be taken of and allowance made for two points. First, that the
metal plate not only cuts off, but itself radiates; and
secondly, that the duration of the induced currents radiated by
the plates varies with each different metal under experiment.
This explains the fact before pointed out that the apparent
percentage of inductive radiant energy intercepted by metal
plates varies with the speed of the reversals; for in the case
of copper the induced current set up by such a plate has so long
a duration that if the speed of the reverser is at all rapid the
induced current has not time to exhaust itself before the
galvanometer is reversed, and thus the current being on the
opposite side of the galvanometer tends to produce a lower
deflection. If the speed of the reverser be further increased,
the greater part of the induced current is received on the
opposite terminal of the galvanometer, so that a negative result
is obtained. We know that it was the strong analogies which
exist between electricity and magnet