THE CONQUEST OF TIME AND SPACE 



could be applied with so much more flexibility. The 

 defects of the parallel rail system are apparent both in 

 construction of the roadbed and the operating of trains. 

 It is almost impossible to lay and maintain the rails in 

 exact parallels, and even more difficult to keep each rail 

 at the proper height at all points. Both these factors 

 enter very largely into the determination of the speed 

 that a train can make over such tracks, any very great 

 variation from the parallel causing derailment, while 

 slight depressions or elevations of either rail cause 

 violent and dangerous rocking of the cars travelling at 

 high speed. 



In any monorail system the first of these difficulties, 

 the deviation of the rail from the parallel, is, of course, 

 eliminated; and it is found that on a single rail the 

 elevations and depressions are not serious obstacles. 

 Moreover, the cost of construction of a single-rail track 

 must obviously be less than for a double-rail track, and 

 the power necessary to operate cars over such a track far 

 less. But until the invention of the gyrocar (which is 

 referred to at length in the following chapter) the meth- 

 ods of balancing the car on a single rail presented 

 difficulties which quite offset the advantages of the 

 monorail system. Some of these methods are unique 

 and a few of them are practical in actual operation. 



In Germany a suspension monorail system is in 

 operation, the cars being suspended from an overhead 

 track. But obviously such a system, which requires 

 elaborate and expensive steel trestle-work along every 

 fork of the road, is not adapted to the use of long-distance 

 roads except in thickly populated districts. A less ex- 



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