FIG. 31. -BULB SHOWING RADIANT LIME STREAM AT LOW EXHAUSTION.

I have prepared a bulb to illustrate by an experiment the correctness of these assertions. In a globe L (Fig. 31, I
have mounted upon a lamp filament a piece of lime l. The lamp filament is connected with a wire which leads into
the bulb, and the general construction of the latter is as indicated in Fig. 19, before described. The bulb being
suspended from a wire connected to the terminal of the coil, and the latter being set to work, the lime piece l and
the projecting parts of the filament/ are bombarded. The degree of exhaustion is just such that with the potential the
coil is capable of giving phosphorescence of the glass is produced, but disappears as soon as the vacuum is
impaired. The lime containing moisture, and moisture being given off as soon as heating occurs, the phospho-
rescence lasts only for a few 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

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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 difference of potential between the terminals is raised, the dielectric breaks down. But with very high
frequency impulses there is no necessity for such breaking down, since any amount of work can be performed by
continually agitating the atoms in the exhausted vessel, provided the frequency is high enough. It is easy to reach--
even with frequencies obtained from an alternator as here used-- a stage at which the discharge does not pass
between two electrodes in a narrow tube, each of these being connected to one of the terminals of the coil, but it is
difficult to reach a point at which a luminous discharge would not occur around each electrode.
A thought which naturally presents itself in connection with high frequency currents, is to make use of their pow-
erful electro-dynamic inductive action to produce light effects in a sealed glass globe. The leading-in wire is one of
the defects of the present incandescent lamp, and if DO other improvement were made, that imperfection at least
should be done away with. Following this thought, I have carried on experiments in various directions, of which
some were indicated in my former paper. I may here mention one or two more lines of experiment which have been
followed up. Many bulbs were constructed as shown in Fig. 32 and Fig. 33.