the further is forced the incandescence the more work, comparatively,
is performed on the gas, and the less on the electrode. The formation
of a powerful photosphere is consequently the very means for
protecting the electrode. This protection, of course, is a relative
one, and it should not be thought that by pushing the incandescence
higher the electrode is actually less deteriorated. Still,
theoretically, 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,