272 Upon Caloric as a cause of Galvanic Currents. 



originate at the very point of contact. This fact, taken in connec- 

 tion witii the views advanced by Volta, in order to explain the action 

 of his pile, seems to have led persons to suppose that the contact of 

 dissimilar metals was necessary, and accordingly, almost all the re- 

 sults obtained, upon the subject of thermo-electricity, relate to the 

 combination of different metals. Yet it is easy to show, by the gal- 

 vanometer, that two portions of the same metal, are capable of act- 

 ing upon each other, and that the currents, thus generated, depend 

 solely upon the direction which the caloric is made to take. Thus, I 

 found, that, when a hot fragment of bismuth, was made to touch a 

 cold one, the former constantly transmitted a positive current to the 

 galvanometer ; whereas, when fragments of antimony, unequally 

 heated, were brought into contact, the hot portion, invariably, con- 

 ducted the negative current. These two metals are, therefore op- 

 posite to each other, in this respect, and when combined, must from 

 the point of contact, send forth the two fluids in opposite directions. 

 All the other metals, tried, were capable of producing currents by 

 the simple contact of their own particles, unequally heated, but bis- 

 muth and antimony possess the greatest power. The currents cease 

 almost immediately, upon the contact of particles, obviously, because 

 the inequality of temperature, is thus at once destroyed ; v^rhereas, 

 when dissimilar metals, are heated in contact with each other, the 

 difference of temperature, must still subsist owing to the greater ca- 

 pacity for caloric and conducting power of one of the metals. In 

 such cases, the direction of the galvanic current, is determined by 

 the direction which the excess of caloric takes through the metallic 

 medium. Heating one fragment before its contact with the other, 

 enabled me, in most cases, to determine the directions which the 

 caloric and galvanic currents take, and the results, t think, will show 

 that this mode o^ investigation is of the utmost importance. The 

 following tabular view represents, nearly, the order in which the met- 

 als stand in relation to their elementary galvanic powers. The caloric, 

 it is obvious, must be considered as proceeding from the hot fragments 

 to the cold as long as there is any difference of temperature. 



Contact between portions of the same 7netal unequally heated. 



rpos. current in — antimony, arsenic, platinum, copper and 

 Increase i silver. {Law — caloric and pos. current move togeth- 

 of heat ' *3 'rHh\ 



opes a I '^^S- current, in lead, tin zinc, gold, iron, me rcury? nickel 

 [ and bismuth. Law — opposition ^- '^ ) 



