But much of his labour was heavy hackwork of a very uninteresting character. During the sittings of the committees of Parliament, almost every moment of his time was occupied in consultations, and in preparing evidence or in giving it. The crowded, low-roofed committee-rooms of the old Houses of Parliament were altogether inadequate to accommodate the rush of perspiring projectors of bills, and even the lobbies were sometimes choked with them. To have borne that noisome atmosphere and heat would have tested the const.i.tutions of salamanders, and engineers were only human. With brains kept in a state of excitement during the entire day, no wonder their nervous systems became unstrung. Their only chance of refreshment was during an occasional rush to the bun and sandwich stand in the lobby, though sometimes even that resource failed them. Then, with mind and body jaded-probably after undergoing a series of consultations upon many bills after the rising of the committees-the exhausted engineers would seek to stimulate nature by a late, perhaps a heavy, dinner. What chance had any ordinary const.i.tution of surviving such an ordeal? The consequence was, that stomach, brain, and liver were alike irretrievably injured; and hence the men who bore the brunt of those struggles-Stephenson, Brunel, Locke, and Errington-have already all died, comparatively young men.
In mentioning the name of Brunel, we are reminded of him as the princ.i.p.al rival and compet.i.tor of Robert Stephenson. Both were the sons of distinguished men, and both inherited the fame and followed in the footsteps of their fathers. The Stephensons were inventive, practical, and sagacious; the Brunels ingenious, imaginative, and daring. The former were as thoroughly English in their characteristics as the latter were perhaps as thoroughly French. The fathers and the sons were alike successful in their works, though not in the same degree. Measured by practical and profitable results, the Stephensons were unquestionably the safer men to follow.
Robert Stephenson and Isambard Kingdom Brunel were destined often to come into collision in the course of their professional life. Their respective railway districts "marched" with each other, and it became their business to invade or defend those districts, according as the policy of their respective boards might direct. The gauge of 7 feet fixed by Mr. Brunel for the Great Western Railway, so entirely different from that of 4ft. 8in. adopted by the Stephensons on the Northern and Midland lines, was from the first a great cause of contention. But Mr.
Brunel had always an aversion to follow any man"s lead; and that another engineer had fixed the gauge of a railway, or built a bridge, or designed an engine, in one way, was of itself often a sufficient reason with him for adopting an altogether different course. Robert Stephenson, on his part, though less bold, was more practical, preferring to follow the old routes, and to tread in the safe steps of his father.
Mr. Brunel, however, determined that the Great Western should be a giant"s road, and that travelling should be conducted upon it at double speed. His ambition was to make the _best_ road that imagination could devise; whereas the main object of the Stephensons, both father and son, was to make a road that would _pay_. Although, tried by the Stephenson test, Brunel"s magnificent road was a failure so far as the shareholders in the Great Western Company were concerned, the stimulus which his ambitious designs gave to mechanical invention at the time proved a general good. The narrow-gauge engineers exerted themselves to quicken their locomotives to the utmost. They improved and re-improved them; the machinery was simplified and perfected; outside cylinders gave place to inside; the steadier and more rapid and effective action of the engine was secured; and in a few years the highest speed on the narrow-gauge lines went up from 30 to about 50 miles an hour. For this rapidity of progress we are in no small degree indebted to the stimulus imparted to the narrow-gauge engineers by Mr. Brunel. And it is well for a country that it should possess men such as he, ready to dare the untried, and to venture boldly into new paths. Individuals may suffer from the cost of the experiments; but the nation, which is an aggregate of individuals, gains, and so does the world at large.
It was one of the characteristics of Brunel to believe in the success of the schemes for which he was professionally engaged as engineer; and he proved this by investing his savings largely in the Great Western Railway, in the South Devon atmospheric line, and in the Great Eastern steamship, with what results are well known. Robert Stephenson, on the contrary, with characteristic caution, towards the latter years of his life avoided holding unguaranteed railway shares; and though he might execute magnificent structures, such as the Victoria Bridge across the St. Lawrence, he was careful not to embark any portion of his own fortune in the ordinary capital of these concerns. In 1845, he shrewdly foresaw the inevitable crash that was about to follow the mania of that year; and while shares were still at a premium he took the opportunity of selling out all that he had. He urged his father to do the same thing, but George"s reply was characteristic. "No," said he; "I took my shares for an investment, and not to speculate with, and I am not going to sell them now because folks have gone mad about railways." The consequence was, that he continued to hold the 60,000 which he had invested in the shares of various railways until his death, when they were at once sold out by his son, though at a great depreciation on their original cost.
