Producible by Attrition and Contact of Metals. 11 



the temperature equally in both metals above or below that standard, the de- 

 flection would take place. There is in this proposition more than those who 

 rely on it are perhaps aware of, as will be shown under the consideration of the 

 fourth Law. For tlie present it is only necessary to observe, in support of Law 

 in., that the temperature of the surrounding media has no connexion with the 

 subject ; that the cause of deflection is difference* of temperature between the 

 two metals, and not its elevation above, or depression below, that of the air. 

 Thus, when the temperature of the air was 60', a pair of bismuth and antimony 

 would produce deflections, whether one of the metals was at 30°, 60°, or 100°, 

 the other being 212°. The deflection of greatest amount is produced by the 

 greatest diflerence of temperature. 



Law IV. I have verified this Law in the case of gold, platinum, palladium, 

 silver, copper, brass, German silver, nickel, zinc, cadmium, tin, lead, antimony, 

 arsenic, iron, bismuth, and mercury. Hemispheres, or plates, of the first six- 

 teen of these metals, mounted with capillary rheophores and wooden handles, 

 in the manner already described, were left in pairs, lying near each other for 

 some hours, so that they all assumed the same temperature. By bringing the 

 metals of each pair into contact, taking care to avoid friction, there was not the 

 slightest deflection of the galvanometer with which they were connected. The 

 trials were made at difierent temperatures of the air, between 36° and 70°. 

 They were also made at temperatures varying from 70° to 212°, in which case 

 the method adopted was to place the two hemispheres in a vessel of water, of 

 the required heat, at a little distance from each other: the chemical action of 

 the water on the metals caused deflection ; when it was judged that both were 

 at the same temperature they were brought into contact ; the needle came to 

 zero, all deflection being at an end. In these experiments the rheophore wires 

 must be of the greatest tenuity, for reasons that will hereafter appear under 

 consideration of Law ix. 



This statement difiers from that of Eeman, in which he informs us, that 

 having equally heated a bar of bismuth, and another of antimony, to 100° or 

 lir Fahr., their contact produced 30° of eastern deflection; and also from his 

 experiment, in which, by equal reduction of the temperature of both bars, their 



* The term is here used for sake of brevity : under consideration of Law ix. the exact meaning 

 will appear. 



c 2 



