towards the Theory of Thermo-electricity, 265 



ingly negative. — Silver, platinum, copper, tin, lead; and zinc 

 below 200°. 



Of the first class, the thermo-electric order (acting in pairs 

 of different metals,) is nearly the reverse of that of conduction. 



Of the second class, the thermo-electric order nearly cor- 

 responds with that of conduction. 



Tables of conduction from Mr. Forbes. Thermo-electric table 



from Prof. Cumming. 



Antimony. 



Iron. 



Zinc*. 



Silver. 



Copper. 



Gold. 



Lead. 



Tin. 



Platinum. 



Bismuth. 



Mr. Forbes considers the electrical table better authenti- 

 cated than that for heat, and seems inclined to the opinion, 

 that the order is really identical for the two. 



Thermo-positive class, ^_j c Order of 



* Becquerel brings zinc below silver, for reasons already adverted to (22.). 



f Iron is well known to have its thermo-electric reaction reversed at a 

 bright red heat, and to undergo the same change in its magnetic relations, — 

 a remarkable analogy between the two. This would have been noticed 

 above, but from the difficulty of the investigation having rendered my re- 

 sults hitherto inconstant. When the red-hot part is thin, its surface of 

 contact loses its redness on touching the cold face ; when substantial enough 

 to prevent this, it is not easy to heat it high enough, without oxidation, and 

 without the communication of some warmth to the points in contact with 

 the mercury. 



Third Series. Vol. 3. No. 16. Oct. 1833. 2 M 



