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



WEEKLY EVENING MEETING, 



Friday, February 21, I'Jli). 



General E. H. Hills, C.M.G. D.Sc. F.R.S., Secretary, 

 in the Chair. 



A. T. Hare, M.A. 



Clock Escapements. 



The most ancient instruments for measuring time were probably 

 some kind of sundial. Something- of the kind is, no doubt, referred 

 to in 2 Kings xx. and Isaiah xxxviii., where it is stated that the 

 shadow moved back ten steps on the steps of Ahaz (for that is the 

 literal translation). Herodotus (" Euterpe," cix.) tells us that the 

 Babylonians introduced to the Greeks the ttoAos and the yj^co/xoji/, no 

 doubt some forms of sun -instruments. Frequent allusions are found 

 in the classics to the clepsydra, which was made in various forms, 

 always depending, however, upon the approximately uniform flow of 

 water through a small hole. 



But clocks, properly so called, cannot be traced with certainty 

 earlier than the fourteenth century. In 1;)48 a curious iron clock 

 was sent over from Switzerland, and was until recently kept in Dover 

 Castle. It is now in the Science Museum at South Kensington. It 

 is interesting as having no pendulum or balance-spring (both much 

 later inventions), but, instead, a vertical spindle carrying a horizontal 

 traverse loaded at the ends with weights. This vertical spindle has 

 two pallets projecting from its sides, approximately at right angles 

 to each other, which engage alternately the uppermost and lowermost 

 tooth of a contrate wheel the axis of which is horizontal and in the 

 same plane with the vertical axis first referred to. This is the 

 " verge " escapement, which was for long afterwards used in both 

 clocks and watches. No good timekeeping was possible with such an 

 arrangement. Gravity did not come into the problem, and the speed 

 of the movement was only restrained by itsenergy having alternately 

 to create and destroy angular momentum in the swinging arms. The 

 force of the train, however variable, was paramount. 



The next step in horology, and undoubtedly the most important 

 which has ever been made, was the application of the pendulum to 

 clocks by the Dutch physicist and astronomer. Christian Huygens, in 

 1657. Galileo had discovered, about sixty years earlier, the 

 isochronism (since found to be only approximate) of a swinging body. 



