The question is, how far can we go with frequencies?  Ordinary conductors rapidly lose the facility of transmitting electric impulses when the frequency is greatly increased.  Assume the means for the production of impulses of very great frequency brought to the utmost perfection, every one will naturally ask how to transmit them when the necessity arises.  In transmitting such impulses through conductors we must remember that we have to deal with 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 affecting greatly the character of the vibrations.