they are good conducting, and it is a fact that conductors do not
phosphoresce; second, the powder, being exceedingly fine, would not be
apt to exhibit very prominently this quality, since we know that when
crystals, even such as diamond or ruby, are finely powdered, they lose
the property of phosphorescence to a considerable degree.
The question presents itself here, can a conductor phosphoresce? What
is there in such a body as a metal, for instance, that would deprive
it of the quality of phosphorescence, unless it is that property which
characterizes it as a conductor? for it is a fact that most of the
phosphorescent bodies lose that quality when they are sufficiently
heated to become more or less conducting. Then, if a metal be in a
large measure, or perhaps entirely, deprived of that property, it
should be capable of phosphorescence. 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
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