466 31r. Alexander Siemens [Feb. 26, 



loops are provided for transferring the car from one line of girders 

 to the other. 



In all these railways continuous current motors have been em- 

 ployed, as these can be easily regulated to run at various speeds, 

 and they automatically adapt themselves to their load. It is, 

 however, difficult to construct such motors for high voltages or to 

 transform high tension continuous currents into low tension currents. 

 When the question of applying electric motors to the traffic of 

 main lines was seriously taken up, it became at once evident that the 

 necessary energy could only be supplied if high tension currents 

 were emj^loyed. 



Owing to the facilitj'' with which alternate currents can be trans- 

 formed by means of stationary contrivances, which require no super- 

 vision or manipulation, it is natural that most attempts to solve the 

 problem are based on the use of alternate currents. For this purpose 

 single-phase as well as multi-phase alternate currents have been 

 employed, and either has been used direct or transformed into con- 

 tinuous current. 



As long ago as 1884, Dr. John Hopkinson and Prof. Adams 

 read pa})ers before the Institution of Electrical Engineers on alter- 

 nate current motors, and in the discussion experiments were men- 

 tioned, which had been carried out at the works of Siemens Brothers 

 at Woolwich, in which a continuous current dynamo, with laminated 

 poles, had been driven as a motor from a single-phase alternate 

 current generator. The dynamo even turned round when the alter- 

 nate current was only sent through the armature ; in other words, 

 it worked as an induction motor. 



These experiments did not give ver}^ promising results, as the 

 periodicity of the alternate currents was too high ; they were, there- 

 fore, dropped in favour of more promising work. 



A few years later, when three-phase currents found general favour 

 for transmission of electrical energy to great distances, Mr. Wilhelm 

 von Siemens came to the conclusion that electricity could only be 

 applied to main lines by means of overhead conductors and in the 

 form of alternate currents. He, therefore, had a short line laid 

 down in the works of Siemens and Halske in Charlottenburg, on 

 which a small three -2)hase locomotive was shown to the German 

 railway authorities in December 1892. 



The experiment was to demonstrate to them the feasibility of 

 using overhead conductors for main lines, and to induce them to 

 place a suitable length of the State railways at the disposal of the 

 firm, to make their trials on a sufficiently large scale. Unfortunately, 

 the railway officials could not be convinced that practical results 

 could be attained on these lines, and the request of the firm was 

 refused. 



In order to demonstrate in a practical manner the feasibility of 

 their proposals, the firm constructed an experimental line of full 

 size in 1898, near Gross-Lichterfelde, which was visited in May 1901 



