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



rated is equivalent to the loss of vis viva. The question, there- 

 fore, is without any bearing upon the present dispute. 



Nevertheless I shall not keep back my opinion, as Messrs. 

 Stewart and Tait wish for it. In answer to the question put to 

 me I answer simply, yes. But I do not admit the following 

 statement to be correct : — " he merely repeats one of many ob- 

 jections long ago perceived by ourselves, and also pointed out to 

 us by others, an objection which we have already at least partially 

 met by experiment and calculation." No, not even partially; 

 because there is a difference between my objection and that of 

 Messrs. Stewart and Tait*. They refer to the 250 vibrations per 

 second, which correspond to the fundamental note of their disk. 

 The agitations and impacts I refer to correspond to 2 x 2500 vi- 

 brations in 30 seconds, or to 83 vibrations to and fro per second. 

 The corresponding note would be of a lower pitch than the fun- 

 damental one ; and as it would consist simultaneously of longitu- 

 dinal and transversal vibrations, it cannot exist, and therefore 

 must appear as heat. 



The reply of Messrs. Stewart and Tait contains only a single 

 positive argument against my explanation of the experiment. 

 Placing too implicit confidence in the accuracy of a figure ad- 

 joined to one of the papers f, I made a mistake as to the length 

 of the axis. This may invalidate my supposition that the vibra- 

 tions were produced by impacts of the axle upon the bearings. 

 But this supposition is not essential. What is essential to my 

 explanation is only the conception of impulses occurring periodi- 

 cally and twice during each revolution of the disk. The irregu- 

 larity in the rotation of the disk can be explained just as well 

 by supposing that the axle had a slight bend, or that the pinion 

 attached to it was slightly excentric. Such irregularities produce 

 by impulses sudden changes in the speed of the rotation. Alter- 

 nately the velocity increases and decreases ; the excentric wheels 

 and pinions striking one another and then again being thrown 

 asunder. My assumption, therefore, of impulses occurring pe- 

 riodically backwards and forwards, remains intact, as also the 

 calculation ; and I maintain that my explanation, in spite of the 

 error mentioned^ is still correct. 



On the other hand I admit, without reserve, that my explana- 

 tion is not positively proved. Still it can be very easily verified, 

 for instance by repeating the observations with a different velo- 

 city of rotation. And as both gentlemen are about to make new 

 experiments with regard to the objections raised by Professor 

 Helmholtz, I would request them kindly to take into considera- 



* Art. 20 of the third paper. Proc. Roy. Soc. vol. xv. p. 295. Phil. 

 Mag. S. 4. vol. xxxiii. p. 230. 



t Proc. Roy. Soc. vol. xiv. p. 339. Phil. Mag. S. 4. vol. xxx. p. 314. 



