 12 leaves acting in the minute- wheel, of 48 teeth, causing the latter 

 to revolve once in four hours. Concentric with the minute-wheel, 

 and attached to it, is a pinion, having a hole through their common 

 centre, through which passes a stud fixed on the plate. This pinion, 

 having 14 leaves, drives the hour-wheel m, of -12 teeth, once round in 

 12 {lours ; this wheel is placed over the cannon-pinion by a socket, 

 which has a hole through it for the cannon -pinion to pass through; 

 on tliis socket is fixed the hour-hand k. It will be perceived that 

 by this arrangement the cannon-pinion, minute-wheel, pinion, and 

 hour-wheel, together with the hands, can all be turned backward or 

 fnrvv.ml without affecting the interior mechanism of the watch, simply 

 by the application of a key to the squared end of the cannon-pinion. 

 The assemblage of wheels, Ac., thus put in motion is called the I 



>f the watch ; that between the plates, the movement, which we 

 shall next describe, ,'fbe centre- wheel gives motion to the third 

 ABTS AJTD 8CI. DIV. VOL. IV. 



wheel-pinion, to which is attached the third wheel o, acting upon 

 the contrate-wheel pinion. On this is placed the coutrate-wheel 

 acting in the pinion of the balance-wheel L, which ia also called tht 

 soape-wheel. \Ve have already explained the mode by which the balance- 

 wheel teeth act upon the pallets, so as to cause an alternating motion 

 in the balance M. One end of the balance-wheel arbor works in a piece 

 called the dovetail, which is inserted in a piece p, called the potencc, 

 firmly attached by a screw to one of the plates of the watch ; the other 

 end works in a piece called the follower, which is inserted iu another 

 piece riveted into the plate called the counter-potence, (left out of the 

 .figure to prevent confusion). Another part of the potence, called the 

 foot, receives one end of the balance arbor or spindle, called the vergo 

 (on which are the pallets) ; the other end works in a hole in the pin , 

 which passes through the centre of the cock 7 q, which is secured to 

 the upper plate of the watch ; the pendulum-spring (also called the 

 regulating-spring and hair-spring) has one end, immediately below the 

 balance, secured to a stud fixed in the plate, and the other pinned fast 

 to a small collet, which goes spring-tight unto the axis of the verge, and 

 is seen just under the balance. l''i'jS. 13, 14, and 15, represent some nf 

 the parts separately. /.'/ 1<* sl,os the main-spring in a relaxed state 

 as it would appear out of the btrrel ; to which, when in, one end of it 

 is attached, the other being held by a hook iu the arbor of the barrel, 

 which comes through the plate, as shown in ff/. 12, and is kept from 

 turning by a ratchet and click. The spring is wound up by the 

 chain acting on the barrel and pulling it round, which operation is 

 performed by turning a key placed on the squared end of the fusee- 

 arbor. The effort of the spring to unbend itself after being wound up 



3 A 



