EFFECTS OF ROTATION OF MAGNETS. 
71 
live effect is produced ; not therefore that two disturbances of 
the electric equilibrium exist in the wire and magnet, and 
oppose each other, but that no inductive effect at all is produced 
(there being no relative motion). In this respect also the 
magnet and the helix agree. For it is well known in the case 
of a helix traversed by a current, if a conductor of any shape be 
rigidly fastened to the helix and rotated with it, no inductive 
effect whatever will be produced, simply because the two are 
relatively at rest. It may be observed that it is here the case 
of one and the same hypothesis affecting all the results we have 
considered, for as soon as it was believed that the experimental 
results necessitated the above hypothesis, it necessarily (to be 
consistent) influenced the theoretic deductions throughout. 
The hypothesis arose, as is sufficiently evident, from a simple 
oversight, or from not observing the rather curious fact that the 
experiment, on which it was based, admitted of a double inter- 
pretation. 
8. To summarize the conclusions therefore : — 
I. When a magnet rotates on its axis, it produces an induc- 
tive effect on bodies external to it. This inductive effect is the 
same as if the external bodies were themselves (conversely) 
caused to revolve with the same relative velocity about the fixed 
magnet. The action of the helix agrees with that of the mag- 
net in this respect ( i.e . in the effect being dependent on relative 
motion). 
II. A rotating magnet does not produce an inductive effect 
on itself \ i.e. does not become statically charged. The system 
of force about the magnet must be considered as at rest relatively 
to the magnet , and this holds true whatever the nature of the 
motion of the magnet (whether rotatory or translatory). The 
system of force about the earth (as a rotating magnet) must 
therefore be considered as at rest relatively to the earth , so that 
the earth cannot become statically charged at the poles by its 
rotation. On the other hand in the case of the tides, when 
there is relative motion (in regard to the earth), an electric dis- 
turbance may thus be brought about. 
III. The inductive effect produced by the movements of 
magnets and external conductors depends solely on relative and 
not on absolute motion, and this holds true independently of 
the nature of the motion of the magnet (whether rotatory or 
translatory). In this the helix agrees with the magnet, inas- 
much as the inductive effect produced by a helix depends on the 
relative motion of it to external conductors, and no exception 
has to be made to this, whether the motion of the helix be 
rotatory or translatory. 
IV. So then, when a magnet and an external conductor 
rigidly attached to it are rotated together with whatever 