One of the hardest battles fought between the Stephensons and Brunel was for the railway between Newcastle and Berwick, forming part of the great East Coast route to Scotland. As early as 1836, George Stephenson had surveyed two lines to connect Edinburgh with Newcastle: one by Berwick and Dunbar along the coast, and the other, more inland, by Carter Fell, up the vale of the Gala, to the northern capital; but both projects lay dormant for several years longer, until the completion of the Midland and other main lines as far north as Newcastle, had the effect of again reviving the subject of the extension of the route as far as Edinburgh.
On the 18th of June, 1844, the Newcastle and Darlington line-an important link of the great main highway to the north-was completed and publicly opened, thus connecting the Thames and the Tyne by a continuous line of railway. On that day the Stephensons, with a distinguished party of railway men, travelled by express train from London to Newcastle in about nine hours. It was a great event, and was worthily celebrated. The population of Newcastle held holiday; and a banquet given in the a.s.sembly Rooms the same evening a.s.sumed the form of an ovation to George Stephenson and his son. Thirty years before, in the capacity of a workman, he had been labouring at the construction of his first locomotive in the immediate neighbourhood. By slow and laborious steps he had worked his way on, dragging the locomotive into notice, and raising himself in public estimation; until at length he had victoriously established the railway system, and went back amongst his townsmen to receive their greeting.
After the opening of this railway, the project of the East Coast line from Newcastle to Berwick was revived; and George Stephenson, who had already identified himself with the question, and was intimately acquainted with every foot of the ground, was called upon to a.s.sist the promoters with his judgment and experience. He again recommended as strongly as before the line he had previously surveyed; and on its being adopted by the local committee, the necessary steps were taken to have the scheme brought before Parliament in the ensuing session. The East Coast line was not, however, to be allowed to pa.s.s without a fight. On the contrary, it had to encounter as stout an opposition as the Stephensons had ever experienced.
We have already stated that about this time the plan of subst.i.tuting atmospheric pressure for locomotive steam-power in the working of railways, had become very popular. Many eminent engineers supported the atmospheric system, and a strong party in Parliament, headed by the Prime Minister, were greatly disposed in its favour. Mr. Brunel warmly espoused the atmospheric principle, and his persuasive manner, as well as his admitted scientific ability, unquestionably exercised considerable influence in determining the views of many leading members of both Houses. Amongst others, Lord Howick, one of the members for Northumberland, adopted the new principle, and, possessing great local influence, he succeeded in forming a powerful confederacy of the landed gentry in favour of Brunel"s atmospheric railway through that county.
George Stephenson could not brook the idea of seeing the locomotive, for which he had fought so many stout battles, pushed to one side, and that in the very county in which its great powers had been first developed.
Nor did he relish the appearance of Mr. Brunel as the engineer of Lord Howick"s scheme, in opposition to the line which had occupied his thoughts and been the object of his strenuous advocacy for so many years.
When Stephenson first met Brunel in Newcastle, he good-naturedly shook him by the collar, and asked "What business he had north of the Tyne?"
George gave him to understand that they were to have a fair stand-up fight for the ground, and, shaking hands before the battle like Englishmen, they parted in good humour. A public meeting was held at Newcastle in the following December, when, after a full discussion of the merits of the respective plans, Stephenson"s line was almost unanimously adopted as the best.
The rival projects went before Parliament in 1845, and a severe contest ensued. The display of ability and tactics on both sides was great.
Robert Stephenson was examined at great length as to the merits of the locomotive line, and Brunel at equally great length as to the merits of the atmospheric system. Mr. Brunel, in his evidence, said that after numerous experiments, he had arrived at the conclusion that the mechanical contrivance of the atmospheric system was perfectly applicable, and he believed that it would likewise be more economical in most cases than locomotive power. "In short," said he, "rapidity, comfort, safety, and economy, are its chief recommendations."
But the locomotive again triumphed. The Stephenson Coast Line secured the approval of Parliament; and the shareholders in the Atmospheric Company were happily prevented investing their capital in what would unquestionably have proved a gigantic blunder. For, less than three years later, the whole of the atmospheric tubes which had been laid down on other lines were pulled up and the materials sold-including Mr.
Brunel"s immense tube on the South Devon Railway-to make way for the working of the locomotive engine. George Stephenson"s first verdict of "It won"t do," was thus conclusively confirmed.
