TRANSACTIOXS OP THE SECTIONS, 35 



Facts relating to the Effects of Temperature on the Regulators of Time- 

 keepers ; and. description of some recent improvements in Pendulums, 

 with Observations, and Tabulated Experiments. By Edward John 

 Dent, F.E.A.S. 



The subjects contained in Mr. Dent's pajier may be arranged under 

 three heads. 



1st. The continuation of an inquiry into the compound effect of 

 , variable temperature upon the regulating machinery of Time- 

 keepers, the commencement of Avhich had been laid before the 

 Association some years before. 



2nd. A description of improvements in mercurial pendulums, princi- 

 pally with a view of making them portable. 



3rd. Improvements in the suspension of pendulums in general ; and 

 incidental remarks connected with the subject. 



In all estimates of the eifect of variable temperature upon the regu- 

 lating part of timekeepers, made for the purpose of ascertaining the 

 necessary amount of compensation, it had generally been assumed 

 that the effect was confined to an alteration of length in a part of the 

 regulator. Mr. Dent, having long felt that this view of the subject was 

 insufficient to account for facts which his daily practice brought be- 

 fore him, at length commenced a series of experiments with a view to 

 a more complete and consistent explanation of them; and, in 1833, at 

 the meeting of the Association in Cambridge, he endeavoured to show 

 that the effect of variable temperature upon the balance-springs of 

 chronometers might be resolved into two distinct portions : viz. the 

 one, long known, which produces the variation of length ; and an- 

 other, which had hitherto escaped attention, affecting the elasticity of the 

 spring. 



Mr. Dent afterwards extended the inquiry to the pendulums of clocks, 

 and succeeded in separating and determining the respective amounts of 

 effect which changes of temperature produce upon the elasticity of the 

 spring and the length of the rod. The details of this subsequent in- 

 quiry, with descriptions of the apparatus invented and used for the pur- 

 pose, were described at length. As an illustration, the following ex- 

 periment is taken from amongst many others : — 



A clock provided with a spring-pendulum, and adjusted to keep cor- 

 rect time at an ordinary temperature, was found, when the temperature 

 was maintained at 48° Fahr. higher, to lose twelve seconds in twenty- 

 four hours. 



Mr. Dent attempts to demonstrate by experiment that eight parts 

 and a half only of this difference belong to the effect of elongation in 

 the rod, and the remaining one and a half are produced by a decrease 

 of elasticity in the spring. 



From the epoch of the introduction of the mercurial cistern to the 

 present time, this admirable modification of the pendulum has remained 

 nearly in the state in which it was left by its inventor. 



The mercurial pendulum cannot even now be filled and transported 

 in a state proper to be immediately attached to a timekeeper ; conse- 



d2 



