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IV
KINETIC ENERGY OF ELECTRICITY IN MOTION [II]
3. A part whose sign depended on the direction of rotation
as well as on the connections. Thus:-
(a) If such a part occurred in the momentary deflection
no other cause perhaps could be assigned except the inertia of
the electricity moved.
(b) In the permanent deflection such a part might be
produced, because during rotation two diagonally opposite
branches of the bridge moved in front of the other two, and
thus were more strongly cooled by the air-currents than the
latter. As the conducting layer of silver was very close to
the brass disc, I had not anticipated such an effect; but it
proved to be very large, and was especially inconvenient, since
it only differed from the effect of inertia in lasting for a time
after the rotation ceased. By surrounding the plate and brass
disc by cotton wool and by a drum of paper I was able to
diminish this disturbance considerably; and still further
by hermetically sealing the paper drum by a coating of
paraffin. But even then the disturbance did not completely
disappear.
I performed two series, each of twenty, of the experiments
described. They differed in the strength of the current
employed, in the sensitiveness of the galvanometer, and especi-
ally in this, that in the first series the paraffin coating
mentioned was wanting. The second series was by far the
better, and what follows refers to it alone. To it also refers
the statement made above respecting the sensitiveness of the
galvanometer. The strength of the current was 1·17 mgł
mm/sec magnetic units; the velocity of rotation, according
to what has been said above, was on the average 290/834
turns per second. The galvanometer deflection at the end of
the rotation amounted on the average to 10 to 15 scale divi-
sions, and in the succeeding seconds changed mostly by only
a few divisions. The greater part of this deflection cor-
responded to the causes (2 b) and (2 c), which could no longer be
separated the effect of disturbances (1) and (3 b) was found
to be 2 to 4 scale divisions; the disturbance (2 a) was small.
The practicability of the method followed from the fact that
the separate disturbances were found to be of the same sign and
of the same order of magnitude in all the experiments, almost
without exception. The following are the twenty values, in