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ELECTRO-MAGNETISM. 



tive, is, according to dimming — bismuth, mercury, platinum, tin, lead, gold, 

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

 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 increased 

 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 of 

 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. 



