I
5
KINETIC ENERGY OF ELECTRICITY IN MOTION [I]
m =
i'J
-
;P' — P, or if i' = i,
¿JP'.
iJ
m = P
(JP-1).
The experiments were carried out according to this
principle. The system of conductors through which the
currents flowed consisted in the earlier experiments of spirals
wound with double wires, in the later ones of two wires
stretched out in parallel straight lines side by side. These
systems of wires could without change of resistance be coupled
in such a way that the currents in the two branches flowed in
the same or in opposite directions. The inductances follow-
ing from the two methods of coupling were calculated and
the integral flows of the corresponding extra-currents were
determined by experiment. If these flows were proportional
to the calculated inductances, no effect of mass would be
demonstrated; if a deviation from proportionality were observed,
the kinetic energy of the currents would follow by the above
formulæ.
The extra-currents were always measured by means of a
Wheatstone's bridge, one branch of which contained the system
of wires giving the currents, while the other branches were
chosen to have as little inductance as possible. The bridge
was adjusted so that a steady current flowing through it pro-
duced no permanent deflection of the galvanometer needle ;
but when the direction of the current outside the bridge was
reversed, then two equal and equally directed extra-currents
traversed the galvanometer, and their integral flow was measured.
by the kick of the needle. As soon as the needle returned
from its kick the reversing could be repeated, and in this
manner the method of multiplication could be applied.
The chief difficulty in these measurements was to be met
in the smallness of the observed extra-currents, and on this
account the method described was impracticable in its simplest
form. It is true that by merely increasing the strength of
the inducing current the extra-currents could be made as
strong as desired, but the difficulties in exactly adjusting the
bridge increased very much more quickly than the intensities