[ 314 ] 

 XLI. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 157.] 

 June 15, 1865. — Major General Sabine, President, in the Chair. 

 RpHE following communication was read: — 



■*- " On the Heating of a Disk by rapid Rotation in vacuo." By 

 Balfour Stewart, M.A., F.R.S., and P. G. Tait, M.A. 



1 . The authors were led, by certain views which they entertain re- 

 garding the loss of energy by a body, to make experiments in order 

 to test these views, and about the end of 1863 they obtained results 

 in air, which encouraged them to have constructed an apparatus where- 

 with to procure rotation in vacuo. 



2. The apparatus for this purpose was devised and executed by 

 Mr. Beckley, mechanician at the Kew Observatory, at which place 

 the experiments about to be described were made. In this apparatus 

 a slowly revolving shaft is carried up through a barometer tube, 

 having at its top the receiver which it is wished to exhaust. When 

 the exhaustion has taken place, it is evident that this shaft will re- 

 volve in mercury. In the receiver the shaft is connected with a train 

 of toothed wheels, and ultimately causes a circular disk to revolve 1 25 

 times for each revolution of the shaft. The disks used have a dia- 

 meter of 13 inches, and their plane is vertical. Two insulated wires, 

 connected with a Thomson's reflecting galvanometer, are carried 

 through two holes in the bed-plate of the receiver, and are then 

 connected with a thermo-electric pile, having the usual reflecting 

 cone attached to it. The outside of the pile, and of its attached cone, 

 is wrapped round with wadding and cloth, so as to be entirely out of 

 the reach of currents of air. The vacuum-gauge is on the siphon 

 principle ; it was constructed by P. Adie, and there is every reason to 

 believe that it is perfectly deprived of air. The following figure will 



AB= 



6 inches. 





BE = 



8 „ 





EG= 



8* „ 





FH= 



:13 ,, (diam 



ofdisk.) 



AC= 



*H jj 





CD = 



H „ 





M. Multiplying gear. 





