Royal Society. 



BT 



would show the law according to which the difference of the spe- 

 cific heat of electricity in the two metals varies with the tempera- 

 tures ; but I have not even as yet ascertained with certainty the ex- 

 istence of such a deviation in any particular case. The following is 

 a summary of the principal results I have already obtained in this 

 department of the subject. 



The metals tried being, — three platinum wires (P^ the thickest, 

 Pg the thinnest, and Pg one of intermediate thickness), brass wires 

 (B), a lead wire (L'), shps of sheet lead (L), copper wires (C), and 

 iron wire (I), I find that the specimens experimented on stand 

 thermo-electrically at different temperatures in the order shown 

 in the following Table, and explained in the heading by reference to 

 bismuth and antimony, or to the terms " negative " and " positive " 

 as often used : — 



Temp. 

 Cent. 



Bismuth 

 " Negative. 



Antimony 

 * Positive." 



-20 







37 



64 



130 



140 



280 



300 



...P, 



..R...r 



.Pi. 

 .Pi. 



...P3 6...{L'PJ C.Pi I. 



...P3. 

 ...P3. 

 ...P3. 

 ...P3. 



...Ps. 



.Pa... h...V {CPi} I 



P^ {BP.}...L... C I 



.P2 rTPx...{BL} C ...I 



.P2 Pi.^ b... {CI} ...... 



.Pa Pi b,...,.l C 



It must be added, by way of explanation, that the bracket en- 

 closing the symbols of any two of the metallic specimens indicates 

 that they are neutral to one another at the corresponding temperature, 

 and the arrow-head below one of them shows the direction in which 

 it is changing its place with reference to the other, in the series, as 

 the temperature is raised. When there is any doubt as to a posi- 

 tion as shown in the Table, the symbol of the metal is a small letter 

 instead of a capital. 



The rapidity with which copper changes its place among some of 

 the other metals (the platinums and iron) is very remarkable. Brass 

 also changes its place in the same direction possibly no less rapidly 

 than copper ; and lead changes its place also in the same direction 

 but certainly less rapidly than brass, which after passing the thick 

 platinum wire (PJ at 130° Cent, passes the lead at 140°, the lead 

 itself having probably passed the thick platinum at some tempera- 

 ture a little below 130°*. 



* I have since found that it does pass the thick platinum, at the temperature 

 118°. [May 16, 1854.] 



F2 



