between Metallic Masses having different Temperatures. 437 



a lecture at the Royal Institution in April 1831, and were pub- 

 lished in the Journal edited there. 



17. Mr FARADAY having pointed out the arrangement of 

 metals alluded to as a theoretical result, though confirmed in some 

 points by experiment, I conceived that the only true way of ar- 

 riving at an explanation of the phenomena, would be to classify 

 the metals by experiment in the order of their intensity and dis- 

 tinctness of vibrating power. In this inquiry I found many diffi- 

 culties, chiefly arising from the apparently capricious nature of 

 the effects produced, which for a long time seemed almost to 

 baffle an attempt at classification j and it was only by reiterated 

 series of experiments, at different times, and made in different 

 ways, that I could satisfy myself of the degree of accuracy to 

 which my results were entitled. 



18. I soon found that the conditions of vibration depended 

 simply on the distance between the places of the two metals em- 

 ployed for the bar or block, in a certain scale required to be 

 determined. The remarkable case of iron already observed by Mr 

 FARADAY made me very desirous to extend such a law ; here we 

 have a metal which must be placed towards the middle of such 

 a scale, since a metal above it in the scale vibrates upon it when 

 hotter than the iron, whilst iron itself vibrates upon cold lead, 

 which, therefore, must be placed lower in the scale ; and as the 

 intensity of vibration may be expected to be proportional to the 

 interval in the scale, so we actually find that silver vibrates on 

 lead much more actively and steadily than iron does. 



19. I first prepared bars similar to those which have been 

 already described, of copper, zinc, brass, iron, tin, lead, antimony, 

 and bismuth. My earliest experiments demonstrated the small 

 number of pairs of metals between which vibrations took place. 

 The superiority of lead to all other metals, as the cold substance* 

 was manifest ; and in order to establish, in relation to it, the in- 

 tensity of vibration of the different heated metals, it was neces- 



