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These diminutions of current and reversals of its direction by rise of 

 temperature indicate irregular molecular changes in the layer of liquid 

 next to the heated plate ; and the examination of electrically conduct- 

 ing solutions by this apparatus and process constitutes a new mode of 

 discovering such alterations in them. By obtaining also a sufficient 

 variety and number of instances of such change, for comparison, classi- 

 fication and generalization, we may probably be enabled to infer and 

 discover some general truths respecting molecular action, or gain some 

 knowledge of the molecular conditions necessary for the conversion of 

 heat into dynamic electricity. As also molecular change is a funda- 

 mental action in bodies, and many of the secondary properties of sub- 

 stances depend upon molecular state, an alteration of the former is 

 usually attended by more than one of the latter ; and we may there- 

 fore reasonably infer that the foregoing change in the electrical pro- 

 perties of a solution of chrome alum and other liquids is attended by 

 other coincident physical changes, such, for instance, as that of expan- 

 sion, or of specific heat capacity. 



According to the contact theory of voltaic action, a metal touching 

 another metal, or touching a liquid, tends to produce an electric cur- 



