Popular Science Monthly 



707 



magnets depends on the degr.ee of cursa- 

 ture and their total number on the angle 

 at which the curve is entered and left b>- 

 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 countr>^ de- 

 mands. In the part of the tube where it is 

 convex relatively to the 

 IPBPHI^ ground (that is, where the 

 l9r '^jfe* slope upwards increases or 



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 passen- 

 gers. Professor Christian Birkeland. the 

 distinguished Xorwegian physicist, in- 

 vented 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 



SOLEXOID 



^^^ i^P" 



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 slope downwards decreases) the sus- 

 taining electromagnets must be closer to- 

 gether 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 accen- 

 tuate ever>' departure 

 of the rectilinear pro- 

 gressive motion. Since 

 it is intended to travel 

 at a very high speed, 

 even the slightest 

 change of the direc- 

 tion of motion or any 

 rotation must be con- 

 trolled so that it ma>' 

 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 supplemen- 

 tary electromagnets which would return 

 the car to its proper course. It is super- 

 fluous to describe these supplementary safe- 

 ty devices in detail here. 



The direction of motion of a high-SF>eed 

 car cannot be easily changed. But like 

 any railway, the vacuum tube must have 

 its CTirves. Electromagnets are placed at 

 the proper side of the tube and spaced 

 according to the degree of curvature 



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 dia- 

 gram in which an air- 

 lock 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 be- 

 tween are placed sus- 

 taining electro- 

 magnets. The main 

 chamber is succes- 

 sively put in commu- 

 nication 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 air- 

 locks 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 



