194 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[June, 



of wire, tlieir s|)aiis were 1 ft. (i in., their deflections (J inches, and 

 flieir platforms were 2 feet. The parallel chain model (old system) 

 broke down on putting six sacks of beans on its platform, weighing 

 about 13 cw*. ; the taper chain model (new system) bore the six sacks 

 of beans, seven sacks of malt, weighing 10 cwt., 2 cwt. of iron, and 11 

 men at the same time, all of which did not break it down. In Bristol, 

 Jan. I5, 183s, before Messrs. Protheroe, Guppy, and others, two otlier 

 models of eipial materials and dimensions were tried. The parallel 

 chain model bore 1,56.') lb. ; the taper model bore 3,GS1 lb. Again, 

 in Bristol, Jaimary 10, 1838, more trials were made before Messrs. 

 Acraman, Daniels, Hillhouse, and many others of the first merchants 

 of Bristol, Dr. Waldron, and many others of Bath, with models of 

 equal material ; the parallel chains bore 1,155 lb. ; the taper chains 

 bore 3,691) lb. Another trial before the same party on the same dav 

 ■was made with models constructed by Mr. Cross, of Bristol, unknown 

 to Mr. Dredge, in order to prove that all was fair in the former trials ; 

 the result was, the parallel chains bore 2,632 lb., and the taper chains 

 bore 6,849 lb. Each model broke on adding more weight, and the 

 wire throughout on the taper principle was reduced one size by the 

 experiments. 



Now, my Lord, all I request is, in the event of further repairs or 

 improvements being about to be undertaken of the Menai bridge, that 

 you will allow Mr. Dredge to exhibit some similar experiments before 

 your lordship or the Treasury, or before the Bridge Commissioners, 

 and in the presence of any of the most eminent engineers you mav 

 choose to summon. Finally, my lord, Mr. Dredge declares that such 

 is his thorough conviction of the truth of his theory, and its facility 

 of execution, that he would gladly undertake, at his own expense and 

 risk, the whole of the iron iiork, if he should be allowed to recon- 

 struct it, which he believes he could do, the bridge standing all the 

 time, and that it should be competent to sustain lOUO tons on transit; 

 the superfluous iron of the present bridge he is pi-etty confident 

 would pay him, and give a balance in favour of Government. 



Questions may, after all, fairly be put to me to learn why, with all 

 these advantages of Mr. Dredge's system, exhibited witli so much 

 apparent fairness, has not his principle been at once generally acted 

 upon? Why has he not been called upon in many cases to execute 

 what he thus promises i Why, if he can build the proposed Clifton 

 bridge, as he says he could, for one-third or less than Mr. Brunei's 

 estimate, is he not called upon to do so ? One good reason is obvious 

 ^a prudent caution on the part of the public di.->inclines them to over- 

 throw long-established systems, and to oppose or even question the 

 judgment of long known and respected authorities ; this feeling ope- 

 rates very naturally and happily in philosophy as well as in politics ; 

 but it should not in cither be carried to the extent of checking the 

 progress of improven)ent by well-considered means; too great a te- 

 nacity for old systems may exist in the minds of many persons, though 

 their motives may be good and their minds not illiberal ; Mr. Dredge's 

 principle of suspension bridge building completely overthrows the 

 theory and practice of a Telford, a Brunei, whose experience and 

 talents we are bound highly to respect, and to w'hose genius I readilv 

 offer the humble tribute of uiy admiration; can we then be surprised 

 that the public should evince some fear, and some reluctance, hastily to 

 adopt Mr. Dredge's novel principle or theory, in substitution of that 

 which has been so long acted upon? They ought, therefore to pause, 

 they ouglit to inquire if there are any persons about to direct the con- 

 struction of other suspension bridges ; it is a duty they owe to those 

 for whom they may be acting, to examine fully into the merits of a 

 novel system which pruinisca fairly such advantages, before they de- 

 termine to persist in the further adoption of the present, of the cor- 

 rectness of which the state of the Menai bridge, and the vast expen- 

 diture it occasions, may well create a doubt, independent of the ob- 

 viously faulty principles on which it is, I think, clearly shown to be 

 constructed. No Ijuman being was ever exempt from error, and 

 Messrs. Telford, Brunei, and others, must not be considered to be 

 infallible. I have only to add, my dear lord, that in making this 

 address to you, I have no other motive than the desire of assisting to 

 bring forward genius, and secure for the country the benefit of a most 

 valuable discovery and work of art, which apjiears to me, for want of 

 form or road, which are still of insufficient dimensions and strength, 

 but which, of course, are quite unconnected with the principle on 

 which the bridge is built; the chains are under 10 tons, and are equal 

 to sustain 5U0 tons on transit. In November he began putting the 

 chains of this bridge together, and in the following mon'di it was 

 opened for general use ; its road is stoned like common roads. In 

 further proof of the correctness of this system, tests have been made 

 before various parties at various times, viz., at Bath, January 2, 1838, 

 before Messrs. Worsams from London, Ball of Cambridge, and others 

 of Bath, with models whose lengths, deflections, and weight were 

 equal, the chains of each model between the I'ulcruras were onlj' 9 oz, 



that encouragement which I think it merits, to be in danger, like very 

 many others, of being lost sight of altogether. 



