at least changing periodically in intensity. The metal piece would
rise in temperature until equilibrium was attained--that is until the
energy continuously radiated would equal that intermittently supplied.
But the supplied energy might under such conditions not be sufficient
to bring the body to any more than a very moderate mean temperature,
especially if the frequency of the atomic impacts be very low--just
enough that the fluctuation of the intensity of the light emitted
could not be detected by the eye. The body would now, owing to the
manner in which the energy is supplied, emit a strong light, and yet
be at a comparatively very low mean temperature. How could the
observer call the luminosity thus produced? Even if the analysis of
the light would teach him something definite, still he would probably
rank it under the phenomena of phosphorescence. It is conceivable that
in such a way both conducting and non-conducting bodies may be
maintained at a certain luminous intensity, but the energy required
would very greatly vary with the nature and properties of the bodies.
These and some foregoing remarks of a speculative nature were made
merely to bring out curious features of alternate currents or electric
impulses. By their help we may cause a body to emit _more_ light,
while at a certain mean temperature, than it would emit if brought to
that temperature by a steady supply; and, again, we may bring a body
to the point of fusion, and cause it to emit _less_ light than when
fused by the application of energy in ordinary ways. It all depends on
how we supply the energy, and what kind of vibrations we set up: in
one case the vibrations are more, in the other less, adapted to affect
our sense of vision.
Some effects, which I had not observed before, obtained with
carborundum in the first trials, I attributed to phosphorescence, but
in subsequent experiments it appeared that it was devoid of that
quality. The crystals possess a noteworthy feature. In a bulb provided
with a single electrode in the shape of a small circular metal disc,
for instance, at a certain degree of exhaustion the electrode is
covered with a milky film, which is separated by a dark space from the
glow filling the bulb. When the metal disc is covered with carborundum
crystals, the film is far more intense, and snow-white. This I found
later to be merely an effect of the bright surface of the crystals,
for when an aluminium electrode was highly polished it exhibited more
or less the same phenomenon. I made a number of experiments with the
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