88 Galvanism, from Galvani to Ohm. 



between circuits carrying electric currents may be due to " the 

 reaction of the elastic fluid which extends throughout all 

 space, whose vibrations produce the phenomena of light," and 

 which is " put in motion by electric currents." This fluid or 

 aether can, he says, " be no other than that which results from 

 the combination of the two electricities/' 



In the second conception,* Ampere suggests that the 

 interspaces between the metallic molecules of a wire which 

 carries a current may be occupied by a fluid composed of the 

 two electricities, not in the proportions which form the neutral 

 fluid, but with an excess of that one of them which is opposite 

 to the electricity peculiar to the molecules of the metal, and 

 which consequently masks this latter electricity. In this inter- 

 molecular fluid the opposite electricities are continually being 

 dissociated and recombined ; a dissociation of the fluid within 

 one inter-molecular interval having taken place, the positive 

 electricity thus produced unites with the negative electricity 

 of the interval next to it in the direction of the current, while 

 the negative electricity of the first interval unites with the 

 positive electricity of the next interval in the other direction. 

 Such interchanges, according to this hypothesis, constitute the 

 electric current. 



Ampere's memoir is, however, but little occupied with the 

 more speculative side of the subject. His first aim was to 

 investigate thoroughly by experiment the ponderomotive forces 

 on electric currents. 



" When," he remarks, " M. Oersted discovered the action 

 which a current exercises on a magnet, one might certainly have 

 suspected the existence of a mutual action between two circuits 

 carrying currents ; but this was not a necessary consequence ; 

 for a bar of soft iron also acts on a magnetized needle, although 

 there is no mutual action between two bars of soft iron." 



Ampere, therefore, submitted the matter to the test of the 

 laboratory, and discovered that circuits carrying electric 

 currents exert ponderomotive forces on each other, and that 



* Recucil d' observations electro-dunamiques, pp. 297, 300, 371. 



