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 § 150, and arranging the spaces 
so that each line shall be as nearly straight as possible, if not exactly so. 
100° 150° 
50 100 150 
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, 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, , ay . Positive. 
SF DIASRS 
» Copper, * 9 ; : 30 
{ sive ae : Positive, zero, or negative 
» | Silver, ‘ ¢ y F 8 , 
» Platinum, A : 3 . Probably negative. 
» Iron, Negative. 
Zine probably stands high, certainly above platinum. 
* See § 140, below. 
