64 
POPULAR SCIENCE REVIEW. 
net on its axis its periphery is translated in a curve, and evi- 
dently a different law could not apply to the behaviour of the 
system of force according as to whether it is translated in a 
curved or in a straight line. We should have considerable diffi- 
dence in criticizing anything put forward by so eminent an 
authority, but scientific truth is admittedly paramount, and no 
one would claim immunity from an oversight. We think it 
may be distinctly shown that the above is an oversight resting 
upon the rather curious accident that the particular experiment 
tried admits of a double interpretation. 
4. Thus if we make no distinction between the behaviour of the 
system of force whether the magnet is translated or rotated, or 
assume that the system of force about the magnet is invariably 
at rest relatively to the magnet , then by the rotation of the 
magnet on its axis the system of force accompanying the magnet 
will cross both the wire w and the disk d , thereby tending to 
generate a current in them both in opposite directions — so that 
there will be no actual current at all. This is therefore why 
the magnet when rotated in either direction produces no differ- 
ence in the results. The final result is the same, not because 
the rotating magnet produces no inductive effect, but because 
the inductive effects upon the wire and disk oppose each other ; 
or the rotating magnet causes an electric disturbance both in 
the disk and in the external wire in such a way as to produce a 
balanced static charge, so that no current is possible. To prove 
that the inductive effects in the disk and wire exactly balance 
each other, it is only necessary to rotate the disk and wire toge- 
ther through the lines of force of the stationary magnet, when 
there will be (as is known) no current in the circuit made up of 
the disk and wire, the effects in the disk and wire therefore 
exactly opposing each other. So therefore it becomes clear how 
the rotation of the magnet on its axis can make no difference in 
the results ; and therefore the experimental result does not 
warrant the above singular distinction drawn in regard to the 
behaviour of the system of force when a magnet rotates on its 
axis. This distinction would indeed involve the conclusion that 
there is no inductive effect on the disk when the magnet rotates 
below the disk, but that there is an inductive effect when the 
disk rotates above the magnet, i.e. that the effect is different 
when the relative motion of the disk and magnet is the same, or 
in other words, that the inductive effect would depend on abso- 
lute and not on relative motion. This is negatived by the 
behaviour of the helix, whose inductive influence depends (as is 
known) on relative motion ; and the same with electrodynamic 
phenomena generally. It would therefore be strange that the 
magnet when rotated on its axis should form an exception to the 
general law, and we think that after it has been shown that the 
