Page:Popular Science Monthly Volume 45.djvu/649

Rh the body of the metal of which the carrying wire is composed, instead of, as in the case of a direct current, flowing across the whole cross-section of the wire in an even manner. This also is less serious the lower the periodicity. In the case of a lightning flash (which is an alternating-current discharge) the periodicity is enormously high, and it is known that in its flow over wires it travels almost entirely through the mere surface skin of the metal. It may be mentioned here, as having possibly a very important bearing on work such as that under discussion, that a most remarkable claim has recently been brought forth that bimetallic wires, or wires of one metal coated with a different one on the outside, give remarkably improved results for the conduction of alternating currents over the conductivities of the two metals in the weights used, laid together as separate wires.

The form decided on in which to construct the conveying lines is that of a conduit or subway of large proportions. One which has been already constructed for a length of half a mile is as follows: The walls are arched, and the width is greatest at about two thirds of the height. The conductors are carried on insulated brackets along the sides, spaced at intervals of thirty feet. The subway is lined with concrete, and manholes at intervals allow of access; besides, there are small pieces of pipe let in at the bottoms of the manhole ducts for the purpose of inserting such wires as may from time to time be required to tap the line conductors. The subway is five and a half feet high and three feet ten inches wide. A track runs along it, and the line inspectors will make their trips on an electrically propelled car; heavy wire screens the height of the subway, extending on both sides of the track, protecting the occupants from any possible discharge from the main conductors.

The Cataract Construction Company expect to be able to deliver power in Buffalo at a cost per horse power, for twenty-four hours a day yearly, greatly below the cost of steam power as now produced in Buffalo with coal at one dollar and a half per ton. The generators are expected to operate at five thousand horse power each, with an efficiency of ninety-eight per cent on the power delivered to them by the turbines, and there will be only three and a half per cent drop of pressure in transmitting at twenty thousand volts to the northern part of Buffalo. This last appears wonderful when we consider that it is less than the drop from the generators of an electric railway system to the motors of cars within as short a distance as half a mile, quite apart, moreover, from the extra losses in the latter case due to imperfect trolley contacts. It is hoped also to transmit power before long to the Erie Canal, on which at the close of last season there was an interesting development in the line of electrical