“Not fully. It has always been quite a mystery to me, but I do know that radio has something to do with it.”

“Yes it is radio, of a sort. You see the so-called air tunnels are hollow cylinders of etheric vibrations projected from point to point in the same manner as the regular beams over which industrial power is trans- mitted. In the case of the great transcontinental tunnel there are twin tubes of these vibrations stretching in a huge arc from coast to coast, one for eastbound and the other for westbound traffic. The cars travel within these cylinders. The vibrations themselves are very complex in nature. One component provides insulation against the elements as effectively as though the cars traversed a solid metal tube. Another provides the dark color by day and the brilliance by night that warns standard aircraft of the location of the tubes. Still another energizes the coils in the cars, which coils provide the powerful repulsive force that neutralizes gravity and allows the cars to remain suspended either when stationary or when in motion. But the method of propulsion is what makes travel at extremely high speed impossible.”

"But Jimmy, the trip is made in about six hours. Surely that is fast enough for anyone.”

“No, dear, it is not fast enough under present traffic demands. Of course the cars travel much faster than the standard aircraft but with my scheme they can be made to operate at five or possibly six times their present velocity. You see, as it is now, the tubes are filled with air at atmospheric pressure and the cars are drawn though this medium by means of motor- driven propellers as on the standard planes. It is the friction of this air that makes higher speeds impossible and it is the removal of the air that was the basis of my original investigations.”

(Through the Air Tunnel, Harl Vincent, 1929)

“You are being a little too technical for me,” laughed Doris, “but I think I get a fair idea of what you are talking about. And it really is interesting. How is the rest of it done?”

“By superimposing certain other frequencies on the carrier waves that comprise the tunnel walls. These are the ones I have discovered and am now ready to put to practical use. The first of these causes almost complete evacuation of the interior of the tubes so that the air pressure is negligible. The other is a wave that provides the new propulsive energy for the cars. You see, it will no longer be possible to use the propellers, since there will be no air for these to work on. But my method will draw the cars forward by an inductive action that is capable of providing tremendous speeds. I am afraid I can not describe it to you because it can not be explained without going into great technical detail and that would bore you to extinction. The important thing is that I have my chance at last.”