moments. When the lime has been sufficiently heated, enough moisture
has been given off to impair materially the vacuum of the bulb. As the
bombardment goes on, one point of the lime piece is more heated than
other points, and the result is that finally practically all the
discharge passes through that point which is intensely heated, and a
white stream of lime particles (Fig. 31) then breaks forth from that
point. This stream is composed of "radiant" matter, yet the degree of
exhaustion is low. But the particles move in straight lines because
the velocity imparted to them is great, and this is due to three
causes--to the great electric density, the high temperature of the
small point, and the fact that the particles of the lime are easily
torn and thrown off--far more easily than those of carbon. With
frequencies such as we are able to obtain, the particles are bodily
thrown off and projected to a considerable distance; but with
sufficiently high frequencies no such thing would occur: in such case
only a stress would spread or a vibration would be propagated through
the bulb. It would be out of the question to reach any such frequency
on the assumption that the atoms move with the speed of light; but I
believe that such a thing is impossible; for this an enormous
potential would be required. With potentials which we are able to
obtain, even with a disruptive discharge coil, the speed must be quite
insignificant.

As to the "non-striking vacuum," the point to be noted is that it can
occur only with low frequency impulses, and it is necessitated by the
impossibility of carrying off enough energy with such impulses in high
vacuum since the few atoms which are around the terminal upon coming
in contact with the same are repelled and kept at a distance for a
comparatively long period of time, and not enough work can be
performed to render the effect perceptible to the eye. If the