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James Dredge (1794-1863), brewer and bridge designer.
1794 Born in Spring, 1794, in Great Corsley, Wiltshire, the son of William Dredge (1764-1849) and his wife Sarah Barber (1760- )
1820 May 13th. Married at Trowbridge to Ann Vine.
1821 Birth of son William Dredge at Devizes
By 1822 he had moved with his family to Bath, where he became the owner of the Norfolk Brewery and Malthouse on the Upper Bristol Road.
1826 Birth of daughter Isabella
1831 Birth of daughter Emily
1834 Birth of daughter Louisa
1836 Birth of daughters Ellen
1840 Birth of son James Dredge at Bath
1841 Living at Walcot: Ann Dredge (age c40), Brewer. With her children William Dredge (age c20); Isabella Dredge (age c15); Emily Dredge (age c10); Louisa Dredge (age c7); Ellen Dredge (age c5); James Dredge (age c2). Two servants.
1863 Died in Bath
James Dredge was a brewer, but he came to wider prominence as the inventor of a new type of bridge which could be constructed cheaply and speedily.
The bridges were often referred to as suspension bridges, having chains suspended from the towers, but authoritative sources now refer to the type as a 'double cantilever' bridge. Unlike a suspension bridge, in which the deck is suspended by more or less vertical rods, Dredge's bridges have tie rods which come off the chain (or the towers) at prescribed angles, becoming more acute towards the centre of the span. This induces some compression in the deck, in contrast with a suspension bridge, whose deck is freely suspended from the chains, with no end support from the towers. In theory, if the bridge were to be cut through the middle, we would have two decks cantilevered from the towers. However, the theory depends on a number of idealised assumptions. In practice, the distribution of loads in the various members is complex, and 'tuning' the stays in an effort to share the load must have been a frustrating business.
A mathematical analysis of the bridge design was published in 1841 . The author's preface explained its purpose by stating that James Macneill proposed addressing the principles in the following way:-
'To trace the principle which induced Mr. Dredge to adopt the tapering chain and the oblique suspending rods, and to prove mathematically, that the principle thus adopted is strictly in accordance with the maxims of accurate mechanics.'
It is not clear to what extent Dredge was a bridge builder. Also, for some of the bridges designed on 'Mr. Dredge's principles' he may have had little or no involvement.
Some sources state that 50 Dredge bridges were built. A recent thorough study identified 36 examples of Dredge bridges known to have been started or completed, of which 7 survive in one form or another. Known survivors are listed below, in chronological order.
Victoria Bridge, Bath. 150 ft span. Built 1836. Extensively refurbished and reopened in 2015
Glenarb Bridge, River Blackwater, Caledon, Northern Ireland. Built 1844. Dismantled, moved and re-erected in 1990, back in service.
Caledon Estate Bridge, River Blackwater, Caledon, NI, built 1845.
Stowell Park Footbridge, Pewsey, Wiltshire, built 1845. In private use.
Second Moyola Park Bridge, Castledawson, NI, 1847. In place but closed due to poor condition
Bridge of Oich, or Aberchalder Bridge, River Oich, Fort Augustus. Built 1854. Restored 1997
Ness Islands Footbridges One of two has survived, in a new location, with a strengthened deck.
SOME LOST BRIDGES:-
Victoria Bridge, A830, Lochybridge, Fort William. Replaced.
Five small bridges in Regent's Park, London. One fell when only 10 or 12 boys were playing on it. Another, anchored in soapy clay, collapsed during heavy rain, but it was repaired for just £50. Another lasted only 20 years before it was replaced 
Balloch Ferry Bridge, built before 1841 for Sir James Colquhoun. Length of 'suspended roadway 292 ft., span between centre of towers 200 ft..
Queen's Park Bridge (Chester). Built 1850, replaced in 1923.
Welshmill Bridge, Frome. Built in 1842 for solicitor Henry Miller of Welshmill House. Span 51ft, width 7ft 3". Demolished at the start of the Second Wold War.
Several bridges in India, including Ballee Khâl, also known as Kubbuduk Bridge, with a variety of spellings, designed by Captain Goodwyn.
It was intended to construct a bridge for a carriage drive at Sir Bruce Chichester's Arlington Court in Devon. For some reason, only the masonry towers were built. These have survived. A sketch by William Dredge, dated 1849,m is displayed in the reception hall of Arlington Court.
1837 Advertisement: 'MATHEMATICAL SUSPENSION CHAIN. To Noblemen, Gentlemen, and Others, interested in Railways, Viaducts, Bridges, Chain Piers, &c. &c.
DREDGE'S IMPROVED PATENT
Mechanical Suspension Chain is offered to the notice of the above.
It possesses the advantage of economy, combined with power, upon any scale,to an almost unlimited extent. The security of its construction prevents longitudinal and lateral vibration; and, compared with large structures on the old principle, only one-twentieth part the Iron is required!!! The strain on the centre of the Menai Bridge, caused by its own weight, is upwards of 2000 Tons; which ponderous weight this improved principle entirely prevents.
