overed with a substantial coating of bronze, the coating allowing
barely the light to shine through. A metallic clasp, with a hook for
suspending the tube, is fastened around the middle portion of the
latter, the clasp being in contact with the bronze coating. I now want
to light the gas inside by suspending the tube on a wire connected to
the coil. Any one who would try the experiment for the first time, not
having any previous experience, would probably take care to be quite
alone when making the trial, for fear that he might become the joke of
his assistants. Still, the bulb lights in spite of the metal coating,
and the light can be distinctly perceived through the latter. A long
tube covered with aluminium bronze lights when held in one hand--the
other touching the terminal of the coil--quite powerfully. It might be
objected that the coatings are not sufficiently conducting; still,
even if they were highly resistant, they ought to screen the gas. They
certainly screen it perfectly in a condition of rest, but not by far
perfectly when the charge is surging in the coating. But the loss of
energy which occurs within the tube, notwithstanding the screen, is
occasioned principally by the presence of the gas. Were we to take a
large hollow metallic sphere and fill it with a perfect incompressible
fluid dielectric, there would be no loss inside of the sphere, and
consequently the inside might be considered as perfectly screened,
though the potential be very rapidly alternating. Even were the sphere
filled with oil, the loss would be incomparably smaller than when the
fluid is replaced by a gas, for in the latter case the force produces
displacements; that means impact and collisions in the inside.

No matter what the pressure of the gas may be, it becomes an important
factor in the heating of a conductor when the electric density is
great and the frequency very high. That in the heating of conductors
by lightning discharges air is an element of great importance, is
almost as certain as an experimental fact. I may illustrate the action
of the air by the following experiment: I take a short tube which is
exhausted to a moderate degree and has a platinum wire running through
the middle from one end to the other. I pass a steady or low frequency
current through the wire, and it is heated uniformly in all parts. The
heating here is due to conduction, or frictional losses, and the gas
around the wire has--as far as we can see--no