cence. Therefore it is quite possible
that at some extremely high frequency, when behaving practically as a
non-conductor, a metal or any other conductor might exhibit the
quality of phosphorescence, even though it be entirely incapable of
phosphorescing under the impact of a low-frequency discharge. There
is, however, another possible way how a conductor might at least
_appear_ to phosphoresce.

Considerable doubt still exists as to what really is phosphorescence,
and as to whether the various phenomena comprised under this head are
due to the same causes. Suppose that in an exhausted bulb, under the
molecular impact, the surface of a piece of metal or other conductor
is rendered strongly luminous, but at the same time it is found that
it remains comparatively cool, would not this luminosity be called
phosphorescence? Now such a result, theoretically at least, is
possible, for it is a mere question of potential or speed. Assume the
potential of the electrode, and consequently the speed of the
projected atoms, to be sufficiently high, the surface of the metal
piece against which the atoms are projected would be rendered highly
incandescent, since the process of heat generation would be
incomparably faster than that of radiating or conducting away from the
surface of the collision. In the eye of the observer a single impact
of the atoms would cause an instantaneous flash, but if the impacts
were repeated with sufficient rapidity they would produce a
continuous impression upon his retina. To him then the surface of the
metal would appear continuously incandescent and of constant luminous
intensity, while in reality the light would be either intermittent or
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 somet