18 



cessive vibration, which was concuived 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. This seems completely 

 proved by observation, and the note depends upon the frequency 

 of the oscillations, which have been observed as hiffh 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 nn the list. 

 Silver, Copper, Gold, Zinc, Brass, Platinum, Iron, Tin, Lead, Anti- 

 mony, 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. 

 1. As far as has been observed, the vibrations never take place be- 

 tween substances of the same nature. 2. Both substances must be 

 metallic. 3. Tlie vibrations take place with an intensity propor- 

 tional, within certain limits, to the difference of the conducting 

 powers of the metals for heat (or electricity,*) the metal having the 

 least conducting power being necessarily the coldest. 4. The time 

 of contact of two points of the metals (between which the oscillations 

 take place) must be longer than that of the intermediate portions. 

 5. The impulse is received by a distinct and separate process at 

 each contact of the bar with the block, and in no case is the connec- 

 tion of these points in any way essential. 6. The intensity of vibra- 

 tion is (under certain exceptions), proportional to the difference of 

 temperature of the two metals. 



From these data, the author first endeavours to show, that the 



hypothesis of expansion is untenable, by tracing closely the process 



of communication of heat, and proving that it must lead to several 



conclusions totally at variance with experiment, and particularly 



* See the abstract of a former paper on the identity of those arrangements. 



