The construction of a railway is the business of contractors, who execute the,works by estimate, according to the plans and specifications of the engineers. A railway con tractor is a eapilalist with a practical knowledge of earth-digging, blasting rocks, pmhp ing, embanking, boring and building tunnels, erecting bridges, and other rough opera tions. He possesses a stock of the various necessary apparatus, light rails, tools, etc., including horses, wagons, and locomotives for dragging materials. He has subordinates called time-keepers, foremen, gangers, and under-gangers, placed over detachments of operatives. These operatives are a remarkable class of men. Originally from Lincoln shire and Lancashire, they are popularly known as navvies (contracted from "navi gators"), from having been engaged in excavating navigable canals. Navvies some lilacs labor in bands called batty-gangs, by piece-work, and are known to draw large sums, but more generally they are employed at days' wages.
Signals.—The signaling arrangements form an important part of railway construction. The most common form of signal is the semaphore, and at night, colored lights. A red light signifies danger; a'green, caution; and a plain light, that the line is clear. Much care is given to the arrangement and construction of crossings, jurktions, etc.,with their numer ous witches, or movable rails, used for changing the direction of a train from one line to another. The switches are generally worked directly from the signal-stations, and are,so arranged that their points shall 'not face toward the advancing traffic. Numerous accidents have been caused by "facing points." Many improvements have been lately introduced in signaling, crossings, etc., all with a view to increased safety. The "block" system has been adopted by the principal railway companies, particularly in the neigh borhood of busy centers of traffic. Under this system each signal-station is in direct telegraphic communication with the nearest signal-stations, both up and down the line, and a train is not allowed to pass py signal-station until the train immediately preceding it has..started from the next station in advance. Thus the driver may push on without hesitation from point to point; and thereby the traffic is expedited, and at the same time safety increased. The system of interlocking has also been extensively introduced. Under this system the pointsman can only lower one signal—namely, that which corre sponds to the line which, from the position of the switches, is clear; and before lie can alter the position of the switches he is compelled to return this signal to "danger." Curves and Gradients.—Engineers endeavor to render their lines as level and straight as possible, but circumstances often necessitate the use of considerable curves and gradi ents. As a general rule there are few curves of less than three-eighths of a mile, or 30 chains' radius; when they are employed. the exterior rail is super-elevated; to counteract the centrifugal force. otherwise a quickly moving train might leave the rails. Gradients being expensive to work according to their degree of inclination, few are more steep than 1 in 60, though 1 in 30 is not unknown. On steep gradients, stationary engines were sometimes emploved, but in nearly every case these have been abandoned for locomo tive power. On local and private lines, much steeper gradients and sharper curves are common. One of the earliest, if not the first trial of a locomotive on au iu, ling or. I in 19, was made in Scotland in 1862, by Mr. George Gray, on his private line near Bathgate.
Gauge and Earth-works.—In the early stage of railway operations, the or width between the mist excited considerable discussion. When way-leaves, or tramways, were introduced in the coal districts, their gauge was adapted to the common road-wagons that were to be put upon them, and it happened that the gauge between the wheels of these wagons was 4 ft. 8} inches. Accustomed to this width, George Stephenson believed
that it " was most economical in construction, not only as regarded the engines and car. riages, but more particularly of the railway itself." This gauge was accordingly adopted on most of the earlier-made railways, and, notwithstanding the keen contests of engineers, who were generally favorable to a 5 ft. or 5 ft. 3 in. gauge—Brunel contend ing for 7 ft.—this original 4 ft. 81 in. gauge—measured from the inside of one rail to the inside of the other—was irrevocably fixed by a public act, 1846, as applicable to all the railways in England and Scotland, the Great Western and certain branches excepted, on which the gauge was regulated at 7 feet. Owing to inconvenience in communicating with other lines, and from other causes, the Great Western has found it advisable to con form to its neighbors, and has now relaid its lines on the standard gauge. By the same act, the gauge in Ireland was fixed at 5 ft. 3 inches. The government of India fixed the gauge of all the railways in that country at 5 ft. 6 inches. But a movement in an oppo site direction has set in within the last few years, and the battle of the gauges is renewed. A horse tramway at Festiniog in Wales, constructed in 1832 for the conveyance of slates from a quarry, and laid with a 1 ft. 11/ in. gauge, was, in 1863, transformed into a loco. motive railway for passengers and goods, and WAS found to work with perfect safety, and with remarkable economy. The success of this experiment has awakened the atten tion of many engineers to what they believe to be the needless extravagance of the standard gauge; and railways with gauges varying from 2 ft. 6 in. to 3 ft. 6 in. are now in operation in the Isle of Man, Norway, Sweden, Russia, Queensland, Peru, Chili, Brazil, Canada, and the United States, where a vast mileage is built or in course of con struction. The great argument for the narrower gauge is the obvious economy both in first cost and in working. It is calculated that, on an average, companies have to haul over their lines seven tons of dead-weight in order to carry one ton of goods; and in the case of passenger carriages the excess is even greater. With the whole apparatus on a smaller scale, this waste is greatly reduced. Another advantage of the narrow gauge is, that much sharper curves may be adopted than are possible on the broader one, and thus the route may be chosen to much greater advantage. While it may be an open question whether the narrow gauge is adequate for a thickly peopled district, where "express" trains may be indispensable, and where traffic may at times be exceptionally heavy, it is, without doubt, especially KLitable for sparsely peopled districts and half-developed terri tories. Indeed, it anrds the means of supplying the benefits of railway communication where otherwise they would he hopeless. After careful investigation, the Indian govern ment of the late lord 2layo decided to adopt the meter gauge, about 3 ft. 3 in., for the greater part of an extensive series-1500 m.—of state railways, and considerable prog ress been made in their construction. In Canada there are already 5,230 in. of narrow-gauge railway. ' Ballast.—This is the name given to the mass of broken stones or dry gravel on which the sleepers are placed, and which serves to keep them steady. Material for ballast is generally got in the cuttings or near the line, but is often brought a considerable dis tance. The term ballast originated in the practice of using the gravel-ballast emptied from the ships in the Tyne, for the tram and railways in the neighborhood of Newcastle.