1893.] on Electrical Railways. 55 



motive force balances the electro-motive force of the line, the speed 

 can be increased by diminishing the magnetic field by reducing the 

 effective coils on the magnets, but this device does not give any 

 assistance at the lower speeds, as the magnets ought to be so wound 

 as to be high on the characteristic curve, or nearly saturated with 

 the normal current, and it is therefore not possible to obtain any 

 increased intensity of field by increasing the convolutions of the 

 magnet coils. If it were possible to use alternate current motors for 

 traction work, the difficulty could at once be met by introducing a 

 transformer in the circuit, and placing the motor in its secondary. 

 The effective convolutions of the secondary circuit on the transformer 

 could then be varied as the speed increases in such wise that the 

 electro-motive force of the line is balanced by the back electro-motive 

 force of the motor and the fall of potential due to the resistance of 

 the motor coils, so avoiding all need for resistances. 



The City and South London line has enabled experiments to be 

 made on the efficiency of the railway system as a whole, taking into 

 account the loss of power in the generators, on the line, and in the 

 motors, and in the resistances of the locomotives. The loss in 

 the line is about 11 per cent, of the electrical power generated, and 

 the efficiency of the locomotives as a whole is, as I have shown, 

 70 per cent. ; thus the electrical efficiency of the entire system 

 is 62 per cent. The trains weigh with full load of 100 passengers 

 about 40 tons, and the average speed between stations is 13*5 

 miles per hour. The cost of working, including all charges, during 

 last half year was 7 * Id. per train mile, of which 4 * Id. represents 

 the cost of production of the electric power, and 2 ■ 4d. the cost of 

 utilising it on the locomotives. It is perhaps hardly a fair com- 

 parison to compare the cost of working such a line as the South 

 London line with the cost of steam traction on other lines, inasmuch 

 as steam could not possibly be used in the tunnels, only 10 feet 

 6 inches diameter, in which this line is constructed, but the com- 

 parison is not uninstrnctive. Take the Mersey Railway, where the 

 gradients and nature of the traffic are similar. On the Mersey 

 Railway the locomotives weigh about 70 tons, and the train, which is 

 capable of carrying about 350 passengers, 150 tons. According to 

 the published returns of the company, the cost of locomotive power is 

 14d per train mile, i. e. double the cost on the South London line, 

 but for a train weighing between four and five times as much, but 

 capable of carrying only 3 J times the number of passengers ; thus 

 the cost of steam traction per ton mile of train is about half that per 

 ton mile of train for electric traction. But it is not on the cost 

 per ton mile that the success of a passenger line depends. The real 

 basis of comparison is the cost per passenger mile, and here electric 

 traction has great advantage over steam, as the dead weight of the 

 electric motor is small compared with the dead weight of steam 

 locomotives of the same power, and with electric motors the trains 

 can be split up into smaller units, at but slightly increased cost, so 