The Invention is founded on the unerring principle of nature; and, beyond a doubt, will be of the greatest National importance.
Every information may be obtained by applying personally or by letter, post paid, addressed to the Patentee, JAMES DREDGE, Brewer, Bath.' 
1849 'TO SOLD BY AUCTION, By Mr. EDMUND COLES, (By order of the Weston-super-Mare Pier Company, and the Assignees of James Dredge, Bankrupt), at the PREMISES of the said Companv, at WESTON-SUPER-MARE aforesaid, on TUESDAY, the 30th day of January, 1849, at One o’Clock in the Afternoon, either together in such Lots as shall be agreed on at the time of Sale,
A QUANTITY of IRON-WORK, TIMBER, STONE, and MATERIALS, intended to have been used in the Erection of the Weston-super-Mare Pier Bridge: consisting of from to 50 to 70 Tons of Wrought and Cast-Iron, in short lengths, from 2 feet to 9 feet, principally round bolt Iron,from 3/8 to 1¼ in diameter, with about 10 Tons of Bolts, Screws, and Nuts; 4 Tons Cast-Iron and 8 Cwts. of Chain; a quantity of Timber, Foreign Poles, of good lengths ; Ropes and Barrows; 4 Smiths’ Bellows; 5 Anvils and Tools; Vices; Iron and Wood Blocks; Navigators' Tools, &c., &c. The whole of the above can seen at any time prior to the Sale.
Also a certain Patent granted to the said Bankrupt for certain Improvements in the Construction of Suspension Chains for Bridges, Viaducts. Aqueducts, and other purposes, and in the Construction of certain Bridges, Viaducts, or Aqueducts. Applications to be made to....'
1851 'TO THE EDITOR OF THE INVERNESS COURIER.
Aberchalder, 5th September 1851.
Sir, —Mr James Dredge of Bath having recently provided us with excellent suspension bridges over the rivers Lochy and Oich, at a very moderate expense, I trust you will, in justice to him, give the following quotation from a communication I lately had from him a place in your valuable columns. He wrote in reference to one of his bridges which had given way, and said — "The report of the failure of the Dredgeian bridge across the Loch-Lomond, which found its way into the papers some months ago, was incorrect. The fact of the case was simply this:—The centre links of one of the main chains broke, in consequence of a flaw in the iron, and the unnecessary use of any centre links. But, notwithstanding, the traffic was continued; and, without interrupting it, I have removed those links, and repaired the bridge; and thus rendered it one of the most substantial and inflexible suspension bridges in the kingdom. This was the second large bridge erected under the patent of 1841, and it is the only instance of fracture that has occurred in all the bridges I have put up. It is seldom an approximation to truth is arrived at in the first or second attempt of carrying out anything important in mechanics (for example, the steam-engine and hydraulic press), whilst often from the smallest accident springs the most useful discovery. The accident in this instance was of so trivial a nature that it did not even alarm the passers upon the bridge when the links broke; but had it been on the old vertical system, as that of Menai, Montrose, and Hungerford bridges, like the Yarmouth catastrophe, a total destruction of the bridge and great loss of life would have been inevitable."—Yours truly, P. R. Latham.'
1852 Advertisement: 'IRON BRIDGES AND PIERS. DREDGE'S PATENT TENSION PRINCIPLE has been established 16 years, and one-half of the Suspension Bridges the Kingdom have been erected Mr Dredge. It is proved to combine every valuable element in BRIDGE ARCHITECTURE; hence its applicability to Bridges for all purposes and its security are indisputable. The principle will effect much longer Spans, and its average cost is only one-tenth of that of any other mode of construction. On such a Bridge as the Britannia Tube it would save £500,000. Mr Dredge will join in the erection of Toll Bridges of any dimensions, and guarantee them. For particulars apply to James Dredge, Inventor and Patentee, Bath.'
1855 'IRON BRIDGES—THE MAIN CAUSE OF THEIR DESTRUCTION.
TO THE EDITOR, THE INVERNESS COURIER.
