connection with experiments with such a coil, it should be an oil
condenser by all means, as in using an air condenser considerable
energy might be wasted. The wires leading to the plates in the oil
should be very thin, heavily coated with some insulating compound, and
provided with a conducting covering--this preferably extending under
the surface of the oil. The conducting cover should not be too near
the terminals, or ends, of the wire, as a spark would be apt to jump
from the wire to it. The conducting coating is used to diminish the
air losses, in virtue of its action as an electrostatic screen. As to
the size of the vessel containing the oil, and the size of the plates,
the experimenter gains at once an idea from a rough trial. The size of
the plates _in oil_ is, however, calculable, as the dielectric losses
are very small.
In the preceding experiment it is of considerable interest to know
what relation the quantity of the light emitted bears to the frequency
and potential of the electric impulses. My opinion is that the heat as
well as light effects produced should be proportionate, under
otherwise equal conditions of test, to the product of frequency and
square of potential, but the experimental verification of the law,
whatever it may be, would be exceedingly difficult. One thing is
certain, at any rate, and that is, that in augmenting the potential
and frequency we rapidly intensify the streams; and, though it may be
very sanguine, it is surely not altogether hopeless to expect that we
may succeed in producing a practical illuminant on these lines. We
would then be simply using burners or flames, in which there would be
no chemical process, no consumption of material, but merely a transfer
of energy, and which would, in all probability emit more light and
less heat than ordinary flames.
[Illustration: FIG. 8.--EFFECT PRODUCED BY CONCENTRATING STREAMS.]
The luminous intensity of the streams is, of course, considerably
increased when they are focused upon a small surface. This may be
shown by the following experiment:
I attach to one of the terminals of the coil a wire w (Fig. 8), bent
in a circle of about 30 centimetres in diameter, and to the other
terminal I fasten a small brass sphere s, the surface of the wire
being preferably equal to the surface of the sphere, and the centre of
21