SECT. XXXIII. THERMO-ELECTRICITY. 333 



ring, is heatecl at one of the junctions by a lamp, a current of 

 electricity flows through the circuit from the antimony to the 

 bismuth ; and such thermo-electric currents produce all the elec- 

 tro-magnetic effects. A compass needle, placed either within or 

 without the circuit, and at a small distance from it, is deflected 

 from its natural position, in a direction corresponding to the way 

 in which the electricity is flowing. If such a ring be suspended 

 so as to move easily in any direction, it will obey the action of 

 a magnet brought near it, and may even be made to revolve. 

 According to the researches of M. Seebeck, the same substance, 

 unequally heated, exhibits electrical currents ; and M. Nobili 

 observed, that in all metals, except zinc, iron, and antimony, the 

 electricity flows from the hot part towards that which is cold. 

 That philosopher attributes terrestrial magnetism to a difference 

 in the action of heat on the various substances of which the crust 

 of the earth is composed ; and, in confirmation of his views, he 

 has produced electrical currents by the contact of two pieces of 

 moist clay, of which one was hotter than the other. 



M. Becquerel constructed a thermo-electric battery of one 

 kind of metal, by which he has determined the relation between 

 the heat employed and the intensity of the resulting electricity. 

 He found that, in most metals, the intensity of the current in- 

 creases with the heat to a certain limit, but that this law extends 

 much farther in metals that are difficult to fuse, and which do 

 not rust. The experiments of Professor Gumming show that 

 the mutual action of a magnet and a thermo-electric current is 

 subject to the same laws as those of magnets and galvanic 

 currents ; consequently all the phenomena of repulsion, attrac- 

 tion, and rotation may be exhibited by a thermo-electric current. 

 M. Botto, of Turin, has decomposed water and some solutions by 

 thermo-electricity ; and the Cav. Antinori of Florence succeeded 

 in obtaining a brilliant spark with the aid of an electro-dynamic 

 coil. 



The principle of thermo-electricity has been employed by MM. 

 Nobili and Melloni for measuring extremely minute quantities 

 of heat in their experiments on the instantaneous transmission of 

 radiant heat. The thermo-multiplier, which they constructed 

 for that purpose, consists of a series of alternate bars, or rather 

 fine wires of bismuth and antimony, placed side by side, and the 

 extremities alternately soldered together. When heat is applied 



