02 
OX THE INTERPRETATION OF SOME EXPERIMENTS 
RELATING TO THE INDUCTIVE EFFECT PRODUCED 
BY THE ROTATION OF A MAGNET ON ITS AXIS. 
By S. TOLVER PRESTON. 
1 . A curious and interesting question is raised by some experi- 
ments of Faraday, described in the “ Philosophical Transactions,” 
in regard to the inductive effect attendant on the rotation of a 
magnet on its axis. Faraday appears to have considered that 
experimental results rendered it necessary to draw a distinction 
between the motion of rotation and the motion of translation 
of a magnet, in regard to the behaviour of the system of force 
about it; for he says ( 66 Phil. Trans.” 1852, p. 31), “ When 
lines of force are spoken of as crossing a conducting circuit, it 
must be considered as effected by the translation of a magnet. 
No mere rotation of a bar magnet on its axis produces any in- 
ductive effect on circuits exterior to it. The system of power 
about the magnet must not be considered as revolving with the 
magnet, any more than the rays of light which emanate from the 
sun are supposed to revolve with the sun. The magnet may even 
in certain cases be considered as revolving amongst its own forces, 
and producing a full electric effect sensible at the galvanometer.” 
2. At the first sight it will appear theoretically a strange con- 
clusion (and Faraday himself designates it afterwards as “sin- 
gular ”) that the above distinction between a motion of rotation 
and a motion of translation should hold. For even if we take 
the above illustrative case of the sun, it must appear evident (as 
regards the light emitted from any luminous portion of the sun) 
that any effect that was produced by the translation of that 
luminous portion through space would equally be produced by 
the rotation of that same portion about the axis of the sun, for 
rotation is simply translation in a circle . ,So by the rotation of 
a magnet on its axis, its constituent parts are translated in 
circles. It would therefore seem necessarily to follow theoretically 
that any law that applied to the translation of a magnet would 
equally apply to its rotation. It is an observed fact that by the 
translation of a magnet, the inductive effect produced on 
