266 Mr. Prideaux's Experimental Contributions 



25. On comparing these tables, the thermo-electric reac- 

 tion, in pairs of different metals, would seem to be compounded 

 of the idio-thermo-electric force of each, and its conducting 

 power. 



In the thermo-positive class, the order of conduction is re- 

 versed : here iron and antimony differ little in thermo-positive 

 quality; but antimony is the worst conductor, and stands 

 highest in Cumming's table. 



Zinc and iron differ little in conducting power ; but iron is 

 considerably more thermo-electric than zinc, and accordingly 

 predominates in action when the metals are acting together. 



In the thermo-negative class, the arrangement corresponds 

 with the order of conduction ; the conducting power tending 

 to raise, the thermo-negative to lower, the metal in Cumming's 

 table. 



Silver is a better conductor than copper, but at the same 

 time more thermo-negative, and their thermo-electric reaction 

 is slight and uncertain ; copper, though usually described as 

 negative to silver, being sometimes positive, particularly at 

 high temperatures: I have, indeed, most frequently found 

 it so. 



Copper is a better conductor than platinum, and much less 

 thermo-negative ; the one property tends to keep up the cop- 

 per, the other to lower the platinum, which accordingly stands 

 much below copper in Cumming's table. 



Platinum is a little better conductor than tin, but much 

 more thermo-negative; the latter quality accordingly predo- 

 minates, and tin rises above platinum. 



Lead, a worse conductor than either of these metals, is very 

 much behind them in thermo-negative property, and both ac- 

 cordingly fall below it in the table of mutual reaction. 



Bismuth, the worst conductor, and the strongest thermo- 

 negative metal, has both properties coinciding to place it at the 

 bottom of the table, and would, if the forces were measured, 

 stand as far below platinum as that metal does (the tempera- 

 ture being alike,) below silver. 



The place of zinc, in this class, cannot be so well settled, as 

 it changes with the temperature. 



To reduce these proportions to numbers would require more 

 precise knowledge of the conducting powers than we yet pos- 

 sess, and a greater variety of experiments on the idio-thermo- 

 electric powers than an individual is likely to make. The 

 proximate cause of this peculiar faculty comes first in the order 

 of inquiry. 



