1S47.J 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



75 



centre span of the platform wouH produce a sudden or impulsive horizontal 

 force on the top of the piers which could never be estimated from statical 

 principles. There is, moreover, the apprehension of the rollers becoming, 

 from long disuse, settled and fast in their place, by indentation, the accumu- 

 lation of rust, or other foreign substances, &c. : from not being called into 

 action under ordinary circumstances, they might be inoperative just at the 

 time when they were wanted.* This point ought also to be examined ex- 

 perimentally. 



We have confined our attention almost exclusively to the stability, and 

 have said little of the strength, of the Bridge. The following seems a 

 simple and satisfactory method of ascertaining the tension of the main 

 chains at the points of suspension. If t be that teusion, I the load borne 

 by each half of the main chain, and fl the inclination to the vertical at the 

 point of suspension, we know that 



t. cos e = I, or t = I. sec 9, 

 whatever may be the form of the chain. In other words, we may ascer- 

 tain the tension of the chain at its highest point, by multiplying half the 

 total load by the secant of the augle at which the chain is inclined to the 

 vertical at that point. The advantage of this method is, that it is inde- 

 pendent of any assumption respecting the form of the catenary, and is 

 strictly true, if we suppose what, in fact, is the case, that no part of the 

 load is sustained by the platform itself resting on the piers. In answer 

 to an application for the value of the angle in Hungerford Bridge, we 

 were promised the particulars by Mr. Brunei, but subsequently found that 

 he had been too much engaged to send them. Probably, the subject (the 

 mere question of a few hundred lives) was too trivial to engage his atten- 

 tion. 



There are many points in Sir Howard Douglas's paper on which re- 

 marks might be offered, but, for the sake of brevity, we refrain from 

 making them ; though, in one or two cases, our arguments seem to have 

 been somewhat misunderstood. However, there can be no doubt that, if 

 tl»e traffic of Hungerford Bridge should appear likely, from a change of 

 circumstances, to be hereafter greatly increased, the question will engage 

 the attention of those who have more power than ourselves to demand 

 information upon it. The inquiry which Sir Howard Douglas has per- 

 sonally undertaken (notwithstanding great obstacles), has, we believe, been 

 most minute and laborious : such exertions can have no possible object 

 but the public security and the advancement of engineering science, and 

 ought, therefore, to be appreciated in proportion to their disinterested- 

 ness. 



t The powerful eflFect of the accumulation of rust and concretions is frequently ex- 

 hibited in a strilting degree in the second or subsidiary safety-valves of steam boilers. 

 These valves are never called into use except in unusual emergencies, and then, from 

 long disuse, are often clogged and stick fast, uotwithstaodiug the very great pressure exert- 

 ed to open them. 



HISTORY OF ENGINEERING. 



By Sir J. Rennie, President of the Institution of Civil Engineers. 



{Continued from page 55.) 



Drainage. 



In works of draining extensive districts of low marsh or fen lands, the 

 Bomaos, with their usual energy and ability, elTecled much, and the Po- 

 dike,Caer-dike, and the embankment of the Thames, amongst other works, 

 are good examples. After they left the country, it relapsed into its former 

 state of barbarism, and so remained for ages, until the art of drainage may 

 be said to have been lost. Upon its revival the Dutch, from necessity, had 

 become extremely skilful, and were celebrated throughout Europe at a re- 

 mote period, almost before engineering commenced in Great Britain. On 

 account of the proximity to England, and their experience in these kind of 

 works, when it became a question of draining the extensive districts of low 

 marshy land on the east coast of England bordering upon the Humber, the 

 Wjtham, the Ancholme, the Welland, the Nene, and the Ouse. it was na- 

 tural that recourse should be had to those who, from their skill and expe- 

 rience, had already acquired such reputation as the Dutch; accordingly 

 we find, in the reign of Charles the First (when it was determined to ditain 

 the great level of the fens, afterwards called the Bedford Level, from the 

 name of the Earls of Bedford,) Cornelius Vermuyden came over from Hol- 

 land, and after draining the level of Halfield Chase, adjoining the Trent, 

 and acquiring considerable celebrity and influence, was knigiited by the 

 king. He planned great works in 1040, at the Bedford Level, for Francis 

 Earl of Bedford, but the execution of Vermuydeu's plans were prevented 

 by the Civil War, and were afterwards carried into elTect by William, (he 

 successor to Francis, Earl of Bedford, after much discussion and contro- 

 veuy, and were successful in draining the level to a certain extent. The 



plan in 1G51 consisted in placing a sluice across the River Ouse, at Den- 

 ver, about 15 miles from the sea at Lynn, where the Ouse enters Ihc (ireat 

 Wash, so as to exclude the tidal waters, leaving the channel of the liiver 

 Ouse, above that sluice, for discharging the fresh waters only ; these it 

 was proposed to conduct from all parts of the land by small lateral drains 

 or canals, carried to the river in as direct courses as practicable, having 

 sluices at their junction with the river, to prevent the Hoods from enlering 

 them and covering the adjacent lands. He also cut a new channel, about 

 20 miles long, called the Bedford, or Hundred Foot River, for a part of 

 the River Ouse, from the point where Denver Sluice was erected, lo the 

 old channel of the Ouse, at Karilh, where another slauch or sluice was 

 placed for preventing the tide from goiug beyond that point. 



