﻿M. 0. E. Meyer on the Heating of a Disk rotating in vacuo. 287 



force, and that its fundamental principles have not been dis- 

 turbed/' I am sorry to think that I am still justified in main- 

 taining the contrary. I leave it to a man of his thoughtful 

 mind to weigh the reasons which compel me, however reluct- 

 antly, to differ from him. 



[To be continued.] 



XXXVIII. Further Remarks on the Explanation of Stewart and 

 Tait's Experiments on the Heating of a Disk rotating in vacuo. 

 By Oscar Emil Meyer*. 



WITH reference to the paper " On the Explanation of 

 Stewart and Tait's Experiments " contained in one of 

 the previous Numbers of the Philosophical Magazine f, the gen- 

 tlemen in question have published a reply J which I cannot leave 

 unanswered, although I should prefer doing so, for I fear it may 

 lead to a protracted controversy about trifles. 



They consider "the assumption that a change of position of 

 the instantaneous axis of the disk necessarily implies loss of vis 

 viva " to be " contrary to the usual principles of ordinary dyna- 

 mics." I consider it to be an application, that was perhaps not 

 indicated clearly enough, of Carnot's theorem, that every sud- 

 den change in motion is accompanied by loss of vis viva. 



Messrs. Stewart and Tait think the calculations based on this 

 assumption " very peculiar," and a little further on they confess 

 " that they cannot pretend to understand them." For this 

 reason they ask for an explanation of the manner in which vis 

 viva is transformed into heat. They ask especially whether I 

 " mean that impact of the axle on the bearings may produce vi- 

 brations of the disk which in time will by viscosity be frittered 

 down into heat." 



I have not expressed my opinion on this point, because I think 

 it to be quite immaterial. The principle of vires viva has the ad- 

 vantage of holding good quite independently of any considera- 

 tion as to the mode of the transition- of vires viva out of one state 

 into another. It is sufficient to know the amount of vis viva at 

 the commencement and at the end. 



If mechanical force be transformed into heat either by means 

 of sonorous or non-sonorous vibrations, by compression, by elec- 

 tricity, by chemical combination, or by any means whatever, in 

 all these cases the law holds good, namely, that the heat gene- 



* Communicated by the Author. 



t Pogg. Ann. Oct. 1868, vol. cxxxv. p. 285. Phil. Mag. Jan. 1869, 

 vol. xxxvii. p. 26. 



X Pogg. Ann. Jan. 1869, vol. cxxxvi. p. 165. Phil. Mag. Feb. 1869, 

 vol. xxxvii. p. 97. 



