latter must rise into vapor, and so also must those which supply their place. And the atoms of water, as they rise, will necessarily become intermingled with those of the air, and will be detained among them by their attraction for them. But, since the repulsion varies in a greater inverse ratio of the distance than the attraction it will form a stable equilibrium with it, at a certain point, within which it will prevent the atoms of water from approaching those of the air; that is, prevent an intimate combination from ensuing.

Thus is explained the fact, that an attraction between the air and water may favor the transition of the latter into vapor, and yet not bring the atoms of water into intimate combination with those of the air, a fact, which I do not think can be explained by any other doctrine.

Sixthly. To the constitution of mixed gases.

The minute investigation into the various theories proposed to explain the nature of a gaseous mixture, which I have endeavoured to pursue, has shewn, that each of them is liable to one or more insuperable objections.

It appears to me that this phenomenon also, may be explained by the application of the present doctrine.

Having first stated the theorem, I shall endeavour to demonstrate it. If a cylindrical vessel, of any given length, be filled with hydrogen gas, and inverted (so as to fit closely) over a similar vessel filled with carbonic acid gas; part of the former gas, although of far less specific gravity than the latter, will descend, and part of the latter will ascend, until the atoms of hydrogen gas, are perfectly mixed with those of carbonic acid gas, and, when mixed, they will not enter into combination.

This may be demonstrated in the following manner.

Since the repulsive force, operating from the atoms of the one gas towards those of the other, varies in a greater inverse ratio of the distance, than their attraction, it must form with this force, at a certain point, a stable equilibrium. Since when the hydrogen gas is placed on the carbonic acid gas, the lowermost atoms, of the former, press upon the upper stratum, of the latter, these contiguous strata, of the two gases, must be brought within the point of equilibrium, between their attraction and mutual elasticity; and must therefore have an effective repulsion for each other.

But, excepting the contiguous strata, all the atoms of the one fluid must be farther from those of the other, than the point of stable equilibrium, and must therefore, exert an effective attraction for them.

If then their mutual effective attraction be superior to their difference of gravity, atoms of hydrogen gas must descend, and of carbonic acid ascend until the mixture is complete. When mixed however, no atom of the former can approach nearer to one of the latter gas, than the distance at which the forces, operating between them, form a stable equilibrium: for within that distance an effective repulsion exists. This distance, owing to the great quantity of heat round gaseous atoms, will be so considerable, that the atoms of the two fluids cannot produce on each other those changes, attendant on combination. From which, the gases must be considered, as merely having their atoms detained approximate to each other, by their mutual attraction.

In like manner, may the constitution of the atmosphere be elucidated;-its consisting of gases in a state of mixture, though of different specific gravities, and yet not entering into intimate combination with each other.

CONCLUSION.

The inquiry into the law of the repulsive force, with which heat endows atoms, namely, of that compound repulsion resulting from the op posed action of the two ultimate powers of heat, themselves, which it has been my endeavour to pursue with such minuteness, as the length of this essay would permit, has, I trust shewn, that this power must vary in a higher inverse ratio of the distance, than the attraction.

By way of illustration, I have imagined this ratio to be the inverse cube, that of attraction being the inverse square of the distance; but I would by no means be understood as intending to enforce this as the actual ratio. Since (as has been above remarked) the actual ratio of this compound repulsion, it is probable, differs in bodies according to the force of their attraction for the particles of heat, it will perhaps never be possible to ascertain it exactly in any individual case. But the limit, which has been laid down, is of the highest importance, since (as I trust) I have deduced from it a simple doctrine, which accounts for the stable residence of atoms at various distances from each other, constituting in nature, solids and liquids, combinations of solids with liquids, liquids with aerial fluids, and mixtures of aerial fluids with each other; and without which none of these phenomena can be accounted for, but they may even be demonstrated impossible.

IV.-Iron Suspension Bridge over the Beosi River, near Ságar, Central India. Pl. XVI.

We take peculiar pleasure in bringing to the notice of our readers the completion of this work of art, because it has been constructed entirely out of the resources of the country, and being the first attempt at such an adaptation of native material and native workmanship, more than ordinary credit is due to the skilful engineer who planned and executed it, and who moreover, from his long residence in India, could have acquired only a theoretical acquaintance with the system of suspension bridges introduced within these few years, and now so rapidly spreading, in Europe.

The bridge was erected at the suggestion of T. H. MADDOCK, Esq. agent to the Governor General in the Ságar and Nerbada territories, upon the plans and under the sole superintendence of Major DUNCAN PRESGRAVE, mint and assaymaster at Ságar.

Engineers in Europe, accustomed to find every thing provided to their wants, can have little idea of the personal labour which devolves upon their brethren of the craft in this country, where to the duties of architect and draughtsman are not only added those of builder and overseer, but the whole of the subordinate trades of the brick-maker, mason, carpenter, and iron-manufacturer; in a climate too where a trifling exertion produces exhaustion; and incautious exposure, fever or death: and where the tools must be made and the hands that employ them instructed ab initio. We will not say that the native mistrees and labourers are not capable of learning or of working well, especially in upper Hindustán; the bridge before us is a sufficient refutation of that common and indolent remark: but all will agree that a peculiar talent is requisite to manage, instruct, and drill them; and this faculty is possessed by Major PRESGRAVE in an extraordinary degree. The secret of his influence may be easily traced; he is a workman himself: he wields the hammer; makes and works the lathe; surveys the ground; searches the mines; smelts the ore; and has all the skill of contriving with the simplest means*, for which the people of this country are themselves so conspicuous.