Sir, —In reference to the late catastrophe at Bristol, and as your town is much interested in the subject of bridges, I send you the following remarks, which may amuse or inform your readers. The Bristol Bridge had been erected 46 years ago, but at its first opening met with the same misfortune as recently, and has thus given rise to conjecture to the real cause of such accidents. In common with others I have ventured on an opinion on the subject, and the more readily because the Bedminster Bridge is an iron structure of the same dimensions, and on the same principle as that recently destroyed, and the public are consequently very uneasy for its safety. And there are good grounds for uneasiness, for the cause that destroyed the one will sooner or later destroy the other also. It was quite a chance that the Bristol Bridge fell first. I publicly foretold the event eighteen years ago, and a gentleman, Mr Tunstall, has just told me that he remembers how, whilst were passing over this identical bridge sixteen years ago, I pointed out to him the inherent fault in the principle the structure which would one day cause its destruction. In 1840 the late Lord Westerne clearly explained to Lord Melbourne that bridges erected on the parallel principle contained the elements of self-destruction, and that these increased as the bridge increased in length. But his lordship's admonition has been little regarded. Time, however, and repeated accidents, will force the conviction that there is something fundamentally wrong these bridges. To me the parallel principle appears to antagonistic to every known law in natural mechanics, while the principle laid down by Lord Westerne, in 1840, is in strict accordance with the universal law of nature. ....... At the time Lord Westerne so strenuously advocated the taper principle, as it had been applied in one instance, in the Victoria Bridge over the Avon, Bath; and since then across the following rivers with success— namely, the Lochy, Oich, Ness, Leven, Clyde, Dee, Wye, Lee, Severn, Black water, Baner, Mayola, Frome, Avon in Wiltshire, besides numerous other rivers and canals at home and abroad, in some instances two and three on the same river—there are five in the Regent's Park on this principle. The Taper Suspension Bridge was patented in 1836, and the Taper Compression Bridge was registered in 1847, but both rights are now expired, therefore, the inventions are become the property of the public, and they are not unworthy of their most serious consideration and attention — I am, Sir, your obedient Servant, James Dredge.' 
1862 'Dredge's Bridges at the Islands.— These elegant and substantial bridges have attracted the attention of many persons in the north, on the outlook for cheap and serviceable works of the kind combined with a wide and clear span. There is some talk of erecting one of them across the Nairn near Cawdor, and the Elgin Courier suggests them as suitable for the Lossie bridges at Morriston Ford and Marywell, which are falling into disrepair. The Island bridges, we may mention, were erected in 1853-54, by James Dredge, Esq., C.E., of Bath. They consist of two iron suspension bridges across the Ness, and a small bridge over the mill-lead of the Water Company. The total sum paid for the three was £337. 10s. 10d. Except for the cost of painting and screwing up annually, and a pound note spent in 1860 in repairing one of the buttresses which had suffered from a very heavy spate, these bridges have not put Inverness to any expense whatever for their maintenance.'
1863 'Mr. James Dredge. —The death of this gentleman, long known as the inventor of the suspension bridge system, which bears his name, recently occurred at his residence, Gothic Cottage, Sion Hill, Bath, after long illness. Mr. Dredge has left in his bridges a proved theory of great public good whenever the public shall be wise enough to avail themselves of it. It is the least costly and the strongest of all bridges built on the suspension principle. That over the Avon in this city has suffered all kinds of traffic, and the tramp of the Militia, for upwards we believe, of a quarter of century, and its capability and durability are placed beyond doubt. It is Macadamised like a public road, with equal depth and weight, and any one who can appreciate the comparative strength and stress of iron in the horizontal and vertical directions, will see how so aerial structure should so greatly exceed in power of resistance the clumsy and costly ones generally adopted, whose central weights, instead of giving strength, tend only to their destruction. Mr. Dredge leaves behind him a name that will be honoured by future generations; such will be the reward of his life of unrewarded labour. He has contended in vain against intrests and prejudices, but the sound mathematical principles of his bridge, and its adaptation for cheap structures for every variety of purpose, from that of crossing a rivulet to the magnificent spans of broad streams cannot fail, ultimately, to gain for his invention an ascendancy over all others. Mr. Dredge will leave behind him enduring remembrances of his perseverance, patient endurance, inflexible integrity, and social virtues.'
1935 'BUILDER OF BRIDGES. BATH ENGINEER OF OVER A CENTURY AGO
The work of a celebrated Bath engineer of over a century ago, James Dredge, was referred to in considerable detail by Mr. J. S. Wilson, M.I.C.E., in his presidential address to the last meeting of the Engineering Section of the British Association. Dredge, who lived at Bath, was interested in the construction of suspension bridges, and introduced a supposed improvement on constructional methods previously in use.
In 1836 Dredge was granted a patent for a taper chain bridge, and his first structure was built in the same year across the Avon in this city. The name "Dredge" still appears on the ironwork, and it is often referred to in old plans by the name of its inventor. It is more generally known as the Victoria Bridge, and is now scheduled for replacement by the City Engineer's department. Dredge attended the Newcastle meeting of the British Association in 1838, and read a paper on his bridges and "Mathematical Principle" to the Mechanical Section.
Five bridges on Dredge's system were constructed in Regent's Park, London, four in Wiltshire, and a number in India. The failures of the system began in that country. A bridge of 200 ft. span collapsed before it was completed, and another one failed to carry its proof load and collapsed also. A paper published in 1849, in which the failure of these bridges is referred to, states that seven bridges in India had had to re-modelled by engineers there on an "improved principle." One of the early suspension bridges still in use, said Mr. Wilson, is that across the Thames at Marlow, built by W. Tierney Clark, F.R.S., in 1829. I examined and reported on this bridge some years ago, and found it in a remarkably good state. Tierney Clark was the engineer of our own North Parade Bridge, which is now nearly a century old.'