The adoption of cast-iron plates to cover and strengthen the wooden fabric, was the first application of metal to railways; and this was effected by the Colebrook-dale Company, at their iron works in Shropshire, in 17G7. This information we derive from a published letter of the ingenious Hornblower, the contemporary of the celebrated Watt; wherein he says, " Railways have been in use in this kingdom time out of mind, and they were usually formed of scantlings of good sound oak, laid on sills or sleepers of the same timber, and pinned together with the same stuff'. But the proprietors of Colebrook-dale Iron Works, a very respectable and opulent company, eventually determined to cover these oak rails with cast-iron, not altogether as a necessary expedient of improvement, but. in part as a well-digested measure of economy in support of their trade. From some adventitious circumstances, (which I need not take time to relate,) the price of pigs became very low, and their works being of great extent, in order to keep the furnaces on, they thought it would be the best means of stocking their pigs, to lay them on the wooden railways, as it would help to pay the interest by reducing the repairs of the rails; and if iron should take any sudden rise, there was nothing to do but to take them up, and send them away as pigs.
But these scantlings of iron (as I may call them) were not such as those which are now laid in some places; they were about five feet long, four inches broad, and one inch and a quarter thick, with three holes, by which they were fastened to the rails, and very complete it was both in design and execution. Hence it was not difficult, if two persons on horseback should meet on this road, for either to turn his horse out of the road, which, on the railways now introduced, would be attended with some serious doubt as to the consequences. But it would be impossible on the best railways to afford that facility of travelling which we now enjoy on a spacious well-managed road." So able a man as Hornblower would never have hazarded this prediction, had the plans for locomotion on rails as now developed, been submitted to him as an engineer, for his opinion of their feasibility.
The introduction of metallic surfaces to wooden rails was, however, at first productive of serious evils, for the resistance of, or adhesion to the surface in descending inclined planes was thereby so much lessened, that the ordinary brake was found to be quite ineffective in counteracting the force of gravity. Recourse was therefore had to the double self-acting inclined planes, by which the surplus force of gravity of the load descending one plane, was employed to drag up the empty waggons on the ascending plane. As the acting principle of mechanism of this kind is so very simple and obvious, we shall not detain the reader by describing any of their details in their pristine state, but refer him to the matured plans of more recent times, which will be described hereafter in their proper place.
We now come to the period 1776, when cast-iron plates were used, not as coverings to wooden rails, but in the place of the rails themselves; such plates having cast to them an upright ledge, to keep the carriage wheels from running off them. These plates, being used by the waggons called trams, acquired, and have ever since been distinguished by the term "tram-plates." They were the subject of a patent granted to Mr. Carr, of the Sheffield Colliery, and were undoubtedly an important improvement, as from the date of the patent to the present time, they have been in constant requisition to an immense extent, both on the surface, and in mines. The form given to them, as used in the above mentioned colliery, is delineated in the following transverse section. a represents an oaken sleeper; b b the tram-plates of cast-iron, which are about six feet long, and fastened down at each end and in the middle to three parallel sleepers. In situations where stone is less valuable than timber, blocks of that material are substituted.
The mode of fastening down tram-plates by bolts or spikes was found to be attended with several inconveniences, owing to the occasional projection of their heads, their becoming loose, and hence both the plates and bolts being frequently stolen, to the entire stoppage of the traffic upon the road. To remedy these evils, Mr. Charles le Caan, of Llanelly, in South Wales, contrived a mode of forming the plates, so that no bolting or nailing was requisite, but each plate in succession fastened down the previous one. Fig. 1 represents a plan of the junction of two plates, placed on a stone sleeper D; and Fig 2 shows a longitudinal section of the same. The plates are joined by a dove-tailed notch and tenon,and an oblique plug is cast on each plate, which is let into the stone sleeper; but for the advantage of taking up the plates to repair any defect, there are plates at every thirty yards, with perpendicular plugs; such plates are called stop-plates. The diameter of the plug near the shoulder is one inch and three quarters, at the point one inch, its length two inches and a halt, and its obliquity, shown in Fig. 2, about eight degrees.
A small groove in the whole length of the exterior of such plug is made to allow the water in the hole to expand in freezing; and it also serves to admit a wire to draw a broken plug out by it. The holes for the plugs should be cut to the depth of three inches by a standard gauge of cast-iron, and countersunk so as to allow the end of the plate to bed firmly on the block which supports'it. Fig. 3 is one of the ends of a tram-plate, in which H shows the flange or upright edge; I the flat part or sole, in which the wheels of the waggon run; D one of the plugs; and K a projection behind, to render the plates firmer upon the blocks. The usual length of one plate is three feet; the flanch H is one and a half inch high; the sole, or bed, three and a half, or four inches broad, and three fourths of an inch thick; but these dimensions are varied according to circumstances. The most approved weight has been forty-two pounds for each plate; the ends from which the plugs project, under which the tenons and notches are made, should be a quarter of an inch thicker than the other parts of the plate. The weight of the blocks or sleepers should not be less than about 120 pounds each; and some kinds of ground will require heavier.