"they are kept by the contact of the wheels, has the "usual effect of polish, in presenting to the destroying "influence a smaller surface to act upon. The black "oxide or crust, which always remains upon iron, appears to act as a defence, against the oxidising "power of the atmosphere or water. This is the reason why the rail does not rust on its sides."

66

66

One phenomenon, in the difference of the tendency to rust, between wrought iron laid down as rails, and subjected to continual motion, by the passage of the carriages over them, and bars of the same material, either standing upright, or laid down, without being used at all, is very extraordinary.

A railway bar of wrought iron, laid carelessly upon the ground, alongside of one in the railway in use, shows the effects of rusting, in a very distinct manner; the former will be continually throwing off scales of oxidated iron, while the latter is scarcely at all affected.

Experience of the use of these rails, has now established the fact, that there is no waste or destruction, from oxidation or exfoliation, in rails of the proper quality of iron, and well manufactured, and that the wear is less than cast iron; there cannot, therefore, exist any doubt, at present, which of the two descriptions of material is preferable, as rails for public railways.

The rapid rate of travelling, now adopted on all those railways for the conveyance of passengers, renders the use of cast-iron rails absolutely dangerous, as breakage of a rail might be attended with the most disastrous consequences.

Upon private railways, the cast-iron rail is still considered by some as the most economical, especially as the first cost is less than that of the wrought-iron rail. There seems no doubt, that the wear of the wrought, is

less than that of the cast iron; this point, therefore, rests entirely upon the relative price of the two kinds of iron, the comparative strength and stiffness being well ascertained. But the fact of malleable iron rails, being gradually more and more extensively used on private railways, where economy is strictly considered, and of their being exclusively used on public lines of railway, is a strong proof of the opinion of engineers in their favour; and goes far towards, if it does not completely establish, malleable iron, as being the best material for railways. § 7.- Comparative Properties of Edge and Plate Rails.

It seems to us a matter of great astonishment, that the plate rails have yet many advocates; and what seems more unaccountable, on the mistaken notion of the friction being less upon them, than upon the edge rail. We should have thought, that the number of railways of both kinds, now in existence, would have afforded sufficient opportunity of ascertaining this fact, without having recourse to surmise or opinion. Sufficient proof will be adduced hereafter, in the account of experiments on friction, to show the absurdity of retaining such a supposition, which is also apparent from the nature of the action of the carriage wheels upon the two rails. Certainly, if the rolling part of the wheels, used on the plate-rails, was equal in breadth, to the surface of the edge-rails, and if the wheels on the plate-rail always rolled along it, without rubbing against the upright ledge, more than the flanch of the wheel rubs against the side of edge-rail, then the friction in the two cases might be equal; but the rubbing of the wheels, against the upright ledge of the plate-rails, is considerably greater than the rubbing of the flanch of the wheels, against the sides of the edge-rails. The general height of the ledge of the flat rail, is three

inches; and the projecting flanch of the wheels of the other, one inch; and supposing the tendency to rub against the sides, to be the same in each, the friction will be as the height of the respective ledges, and consequently greater in the plate-rail. This is supposing each of the rails equally free from obstruction, or extraneous matter, affecting the free rolling of the wheels upon them. But any person will see, that the form of the plate-rails necessarily causes them to be more subject to the presence of such an obstruction, than the edge-rail; the one forming a sort of receptacle for the dust, dirt, and other substances, falling upon them; while the other, from its narrow surface and elevated position, tends to throw off any extraneous matter, which may accidentally fall upon it. Mr. Palmer, in his description of a patent railway, gives a very interesting experiment, on the obstruction caused to the carriages, by the dust upon the plate-rails, which we shall take the liberty of inserting. He states, "I made

66

an experiment on a branch of the Cheltenham tram"road (which was nearly new, and in good condition), "with a view to ascertain the difference of resistance, "occasioned by dust lying upon the rails. The carriage "and its load weighed 5264 pounds; the rails being

66

66

swept clean, the resistance was thirty-six pounds; the "rails being slightly covered with dust, the resistance was forty-three pounds; consequently, the difference of "resistance to that weight was seven pounds, being upwards of one fifth increase.”

The tendency of the edge-rail to form a rut or groove, on the periphery of the wheels, and thus to increase the friction, was, for a long period, a motive for preferring the other; and this was considerable at first, owing to the narrow surface of the rails, and the

the softness of the metal of the wheels; afterwards, when the bearing of the rails was made greater, and now, since the introduction of case-hardened wheels, this objection is entirely removed. Certainly, when the wheels were indented, the increase of friction occasioned thereby, might cause an uncertainty which ought to be preferred. This having been obviated, and the other reasons for preferring the edge-rail still remaining good, together with the saving of weight, by the more proper distribution of the metal, to resist the transverse strain of the carriages; renders it no longer a subject of dispute, that the edge-rail is decidedly the best.

§ 8.-Stone Railways.

There is another description of railway, which originated in Italy several centuries ago, and is still in use in the streets of Milan, and which requires a casual consideration. It is composed of long stone blocks, laid in a continuous line, on each side of a paved horse-path, on which common carriages run. A portion of the commercial road in London, was thus paved by Mr. Walker; and when first laid down, a horse could drag very considerably more, than upon the common road, the common carriages of the latter running upon it. Experiments were made by Mr. Walker, which shewed that, when perfectly smooth, and free from dust or dirt, the resistance was not much greater, than upon an iron railway; a few years use of it has, however, shewn that, though the stones were granite, and basalt, they wear into ruts, and that these ruts increase the resistance very considerably, still, when heavily loaded, the carters prefer travelling upon it, to that of the common road adjoining. Von Baadar, of Munich, in Germany, proposed an improvement to this form of railway, by laying

a bar of iron upon the upper surface of the stone, on which the wheels of the carriages should move; to protect the stone from abrasion, and to lessen the resistance. A few furlongs of the Quincy railroad, near Boston, have been made in this manner, and is stated to have been attended with success; and it has since been extensively adopted on the Baltimore and Ohio, and on the Pennsylvania railroads, in the United States of America.

Forty miles of the Baltimore and Ohio railway, of a single line, is laid with granite sills, these sills are continuous, and are eight inches thick, and fifteen inches broad; they are laid in trenches, filled with broken stone. The iron rail is attached to the inner edge of the stone, but the bearing not being uniform, the stability of the railway is stated to be impaired, although that has been lessened, by placing the iron rail nearer the centre of the stone sill.

On the Philadelphia and Columbia railroad, the first ten miles, westward from Philadelphia, are laid with granite sills. It is thus described, by the Editor of the American copy of the second edition of this Work. "The granite sills are from five to nine feet long, "one foot wide, and one foot thick; and the trenches "are twenty-two inches deep, including the thickness "of the road metal, and are filled with small broken "stone; these sills are arranged in continuous parallel "lines. On the upper surfaces, near the inner edges, "flat iron bars, fifteen feet long, two inches and a "quarter wide, and five eighths of an inch thick, are "attached by square nails, three and a half inches long, "and eleven thirty-seconds of an inch in diameter, "driven into cedar plugs, five eighths of an inch in

66

diameter, which are inserted in holes, three and a