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 438 THE AMERICAN JOURNAL OF SOCIOLOGY

which are largely electric. Indeed, the chief use of electricity in Hamburg is for street railways ; and in Dresden electricity was first used for street railways, and afterward introduced for lighting purposes. The expansion of the network of tracks over the city territory and out to the suburbs shows the possibility of street-railway rapid transit helping in the distribution of popula- tion, and thus aiding a solution of the housing question. Low fares, good transfer system, excellent service and connections characterize the German city railways. The overhead trolley, with double or single poles, is used almost universally, except in the busiest districts, where, in Dresden, for example, for some distance power must be otherwise supplied underground conduit or storage battery. The cars are so equipped as to make this change when they enter the city district, using the overhead trolley again wherever it is permitted.

The concrete street foundation is increased about one-third under the car rails. For example, in Leipzig the car rail is set upon a block of Australian tallow wood, which latter is imbedded in cement from 9 to 1 3 cm. thick ; this is laid upon I o to 14 cm. of concrete, under which is 10 cm. of packed gravel. Such founda- tions give a solid bed; and the rail itself is, with the wood block, partly imbedded in the cement, which holds it fast. All street- railway rails are grooved and, in Dresden, Breslau, and Leipzig, for example, are drained into the sewers by pipes or shafts. Where rails are laid in asphalt pavements they are now always bordered by a row of wood blocks such as are used in wood pavements. As has been suggested, the street-railway tracks are a differentiation of the street surface, just as are sidewalks, and are hardly more available for other traffic than are the latter.

Elevated or underground roads have not yet appeared to any great extent except in Berlin; though Elberfeld presents its hanging railway as the only one of its kind. This, as is well known, makes use of canals as well as of streets for its line.

Bridges. Bridges form an important part of a complete sys- tem of thoroughfares. They not only give access to highroads, but serve to unite closely the parts of the city lying on opposite banks. Trade and commerce, and also the distribution of popu-