# Page:Popular Science Monthly Volume 90.djvu/724

708 Popular Science Monthly

proceeding being not unlike that of feeding cartridges from a belt or clip to a machinegun.

### A Car Can't Be Safely Stopped in Less Than Two Miles

The stations at which the cars arrive are similarly constructed. Each solenoid is energized at the moment when the middle of the car has passed its middle and is deenergized when the rear of the car has passed through. The stations must be some two miles long in order that the cars may be stopped gradually.

What will be the speed of such a system? My experiments have given me the data necessary to calculate the amount of attraction between the core of an electromagnet and an armature separated at a considerable distance from it, so that I have been able to fix the maximum speed attainable. That maximum depends on the maximum attractive force of the electromagnets which can be developed to overcome the centrifugal force on the curves.

Assuming electromagnets of reasonable size and currents of reasonable strength I found on the basis of my aforesaid experiments that with curves having a radius of two thousand feet it would hardly be possible to attain a speed of more than five hundred miles an hour. But think what that means! New York would be no more distant from Chicago than it is now from Philadelphia, so far as relative times are concerned. Florida might easily become a kind of winter Coney Island for all New York. A journey from New York to San Francisco would occupy only half a day.

This is the experimental apparatus which Prof. Weinberg used in working out the details of his proposed electromagnetic vacuum system of passenger transportation

### Lifting an Ordinary Train off the Rails

While the vacuum tube is an electrical possibility, it is more likely that some method of transportation proposed here, or one like that proposed by Emile Bachelet a few years ago, will be more seriously considered first. Bachelet did not propose the propulsion of a car in a partial vacuum so as to cut down air resistance, but he did propose the idea of overcoming gravity by the use of alternating-current electromagnets. Every amateur electrician knows that an electromagnet through which an alternating current is passed has the curious property of repelling a light metal object brought near it. Bachelet intended to build his cars with aluminum bottoms. When the cars ran over the magnets successively they were to be repelled — literallylifted off the rails. The system is objectionable because very much power is wasted per mile (contrary to my system where the waste of energy is insignificant) and the passengers would be very uncomfortably heated by the action of the currents from below. In my opinion an electric system, such as that which I have here outlined, but without the vacuum tube and with approximate (not complete) neutralization of gravity would be safer, cheaper, and simpler. The loss in speed due to the resistance of the air would not be excessive if the cars were properly designed, and might be compensated for by cutting the electromagnets out just as the front of the car left them one after the other. In this way the electromagnets would not only sustain the car but would also accelerate its speed. Moreover it would be much simpler to run on wheels instead of moving freely through space, gravity being only so far neutralized that the wheels would barely touch the tracks and a pressure would be exerted that would be almost negligible.