CONTINUOUS-CURRENT DYNAMOS. 315 



diameter with 6 ft. 6 in. commutator. Similar dynamos are 

 in use at the central stations of Altona and Aix-la-Chapelle. 

 Space does not permit of more than a passing mention 

 of recent progress in traction and transmission of power by 

 continuous currents. For the latter purpose, where the 

 distances are great, the alternating current with single- or 

 double-phase generators and motors, has lately proved a 

 serious rival, but up to the present, for traction, the con- 

 tinuous current reigns supreme, since the distances are 

 usually not so great as to demand a higher pressure than 

 about 500 volts. After the Bessbrook-Newry electric 

 railway and the pioneer lines of Portrush and Blackpool, 

 little was done for many years in England, and the advance 

 was chiefly on the other side of the Atlantic. Once again, 

 however, England has come to the front by the recent 

 construction of the City and South London Electric Rail- 

 way and the Liverpool Overhead Railway, both of which 

 for size and successful working are, in many respects, un- 

 rivalled. In the former, the current is delivered by 225- 

 kilowatt belt-driven dynamos at 500 volts pressure to 

 electric locomotives each containing two 50 horsepower 

 motors. In the latter, each car is furnished with a motor 

 of 40 horsepower, which is built direct on the axle, and 

 the dynamos are driven from horizontal engines by cotton 

 ropes. At the Chicago Exhibition of 1893, the supposed 

 requirements of the future in the direction of rapid muni- 

 cipal traction were exemplified on a large scale by the 

 gigantic generator of 2000 horsepower, which was em- 

 ployed in connection with the Intramural Electric Railway. 

 Nor can this estimate be regarded as much exaggerated, 

 when we find that the West-end tramways of Boston, which 

 form the largest electric system in the United States, are fed 

 by six triple-expansion engines, each of about 1000 indicated 

 horsepower driving by belt eighteen Thomson- Houston four- 

 pole dynamos. Of a different class is the electric rack- 

 railway which ascends Mont Saleve near Geneva : here 

 the power station is situated on the Arve, and is furnished 

 with two turbines, the vertical shafts of which drive multi- 

 polar Thury dynamos yielding 275 amperes at 600 volts, 



