He visited the great tunnels which connect East and West New York to the city proper, Brooklyn and Jersey City having become a corporate part of New York City. The double streets of the city were a wonderful realization of what the needs of a great commercial center will demand of its people. From One Hundredth street south, and over the whole island from the East to the North River, was a double street--a city on top of a city. The lower streets were the originals, and were paved with roughened glass. On one side, covered, and just below the street level, were the great sewers of the city. The height from lower to upper street was twenty feet. In the center of Lower Broadway, Lower Fourth, Sixth, and Ninth Avenues (for such the under streets were designated), and below the level of the pavement, was a double tunnel carrying the rapid-transit electric trains. These trains were composed of light, cylindrical cars, about ten feet in diameter; they had no windows, light being obtained from electricity. The air was received through ventilators, a steady stream of pure, fresh air being kept circulating through the tunnels by immense fans. Automatic indices gave warning of the different stations. The normal speed of these trains was forty miles per hour, and stops were made at every half-mile between Three Hundred and Fifty-third street and the Battery, East New York (Brooklyn); and West New York (Jersey City). Handsome stations along the line, connected by hydraulic lifts with the upper-street stations, enabled the passengers to quickly take the surface lines to all parts of the city. All vehicles devoted to business purposes were confined to the lower streets, and all merchandise, also, was here received and shipped. In the roof of the street were the water-pipes, electric light, telephone, power, and other wires--all easy of access. Like the lower, the upper streets and sidewalks were of glass, which was molded into huge blocks, these resting on steel girders running across and down the streets. The sidewalks were light gray, and the street light steel-color. The thickness of these blocks of glass was four inches, and the light transmitted to the under-street had nearly its natural intensity. On the upper streets, light electric cars ran in every direction, stopping whenever desired. These surface trains were peculiar in that they sat two feet above the pavement, held aloft and in position by two wide but thin rods of steel passing through a slot in the street, the trucks for the cars running upon a roadbed just under the center of the street, or in the roof of the lower street. Upon inquiry, he was informed that the reasons for the elevation of the cars and the subterranean roadway were to avoid accidents; as a person who was so unfortunate as to be struck by a train would be knocked down but passed over by the elevated car without much injury, the steel bars having rounded guards in front to push any object aside. Cobb observed