RAILWAYS.
The great advantage of railways over ordinary roads is the diminished friction, which is produced by the wheels passing over the smooth iron instead of rough stones. It was found when iron rails were first used, before the introduction of locomotives, that the horse-power requisite was diminished to one-fortieth; for instance, ten horses on a railway could do the work of four hundred on a common road, this being the case, and the great power of the locomotive engine being superadded, there can be no wonder that the difference of the rate of speed between the train and the wagon should be so great. When it has been settled what general direction the railway shall take, it is then to be determined whether or to what extent the elevations or depressions that may occur can be conveniently overcome, so that the line may take a straight course, or whether the road shall go out of the straight line, and how far to avoid them. The route it should therefore take ought to exactly balance the objections to each extreme, that is the expense, &c., of going straight on through hills and over valleys on the one side, and the increased distance and consequent loss of time which a winding track would cause to the transit on the other.
FIG. 1.
FIG. 2.
FIG. 3.
FIG. 4.
With respect to the “level” at which the line should be laid, a section of the route, showing all the elevations and depressions, is first made, then such a course is chosen that the material produced by cutting through the higher parts shall be just sufficient to form the embankments for filling up the lower parts; [fig. 1] will give some idea of this arrangement. Of course a line perfectly level would be the best, just as would be one perfectly straight; but as the difficulties of the one must be balanced, so must those of the other, and a line as nearly level should be obtained as is consistent with expense. For instance, suppose A and B, [fig. 2], to be towns to be connected by a line of railway, and the chief of the intermediate ground to be above their level; of course it would be very expensive to cut through the whole distance, as shown at the dotted line a, this level would therefore be too low; but if a higher level were taken, as at the dotted line b, then only the centre of the distance would have to be cut through, and the material (earth, &c.) produced by the cuttings would suffice to fill up the hollows at the ends. These considerations and many others must therefore determine the level at which the railway shall be constructed; but the line is seldom (if ever) on one level from end to end, nor at one continuous “gradient” or slope, for the course of the line is so arranged as to make as little cutting and filling up as is consistent with a road whose gradients shall never exceed a specified amount, which must be determined by local circumstances. The excavation and filling up being finished, the “trams” have to be laid; these are bars of wrought iron about fifteen feet long, of the form shown at A and B, [fig. 3]. The most usual form is that marked A. They are made of wrought-iron, passed while hot between rollers cut at their edges into the form required. These trams are laid upon bars of wood called “sleepers,” at about four feet apart, and united to them by what are called “chairs,” which are pieces of cast-iron of the form shown at [fig. 4], fastened to the sleepers by iron spikes, and into these the trams, or “metals,” as they are called by the workmen are wedged. These bars of iron are laid very evenly and perfectly parallel at a certain distance apart, which must exactly correspond to the distance between each wheel of a pair belonging to the carriages and engines; this distance is called the “gauge,” the wide gauge (as on the Great Western) is seven feet, and that called the “narrow gauge,” is four feet eight-and-a-half inches, and the space between the lines is of sufficient width to prevent any danger of collision in the trains on passing each other; they are generally six feet apart.
FIG. 5.
FIG. 6.
FIG. 8.
FIG. 7.
FIG. 9.
FIG. 10.
