128 



ELECTRO-MAGNETISM. 



live, is, according to Gumming bismuth, mercury, platinum, tin, lead, gold 

 copper, silver, zinc, iron, antimony. When heat is applied to the junction o 

 any pair of these, the current passes from that higher in the list to that lower 

 Thermo-electric batteries have been made by a combination of pairs in series 

 Baron Fourier made a hexagon of three pairs of bismuth and antimony : by 

 heating with a lamp or cooling with ice three junctions, he obtained increasec 

 effects ; by heating and cooling the alternate junctions at the same time, he in 

 creased the effect. From experiments by Oersted, " it appears that the thermo 

 electric current produces a prodigious quantity of electricity, but in a state o 

 very feeble intensity, while the Voltaic current has a very great intensity ;" so 

 that short elements are most advantageous. M. Pouillet found that if the elec 

 tro-motive power of a constant Voltaic pair were 95, that of a thermo-pair of 

 bismuth and antimony would be 1. Mr. Wheatstone, by his admirable appli- 

 cation, of Ohm's law, found the proportion 1 : 94 - 6. 



