Page:Popular Science Monthly Volume 90.djvu/723

 Popular Science Monthly

707

magnets depends on the degree of cursature and their total number on the angle at which the curve is entered and left by the car.

Rounding Curves at Five Hundred Miles an Hour
But the tube will be curved not only horizontally, like an ordinary railway: it will sometimes be bent up and sometimes down, as the nature of the country demands. In the part of the tube where it is convex relatively to the ground (that is, where the slope upwards increases or the slope downwards decreases) the sustaining electromagnets must be closer together than over the straightaway portions. Where the tube is convex relatively to the sustaining magnets they are separated by relatively greater distances.

It is evident that the car is really a free body and as such it must gradually accentuate every departure of the rectilinear progressive motion. Since it is intended to travel at a very high speed, even the slightest change of the direction of motion or any rotation must be controlled so that it may not be wrecked. Even ordinary railway trains run off the track often enough. Here is a car which has no track but which should never be permitted even to touch the walls of the vacuum tube lest it be destroyed. Special devices must obviously be employed to prevent the car from swerving from a normal course. They would serve to energize supplementary electromagnets which would return the car to its proper course. It is superfluous to describe these supplementary safety devices in detail here.

SOLENOID

The car of the vacuum electric system is a three hundred-pound cylinder three feet in diameter with conical ends hermetically sealed. You lie prone within it — its solitary passenger. There is no track. The car is really a free body sustained by electromagnets which are placed thirty feet apart

The Strange Stations that Must be Built
A long series of solenoids thrown into circuit when the front of the car approaches them and out of circuit when the middle of the car has passed their middle point constitutes the essential feature of a station which must be used by departing passengers. Professor Christian Birkeland, the distinguished Norwegian physicist, invented an electromagnetic gun, some years ago, in which the projectile was drawn forward by electromagnetic attraction. My station is somewhat similar to Birkeland's gun. Since the cars run in a partial vacuum it follows that the passengers cannot pass into and out of normal surroundings without the aid of something like an airlock.

Referring to the accompanying diagram in which an airlock station — used only for departing cars — is depicted, it will be seen that there is a main chamber which communicates with the vacuum tube at one end. At this end a series of solenoids are mounted, and between are placed sustaining electromagnets. The main chamber is successively put in communication with several side airlocks which are used to increase the frequency with which cars may be started off in the tube. In the main chamber is a platform on which cars from the side airlocks may be rolled and which is moved on rails. When a car is just in front of the opening of the tube it automatically turns on the current of the first solenoid and is sucked into the tube. Thus car after car is drawn from the traveling platform at a rate which I have calculated may be as high as twelve a minute, the whole

The direction of motion of a high-speed car cannot be easily changed. But like any railway, the vacuum tube must have its curves. Electromagnets are placed at the proper side of the tube and spaced according to the degree of curvature