536 



Mr. (Jr. Gore on 



chemical change occur ; and, 2nd, because when chemical action of any 

 kind did take place, it either produced no electric currents, or it pro- 

 duced currents either in a reverse direction, or greater in amount than 

 those due to the heat. It also in nearly all such cases either caused the 

 plates to lose their lustre, produced a deposit upon them, or made the 

 liquids change in colour or become cloudy. In consequence of these 

 different effects, the apparatus and method of experiment may be em- 

 ployed for detecting some of the chemical (as well as the electrical) 

 effects of heat upon electrically conducting liquids. ~No signs of elec- 

 trolytic action, or deposition of metal, even in the most suitable solu- 

 tions, such as those of copper, were observed ; and there was no reason 

 to suppose that the metal plates contained occluded gases. The pheno- 

 mena were also inconsistent with the supposition that the heat operated 

 by temporarily dissociating the constituents of the liquid. (Compare 

 Nos. 77, 94, 159, 160, and 161.) The fact also that the currents pro- 

 duced in acid liquids were opposite in direction to those which would 

 have been produced by chemical action, is very strong evidence against 

 the cause being chemical. From these various circumstances it is clear 

 that, except in those cases where signs of chemical change were 

 detected, heat was the true and only cause of the currents, and not 

 merely an exciting cause of chemical action producing them. 



Although heat is the true and only cause of the currents, it may 

 operate either in a direct manner in producing them, or through the 

 agency of some intermediate force. If it operates through some other 

 force, then an action of that force must form an essential part of the 

 phenomena. As the currents are not confined to magnetic liquids, 

 magnetic action cannot be an essential condition. Light also does not 

 manifestly influence the results, and chemical action can be excluded ; 

 and the only forces likely to be active in the circumstances of the case 

 are those of cohesion and adhesion. We know that rise of tempera- 

 ture usually diminishes both these powers, expands both solids and 

 liquids, and rearranges their molecules ; it usually diminishes the adhe- 

 sion of liquids to solids ; and in certain cases it even disassociates the 

 elements of a compound. As the action, however, which produces the 

 current always requires two substances, viz., a liquid and a metal, and 

 evidently occurs either wholly or chiefly at their immediate surfaces of 

 mutual contact, we may conclude that it is not an effect of heat upon 

 the force of cohesion in the mass of liquid or of metal. 



Although various effects of heat upon cohesion and adhesion must 

 occur in the metals and liquids employed in these experiments, and 

 cannot be excluded, they may still not necessarily fprm an essential 

 part of the phenomena, but be only concomitant circumstances, and the 

 existence of the electric currents may be in no degree dependent upon 

 them. As also the currents continue not only during the rise and fall of 

 temperature, but likewise during a stationary and prolonged difference 



