DESCRIPTIVE ACCOUNT OF THE BRIDGES OVER THE THAMES, BY MR. C.

DAVY.

No. 3.

OLD LONDON BRIDGE.

Proposals for a New Bridge, &c.— Gwilt's design.

A committee having been appointed in 1746, for the purpose of considering and adopting means for the "Improvement of the Port of London," a series of questions were drawn up by them and submitted to George Dance, Esq.* for his answers thereto. Many facts of an important nature were elicited from that eminent architect, and a few of these I shall notice.

The construction of the old bridge, for a work of that magnitude, is exceedingly defective. In common with most ancient structures of that description, it is erected upon stilts, a species of piles driven into the bed of the river, and upon which are raised the piers. These stilts are surrounded, at a short distance, by other rows of piles, forming the starlings-those unsightly and inconvenient portions of the present structure. The space thus enclosed by this description of dam, was filled in with chalk, stones, and loose rubbish. The piles being sawn off at the level of low-water mark, the piers, as before stated, were then carried up. It will be at once seen that this mode of building is subject to many and strong objections. In the first place, it became necessary to wait for the lowest level, for the purpose of continuing the work, a circumstance in the building which may probably account for the bridge having occupied thirty-three years. The thrust of the arch has besides a tendency to overturn the piles, which of themselves, and to add to the danger, consist wholly of loose rubble work, cased with an ashlaring of stone. The water-way too, is so much contracted by the extent of the starlings, that a consequent rise of water takes place under the arches; and this, added to the natural fall in

Surveyor-General of the City of London. It is proper to mention that the questions were open to any architect or engineer, for the purpose of replying to the same.

the bed of the river, taught the expediency of using what are technically termed drip shot piles, and driving the same into the bed of the river, (under the arches) to prevent the water from galling or wearing it away. This, although absolutely necessary, again contracted the extent of the water-way, and according to the observations of Labelyc, made in 1746,† this additional obstruction amounted to one-sixth of the measured width, or in the whole extent to 39 feet, making out of 900, or 926 feet, only 1963 feet of water-way. According to the most accurate observations that have been made, the fall of water caused from the obstructions herein mentioned, is about 4 feet 9 inches. From the answers of Mr. Dance to the interrogatories put to him respecting the depth of the first course of stones or footings to the piers, it appears that they are of various depths, and it seems highly probable, considering the loose and unconnected nature of their materials, that the piers have at different times settled considerably. The footings to the foundations of the piers extended 7 inches on each side of the body of the piers, and the first course of these stones was placed, some at 5 feet, and others at 4 feet, 1 foot, and 2 feet, &c., some above, and others below low-watermark. The piles, Mr. Dance states, were rough, round, and unhewn, driven close, shod with iron, and were not connected together by capciles, but in some instances were planked.§ The timber mostly employed for the latter was of oak; the piles chiefly of elm, and 1 foot in diameter.

Such was the construction of Old London Bridge, an extraordinary spe cimen of the wisdom of our ancestors in bridge buildings, and erected at a time when old English architecture was in other edifices rapidly advancing to that perfection which has ever since called forth the admiration of scientific and practical men. The examination of this structure in 1746, gave rise to great and expensive reparations, but

+ See Hutton's Tracts, No. 1. Philos. Mag. vol. 3, 1700.

§ Supposed to have been added at the time of making repairs.

not till after the lapse of a consider able period. They were made under the direction of a committee, and cost' upwards of £80,000. Notwithstanding this immense expenditure, the bridge still continued subject to great decay, and occupied the attention of committees and sub-committees till the year 1800, when certain voluminous reports appeared under the authority of parliament, intituled, "Reports from the select committee upon the improvement of the Port of London." These reports exhibited the result of the labours of Messrs. Telford and Douglass, Dodd and others, to facilitate the access of shipping between Blackfriar's and London bridges. The project of Messrs. Telford and Douglas for this purpose, attracted much attention for its boldness. They proposed to build a bridge about 200 yards from the present old bridge, so as to make the approaches to range with the Royal Exchange, and the High-street of the Borough, and this bridge was to have been of iron, the arch, (a segment of a circle) 600 feet span, the versed sine from above high water 65 feet, roadway 45, enlarging to 90 feet at each extremity. The ornamental details were to have been in the Gothic style. The drawings, &c., with certain queries, were submitted to Dr. Hutton, of the Military Academy at Woolwich, who in his

answers gave his full approbation of the design. Nothing however was done towards carrying it into effect, and with the exception of further temporary repairs to the old bridge, things remained in the same state. till 1820.

In this year numerous petitions were presented from parties interested in the improvement of the navigation of the Thames, and a special committee of the House of Commons was appointed, which, after hearing witnesses, and examining other evidence, made a report strongly advising the erection of a new bridge. After much delay the corporation, in June 1822, offered premiums of £250, £150, and £100, for the three best designs for the rebuilding of the bridge. This notification produced no less than 48 designs, which were referred to Messrs. Nash, Soane, and Smirke, the three architects of His Majesty's Board of Works, and the City Surveyor, who agreed in recommending the one designed by Mr. Joseph Gwilt, (an engraving of which is prefixed to this communication,) as the best. The Court of Common Council, however, refused to confirm the award of their own referees. "Such conduct," says Mr. J. Gwilt, in his preface to his work, On the Equilibrium of Arches, 2nd

* Hutton's Tracts, No. 5.

edit. " to a young artist, might have been ruinous, and it was fortunate for the author that his dependence was not on such patrons. The sapient body in question, have, however, been since that time sufficiently chastised for their mismanagement, by a committee of the House of Commons, which wisely took from them all controul over the rebuilding of the bridge, and placed it in more independent hands." The apology the court gave for their conduct was very unsatisfactory, As a clever writer observes,*"they gravely recommended that the choice should remain with them, (the court) being alarmed lest the proposed referees should be partial, because themselves or their clerks, or friends, may be amongst the competing candidates. Is it not equally absurd to suppose that that court should have had sufficient knowledge to choose for themselves in such an important matter ?”

