448 Mr. A. T. Hare [Feb. 21, 



wider the arc of swing the more a clock will lose, and, secondly, that 

 a given small variation of arc is less harmful when the wliole arc is 

 small than when it is great. There are practical reasons, however, 

 for not making it too small, which have led to the adoption of arcs of 

 two or three degrees on each side of the vertical as, on the whole, 

 the Ijest. 



This table gives the losing rate for variations of arc : — 



It must be remembered that these figures only relate to a free 

 pendulum, and with some escapements the errors introduced mask 

 this result completely. 



Many attempts, some of great ingenuity, were made to get better 

 results from the verge, especially as regarded the reduction of the 

 arc, but they were all superseded by the anchor, or recoil, escape- 

 ment, invented (most pro])ably) by the celebrated Dr. Hooke, and 

 first made by William Clement in 1675. This is the escapement still 

 used in all common clocks, but it has disadvantages which render it 

 unsuitable for high-class work. The train exercises great 

 '• dominion," as it used to be called, over the pendulum, and is 

 assisting gravity the whole time, hindering the rise of the pendulum 

 and accelerating its fall, so that T may be considerably diminished 

 when the train has been recently oiled, without any corresponding 

 variation of a. 



But in 1715 George (Iraham, pupil of Tompion (both of whom 

 were so esteemed as to be accorded burial in Westminster Abbey), 

 made a most important modification of the anchor. He removed 

 most of the flukes, leaving only a small sloping part near the tip, by 

 sliding along which the extremity of the scape-wheel teeth could give 

 the necessary impulse to the pendulum. The rest of the fluke he 

 fashioned so that it should be a portion of a circle having its 

 centre on the axis of the crutch-arbor, thus entirely preventing 

 recoil of the movement, and, to a great extent, releasing the 

 pendulum from the " dominion " of the train. During the time 

 when the circular part of the fluke is passing along the tooth of 

 the scape-wheel the motion of the train is entirely held up, and 



