retically, with extreme frequencies, this result must be reached,
but probably at a temperature too high for most of the refractory
bodies known. Given, then, an electrode which can withstand to a very
high limit the effect of the bombardment and outward strain, it would
be safe no matter how much it is forced beyond that limit. In an
incandescent lamp quite different considerations apply. There the gas
is not at all concerned: the whole of the work is performed on the
filament; and the life of the lamp diminishes so rapidly with the
increase of the degree of incandescence that economical reasons compel
us to work it at a low incandescence. But if an incandescent lamp is
operated with currents of very high frequency, the action of the gas
cannot be neglected, and the rules for the most economical working
must be considerably modified.

In order to bring such a lamp with one or two electrodes to a great
perfection, it is necessary to employ impulses of very high frequency.
The high frequency secures, among others, two chief advantages, which
have a most important bearing upon the economy of the light
production. First, the deterioration of the electrode is reduced by
reason of the fact that we employ a great many small impacts, instead
of a few violent ones, which shatter quickly the structure; secondly,
the formation of a large photosphere is facilitated.

In order to reduce the deterioration of the electrode to the minimum,
it is desirable that the vibration be harmonic, for any suddenness
hastens the process of destruction. An electrode lasts much longer
when kept at incandescence by currents, or impulses, obtained from a
high-frequency alternator, which rise and fall more or less
harmonically, than by impulses obtained from a disruptive discharge
coil. In the latter case there is no doubt that most of the damage is
done by the fundamental sudden discharges.

One of the elements of loss in such a lamp is the bombardment of the
globe. As the potential is very high, the molecules are projected with
great speed; they strike the glass, and usually excite a strong
phosphorescence. The effect produced is very pretty, but for
economical reasons it would be perhaps preferable to prevent, or at
least reduce to the minimum, the bombardment against the globe, as in
such case it is, as a rule, not the object to excite phosphorescence,
and as some loss of energy results from the bombardment. This loss in
the bulb is principally