1865.] Messrs. Stewart and Tait on the Heating of a Disk, $e. 339 



VII. " On the Heating of a Disk by rapid Rotation in vacua" By 

 BALFOUR STEWART, M.A., F.R.S., and P. G. TAIT, M.A. Re- 

 ceived June 1, 1865. 



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

 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 encou- 

 raged them to have constructed an apparatus wherewith 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 experi- 

 ments about to be described were made. In this apparatus a slowly revol- 

 ving 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 revolve 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 diameter 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 cur- 

 rents of air. The vacuum-gauge is on the siphon principle ; it was con- 

 structed by P. Adie, and there is every reason to believe that it is perfectly 

 deprived of air. The following figure will render the arrangements clear : 



A B= 6 inches. 

 B E= 8 

 E&= 8* 



PH=13 (diam.Jof disk.) 

 A C= 5J 

 CD= 2 

 M. Multiplying gear. 



and it is only necessary to add that the whole is covered over with an air- 

 tight glass shade, 15 inches in diameter and 16 inches high. 



