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DESCRIPTION OF AN IRON SUSPENSIONBRIDGE CONSTRUCTED OVER THE BEOSE RIVER, NEAR SAGAR, CENTRAL INDIA, BY MAJOR PRESGRAVE.

(From the Journal of the Asiatic Society.)

We take particular 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, 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 Assay Master at Sagar.

Engineers in Europe, accustomed to find every thing provided for 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 draftsman are not only added those of builder and overseer, but the whole of the subordinate trades of the brick-maker, carpenter, mason, and iron-manufacturer; in a climate, too, where little 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 Hindustan; the bridge before us is a sufficient refutation of that common and indolent remark: but all will agree that a peculiar talent is necessary 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 even seen iron of the dimensions required. The question has been satisfactorily answered; and even in point of economy, notwithstanding the numberless extra expenses 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 on 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 Irving, 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 Beose 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 Sagar 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 the 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, 6 feet under the land level of the river, are 42 feet high to the roadway; being elevated 2 feet above the ordinary surface of the country. They have a base of 32 feet by 221, decreasing upwards in front 1 in 5, for the sides one in 8 feet; which gives on the road a superficies of 21 by 14 feet for each pier. On the sides are wing walls of abutments running back into the bank 26 feet.

The pillars, or rather arches, of suspen

sion, 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 8,900; in all 91,388.

The platform measures 200 feet in length by 12 feet broad, and is calcu lated to weigh, with the chains, 52 tons. Supposing the bridge crowded with men, at 691bs. 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 twelve 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 fee long, rising at an angle of 27 degrees. The angle of the catenarian is 16 degrees 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 a half inch diameter, bolted together in pairs; they are from

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15 to 15.5 feet long, and so arranged, that the vertical rods may fall from the joints of each chain alternately in paral lel lines 5 feet apart. The descending chains are square, 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 and 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, to regulate its curve and dip (figs. 7 and 9).

The method of constructing the rollers is thus described in the memoir :"The iron rollers, twelve in number, weigh about I 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 are broached out clean and true; and cylindrical axles, 31 inch in diameter, were turned to fit: the ends of these axles rest on broad, thick iron bearings, mounted in very strong, solid frames of timber, well bolted, clamped, and blocked together; covered with pitch cement, and

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secured in the masonry of the pillars." (Figs. 7 and 8.)

The platform was made in a different method 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 ties, 74 vertical round rods, 1 inch in diameter, connected to a short link (fig. 6,) by a 1-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 and 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.

"The flat bars, 4 inches broad by inch thick, and in lengths of 15 feet, are joined at their ends by nicely-turned bolts, passing through bored holes 2 inches in diameter; they are adjusted in their height by double wedges resting on holders that connect the sides of the loops together. The girders are also adjustable in their lengths; the bars that enter the masonry have their ends made broader than the rest of the bars, in which are long openings 2 inches broad to receive wedges (figs. 10 and 11).

"Eight timbers in an upright position are set in the masonry of the pillars, having upright grooves or spaces cut through them, and faced with thick plates of iron; through two of these beams each end bar passes, and may be wedged on either side of the timber towards the land, as occasion may require: thus is the whole length of girder drawn more or less to either end of the bridge, and also rendered exceedingly tight and steady. The grooves in the timbers towards the river, being about 4 inches longer than the breadth of the bars, permit them to adapt themselves to their proper directions when drawn lengthwise, by the wedges acting against the landward beams; by this means the bars have sufficient play to adapt themselves to the motion of the platform, and all jirks at the pillar obviated.

"Thirty-seven double-joists, 12 feet long, are (having their ends notched below for the purpose) laid on the girders; their centres,

6 double main chains, joists, and bolts 74 vertical rods with joints, bolts, &c. Flat bars and bolts

5 feet apart, correspond exactly with the vertical rods that pass through them: the joists are composed each of two cheeks, a foot in depth and 3 inches thick, separated at intervals by four blocks of wood of the same height and thickness, all firmly put together with bolts, screws, and nuts: two cleats are nailed to each end of the joist on their under sides, whose ends fit flat against the girder and keep all steady.