The design in question needs little explanation. In the first place the extreme elegance of its elevation fully justifies the meed of approbation so flatteringly bestowed upon it by the

Palladio's 2nd Letter to John Soane, Esq. note A.

Centre arch span, 150 feet.

referees; and secondly, the practical abilities of Mr. J. Gwilt are so well known, that his competency to conduct so great a work could not with any justice be called in question.

The most ancient bridge in existence, whose arch is the segment of a circle, is the celebrated Rialto at Venice, erected in the 16th century, after a design by Michael Angelo de Beaunorotti. This bridge, however, had but one arch of 100 feet span, and a versed sine of 23 feet. Mr. J. Gwilt's bridge was to have five arches, and all of them much larger than that of the Rialto. There is one reason why the elliptical form would have been better adapted for the purpose; but of this I shall treat hereafter; for the present I shall conclude by giving the particular dimensions of Mr. J. Gwilt's design,*

Mr. George Gwilt, of Union-street (the elder brother of Mr. Joseph Gwilt), the restorer of Bow Church, and of part of that much-neglected edifice, St. Saviour's, Southwark, also designed a plan for a new London Bridge, which plan was submitted to the Committee of the House of Commons, and was acknowledged by impartial members of the profession to be worthy of the head of a highly talented family. The treatment of this plan, and also of that prepared by Mr. Savage, was such as might afford ground for debate whether ignorance or a spirit of jobbery has exercised the most pernicious influence Over this public work,-ED.

Number of arches, 5.

Centre arch, 25 feet.

From high water.

5. Ditto of piers.

GLASS'S FIRE-ESCAPE. Sir, Having some months ago taken notice in your useful and instructive periodical work, of a very ingenious and simple machine for the sweeping of chimneys, invented by

Mr. Joseph Glass, and which has been very successfully and extensively applied since that period, I am induced to transmit to you the description of an apparatus for the preservation of life from fire, forwarded lately to me

by Mr. Glass, and which you are at 1.berty to lay before the public, should you consider it worthy of insertion in your Magazine.

The advantages which the inventor considers his apparatus to possess over the numerous inventions, already brought into notice, are its extreme simplicity, and the ease with which it may be promptly and expeditiously applied in case of fire; and as far as I can judge by seeing its application experimentally tried, I think he is quite justified in his opinion. A common pulley, into one side of which a small iron staple is driven, being procured, a chain 18 inches long is attached to the top, to the other extremity of which is fixed, (if the term be admissable) a comprehensive grap pling iron. A strong line is passed through the pulley and made fast to the moveable iron handle,* of a sort of cradle or box, constructed by a wooden frame, round which a coarse canvas is tightly secured; the size of this cradle is 4 feet deep, 2 feet wide, and 2 feet 2 inches broad; the front side being 18 inches lower than the three others, so that when it is drawn up to the sill of a window by the means hereafter described, a person may step into it without any fear of falling on either side; a seat is also provided, which answers the purpose of a step in getting in or out. In cases of emergency the box is sufficiently large to contain two persons.

This is all common-place enough, but it is to the means of raising this apparatus to a window or parapet, that I wish attention to be called, and which, in fact, are borrowed from the principle of the chimney-sweeping machine, described in 243rd Number, for 12th April, 1829, of your Magazine. A number of stout ash sticks, 1 to 2 inches in diameter, are cut in lengths of about six feet, and furnished at each end with strong brass screws. A double prong is fixed to a small piece of cane, also provided with a screw, which fits exactly to any of the ash rods. To hoist the pulley already described to

Something like the handle of a common pail, but of course considerably larger.

101

its destination, this hook or prong is passed through the small staple, and the ash rods are then joined in suecession, till the elevation required is obtained. The pulley being raised about 2 feet above the window sill, the grappling iron which hangs by the chain, is thrown over, and immediately attaches securely without any assistance from above. The box is then drawn up, and the person waiting to descend, having stepped in, it is lowered and drawn into the middle or opposite side of the street by a guide rope affixed for the purpose.

The whole of this apparatus may be confined in a space of little more than two feet square, and for a ready mode of conveyance from place to place, it is so arranged, as to admit of being carried in the manner of a sedanchair, by making use of two of the ash rods,

Independently of the box and tackle, a rope-ladder, with a grappling iron at one end, has been constructed, the steps being formed of solid cane one inch in diameter, which combines two very important qualities, lightness and strength. This ladder can be fastened in the same manner as the pulley, and might frequently be found very useful, both for the purpose of ascent to secure property, or as an assistance to those, whose agitation and distress might paralyse their own exertions.

The whole cost of the fire-escape, with the rods, tackle and box, 60 feet, is £4.; with the rods and ladder, £3. 5s.; cheapness therefore would also be one of the principal recommendations of this apparatus.

I am, your's, &c.

SIZE OF CARRIAGE WHEELS.

W.

Sir, I will thank you to insert a few observations on the solution of the mechanical problem proposed at p. 304, and answered at p. 439 of the 11th volume of your excellent Magazine.

Both of your correspondents ground their solutions on the 5th corollary to the 20th proposition of Whewell's Meehanics, by which the direction of the line of traction is determined, so