KINETIC ENERGY OF ELECTRICITY IN MOTION [1]
11
The mean value of k = 22.05; the greatest difference
amounts to less than of the whole. As in each impact
40 extra-currents were combined, the deflection produced by
a single one was only 0.551 scale division. The remaining
series of multiplied deflections showed about the same degree
of agreement when the individual impacts were calculated.
DESCRIPTION OF THE APPARATUS.
Before proceeding to discuss the individual experiments
I shall describe those arrangements which were common to all
the experiments.
1. If we desire the strength of the extra-current to be a
maximum in the galvanometer for a given strength of the
inducing current and given values of the inductances, we must
choose the resistance of the galvanometer as small as possible,
and the resistances of the other branches all equal. This
arrangement has another special advantage. For different
paths are open to the currents at make and break, since the
former can also discharge through the external circuit whilst
the latter cannot. In order to reduce all the experiments to
similar conditions a correction has in general to be made
which depends on the resistance of the external circuit. This
correction vanishes when the resistances of the four branches
are the same. In fact, if r be this resistance, r, the resistance
of the galvanometer, and r, that of the battery, we get for the
current in the galvanometer, when an electromotive force E
acts in one of the branches, the value E/2(r+r), which is
independent of re
Hence, when the four branches were made equal, the
results obtained with different batteries could be directly
compared.
2. The passive resistances of the bridge had to be so
chosen that the part of the extra-current due to them was as
small as possible. In this respect columns of large diameter
of unpolarisable liquids would have been most suitable, since
the inductance of such columns is very small. But it was
impossible with the great delicacy of the bridge to obtain