I have the honour to be, my dear lord, 



Your faithful and obedient servant. 

 To the Viscount Melbourne. Western. 



P.S. Your lordship will of co\irse understand that I entertain no 

 idea of expecting or asking anything more of your lordship, than a 

 reference of Mr. Dredge to the proper departments, with a recom- 

 mendation to give his plan of improvement due attention and conside- 

 ration, should Government be under the necessity of engaging in fur- 

 ther expense upon the Menai bridge. 



[At the Adelaide Gallery on the 19th ultimo, Mr. Dredge explained 

 the principles of his patent suspension chain bridge, and performed 

 some experiments in the presence of several gentlemen to show the 

 relative merit of his suspension chain in comparison with one on the 

 ordinary construction. He had made two models of suspension bridges, 

 each 5 feet 8o inches long, and with chains of Sj inches deflection — 

 the first experiment was with a model constructed with two chains on 

 the ordinary principle, each consist! ig of 3 wires laid parallel to 

 each other as in fig 4, to which by the lid of vertical wires as in fig. 5, 

 a plattorm of wood was suspended, this platform was loaded with 7 

 full grown persons, and upon the eighth getting on, it broke ^oi^n. 

 The wire chains were fractured at the point of suspension. ,Jpie 

 weight of tile wire in this model was 6^ ounces. The next experiment 

 was with two wire chains consisting of six wires at the point of sus- 

 pension, and diminishing oft' to one in the centre similar to fig. 2, these 

 chains supported by suspension wires jjlaced obliquely as shown in figs. 

 1 and 3, the platform which was loaded with 11 persons, without pro- 

 ducing any fracture, until one or two of the party stamped on the 

 platform, when it broke down, the fracture taking place at the junction 

 of the oblique wires with the chain of suspension. The weight of the 

 wire in this model was only 6 ounces. — Editor.] 



REFERENCE TO THE ENGRAVING, PLATE X. 



Fig. 1, a view of Victoria bridge, constructed by Mr. Dredge on hi 

 patent principle over the river Avon, at Bristol. 



Fig. 2, a chain constructed on Mr. Dredge's principle. 



Fig. 3, a bridge of large span similar to the Menai, constructed on 

 Mr. Dredge's principle. 



Fig. 4, one of the main chains of the Menai bridge. 



Fig. 5, a view of the centre suspension of Menia bridge. 



Fig. 6 to 10, diagrams to illustrate the principle of Mr. Dredge's 

 chain. 



EXHIBITIONS OF COMPETITION DRAWINGS. 



Sir — In my former letter it did not occur to me to make a sugges- 

 tion that might possibly be deemed worth consideration, which is, 

 that in exhibitions of competition drawings — supposing they do not 

 take place until after the decision has been made, there should be no 

 disclosure as to which among them have obtained premiums, at least 

 not until a given time has elapsed. The advantages that would 

 attend such a regulation are, I conceive, tolerably obvious, because, 

 not knowing which are the rejected and which the approved designs, 

 the public would then give their attention to all, at any rate to such 

 as appeared to them of most mark and likelihood, without prepos- 

 session or bias, whereas, when it is known which are the premiumed 

 drawings, those naturally engross attention, and the rest are looked 

 upon, by the majority of visitors at least, as the doomed, consequently 

 nut entitled to admiration. Public opinion would thus be left free 

 from prejudice, prepossession, and prejudgment ; consequently there 

 would be a stimulus to diligent examination and scrutiny which does 

 not now exist. 



How far such a plan would prove a convenient one for the judges 

 themselves, is a different matter. Probably it would subject them to 

 a severe ordeal, and place them in an awkward situation ; for it is my 

 opinion that had not the fact been made known beforehand, no one 

 would ever have suspected that Mr. Railton's and Mr. Grellier's 

 designs obtained the first premium, the one for the Nelson Monument, 

 the other for the Royal Exchange. 



However, so far from being made any objection to tlie course liere 

 recommended, that becomes an additional argument in favour of it, 

 because those with whom the power of awarding the premiums rest, 

 would feel a much greater degree of responsibility than they now do, 

 and would accordingly exercise greater caution and scrupulousness, 

 lest they should find themselves in a most disagreeable minority. 

 Those who would not care to submit their judgment to such hazardous 

 ordeal, are but ill qualified for the important office they assume. 



I remain, &c., 