"Planks, 16 feet in length, running longitudinally, each plank stretching over three paces, and regularly disposed as to their joints, are spiked down on the joists: in a direction across these, and upon them other planks are spiked down, their lengths being the same as the breadth of the platform. The planks are all embedded in a composition of resin boiled in linseed oil, which in laying on is mixed with ashes. The lower planks are three and the upper ones 34 inches thick; they are only six inches broad to prevent warping, and have two strong squareheaded spikes passing through them near their edges at every crossing of the upper over the lower planks: their joints are clinched below the platform, to accomplish which 16,370 spikes weighing a ton and a half were used; thus the platform has been rendered extremely strong and firm.

"The better to secure the sides of the platform and ends of the timbers from the weather, a cornice or moulding of wood is nailed along the outside.

"The hand-rail is trussed, and consists of iron pillars or stanchions; diagonal braces of iron, and a stout wooden rail running from end to end of the platform: the whole put together with screws and nuts, and adjusting screws for setting up or tightening the diagonal braces whenever required. (Fig. 10).

"The rise in the platform is as before stated, 9 inches, but the curve of the handrail is only 3 inches; to effect which, the stanchions which support the rail are of varying lengths, the rail being 4 feet 6 inches above the platform at its connection with the masonry, but only 4 feet in the centre of the bridge."

The following are the weights of the chains, rods, and materials of the plat form:

ELECTRO-VEGETATION.

Letter 1V.

Sir, We propose next to consider how far the operations of light on vegetation are referable to electrical agency. Light extracts moisture in great abundance, and oxygen in degrees proportioned to the quantity of carbonic acid present in the atmosphere from the under surfaces of the leaves when their vegetation is vigorous. It has been supposed that the moisture exhaled from plants bears a near analogy to the perspiration of animals, and might in like manner be promoted by exposure to heat in the absence of light. It appears, however, to be a process altogether dependent on the action of light; for if two plants be placed under the sun's rays, the one open to their action, the other with an opaque covering, which, while it excludes their light, admits their heat in an equal or greater degree, a glass vessel being placed over both for the purpose of receiving moisture, the first will be quickly suffused with pure water standing in drops, while the latter will remain perfectly dry. This exhalation, therefore, is not a result of any internal process passing in plants, by which heat is generated within them and thrown off in the form of vapour, but is the pure action of the light combining with the aqueous particles of the sap, and transforming them into gas. It proceeds from the under surface of the leaf, which in general is more porous and less resinous and polished than the upper surface: a fact which may be observed by inverting two glass vessels, the one on the back, and the other on the face of a leaf; the first, if exposed to the sun, will be quickly suffused with moisture, while the other will receive no moisture whatever.

This extraction of one of the ele

ments of the sap by the pure agency of

light abstracted from heat, bears a strong analogy to that of electricity; and indicates that this is the principle by which the decomposition is effected; which though partial, as not being sufficiently intense to resolve the water into its elements, is yet the result of such a degree of electric influence as is requisite for the occasion, rendering the sap more dense for its descending course, and removing many of those aqueous particles which by conducing to its fluidity and levity, greatly aided in its ascending direction.

Oxygen gas is now well known to he extracted from the leaves of plants by the agency of light. Of this fact I have satisfied myself, by observing that the production and increase of gas in glass vessels inverted over fresh leaves merged in water, depended wholly on their exposure to the light. In my experiments the increase was slow, in consequence of my not being aware at the time of the necessity of the presence of carbonic acid in the water to the production of the oxygen. I, however, found that the gas thus procured was pure oxygen, which, though slightly diminished during the night season, upon the whole furnished me with a sufficient supply for a satisfactory experiment, proving it to be oxygen in a state of purity. My indefatigable friend, Mr. Weekes, has arrived at the same conclusion, by experiments made by means of his newly-invented pneumatic apparatus, described in your pages, on plants while remaining in air as their natural element. But I do not know whether he was aware, or is prepared to adinit, the necessary presence of carbonic acid in the atmosphere, in order to the production of oxygen, which, however, appears in several very decisive experiments of Sir H. Davy, related in his Elements of Chemistry; and is confirmed by Woodhouse, who drew from his ex