210 THERMO-ELECTRICITY. 



the gymnotus and torpedo (animal electricity) ; magne- 

 tism and its phenomena being reserved for a separate 

 consideration. 



If a bar of metal is warmed at one end and kept cool 

 at the other, an electrical current circulates through the 

 bar, and may be carried off by connection with any 

 good conductor, and shown to exhibit the properties of 

 ordinary electricity. The metals best suited for showing 

 the effects of thermo-electricity appear to be bismuth 

 and antimony. By binding two bars of these metals 

 together at one end, and connecting the other ends with 

 a galvanometer, it will be discovered that an electric 

 current passes off through the instrument by the 

 slightest variation of temperature. Merely clasping 

 the two metals, where bound together, with the finger 

 and thumb, is sufficient to exhibit the phenomenon. 

 By a series of such arrangements, which form what 

 have been called thermo-electric multipliers, we 

 obtain the most delicate measurers of heat with which 

 philosophers are acquainted, by the aid of which 

 Melloni has been enabled to pursue his beautiful 

 researches on radiant caloric. 



That this electricity is identical with the other forms 

 has been proved by employing the current thus excited 

 for the purpose of producing chemical decomposition, 

 magnetism, and electric light.* 



The phenomenon of thermo-electricity the discovery 



* See Le Feu &Umentaire of 1'Abbe Nollet ; Lemons cle Physique, 

 torn. vi. p. 252 ; Du Pouvoir thermoelectrique, by M. Becquerel 

 Annales de Chimie, vol. xli. p. 353; also a Memoir by Nobili, 

 Bibliotheque Universelle, vol. xxxvii. p. 15; Experimental Con- 

 tributions towards the theory of Thermo-Electricity by Mr. J. 

 Prideaux Philosophical Magazine, vol. iii., Third Series ; On the 

 Thermo- Magnetism of Homogeneous Bodies, with illustrative expe- 

 riments, by Mr. William Sturgeon Philosophical Magazine, vol. 

 x. p. 1 116, New Series. Botto made magnets and obtained 

 chemical decomposition. Antinori produced the spark. Mr. 

 "Watkins heated a wire in Harris's Thermo-Electrometer. 



