272 Mr. Prideaux on the Theory of Thermo-electricity . 



metallic contact is facilitated. Tinned iron seems neutral to 

 clean iron when heated together (41.). Fusible metal acts 

 nearly as well as tin. Lead is softer, but much more suscep- 

 tible of tarnish, and does not take so well upon iron. Bismuth 

 will not yield to pressure, and therefore will not facilitate con- 

 tact, whilst its strong thermo-negative property can hardly be 

 subdued. The inefficacy of a copper coating is what we should 

 expect from this explanation. 



From these experiments it seems probable, — 



I. That thermo-electricity differs only in tension from that 

 of the voltaic apparatus, or of the machine. 



II. That it is not produced at the expense of caloric. 



III. That the radiation of heat, or any kindred property, 

 is not the proximate cause of its development. 



IV. That no properties at present known of conduction, 

 either for heat or electricity, are sufficient to account for it. 



V. That the metals are resolved by thermo-electricity into 

 two classes : 1 . thermo-positive, or becoming electro-positive 

 by heating; 2. thermo-negative, or becoming electro-negative 

 by heating ; the first class being always positive to the second 

 when heated : and that their order in their respective classes 

 is dependent on their conductive as well as thermo-electric 

 faculty. 



VI. That this property cannot be traced up to, or explained 

 by, the currents produced by'heat in single masses of bismuth 

 or other metal. 



VII. That foreign metals brought into contact with a ho- 

 mogeneous circuit near the point of heat, participate in the 

 action, and tend to determine the current. 



VIII. That the thermo-electric advantage gained to iron 

 and some other metals by tinning, is due to the improved con- 

 tact, occasioned by the soft and clean metallic surface thus 

 produced. 



These results are far from revealing an opening, even in the 

 remote distance, to the theory of the relations between elec- 

 tricity and heat; but if others who have engaged in different 

 branches of the investigation will likewise communicate their 

 observations to the public as they occur, comparison, assisting 

 the details of the note-book, may expedite the pursuit. By 

 affording the means of such comparison, scientific periodicals 

 are most effective agents in the advancement of science ; and 

 the general interest is much concerned in their extensive cir- 

 culation. 



