146 



PROFESSOR W. THOMSON ON THE 



former case, and from 700° to 1000° in the latter, being a little below the melting 

 point of silver. The following diagram exhibits the results graphically, constructed 

 on the principle of drawing a line through the letters corresponding to any one of 

 the metallic specimens in a table such as that of § 130, and arranging the spaces 

 so that each line shall be as nearly straight as possible, if not exactly so. 



SOO' 



Explanation of Thermo-electric Diagram. 



The orders of the metals in the thermo-electric series, at different temperatures, are shown by 

 the points in which the vertical lines through the numbers expressed by the temperatures centigrade 

 are cut by the horizontal and oblique lines named for the different metallic specimens. 



The object to be aimed at in perfecting a thermo-electric diagram, and per- 

 haps approximately attained to (conjecturally) in the preceding, is to make the 

 ordinates of the lines (which will, in general, be curves) corresponding to the 

 different metallic specimens, be exactly proportional to their thermo-electric 

 powers* with reference to a standard metal (P 3 in the actual diagram). 



135. Judging by the eye from the diagram, as regards the convective agency 

 of electricity in unequally heated conductors, I infer that the different metals are 

 probably to be ranked as follows, in order of the values of the specific heat of 



electricity in them. 



Specific Heat of Vitreous Electricity : — 



In Cadmium, . < . . Positive. 



Brass, .... 

 Copper, .... 

 f Lead, Tin, ~» 

 { Silver, J 

 Platinum, 



Iron, .... 



Zinc probably stands high, certainly above platinum. 



* See § 140, below. 



Positive, zero, or negative. 



Probably negative. 

 Negative. 



