Voltaic Induction. 



41 



through the spinal column, there should be a tendency to produce 

 north and south poles upon opposite sides of the body. Let those, 

 therefore, who indulge in such general speculations, seriously reflect 

 in what a condition the brain must be, with its whirling magnets and 

 electric conflicts ! 



I shall now proceed to the conclusion of this enquiry, by making 

 an application of the hypothesis to those cases of rotation first announ- 

 ced by M. Arago in 1824. The most important facts are as fol- 

 lows — when a copper plate is made to revolve on its centre, under 

 the influence of a powerful magnet placed over its marginal surface, 

 or, indeed, in any other eccentric position, compared with the plate, 

 the magnet receives four distinct impulses, two of which, are the re- 

 sult of suddenly changing its position, so as to place it nearer the cir- 

 cumference or the centre of the revolving plate. 



If, however, the magnet obeys the influence of the plate, alone, 

 and has not its position otherwise altered, it receives the other two 

 impulses — one tending to make it follow the plate in its revolutions, 

 and the other to repel it perpendicularly. Any unmagnetic metal 

 may be substituted for the copper with similar, although, generally, 

 diminished effects ; and as the action and reaction are equal to each 

 other, all the movements may be obtained by giving the rotation to 

 the magnet and the freedom of motion to the plate. In my illustra- 

 tions, I shall adopt the former and suppose the plate to revolve. 



Fig. 7. 



D 



t 



E 



Let D B E, fig. 7, represent a portion of the copper plate, revolv- 

 ing horizontally at its centre C, and in the direction of the arrow at B. 

 Let N represent the position of the magnet, suspended over the plate, 

 and Nx NV two of its north polar forces, projected upon the plate 

 so as to cut it at the points a and b ; these letters also denoting two 



Vol. XXVI.— No. 1. 6 



