=Street Car Service.=--Now that more than one half the population of the United States live in cities makes the matter of local transportation of at least passing interest. Railroads were at first tram cars and many of them were built through the city streets, it was easy, therefore, to make of them street cars caring for such local traffic as desired to take advantage of them. They became a popular means of local transportation in the decade 1850-60. As the demand became greater the one-horse car gave way to the two-horse with its longer body and greater capacity. These not being sufficient steam locomotives were used in some cities, in others the tracks were elevated above the surface, the first in New York in 1876, or depressed below with steam locomotives operating trains of cars rapidly loaded and unloaded at stopping points about four blocks apart. In 1879 or 1880 in San Francisco where the hills were too steep for horses the cable car was designed, whereby an endless cable operated from a central station ran continuously in a trench or conduit under the track. A grip attached to the car could be made to take hold of this cable and the car was thus drawn along. Notwithstanding they were expensive to install cable cars were rapidly replacing horse-drawn cars when electric traction came in and displaced them. =Electric Traction.=--There are reports of attempts to obtain magnetic traction by the use of batteries, but not until the electric dynamo and motor had become practical working machines was anything like a successful working electrically propelled car developed. The ordinary method is to generate the electricity at a central station, carry it along the track by means of a wire, from which it is taken by a trolley or some form of conductor to a motor on the car completing the circuit through the track and ground. Such a car was practically demonstrated at the Berlin Exposition of 1879, by Werner Siemens, with a line 219 yards long.[117] This was the first practical electric railway. But long before this time in America experiments had been made with electric traction. Dever exhibited a model at Springfield, Massachusetts, in 1835.[118] In 1879, the year of Siemens’ exhibition, another model railway having a “third rail” to carry the current was exhibited at Stockbridge, Massachusetts. Edison had a car in operation at Menlo Park, New Jersey, in 1882, and the following year a small road carried passengers at an exhibit in Chicago. Miniature roads were exhibited at Philadelphia, Denver, Cleveland, New Orleans, and possibly elsewhere. The first electric railway built and operated for profit in American streets was at Richmond, Virginia, in 1885 on 2¹⁄₂ miles of track. During the same year 2 miles between Baltimore and Hampton were put in operation.[119] By 1890 the number of cities having trolley cars had increased to forty-nine.[120] From that time on the change from horse-drawn cars was very rapid. Trolley lines were even extended