Vermuyden considered that by adopting this plan, and having only (he 

 fresh waters to contend with, he would get rid of that must powerful enemy 

 to drainage, the tide ; and then, having only to deal with the fiesh water, 

 he anticipated no difliculty in accomplishing the complete drainage of the 

 land. For a time the plan answered tolerably well, and effected consider- 

 able improvement in the drainage ; but he overlooked the iniporlaut facts 

 that the tidal waters formed the most important agent in keeping open the 

 channels of the rivers, iu preserving a good outfall for the drainage waters 

 to the sea; that by excluding the tidal waters, the channel of the rivers 

 would sufler, in pruportiou to the quantity of water which was thus ab- 

 stracted from them, and that thus iu time Ihey would become incapable of 

 effectually discharging the drainage waters ; that the outfalls of the rivers 

 would also suffer in the same proportion, and then the marsh-land districts, 

 depending upon them for their drainage, would revert to their former in- 

 efhcient slate, and so it happeued with the Bedford Level. The mouth of 

 the channel of the River Ouse, which is the chief outfall for the drainage 

 of the district where the Bedford Level is situated, being deprived of its 

 accustomed and natural scouring power of tidal water, became so obstructed 

 by shoals that the land waters could uot pass off to the sea. In proportion 

 as the drainage became defective in process of time, as it necessarily did 

 under the system adopted, windmills were erected to work scoop-wheels, 

 with a lift of 4 or 5 feet, fur raising the water out of the lateral canals into 

 the river. In 1713, Denver Sluice was undermined and blown up by the 

 floods, and the tide recovered, to a certain extent, its ancient receptacles, 

 and if proper measures had then been adopted, both the draiuage and the 

 navigation would have been restored to an efficient state ; but the sluice 

 was rebuilt after a few years on the old system, and the drainage and navi- 

 gation became deteriorated as before. During the past century the drain- 

 age of the Bedford Level, as well as other districts, has been submitted to, 

 and has occupied in succession the attention of the ablest engineers of the 

 day ; among whom may be mentioned the names of Perry, Elsfobb, 

 Grundy, Golborne, Armstrong, Kiuderly, Smeatun, Jessop, Chapman, 

 Page, Robert and William iMylne, Huddart, Rennie, Telford, Walker, G. 

 and J. Rennie, Cubilt, Rendel, and others. 



Amongst the most remarkable operations of this nature, may be men- 

 tioned the works upon the river Ouse, for the purpose of improving the 

 draiuage and navigation, which had become seriously affected by the ac- 

 cumulation of sands at its mouth, and the abstraction of the tidal waters 

 above-mentioned. The principal defect existed immediately above the 

 town of Lynn, where the river look an extraordinary bend almost at right 

 angles lo its general course, for a length of 5J miles, forming almost a 

 semicircle, the diameter of which was only 2| miles ; independently, more- 

 over, of this circuitous course by which so much fall or inclination of the 

 current was lost, the channel was so irregular and disproportionate in 

 width, and so much encumbered with shifting sands, that the tidal and 

 fresh waters were unable to force their way through them ; thus the drain- 

 age waters were penned up above, and being unable to get off, formed a 

 tranquil pool, which during floods frequently broke the banks and inundated 

 the surrounding country, the channel, moreover, being deprived of ils na- 

 tural scour, silted up in the same proportion. In order to obviate this 

 great and growing evil, the ablest engineers of the day were consulted, and 

 they unanimously concurred in the opinion, that the only sure means of 

 providing a remedy was to cut off the bend in the Ouse, by making the 

 shortest channel between its two extremities. This plan was first proposed 

 by Bridgemau, in the year 1724, and was subsequently recoinmeuded by 

 the various engineers of the day who succeeded him. In the year 17t)2, 

 an Act was passed, after great opposition, empowering a certain body of 

 Commissioners to carry info efi'ect this cut, w hicii was called the Eau Brink 

 Cut, the expenses of which, estimated at about 80,000/., were lo be de- 

 fraje-d by a tax of 4d. per acre on the middle and south levels of the Bed- 

 ford Level, comprising about 300,000 acres of land drained by the Ouse. 

 This great work was to have been carried intoetl'ect by Robert iMylne and 

 Sir Thomas Hyde Page; but they disagreed as to the proper form and 

 dimensions of the cut, and referred the matter to Captain Huddart, who 

 decided between them ; so much money, however, had been spent in litiga- 

 tion, that the lax which was levied lo pay for its execution was exhausted. 

 In 1817, another Act of Parliament was obtained, empowering certain 

 Commissioners lo raise additional and increased funds from the lauds 

 which it was supposed would be benefitled by it, and the execution of the 

 work with ils branches was inlrusled to the late Mr. Rennie, as the pritt- 

 cipal engineer. The Eau Brink Cut, which was executed according to 

 the award of Huddart, and the works connected vvilh it, were finished and 

 opened on the Jt)th of July, 1821, and very beneficial eflecis, as had been 

 anticipated, immediately followed ; the extraordinary wet winter of 1821 

 which succeeded, proved its success beyond doubt, for soon after Ihe cut 

 was opened the low water line in the Ouse, immediately above it, fell five 



11* 



