A book of bridges

by Walter Shaw Sparrow

One remarkable thing was the fussy interest that their projects excited. During the eighteenth century, for instance, a ridiculous ado was made about bridge-building. Voluntary guidance came from mathematicians, and chatter and hesitation implied that at last, for the first time in the history of the world, a reputable bridge would be erected. As for the results of all this flutter and fuss, they were usually out of joint with the public interests that bridges ought to have served efficiently. No attention was paid to military defence, and some famous men blundered like amateurs. Perronet was regarded as the most expert bridge-builder of his time; his knowledge was prodigious, and yet he made astounding mistakes, which would have shamed such mediæval masters as Bénézet and Isembert. As an example I will mention his Pont de Neuilly-sur-Seine, which was finished in 1772.[137] The delicate operation of striking the centres, by freeing the arches from their supports, was begun only eighteen days after the keystones were put in their places, when the mortar was not yet hard enough to resist new pressure. In one great arch the crown sank twenty-three inches—truly a historic mishap, and for several reasons. The upper part of this arch in Perronet’s plan was an arc of a circle 320 ft. in diameter; after the mishap it became an arc of a circle whose diameter would be 518 ft., hence a stone arch of this size—518 ft. on the chord line—might be constructed! No wonder that writers have been astounded by the Pont de Neuilly-sur-Seine, for it passed safely through a most dangerous experience. Perronet was saved, not by his good design, nor by his mathematical calculations, but by a rare stroke of good luck. Indeed, there are a good many technical faults in his work at Neuilly. The piers are only fourteen feet broad, too small to be in scale with the wide arches, and all lateral pressure travels along the bridge to the abutments. If one arch were cut the others would be endangered. In later years Perronet became wise, and told the French Government that two or three arches in every long bridge should have abutment piers, as a safeguard against mishaps in war.[138]

Several famous engineers had to learn by experience, like Perronet, that a self-conscious desire to be “scientific” had dangers of its own in bridge-building. Smeaton’s bridge over the Tyne at Hexham was a tragic failure; Labelye produced a very perishable bridge on the Thames at Westminster; and learned engineering did not save the Tay Bridge from catastrophe, though science welcomed it with a din of confident approval.

The Tay Bridge was a railway track to connect the town of Dundee and the North British Railway System in Fife; it crossed the Firth of Tay about a mile and a half to the West of Dundee. Its length exceeded two miles, and journalists with rapture bragged about it as the longest iron bridge in the world. Even the responsible engineers, Thomas Bouch and A. D. Stewart, did not keep their heads while their work was being done, for they published in the “Encyclopædia Britannica” a long article on their unfinished bridge—a fine example of modern vanity. Soon afterwards, on February 4th, 1877, the building work was badly injured by a gale, yet in a few months—on September 25th, in fact—the over-confident engineers had the bridge tested from end to end, and on the 31st of May, 1878, it was opened to train service.

Thomas Bouch became Sir Thomas. No one suspected that a “scientific bridge” might be a trap for railway carriages. The structure was superlatively modern: huge, ugly, vulgar, meretricious, mechanical, and charmed also with a small cost of production, which included twenty human lives and £350,000. At this price, you will understand, the longest metal bridge in the world seemed very cheap and fascinating. Newspapers were overjoyed, of course, and declared that the Tay Bridge was admirably fitted for the rushing enterprise of a commercial time. Yet every part of it was ill with the cancer of cheapness, and in 1879 the disaster came, on a Sunday evening, three days after Christmas. At about seven o’clock a terrific gale struck the eighty-four spans of the bridge, making a gap of about three thousand feet: and a few minutes later a North British mail-train drew near. Into the gap carriage after carriage dived: about eighty passengers perished, down below in the raging waters. It was a lofty bridge, in some places 92 ft. above high tide, so the falling carriages turned more than one somersault before they plunged into the Firth of Tay.

