Proceedings of the Royal Society of Edinburgh. 183 



1833, April 1. — Sm Thomas Makdougall Brisbane, 

 President, in the Chair. At this Meeting the following com- 

 munications were read : — 



1. Continuation of " Experimental Researches regarding cer- 

 tain vibrations which take place between Metallic Masses .^ 

 having different Temperatures.'' By James D. Forbes, 

 Esq. Professor of Natural Philosophy in the University 

 of Edinburgh. 



The vibrations here referred to, are those which with their accom- 

 panying sounds were first observed by Mr Arthur Trovelyan, and 

 communicated to this Society in a paper published in the 12th vol. 

 of their Transactions. The author of the present paper undertook 

 the inquiry as soon as the remarkable fact was announced by Mr 

 Trevelyan, and was induced to prosecute it to a considerable extent [ 

 experimentally, in consequence of being dissatisfied with the only 

 plausible explanation yet offered, — that of the successive expansions 

 of the cold metal by the hot one at the point of contact at each suc- 

 cessive vibration, which was conceived to afford the necessary im- 

 pulse or maintaining power. 



In this paper, the phenomena of sound are first discussed, which, 

 with Mr Faraday, the author imputes solely to the number of vibra- 

 tions taking place in a given space of time. Thjg seems completely 

 proved by observation, and the note depends upon the frequency 

 of the oscillations, which have been observed as high as between 

 700 and 800 in a second, and must often be greatly more frequent. 

 The phenomena of vibration are next considered as affected by the 

 nature of the metals, by the form of the masses, and by temperature. 

 The order of the metals as vibrators, is the following, meaning that 

 the cold metal must always stand lower in the list than the hot one, 

 and that the force or intensity of vibration is, generally speaking, 

 proportional to the space intervening between two metals on the list. 

 Silver, Copper, Gold, Zinc, Brass, Platimim, Iron, Tin, Lead, Anti" . 

 mdni/. Bismuth. Antimony and Bismuth are placed at the bottom ' 

 of the list, because no other metal is capable, under any circum- ^ 

 stances which have been examined, of producing vibrations in con- 

 junction with those two metals : they are the only metals yet ob- 

 served which, when heated, do not vibrate on cold lead. 



From experiments detailed at considerable length in the paper, the 

 author is led to the following practical conclusions, which, whatever 

 may be the fate of the hypothesis which he is disposed to found up- 

 on them, will, he conceives, be viewed as valuable in themselves 



