IV
UPPER LIMIT FOR THE KINETIC ENERGY OF
ELECTRICITY IN MOTION
(Wiedemann's Annalen, 14, pp. 581-590, 1881.)
In a previous paper¹ I have deduced, from experiments on the
strength of extra-currents, the conclusion that the kinetic
energy of an electric current of magnetic strength 1 in a
copper conductor is less than 0.008 mg. mm.²/sec.2 This con-
clusion, however, could only be drawn on the supposition that
a certain relation did not exist between the specific resistance
of metals and the density of electricity in them. In the
present paper I propose to describe an experiment which I
have made with a view to demonstrating kinetic energy in
electrical flow, but equally with a negative result. This
experiment, however, has advantages over the previous ones:
for, in the first place, it is more direct; secondly, it gives a
smaller value of the upper limit; and thirdly, it gives it
without limitation of any kind.
Suppose a thin metal plate of the form shown in Fig. 17
to be traversed by as strong a current as possible between the
electrodes A and B; further, let the points C and D be con-
nected with a delicate galvanometer, and let the system be so
adjusted that no current flows through the galvanometer. Let
the plate be made to rotate about an axis through its centre
and perpendicular to its plane. The current will now tend to
deviate laterally from the direction AB in case electricity in
motion exhibits inertia, for the same mechanical reason that
the rotation of the earth causes the trade winds to deviate
1 See I. p. 1.