The Board of Trade held an enquiry and issued a report, affirming “that the bridge had been badly designed, badly constructed, and badly maintained.” True: but the verdict was without pity. Some excuse should have been made for the engineers’ modernity. The Tay Bridge was no worse than the popular spirit that liked screaming newspapers, and fevered excitements, and wild adventures in the quicksands of jerried workmanship. The Board of Trade published its report on the 3rd of July, 1880; and a few months later, on October 30th, Sir Thomas Bouch died of a broken heart. Perhaps the most humbling trial in his adversity was the foolish article written by his second in command, Mr. A. D. Stewart, who wanted to be quite contemporary with the flying minutes. The “Encyclopædia Britannica” deleted the article from its next edition, and printed ... some tame remarks on the disaster....

No public calamity has much effect on the modern mind. Tay Bridges and Titanics are like strong acts in a tragic play, whose influence we forget very soon. It is a thousand pities, for the next war may teach us, by frequent disasters, that machine-worship has been a mad gambler everywhere. Bridges suffered much from the priggishness of the Renaissance, but they have suffered infinitely more from the obsessions that ruined Sir Thomas Bouch. Poor Bouch! Not only did he wish to astonish the world by constructing an unparalleled bridge, wonderfully long, curved at both ends, and with a varying gradient. He desired also to prove to his employers that he could be a pattern of unusual economy. Worse still, he was so wrapped up in his calculations that he looked upon Nature with little respect. In other words, he tried to achieve “a great feat of engineering”—not often a fortunate enterprise.

From the founding of his piers he ought to have learnt that his work would be endangered partly by the repercussion of railway traffic, and partly by the varied way in which the piers would feel the scour of tidal waters during bad weather. Fourteen piers on the southern side were built on rock, then for six piers the bed was a layer of hard material resting on silt, and from the twenty-second pier northward there was sand, with occasional beds of gravel mixed with boulders. Here was a site to inspire as much awed patience and care as the Bridge Friars gave untiringly to the Pont Saint-Esprit over the Rhône. Yet in Mr. Stewart’s description there is but one emotion—a quiet self-confidence, as if the forces of Nature were as easy to manage as well-trained poodle dogs.

II

To be brief, it is evident that the bridge-building of modern times—from the Renaissance to our own day—has been nothing more than a long series of experiments from which a good many important matters have been excluded. High artistic qualities were divorced from military forethought by the earlier pontists of the Renaissance;[139] then came the delicate swagger of a fidgety dilettantism, like that which built the Palladian Bridge in Prior Park, about A.D. 1750; afterwards, by degrees, the industrial spirit began to assert itself; and in 1779 the first metal bridge was built in Europe. How different the history would have been, how much saner and finer, if bridge-builders had taken for their guide the all-sufficient principle that their work must be self-protective, not vulnerable and defenceless. From this principle the most wonderful varied work could have been evolved, generation after generation. By this time there would have been as much difference between an Elizabethan bridge and a modern stone bridge, as between Drake’s “Golden Hind” and a super-Dreadnought. But the sedulous ape has been active everywhere; and Europe to this day is proud when she builds in stone a few bridges that seem to be as good as their classic foreparents, though they break away from the classic principle of self-defence.

It is in metal bridges alone that we find a virile growth, a genuine evolution; not often artistic, and as sensitive to bombs as card castles are to a touch from your finger; but yet a great evolution because it represents modern times. If we could summon to earth the spirits of the greatest bridge-builders—Caius Julius Lacer, Apollodorus of Damascus, Isembert, Bénézet, Ammanati, and several others—they would learn nothing much from our stonework, whereas a metal bridge here and there could not fail to strike awe into these spiritual beholders. Even Lacer would be awed by the colossal newness of the Forth Bridge, whose technical inspiration might have come from Vulcan, the god of furnaces, after his annual festival on the 23rd of August. And cannot you imagine what Bénézet and Isembert would say to each other, in swift, excited French, when they gazed up and up at the airy film of road suspended over the wide Menai Straits? This would be enough to convince them that a few recent bridge-builders had forsaken ancient forms in order to give expression to generative ideas.