50 



REPOKT — 1876. 



amount, and let a governor giving uniform motion be applied to the train of wheel- 

 work connected with this shaft, and so adjusted that, when the escapement-wheel 

 is um-esisted, it will move faster by a small percentage than it must move to keep 

 time properly. Now let the escapement-wheel, thus mounted and carried round, 

 act upon the escapement, just as it does in the ordinary clock. It will keep the 

 pendulum vibrating, and wiU, just as in the ordinary clock, be held back every 

 time it touches the escapement during the interval required to set it right again 

 from having gone too fast during the preceding interval of motion. But in the 

 ordinary clock the interval of rest is considerable, generally greater tlian the inter- 

 val of motion. In the new clock it is equal to a small fraction of the interval of 

 motion — ^}o in the clock as now working, but to be i-educed probably to something 

 much smaller yet. The simplest appliance to count the turns of this escapement- 

 wheel (a worm, for instance, working upon a wheel with thirty teeth, carrying a 

 hand round, which will correspond to the seconds hand of the clock) completes the 

 instrument ; for minute- and hour-hands are a superfluity in an astronomical clock. 



In various trials which I have made since the year 1865, when this plan of es- 

 capement first occurred to me, I have used several different forms, all answering to 

 the preceding description, although differing widely in their geometrical and me- 

 chanical characters. In all of them the escapement-wheel is reduced to a single 

 tooth or arm, to diminish as much as possible the moment of inertia of the mass 

 stopped by the pendulum. This arm revolves in the period of the pendulum (two 

 seconds for a seconds pendulum), or some multiple of it. Thus the pendu- 

 lum may execute many complete periods of vibration without being touched 

 by the escapement. In all my trials the pallets have been attached to the bottom 

 of the pendulum, projecting below it, in order that satisfactory action with a very 

 small arc of vibration (not more on each side than ^ j^^ of the radius, or 1 centi- 

 metre for the seconds pendulum) may be secured. 



In the clock in my house the seconds pendulum of the fine movement vibrates with 

 great constancy through half a millimetre, that is to say, through an arc of ^i^ of the 

 radian on each side of the vertical. This, I believe, is the smallest range that has 

 hitherto been realized in any seconds pendulum of an astronomical or other clock. 



In the drawing s represents the vertical 

 escapement-shaft, round which is fitted loosely 

 the coUar c, carrying the worm v. The 

 small wheel, d, is worked by v, and carries 

 round the seconds hand of the clock, a repre- 

 sents a piece of fine steel wire, being the single 

 arm to which the teeth of the escapement- 

 wheel are reduced in the clock described in 

 this paper ; pp the pallets attached to bars 

 projecting downwards from the bob, B, of the 

 pendulum ; /, a foot bearing the weight of the 

 collar-worm and escapement-tooth. The bar 

 connecting/ with the collar is of such a length 

 as to give a proper moment to the frictional 

 force by which the collar is carried round. 

 The shaft s carries a wheel, represented in 

 section by to w, "s^^hich is driven by a train of 

 wheel-work (not shown in the drawing) from 

 the governor. This wheel is made to go ^ 

 per cent, faster than once round in two seconds, 

 while the pendulum prevents the cpllar from 

 going round more than once in two seconds. 



My trials were rendered practicallj^ abortive 

 from 1865 until a few months ago by the 

 difficulty of obtaining a satisfactory governor 

 for the uniform motion of the escapement- 

 shaft ; this difficulty is quite overcome in the 

 pendulum governor, which I now proceed to 

 describe. 



