ANIMAL ELECTRICITY. 211 



of Seebeck, is another proof of the very close connection 

 of the physical forces. We witness their being resolved 

 as it were into each other, electricity producing heat, 

 and heat again electricity ; and it is from these curious 

 results that the arguments in favour of their intimate 

 relations and actual identity have been drawn. It will, 

 however, be found to be the best philosophy to regard 

 these forces as dissimilar, until we are enabled to prove 

 them to be only modified forms of one principle or 

 power. At the same time it must not be forgotten that 

 in natural operations we invariably find the combined 

 action of several forces producing a single phenomenon. 

 The important fact to be particularly regarded is, that 

 we have evidence that every substance which is un- 

 equally heated becomes the source of this very remark- 

 able form of electricity.* 



There exist a few fishes gifted with the very ex- 

 traordinary power of producing electrical phenomena 

 by an effort of muscular or nervous energy. 



The Gymnotus electricus, or electrical eel, and the 

 Raia torpedo, a species of ray, are the most remarkable. 

 This power is, it would appear, given to these curious 

 creatures for purposes of defence, and also for enabling 

 them to secure their prey. The Gymnotus of the South 

 America rivers, will, it is said, when in full vigour, send 

 forth a discharge of electricity sufficiently powerful to 

 knock down a man, or to stun a horse ; while it can 

 destroy fishes, through a considerable space, by exert- 

 ing its strange artillery.t 



Faraday's description of a Gymnotus, paralyzing and 



* A very ingenious application of the knowledge of this fact was 

 suggested by Mr. Solly, by which the heat of a furnace could be 

 constantly registered at a very considerable distance from it. See 

 Description of an Electric Thermometer: by E. Solly, Jun., 

 Esq. Philosophical Magazine, vol. xx. p, 391. New Series. 



j Humboldt; Personal Narrative, Chap, xvii. Annales de 

 Chimie, vol. xiv. p. 15. 



