inch square, required a weight of 72 lb. avoirdupois to break it, at the distance of one-fourth of an inch from the prop p where it was supported. Now, as it is a rule in mechanics, that, by doubling the deepness of the timber, the strength is increased fourfold, whilst, by doubling the breadth it only doubles its power; hence by an easy calculation, it may be demonstrated, that a rod of fir-wood, an inch square, would, in like circumstances, require 4608 lb. to break it.

The proportion that iron in point of strength bears to fir I am not informed of, nor have I been able from experiment to ascertain 'precisely the fact. But knowing that malleable iron, in point of weight, is very nearly fourteen times more than fir-timber, I should suppose that we shall not be far wrong in estimating its strength in the same ratio. So far, however, I know, that in an experiment made on a small rod of hammered iron, 4th of an inch square, (and which, on the above estimate, should have broke when 126 lb, were suspended from it at 4th of an inch from its support), it sustained 196 lb. without breaking; but allowing it to remain a few minutes, it bent downwards. But supposing it to have been no stronger than to have sustained 140 lb., it may from this be demonstrated, that an iron-axle, of a single inch in diameter, would sustain 57,344 lb., being upwards of 25 tons on each end, and as there are two axles on each railway-waggon, they would sustain in like proportion. In this calculation, the reduction of the strength, by reducing the square to a circle, is taken into the account.

On railways, therefore, where no jolting to any excess can take place, the axles, with every regard to safety, may be reduced to one inch (and less) in thickness, which, in general, may have an effect to double or triple the power of the wheels; or, in other words, enable the horse to draw twice or thrice the lading with equal ease, without augmenting the size of the wheels. The lower these are, the less liable are they to deviate from the direct track, and less liable to get out of shape.

VI. Of the construction of Waggon Railway Wheels.

The wheels at present in use are generally 27 inches high; some few, indeed, are as low as 18 inches, and some 30. They are formed wholly of cast-iron, and weigh from 1 cwt. to 14 cwt. each, I mean those of 27 inches. Four of these go to a waggon, and, with their ponderous axles, weigh from 7 cwt. to 8 cwt., which, together with the body of the waggon, makes the vehicle seldom less than 14 cwt., while the lading is only from 26 cwt. to 32 cwt.; so that the waggon itself forms about a third part of the whole draught. The expence, or cost, is from L. 10 to L. 11 each.

For waggons on a railway that are calculated to carry such a burden, wheels and axles of that weight are not required. They might be constructed sufficiently strong at less than half of the weight, and, including the body, at little more than half of the

price. The wheels might be made of wood (still 27 inches high), whilst that part of them which comes in contact with the rail, might be shod with iron, and which could be renewed from time to time as required, without renewing the rest of the wheel. These would never snap, and would not be much liable to wear. Cast-iron wheels are very liable to snapping, and when any part of them wears down, or out of shape, the whole must be thrown aside.

VII. Of the Form of the Waggon.

In the present form of the coal-waggon, Fig. 11. Plate II., the whole lading operates like a wedge, with all its force, in bursting the sides of the waggon asunder, and is still more ruinous in the act of taking in, and of giving out, the coals, as these, in both cases, from the acquired velocity, rub and tear the deals to pieces. This has led to an expensive mode of lining them with plate-iron, which adds also to the weight, and increases the burden in the same proportion.

The form should rather be reversed,—making them broader at bottom than at top, as in Fig. 12. It is not necessary that the difference should be great. A single inch would be sufficient. The waggons, relieved of the constant pressure on their sides, would last double the time, without the expensive apparatus of iron stay-props, so copiously required in the present form. Thus, both in weight and in

price, there would be a great saving, whilst the wagitself would be more durable.

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VIII. Of the Size of the Waggon.

It was a great improvement at first the dividing of the 48 cwt. waggon into two of 24 cwt. each, and still further, when 4 tons were found to be within the power of a horse to draw, to divide them into three waggons instead of two. Now that there seems to be a probability that double that lading or more is practicable, some people are of opinion, that the fewer waggons the whole is put into, the better, as concentrating the loading into less space on the railway. There is not much force in that reasoning, although it may be admitted to a certain extent. But the benefits to be derived from having the lading distributed in many waggons, rather than in few, are so many, that the system already introduced, of having as many waggons for as many tons, ought to be adhered to; for the lighter the lading is, the less pressure on the rails, the less shaking, and, in consequence, the less wearing, both of rail and waggon; and these advantages, together with the more smoothly gliding along of the whole train, should determine the question. But more than all these considerations,-the less weighty the lading is, the smaller may be the axles, which alone confers an advantage so very important as ought to set aside every objection that can be offered. At same time, it is capable of demonstration, that a horse can draw the whole lading, when laid on six or ten waggons,

with the same ease as if it were all laid upon one; and these six, or ten, waggons can be made for the same expence as the one, and not be heavier in all, than the single one alone.

IX. Of the general Level of a Railway.

The railways hitherto made, have been constructed either on a dead level, or on a uniform descent, to a certain point. This, in general, has been attended with a great expence, in cutting through rising grounds in some places, and filling up hollows in others; and, after all, the object, when attained, is to a certain extent, detrimental. For the horse in the draught, so far from deriving a continued advantage from it; on the contrary, in a long pull, the unvaried mode of draught, to which he is confined, becomes to him extremely irksome; and nothing but the shortness of the way, in any hitherto mode, makes it bearable. It is not from being level that the excellency of a railway is constituted; it is from the smoothness of the rail, along which the waggon glides. It is this that distinguishes, so very highly, the railway above the ordinary gravelled road, or laid causeway. These, in many instances, are quite level; but in none of them, nor in no part of them, is there such a facility afforded to the draught, as in the railway; for, in no other road yet known, is there such a degree of smoothness as the railway pos

sesses.

Now, as it appears, from what is stated in a preceding section of the power of a horse in drawing,