CHAPTER VI. DESCRIPTION OF THE DIFFERENT KINDS OF MOTIVE POWER USED ON RAILROADS, AND THE DISPOSITION OF THE ROAD FOR THEIR APPLICATION. § 1.-Different Kinds of Motive Power used at various Periods on Railroads. In the early periods of the history of railroads, horses were exclusively used; the disposition of the general line of the road, into proper or uniform degrees of inclination, seems then to have been an object of little moment. Most of the railroads, descending in the direction the goods were to be conveyed, afforded an easy draught to the loaded carriages, and the descent was never so great, but that the empty carriages could be drawn up the acclivities. In some of the deep ravines, mounds of earth were thrown up, and some sudden and abrupt acclivities partially levelled; but trifling undulations do not appear to have been noticed. The horses, therefore, would, along the same line of road, be frequently subjected to very fluctuating degrees of draught. Upon some of the old waggonways, the horse was sometimes very heavily strained, and his action was, at other times, not at all required. When the waggons reached some of the more rapid declivities, it was the custom to unhook the horse from the fore part of the waggon, and cause him to follow behind, the waggons running of themselves. The horse thus followed, until he arrived at a part of the road, where the waggon would no longer run down; he was then again fastened to the waggon, until he arrived at another declivity, where his action was not required; and it was no uncommon thing, to find him thus changed several times in the course of his journey. The only motive power, for a long time after the introduction of railways, was horses, and so long as the wooden rail continued in use, the general load was from two to three tons, including the weight of the carriages. The only guide, in the formation of the road, appears, then, to have been to enable the horse to drag that weight, and the road was sloped accordingly. It is interesting, to trace the gradual advancement towards the present state of improvement, from the old roads, to those successively formed, at the different steps of their progress; and the quantity of goods conveyed, at different periods, exemplify it, in a very distinct manner. While the wooden rails without plates continued, the road followed, almost always, the undulations of the surface, except to avoid steep ascents; and where there was a separate road for the empty carriages, the latter invariably did so. No attempts seem to have been made, to avail themselves of the action of gravity down the steep planes; and the most disastrous effects were occasionally produced, by the waggons running 'amain," down the steep declivities. A brake, or convoy, being used, to regulate their descent, this brake was pressed by the man with more or less force, according to the declivity of the road, or the velocity with which he wished the waggons to descend. In wet or damp weather, the wheels, by licking up the dirt and mud from the rail, became so slippery, that the action of the brake was almost destroyed; and the attendant having thus no power over the loaded carriage, it frequently got away, destroying every thing in its course, perhaps killing the horses that happened to be upon the declivity, and was, finally, dashed to pieces at the bottom. These accidents were not uncommon, and the destruction caused by them, and the narrow escapes which the men themselves frequently experienced, are in the recollection of many now living. To obviate this inconvenience, in wet weather, boys and men were employed, strewing ashes upon the rails down the steep declivities, or, as they were termed, "runs," to cause the brake to take effect and, in some states of the weather, where very steep declivities occurred, the work was obliged to be stopped entirely. Frequently, on these very steep descents, for many days the work was laid off, on account of the weather; a sudden shower of rain occurring, when any of the waggons were upon the declivity, set the whole away; and men were stationed to draw ropes, as booms, across the line of road, to stop their progress. If the ropes could be drawn across before the momentum became very great, the damage was less; but if they broke the ropes, then the most disastrous effects followed. When the double wooden way came into use, plated with iron, and where occasional ascents intervened, more care was taken in forming the road, and a horse was enabled to take á chaldron waggon, containing fifty-three hundred weight of coals, exclusive of the weight of the empty waggon; still, however, the evil occasioned by the waggons "running amain," down the steep declivities, remained. When cast-iron wheels were introduced, the hindwheels of the waggon were still made of wood, that the brake might be enabled to take a better hold, in regulating the descent. The brake, for a long time, only acted upon the hind-wheels, and, in that case, I suppose, they found it necessary to retain the wooden wheels, to secure sufficient hold. After, it was pro longed beyond the fulcrum, and made to act upon both wheels, the effect being doubled; we presume they found its action, upon the cast-iron wheels, sufficiently powerful, on such descents as they traversed, to secure the proper hold, and the wooden wheels were, therefore, relinquished. The next improvement being the adoption of iron rails, the load of the horse was increased, to nearly double the quantity heretofore taken upon the wooden rail, and this also led to a complete change in the formation of the road. By the substitution of iron rails, the resistance was so much diminished, that the brake could no longer afford security to the waggons descending steep hills; and recourse was obliged to be had to other modes of descending them, and restraining the velocity of the waggons. It is supposed, that those circumstances led to the adoption of, what is called, the "self-acting inclined plane," on which the surplus gravity of the loaded waggons was usefully employed, in dragging the empty ones up the plane. The prevailing means of draught then were, horses upon the level, or slightly descending, or ascending, lines of road; and self-acting planes, upon the steep declivities. Afterwards, when the steam engine became the prevalent moving power, for almost every other mechanical purpose, its action was employed upon railroads, in dragging the waggons up ascents, on the line of road, by means of a rope, extending from the engine to the waggons. And, lastly, the power of locomotion was given to the steam engine; and it was, in that manner, applied to drag the waggons, along the more level parts of railroads, without the intervention of a rope. Having thus given a brief outline of the various species of motive power, successively employed in transporting goods along railroads, we shall now describe them under their respective heads, viz.: 1. Horses. 2. Gravity, acting as self-acting planes. § 2.-Horses. Any description of this species of power would be quite superfluous. Of all quadrupeds, the horse is the best adapted for use, as a moving power, especially in the way that his muscular action is here employed. In dragging carriages upon a railroad, we can always adapt the line of draught, to the direction of his muscular force, so that the greatest effect is thrown upon the line of traction. When a horse makes an effort to drag a carriage, he bends his body forward, and throws that part of his weight upon the collar, which is required to overcome the resistance of the carriage; and the muscular force of his legs is employed to keep up his action, and to move his body forward. His effort, then, is resolvable into two parts, viz., the action upon the load, and that required to urge his own body forward. No very satisfactory experiments have yet been made, to ascertain the precise amount of each; or what proportion the constant exertion, which a horse is capable of bestowing upon the load, bears to his own weight. Dr. Desagulier states the effect at 200 lbs., moved at the rate of two miles and a half an hour, for eight hours a day; or 200 lbs., twenty miles a day. Mr. Smeaton found his performance less. Mr. Watt states it at 150 lbs., moving two miles and a half an hour. |