between Metallic Masses having different Temperatures. 21 



Mr. Trevelyan, however, thinks that he observed a vibration 

 upon glass. It is a remarkable fact, substantiated by experi- 

 ments which will presently be mentioned, that all metals do 

 not possess the property alluded to. It was natural to divide 

 the metals into two classes, one of which might form the heated 

 bar, the other the cold block ; and it was also natural to sup- 

 pose that metals excluded from the one class belonged to the 

 other. I have, however, discovered, that at least two metals 

 are perfectly inert, in either situation, namely, antimony and 

 bismuth. 



15. At an early period I found (as Mr. Trevelyan also did 

 independently,) that the position of the bar and block were 

 convertible ; I mean, that the metal commonly used for the 

 block might be employed for the bar, and vice versa, provided 

 always, that the same metal was always hotter or colder (as 

 experience showed to be necessary,) than the other. Thus, 

 Mr. Trevelyan announced that a bar of hot iron or copper 

 placed on a block of cold lead or tin, produced vibrations; but 

 we shall still have the same phenomena, provided we use a cold 

 bar of lead or tin placed upon a hot block of iron or copper. 



16. Mr. Trevelyan having observed that lead and tin were 

 the metals which required to be cold, and that metals which 

 he designates as " hard", such as iron and copper, must be 

 hot, he naturally draws a division between two classes of me- 

 tals quite distinct, each of which require certain conditions to 

 produce the vibrations. Mr. Faraday having taken up the 

 subject, found that hot silver vibrated on cold iron, a fact 

 observed by silversmiths, thus forming a link between the 

 classes, and showing that a metal which requires to be cold 

 relatively to a second metal, must be hot relatively to a third. 

 Some theoretical views, which we shall presently advert to, and 

 to which experience did not seem to be opposed, led Mr. 

 Faraday to the conclusion that the arrangement of the melals 

 with regard to their power of vibrating with one another, was 

 directly as their conducting power for heat, and inversely as 

 their expansibility. The metal standing highest on the scale 

 of metals thus formed, being necessarily the hot one relatively 

 to the other, which stood lower on the same scale. These 

 observations of Mr. Faraday were given in a lecture at the 

 Royal Institution in April 1831, and were published 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 arriving at an explanation of the phenomena, would 

 be to classify the metals by experiment in the order of their 



