36 V oltaic Induction. 
around the wires. I shall illustrate this by supposing the magnet to 
be stationary, and the coil to revolve, at its center, around the mag- 
netic axis. 
Let N, fig. 5, represent a vertical section Fig. 5. 
of the axis, at the north polar surface, and 
a, 6, c, a flat coil, revolving, vertically, at its 
centre, around the pole N, and having its di- 
rection indicated by the terminal arrow at c. 
Any particle, as a, included within two lines 
of polar action, will, in consequence of the 
supposed motion, receive induction from the 
force Nx’, and from the point of intercep- 
tion, a north pole will move around the par- 
ticle towards z, and a south one towards N. b 
But as the force Nz’ lies in the same plane as the coil, so will the 
induced magnetic circle n, s; and the voltaic currents, which result 
from this action, must of necessity move across the wire, at a. 
Hence it cannot be detected at other parts, asb and ¢ of thecoil. If 
we employ a copper plate, the result would be different, but only in 
consequence of an extension of this transverse current; for the plate 
forming a continuous conductor from circumference to centre, the 
positive and negative elements would distribute themselves in this di- 
rection, and even enter the wires of a galvanometer when they are 
placed upon the radius a, N. By the motion, as here represented, 
(fig. 5,) a positive current would issue from this side of a particle, at 
a, and descending over the near surface of the plate, proceed to- 
wards its centre. Reversing the motion, will obviously invert the di- 
rection of the current. 
For the full effect of induction under such circumstances, it is not 
necessary that there should be-a plate at all; for, if a magnet, sup- 
ported at its extremities by pieces of metal, be made to revolve upon 
its axis, these currents will be generated in the supports, and may be 
drawn off by wires placed in contact with either the magnet or the 
metallic fixtures. Nobili is, therefore mistaken, when he says that 
currents cannot be generated by a concentric rotation. The highly 
interesting researches of Faraday, published in the second part of 
his memoir,* place this question beyond a doubt; for he detected 
* Annales de Chimie, June, 1832. 
