HOROLOGY. 



common pocket watches.lt isrepresented 

 in fig. 1. Plate HOROLOGY, and is best suit- 

 ed to the long vibrations of the balance, 

 which was invented earlier than the pen- 

 dulum. A B denotes the rim of a contrate 

 wheel, called a crown wheel, having its 

 teeth pointed and sloped on one side only, 

 so thatthe points advance before any other 

 part of the teeth during the motion. C and 

 D are two pallets or flaps proceeding 

 downwards from the verge E F. The 

 pallets are nearly at right angles to each 

 other ; and when the balance F G, fixed 

 to the verge, is at rest, the pallets remain 

 inclined to the plane of the wheel, in an 

 angle of about forty-five degrees ; but 

 \vhen it is made to vibrate, one of the pal- 

 lets is brought nearer to the perpendicu- 

 lar position, while the other becomes 

 more nearly parallel. The wheel must be 

 supposed to have one of its teeth resting 

 against a pallet, by virtue of the maintain- 

 ing power. This tooth will slip off or es- 

 cape, as the pallet rises towards the hori- 

 zontal position, at which instant a tooth on 

 the opposite side of the wheel will strike 

 against the other pallet which is down. 

 The returning vibration, by raising this 

 last pallet, will suffer that tooth to escape, 

 and another tooth will apply itself to the 

 first-mentioned pallet. By this alterna- 

 tion, the crown-wheel will advance the 

 quantity of half a tooth each vibration, 

 and the balance or pendulum will be pre- 

 vented from coming to rest, because the 

 impulse of the teeth against the pallets 

 will be equal to the resistances from fric- 

 tion and the re-action of the air. 



The common escapement here describ- 

 ed was well known to Leonardo de Vinci, 

 who describes an instrument acting by an 

 escapement of this kind, similar, as he 

 ays, to the verge of the balance in 

 watches, which he does not seem to men- 

 tion as a new thing : he died about 1513. 

 The isochronism of the pendulum was 

 known to Galileo, in 1600, who, before 

 his death, namely, about 1633, proposed 

 to apply it to clocks. The actual applica- 

 tion by Huygens was made before 1658, 

 when he published his " Horologium Os- 

 cillatorium." He applied it by means of 

 the common escapement already in use 

 with the balance, and still retained in our 

 table-clocks. Sanctorius had made the 

 same application aboat forty years before 

 that time, as appears by his " Commen- 

 tarii in Avicennam," (quest. 56,) printed 

 in 1625, in which several instruments are 

 described as having been publicly exhi- 

 bited and explained to his auditors, at his 

 lectures in Padtfa, for thirteen years pre- 

 vious to that time. 



This escapement not being adapted to 

 such vibrations as are performed through 

 arcs of a few degrees only, another con- 

 struction has been made, which has been 

 In constant use in clocks for this century 

 past, with a long pendulum beating se- 

 conds. (Fig. 2.), A B represents a verti- 

 cal wheel, called the swing wheel, having 

 thirty teeth. C D represents a pair of 

 pallets connected together, and movea- 

 ble in conjunction with the pendulum, 

 on the centre of axis F. One tooth of the 

 wheel,5n the present position,rests on the 

 inclined surface of the inner part of the 

 pallet C, upon which its disposition to 

 slide tends to throw the point of the pal- 

 let further from the centre of the wheel, 

 and consequently assists the vibration in 

 that direction. While the pallet C moves 

 outwards, and the wheel advances, the 

 point of the pallet D, of course, ap- 

 proaches towards the centre, in the open- 

 ing between the two nearest teeth ; and 

 when the acting tooth of the wheel slips 

 off, or escapes from the pallet C, another 

 tooth on the opposite side immediately 

 falls on the exterior inclined face of D, 

 and, by a similar operation, tends to push 

 that pallet from the centre. The returning 

 vibration is thus assisted by the wheel, 

 while the -pallet C moves towards the cen- 

 tre, and receives the succeeding tooth of 

 the wheel after the escape from the point 

 of D. In this manner the alternation may 

 be conceived to go on, without limit. 



The celebrated George Graham im- 

 proved this escapement very much, by 

 taking off part of the slope furthest from 

 the points of the pallets; instead of which 

 part, he formed a circular or cylindrical 

 face, having its axis in the centre of mo- 

 tion. Pallets of this kind are seen on the 

 opposite side of the wheel at E and G, 

 having H for their centre or axis. A] 

 tooth of the wheel is seen resting upon 

 the circular inner surface of the pallet G, 

 which is not therefore affected by the 

 whe^l, excepting so far as its motion, 

 arising from any other cause, may be af- 

 fected by the friction of the tooth. If the 

 vibration of the pendulum be supposed 

 to carry G outwards, the slope surface 

 will be brought to the point of the tooth, 

 which will slide along it, and urge the 

 pallet outwards during this sliding action. 

 When the tooth has fallen from the point 

 of this pallet, an opposite tooth will be 

 received on the circular surface of E, 

 and will not affect the vibration, except- 

 ing when the slope surface of E is carried 

 out so as to suffer the tooth to slide along 

 it. In the two former escapements, there 

 is always a certain portion of vibration 



