Horseshoe Falls on the Canadian side in the same manner. It has thus a virtual monopoly of the available water-power of Niagara, and the promoters have not the least doubt that the enterprise will be a great financial success. Already the Pittsburg Reduction Company have begun to use the electricity in reducing aluminum from the mineral known as bauxite, an oxide of the metal, by means of the electric furnace. Another portion of the power is to be used to produce carbide of calcium for the manufacture of acetylene gas. At a recent electrical exhibition held in New York city a model of the Niagara plant was operated by an electric current brought from Niagara, 450 miles distant; and a collection of telephones were so connected that the spectator could hear the roar of the real cataract. Thanks to the foresight of New York State and Canada, the scenery of the Falls has been preserved by the institution of public parks, and the works in question will do nothing to spoil it, especially as they will be free from smoke. Mr. Bogarts, State Engineer of New York, estimates that the water drawn from the river will only lower the mean depth of the Falls about two inches, and will therefore make no appreciable difference in the view. Altogether, the enterprise is something new in the history of the world. It is not only the grandest application of electrical power, but one of the most remarkable feats in an age when romance has become science, and science has become romance. CHAPTER IX. MINOR USES OF ELECTRICITY. The electric "trembling bell," now in common use, was first invented by John Mirand in 1850. Figure 83 shows the scheme of the circuit, where B is a small battery, say two or three "dry" or Leclanche cells, joined by insulated wire to P, a press-button or contact key, and G an electromagnetic gong or bell. On pressing the button P, a spring contact is made, and the current flowing through the circuit strikes the bell. The action of the contact key will be understood from figure 84, where P is the press-button removed to show the underlying mechanism, which is merely a metal spring A over a metal plate B. The spring is connected by wire to a pole of the battery, and the plate to a terminal or binding screw of the bell, or vice versa. When the button P is pressed by the finger the spring is forced against the plate, the circuit is made, and the bell rings. On releasing the button it springs back, the circuit is broken, and the bell stops. Figure 85 shows the inner mechanism of the bell, which consists of a double-poled electromagnet M, having a soft iron armature A hinged on a straight spring or tongue S, with one end fixed, and the other resting against a screw contact T. The hammer H projects from the armature beside the edge of the gong E.