It will be seen that most of the great saving of time in modern construction of bridges and other parts of railways is due to improved machinery. The engineer of to-day is probably not more skilful than his ancestor, who, in periwig and cue, breeches and silk stockings, is represented in old prints supervising a gang of laborers, who slowly lift the ram of a pile-driver by hauling on one end of a rope passed over a pulley-wheel. The modern engineer has that useful servant, steam, and the history of modern engineering is chiefly the history of those inventions by which steam has been able to supersede manual labor--such as pile-drivers, steam-shovels, steam-dredges, and other similar tools. [Illustration: General View of the Poughkeepsie Bridge.] * * * * * After the road-bed of a railway is completed and covered with a good coat of gravel or stone-ballast, and after all the temporary structures have been replaced by permanent ones, that part of the work may be said to be done, requiring only that the damages of storms should be repaired. But the track of a railway is never done. It is always wearing out and always being replaced. [Illustration: Erection of a Cantilever.] Some of the early English engineers, not appreciating this, endeavored to lay down solid stone walls coped with stone cut to a smooth surface, on which they laid their rails. They called this "permanent way," as distinguished from the temporary track of rails and cross-ties used by contractors in building the lines. But experience soon showed that the temporary track, if supported by a bed of broken stone, always kept itself drained and was always elastic, and remained in much better order than the more expensive so-called "permanent way." When the increase in the weight of our rolling stock began to take place, dating from about 1870, iron rails were found to be wearing out very fast. Some railway men declared that the railway system had reached its full development. But in this world the supply generally equals the demand. When a thing is very much wanted, it is sure to come, sooner or later. The process of making steel invented by, and named after, Henry Bessemer, of England, and perfected by A. L. Holley, of this country, gave us a steel rail which at the present time costs less than one of iron, and has a life five or six times as long, even under the heavy loads of to-day. We are now approaching very near the limit of what the rail will carry, while the joints are becoming less able to do their duty. Bad joints mean rough track. Rough track means considerably greater expenditure both for its maintenance and that of all the rolling stock, as the blows and shocks do reciprocal damage, both to the rails and to that which runs on them. Hence all railway managers are now devoting more care and attention to their tracks.