_pressure_ and _flow_, in the
ordinary interpretation of these terms. Let the pressure increase to
an enormous value, and let the flow correspondingly diminish, then
such impulses--variations merely of pressure, as it were--can no doubt
be transmitted through a wire even if their frequency be many hundreds
of millions per second. It would, of course, be out of question to
transmit such impulses through a wire immersed in a gaseous medium,
even if the wire were provided with a thick and excellent insulation
for most of the energy would be lost in molecular bombardment and
consequent heating. The end of the wire connected to the source would
be heated, and the remote end would receive but a trifling part of the
energy supplied. The prime necessity, then, if such electric impulses
are to be used, is to find means to reduce as much as possible the
dissipation.

The first thought is, employ the thinnest possible wire surrounded by
the thickest practicable insulation. The next thought is to employ
electrostatic screens. The insulation of the wire may be covered with
a thin conducting coating and the latter connected to the ground. But
this would not do, as then all the energy would pass through the
conducting coating to the ground and nothing would get to the end of
the wire. If a ground connection is made it can only be made through a
conductor offering an enormous impedance, or though a condenser of
extremely small capacity. This, however, does not do away with other
difficulties.

If the wave length of the impulses is much smaller than the length of
the wire, then corresponding short waves will be sent up in the
conducting coating, and it will be more or less the same as though the
coating were directly connected to earth. It is therefore necessary to
cut up the coating in sections much shorter than the wave length. Such
an arrangement does not still afford a perfect screen, but it is ten
thousand times better than none. I think it preferable to cut up the
conducting coating in small sections, even if the current waves be
much longer than the coating.

If a wire were provided with a perfect electrostatic screen, it would
be the same as though all objects were removed from it at infinite
distance. The capacity would then be reduced to the capacity of the
wire itself, which would be very small. It would then be possible to
send over the wire current vibrations of very high frequencies at
enormous distance without affect