As it is necessary that trains should at certain places be “shunted” or shifted from one line of rails to another, particularly at stations where a great many tracks run side by side, and cross each other to branch off to different parts, there are arrangements called “points,” shifted by a lever or “switch,” so that they shall direct the course of the train, and cause it to leave the former track and enter upon a new one; this arrangement may be seen at [fig. 5], where the points are in the position to direct the engine coming in the direction of the arrow on to the curved line A, and the dotted lines indicate the position into which they would be shifted, if necessary for the train to go straight on to the line B; this action is effected by moving a lever which shifts the two bars a few inches either way. When an engine or carriage has to be turned on to a track at right angles to the one on which it rests, or where there is not room for “shunting,” an apparatus called a “turn-table” is used, which is shown at [figs. 6] and [7]; it is a round platform of iron turning on its centre, and supported by friction rollers at the edge, having on its surface raised rails in two or more directions, so that it may be turned round half or quarter distance, according to the position required. The engines and carriages used to run on railways are of various constructions, but to a certain extent agree in their chief particulars; the wheels are fixed to their axles, so that each pair and the axle which joins them may be considered as one piece.The axle projects a little way beyond the wheel, and on this part it supports the engine or carriage, which is wider than the distance from one wheel to its fellow. They are therefore entirely underneath. They are of iron, made by machinery and have a projecting edge on the inside of the “tire” of each, which is called the “flange” (see [fig. 8]); this flange does not run on the rail but within it to prevent the wheels from slipping off. These flanges, when the pair of wheels and axle are united, exactly fit in between the rails, so as to touch the inside of each and form a sort of guide. Each carriage has two pairs (except in a few cases, where three pairs are used), the engines have usually three, and sometimes four pairs. The carriages rest upon powerful springs, and are moreover furnished with springs to diminish the concussion of one carriage against another; these last are acted on by a sort of piston-rod, one of which is placed at each corner of the carriage, and are called “buffers” ([figs. 9] and [10]); they all coincide with each other, and form a set of springs all along the train, which greatly reduces the shock which would otherwise be felt when it is stopped. Another set of springs is connected with the binding screws which unite each carriage, and these prevent the sudden jerk which would result from the starting off of a train quite inelastic in its length.
The engines used are of that class called high-pressure or non-condensing, and there are two cylinders and pistons, which have a stroke of about eighteen inches. The boiler is so contrived that a large quantity of steam shall be rapidly produced; for this purpose tubes of brass are made to pass side by side from the fireplace through the boiler, and through these tubes the flame and hot air must go before reaching the funnel, giving out in its course a great amount of heat to the water and converting it rapidly into steam. The steam from each cylinder passes at each stroke of the piston into the funnel, assisting to form a draught which draws the flame from the fire through the tubes and increases the fierceness of the combustion. The necessity for two cylinders and pistons is owing to the impossibility of having a fly-wheel, and as the driving wheels of the engine have to be turned at an equal rate, the axle has two cranks so placed that the greatest power of one piston is exerted where the other exerts the least (see “[Steam-engine]”).
FIG. 11.
FIG. 12.
FIG. 13.
As the trains when going at a considerable speed cannot be suddenly stopped, it is necessary to have signals placed in certain conspicuous positions, that the engine driver may begin to stop the train (when necessary) in time; this he effects by what is called a “break,” a contrivance by which two pieces of wood are made (by turning a screw) to grasp firmly each of a pair of wheels, and so prevent them turning round, this produces so much friction against the trams that (after the steam is turned off) the onward motion of the train is soon stopped. The signals are of three kinds generally, a red flag to indicate danger, a green one to caution, and a white one to show that the way is clear; these are (on most occasions) held by a man and waved to and fro to attract attention, but there are however a great many occasions for fixed signals, as at stations and bends in the line where the engine driver can only see a short distance ahead; these fixed signals consist of tall posts placed where they can be seen at a considerable distance. These posts have an arrangement at the top consisting of a lamp with a “bull’s-eye” or lens at each side pointing up and down the line, and a pair of arms capable of being let down into the post, raised at right angles with it, or into a position midway between the post and a right angle (as shown in [figs. 11] and [12]). One side of each arm is painted red, the other white, one arm serving for a signal up the line and the other down; attached to the joint of each arm, close to the post, are two iron frames each holding a piece of colored glass, one red the other green, and so arranged that when the arm is at right angles to the post, the red glass is before the lamp and when the arm is let half way down the green glass comes in front of the lamp ([fig. 13]), thus the same action serves both for day and night signals. When the arm showing the red side projects in a horizontal direction, it indicates (in the day) “danger,” and so does the red light at night; when the arm is let down half way, it shows that caution is required, and the green glass then before the lamp shows the same signal at night; when the arm is let quite down out of sight, it shows safety, and so does the white light of the lamp thus freed from both screens of colored glass.
FIG. 14.
Each engine is provided with a whistle ([fig. 14)] blown by steam turned on from the boiler, which is used as a signal at any particular time, especially in tunnels or when there is a fog; there is also an arrangement by which each engine presses on a lever at the side of the tram as it passes, and causes a bell to ring at the station, to announce its approach, when about a quarter of a mile off. In some cases, as in foggy weather, when the usual signals cannot be seen, a packet of fulminating powder is placed on the rail, and this being exploded by the wheel of the engine as it passes over it, gives notice of its approach, &c. There are other signals, but these are the chief.