158 DR. FARADAY'S EXPERLMENTAL RESEARCHES IN ELECTRICITY. (SERIES XIII.) 



1625. Heat is another direct effect of the current upon substances in which it oc- 

 curs, and it becomes a very important question, as to the relation of the electric and 

 heating forces, whether the latter is always definite in amount*. There are many 

 cases, even amongst bodies which conduct without change, which stand out at pre- 

 sent from the assumption that it is-f- ; but there are also many which indicate that, 

 when proper limitations are applied, the heat produced is definite. Harris has shown 

 this for a given length of current in a metallic wire, using common electricity J ; and 

 De la Rive has proved the same point for voltaic electricity by his beautiful applica- 

 tion of Breguet's thermometer^. 



1626. When the production of heat is observed in electrolytes under decomposition, 

 the results are still more complicated. But important steps have been taken in the 

 investigation of this branch of the subject by De la Rive || and others ; and it is more 

 than probable that, when the right limitations are applied, constant and definite re- 

 sults will here also be obtained. 



1627. It is a most important part of the character of the current, and essentially 

 connected with its very nature, that it is always the same. The two forces are every- 

 where in it. There is never one current of force or one fluid only. Any one part 

 of the current may, as respects the presence of the two forces there, be considered 

 as precisely the same with any other part; and the numerous experiments which 

 imply their possible separation, as well as the theoretical expressions which, being 

 used daily, assume it, are, I think, in contradiction with facts (511, &c.). It appears 

 to me to be as impossible to assume a current of positive or a current of negative 

 force alone, or of the two at once with any predominance of one over the other, as 

 it is to give an absolute charge to matter (1169. 1177-)' 



1628. The conviction of this truth, if, as I think, it be a truth, or on the other hand 

 the disproof of it, is of the greatest consequence. If, as a first principle, we can 

 establish that the centres of the two forces, or elements of force, never can be sepa- 

 rated to any sensible distance, or at all events not further than the space between 

 two contiguous particles (1615.), or if we can establish the contrary conclusion, 

 how much more clear is our view of what lies before us, and how much less embar- 

 rassed the ground over which we have to pass in attaining to it, than if we remain 

 halting between two opinions ! And if, with that feeling, we rigidly test every expe- 

 riment which bears upon the point, as far as our prejudices will let us (1 161.), instead 

 of permitting them with a theoretical expression to pass too easily away, are we not 



* See De la Rive's Researches, Bib. Universelle, 1829, xl. p. 40. 



t Amongst others, Davy, Philosophical Transactions, 1821, p. 438. Pelletiee's important results, Annales 

 de Chimie, 1834, Ivi. p. 371. and Becquerel's non-heating current, Bib. Universelle, 1835, Ix. 218. 

 X Philosophical Transactions, 1824, pp. 225. 228. 

 § Annales de Chimie, 1836, Ixii. 177. 

 11 Bib. Universelle, 1829, xl. 49; and Ritchie, Phil. Trans. 1832, p. 296. 