The Ságar bridge may indeed be called an experiment to try the resources of the country ;—to see whether the iron could be manufactured into bars of a quality fit for bridges;-and whether these bridges could be made by native workmen who had never wrought or

As an illustration of this remark, we refer to the description of the rollers on which the chains rest.

even seen iron of the dimensions required. The question has been satisfactorily answered; and even in point of economy, notwithstanding the numberless extra expences incident to a first undertaking, and the distance, eleven miles, of the work from the yard at Ságar, the bridge has been pronounced cheaper than those in Calcutta made with English materials: while of its design and execution no higher encomium can be given than the assurance of the visiting engineer, Major IRVINE, that he had seen nothing superior to it in Europe. The Governor General is stated to have expressed equal satisfaction after inspection, and only to have regretted that so noble a bridge should be wasted upon so remote a locality!

We have with permission taken a reduced copy of the elevation and plan, lithographed by M. TASSIN, to accompany a private Memoir of the Beosi bridge. The latter authentic source supplies us with the following particulars of the work.

The foundation was laid in April, 1828, and the roadway opened to the public in June, 1830.

The iron of which it is composed is entirely the produce of the Ságar district. When the bridge was projected, it was still in the state of ore in the mines, whence it was extracted, smelted and made into irregular small lumps, in the common native fashion. The working of these crude impure masses into good bars of the requisite dimensions was a matter of very great labour and difficulty.

The bridge is 200 feet in span between the points of suspension. The piers, resting on the solid rock, six feet under the low level of of the river, are 42 feet high to the roadway; being elevated two feet above the ordinary surface of the country: they have a base of 32 feet by 224, decreasing upwards in front one in five, and on the sides one in eight feet; which gives on the road a superficies of 21 by 14 feet for each pier. On the sides are wing walls or abutments, running back into the bank 26 feet.

The pillars, or rather arches, of suspension have a base of 21 by 12 feet, admitting a roadway of 9 feet broad. The arches are 15 feet high, and are faced with accurately wrought stone. The points of suspension are elevated 22 feet 4 inches from the road: the pillars have a total height of 33 feet, and the whole masonry from the rock, 68 feet. The piers and abutments contain 82,488 cubic feet of masonry; the arched standards and bridge parapets, 8900: in all 91,388 cubic feet.

The platform measures 200 feet in length by 12 feet broad, and is calculated to weigh, with the chains, 523 tons. Supposing the bridge crowded with men, at 69 lbs. per superficial foot all over the platform,

the whole weight would be 120 tons, whence it is calculated that the tension to be sustained at each point of suspension would be 85.632 tons.

The suspending chains are 12 in number, arranged in pairs, three pair on either side, two feet above one another. They pass over rollers one foot in diameter, and are securely moored in masonry 16 feet below the surface of the road. The back chains are 101 feet long, rising at an angle of 27 degrees. The angle of the catenarian at the roller is 16° with the horizon the versed sine at the centre of the curve is

14 feet 3 inches.

The twelve main chains are of round bar iron, one and half inch diameter, bolted together in pairs. They are from 15 to 15.5 feet long, and so arranged that the vertical rods may fall from the joints of each chain alternately in parallel lines five feet apart. The descending chains are square bars measuring 1 inch on the side: their lower ends pass through 24 conically wrought stones, below which they are capped and keyed. (Figs. 1 and 2.)

The connecting links of the chains, and indeed all the bolt holes in the bars, and the drops, are bored out of the solid iron, and broached to fit the bolts accurately. (Figs. 5, 6.) None were punched at the forge. The bolts are 1 inch in diameter, and are secured by rings, or washers and keys. Two adjusting links with iron wedges are fitted to each chain, close to the masonry landward, to regulate its curve and dip. (Figs. 7, 9.)

The method of constructing the rollers is thus described in the memoir :

"The iron rollers 12 in number weigh about one cwt. each. They are not solid, but are composed each of about 28 separate pieces of wrought iron, viz. a centre tube or box for the axle over which thick rings are driven; and an exterior drum between which and the inner ringed tube, flattened bars, as spokes, are driven. The centres were broached out clean and true, and cylindrical axles 3.1 inch in diameter were turned to fit; the ends of these axles rest on broad thick iron bearings mounted on very strong and solid frames of timber well bolted, clamped and blocked together, covered with pitch cement and secured in the masonry of the pillars." (Figs 7, 8.)

The platform was made in a different mode from those of our Calcutta bridges, as will be understood by the following explanation:

"From the short links set between the centre plates of the shackles (of the main chains), are suspended alternately from each tier, 74 vertical round rods one inch in diameter connected to a short link (Fig. 6) by a one-inch round bolt passing through it and the socket at the upper end of the bar ; at their lower ends the rods have eyes, through which doubled loops of iron pass (3, 4) for sustaining the flat bars or girders, set on their edges and proceeding from one end to the other on both sides of the bridge.