28 Voltaic Induction. 



rotation r r, r f r', of these induced voltaic currents, lie accurately 

 within those of R R, which give the particle, a, its magnetic power ; 

 and hence, from position alone, they are capable of arising from mag- 

 netic induction, and are more probable to act as a cause of the vol- 

 taic circulation. I shall now proceed to show in what manner this 

 may be accomplished. 



In doing so, I deem it unnecessary to discuss the question 

 which may arise, whether copper and other unmagnetic metals 

 are capable of receiving magnetism by induction. All these bod- 

 ies, when acting as voltaic elements, not only generate, but trans- 

 mit with ease both the magnetic forces ; and we possess the best 

 evidence, derived from the phenomena of thermo electricity, that 

 circumstances connected with a mere change of temperature, and 

 unaided by any thing like chemical action, are fully sufficient for the 

 developement. If, moreover, as I think will appear probable from 

 the view which I propose to take, magnetic induction be the cause 

 of unmagnetic metals rotating under the influence of strong magnets, 

 we shall be disposed to admit the possibility of effecting the same op- 

 eration upon other bodies than the metals, since Arago detected vol- 

 taic currents under like circumstances, in revolving glass, resin and 

 gaseous matter. One circumstance must be remembered, whatever 

 value be attached to the conclusions of this enquiry. No magnetic 

 rotation ever occurs, if the substance operated upon be a bad con- 

 ductor of electricity ; and, accordingly, though magnetic induction 

 should take place, we cannot expect a voltaic current to result when 

 the peculiar cohesion or other physical condition of the matter, op- 

 poses its circulation. Arago's results, just noticed, have been ques- 

 tioned by others ; but their complete rejection would not affect the 

 question under consideration. 



I shall proceed, therefore, upon the supposition, that all bodies 

 possess an unlimited amount of neutralized magnetic forces, capable 

 of being liberated by the ordinary process of induction; and that, 

 when the substance furnishing them is a good conductor of electri- 

 city, they not only revolve in circles around the component particles, 

 but distribute themselves, laterally, so as to create a voltaic current* 

 These magnetic circles become firmly established in a few bodies 

 only, such as steel, loadstone, &c. The cause of this perpetual ro- 

 tation is not apparent, but however w r e may explain the phenomenon, 

 the difficulty will certainly not be greater than that which arises from 

 the supposition of a perpetual voltaic current around the same par- 



