This feature of the repair work is a direct result of an elaborate system of interchange in freight equipment upon American railroads, in order to prevent the breaking of bulk in the shipment of merchandise from one line to another. Cars will break down when they are many hundreds of miles away from home, and the railroad upon which they are operating at the time carts them to the nearest temporary repair yard or to its own shops, makes the necessary repairs, and charges for them in accordance with a scale prepared by the national association of Master Car-Builders. This necessitates a vast deal of bookkeeping and is only one of the many complications brought about by our extensive plan of railroading in America. The railroad will probably build the greater part of its freight equipment, although in these days of the supplanting of wood by steel in car-construction the companies are apt to stand appalled at the cost of the steel working machinery, and to buy their cars direct from the manufacturers very much as they purchase their locomotives. Passenger equipment is almost invariably secured in this way. It is a big railroad indeed that seeks to construct for itself the huge travelling palaces that the passenger of to-day has come to demand for his comfort. The repairing and the painting of these elaborate vehicles is enough of a proposition in itself. * * * * * To begin at the beginning, one first comes in contact with the mechanical department as it comes into constant contact with the operation of the railroad. This is the more quickly observed at the roundhouses, those great circular structures that are a feature of the railroad section of every important town. In England the "engine sheds," as they are there known, are simple enough structures, housing a series of parallel tracks, which are served by either a transfer table or switches. Such a plan is pursued in this country only where space is at a premium--as in the heart of some great city where realty is exceedingly high-priced; for the heads of our railroads have held tenaciously to the easily operated turntable and roundhouse scheme. The table, generally driven by electricity or a small dummy engine, forms the centre, the roundhouse a segment of the entire rim of the wheel. The great advantage of its simple design lies in the fact that it is instantly possible to get at any one of the fifty or more locomotives that it houses. It is this feature that has endeared it to the railroad man for many years. [Illustration: TRIPLE-PHASE ALTERNATING-CURRENT LOCOMOTIVE BUILT BY THE GENERAL ELECTRIC CO. FOR USE IN THE CASCADE TUNNEL, OF THE GREAT NORTHERN RAILWAY] [Illustration: HEAVY SERVICE, ALTERNATING AND DIRECT CURRENT FREIGHT LOCOMOTIVE BUILT BY THE WESTINGHOUSE COMPANY FOR THE NEW YORK, NEW HAVEN & HARTFORD RAILROAD] [Illustration: THE MONOROAD IN PRACTICAL USE FOR CARRYING PASSENGERS AT CITY ISLAND, NEW YORK]