DYNAMICAL THEORY OF HEAT. 



145 



It must be added, by way of explanation, that the bracket enclosing 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 position as 

 shown in the table, the symbol of the metal is a small letter instead of a capital. 



131. " The rapidity with which copper changes its place among some of the 

 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 P x at 130° Cent., passes the lead at 140°, 

 the lead itself having probably passed the thick platinum at some temperature a 

 little below 130° [at 121, as I afterwards found]. The conclusion, as regards spe- 

 cific heats of electricity in the different metals, from the equation expressing 

 thermo-electric force given above, is, — tha/t the specific heat of vitreous electricity 

 is greater in each metal passing another from left to right in the series, as the 

 temperature rises, than in the metal it passes ; thus in particular — 



132. " The specific heat of vitreous electricity is greater in copper than in plati- 

 num or in iron; greater in brass than in platinum or in lead; and greater in lead 

 than in platinum. 



133. " It is probable enough, from the results regarding iron and copper men- 

 tioned above, that the specific heat of vitreous electricity is positive in brass ; and 

 very small positive or else negative in platinum, perhaps about the same as in iron. 

 It will not be difficult to test these speculations either by direct experiments on 

 the convective effects of electric currents in the different metals, or by compara- 

 tive measurements of thermo-electric forces for various temperatures in circuits 

 of the metals, and I trust to be able to do so before long." 



§§ 134, 135. Inserted September 15, 1854. 



134. A continuation of the experiments has shown many remarkable varia- 

 tions of order in the thermo-electric series. The following table exhibits the re- 

 sults of observations to determine neutral points for different pairs of metals : 

 the number at the head of each column being the temperature centigrade at which 

 the two metals written below it are thermo-electrically neutral to one another ; 

 and the lower metal in each column being that which passes the other from bis- 

 muth towards antimony, as the temperature rises. 



14° Cent. 



-12-°2 



-l-°5 



8-°2 



36° 



P 3 

 Brass. 



Pi 

 Cadmium. 



Pi 

 Silver. 



Pi 

 Zinc. 



P 2 

 Lead. 



38° 



44° 



44° 



64° 



99° 



121° 



130° 



lG2-°5 



237° 



280° 



P 2 



Brass. 



P 2 

 Tin. 



Lead 

 Brass. 



Pi 



Copper 



Pi 

 Brass. 



Pi 

 Lead. 



Pi 

 Tin. 



Iron 

 Cadmium. 



Iron 

 Silver. 



Iron 

 Copper 



I also found that brass becomes neutral to copper, and copper becomes neutral to 

 silver, at some high temperatures, estimated at from 800° to 1400° Cent., in the 



