generally it is small and of no consequence as long as the frequencies
are not very great. In using extremely high frequencies, and,
necessarily in such case, also high potentials, the absorption--or,
what is here meant more particularly by this term, the loss of energy
due to the presence of a gaseous medium--is an important factor to be
considered, as the energy absorbed in the air condenser may be any
fraction of the supplied energy. This would seem to make it very
difficult to tell from the measured or computed capacity of an air
condenser its actual capacity or vibration period, especially if the
condenser is of very small surface and is charged to a very high
potential. As many important results are dependent upon the
correctness of the estimation of the vibration period, this subject
demands the most careful scrutiny of other investigators. To reduce
the probable error as much as possible in experiments of the kind
alluded to, it is advisable to use spheres or plates of large surface,
so as to make the density exceedingly small. Otherwise, when it is
practicable, an oil condenser should be used in preference. In oil or
other liquid dielectrics there are seemingly no such losses as in
gaseous media. It being impossible to exclude entirely the gas in
condensers with solid dielectrics, such condensers should be immersed
in oil, for economical reasons if nothing else; they can then be
strained to the utmost and will remain cool. In Leyden jars the loss
due to air is comparatively small, as the tinfoil coatings are large,
close together, and the charged surfaces not directly exposed; but
when the potentials are very high, the loss may be more or less
considerable at, or near, the upper edge of the foil, where the air is
principally acted upon. If the jar be immersed in boiled-out oil, it
will be capable of performing four times the amount of work which it
can for any length of time when used in the ordinary way, and the loss
will be inappreciable.
It should not be thought that the loss in heat in an air condenser is
necessarily associated with the formation of _visible_ streams or
brushes. If a small electrode, inclosed in an unexhausted bulb, is
connected to one of the terminals of the coil, streams can be seen to
issue from the electrode and the air in the bulb is heated; if,
instead of a small electrode, a large sphere is inclosed in the bulb,
no streams are observed, still the air is heated.
Nor should it be thought that the temperature of an air condenser
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