of Heat by Thermo-Electricity, 83 



dinarily attributed to that agent; but I believe it has never 

 yet been recorded that the phjKnomena of heat, as evolved by 

 the metal employed in its transmission, have been observed as 

 a result of this mode of excitation. 



I have lately observed this fact with a delicate air 

 electro-thermometer of the construction suggested by my 

 friend Mr. W. S. Harris, and also with a Breguet's metalline 

 thermometer, arranged with M. De la Rive's contrivance for 

 passing a current through its helix. 



The indications afforded by both instruments were very 

 distinct and satisfactory, and could not be ascribed to any 

 direct conduction of heat, for I placed ice around the wires, 

 which completed the circuit between the battery and the 

 indicating instruments. 



I employed a massive thermo-electric battery, consisting 

 of 18 pairs of bismuth and antimony prismatic rods, four 

 inches long, united consecutively, similar to the arrangement 

 of M. Van der Voort, of Amsterdam. 



When the electricity was excited by applying a hot iron 

 heater near one extremity of the battery and ice at the op- 

 posite extremity, with the circuit complete through the air 

 electro-thermometer, the heating effect on the fine platinum 

 wire in the spherical air reservoir was immediately visible by 

 the ascent of the coloured liquid up the fine glass tube com- 

 municating with it. The elevation of the liquid column was 

 about 20°, which occupied a space on the scale of one inch. 



When the Breguet's thermometer was placed in the circuit, 

 the index attached to the bottom of the compound metallic 

 helix moved round 10° in the direction of the coils, the helix 

 expanding by the elevation of temperature conferred by the 

 passage of the thermo-electric current. 



The elevation of temperature of the metals forming the 

 electric circuit in both instruments, was always manifested 

 when the circuit was completed, and remained constant, but 

 on breaking the circuit the loss of heat was very apparent ; 

 therefore I have no reason to doubt that the heating effects 

 so conspicuously shown, were due solely to the transmission of 

 the thermo-electric current. 



I have repeated the experiments many times with uniform 

 success; and if you consider the fact of sufficient importance 

 to be announced in your Magazine, this brief notice is at your 

 disposal for that purpose. 



I remain, Gentlemen, 

 Yours, &c. 

 5, Charing Cross, 24th Dec. 1838. FiiANCIS Watkins. 



g2 