Robert Stephenson used afterwards to describe with great gusto an interview which took place between Lord Howick and his father, at his office in Great George Street, during the progress of the bill in Parliament. His father was in the outer office, where he used to spend a good deal of his spare time; occasionally taking a quiet wrestle with a friend when nothing else was stirring. {309} On the day in question, George was standing with his back to the fire, when Lord Howick called to see Robert. Oh! thought George, he has come to try and talk Robert over about that atmospheric gimcrack; but I"ll tackle his Lordship. "Come in, my Lord," said he, "Robert"s busy; but I"ll answer your purpose quite as well; sit down here, if you please." George began, "Now, my Lord, I know very well what you have come about: it"s that atmospheric line in the north; I will show you in less than five minutes that it can never answer." "If Mr. Robert Stephenson is not at liberty, I can call again,"
said his Lordship. "He"s certainly occupied on important business just at present," was George"s answer; "but I can tell you far better than he can what nonsense the atmospheric system is: Robert"s good-natured, you see, and if your Lordship were to get alongside of him you might talk him over; so you have been quite lucky in meeting with me. Now, just look at the question of expense,"-and then he proceeded in his strong Doric to explain his views in detail, until Lord Howick could stand it no longer, and he rose and walked towards the door. George followed him down stairs, to finish his demolition of the atmospheric system, and his parting words were, "You may take my word for it, my Lord, it will never answer." George afterwards told his son with glee of "the settler" he had given Lord Howick.
So closely were the Stephensons identified with this measure, and so great was the personal interest which they were both known to take in its success, that, on the news of the triumph of the bill reaching Newcastle, a sort of general holiday took place, and the workmen belonging to the Stephenson Locomotive Factory, upwards of 800 in number, walked in procession through the princ.i.p.al streets of the town, accompanied with music and banners.
It is unnecessary to enter into any description of the works on the Newcastle and Berwick Railway. There are no fewer than 110 bridges of all sorts on the line-some under and some over it. But by far the most formidable piece of masonry work on this railway is at its northern extremity, where it pa.s.ses across the Tweed into Scotland, immediately opposite the formerly redoubtable castle of Berwick. Not many centuries had pa.s.sed since the district amidst which this bridge stands was the scene of almost constant warfare. Berwick was regarded as the key of Scotland, and was fiercely fought for, sometimes held by a Scotch and sometimes by an English garrison. Though strongly fortified, it was repeatedly taken by a.s.sault. On its capture by Edward I., Boetius says 17,000 persons were slain, so that its streets "ran with blood like a river." Within sight of the ramparts, a little to the west, is Halidon Hill, where a famous victory was gained by Edward III., over the Scottish army under Douglas; and there is scarcely a foot of ground in the neighbourhood but has been the scene of contention in days long past. In the reigns of James I. and Charles I., a bridge of 15 arches was built across the Tweed at Berwick; and in our own day a railway-bridge of 28 arches has been built a little above the old one, but at a much higher level. The bridge built by the Kings, out of the national resources, cost 15,000, and occupied 24 years and 4 months in the building; the bridge built by the Railway Company, with funds drawn from private resources, cost 120,000, and was finished in 3 years and 4 months from the day of laying the foundation-stone.
[Picture: The Royal Border Bridge, Berwick-upon-Tweed]
This important viaduct, built after the design of Robert Stephenson, consists of a series of 28 semicircular arches, each 61 feet 6 inches in span, the greatest height above the bed of the river being 126 feet. The whole is built of ashlar, with a hearting of rubble; excepting the river parts of the arches, which are constructed with bricks laid in cement.
The total length of the work is 2160 feet. The foundations of the piers were got in by coffer-dams in the ordinary way, Nasmyth"s steam-hammer being extensively used in driving the piles. The bearing piles, from which the foundations of the piers were built up, were each capable of carrying 70 tons.
Another bridge, of still greater importance, necessary to complete the continuity of the East Coast route, was the masterwork erected by Robert Stephenson between the north and south banks of the Tyne at Newcastle, commonly known as the High Level Bridge. Mr. R. W. Brandling, George Stephenson"s early friend, is ent.i.tled to the merit of originating the idea of this bridge as it was eventually carried out, with a central terminus for the northern railways in the Castle Garth. The plan was first promulgated by him in 1841; and in the following year it was resolved that George Stephenson should be consulted as to the most advisable site for the proposed structure. A prospectus of a High Level Bridge Company was issued in 1843, the names of George Stephenson and George Hudson appearing on the committee of management, Robert Stephenson being the consulting engineer. The project was eventually taken up by the Newcastle and Darlington Railway Company, and an Act for the construction of the bridge was obtained in 1845.
The rapid extension of railways had given an extraordinary stimulus to the art of bridge-building; the number of such structures erected in Great Britain alone, since 1830, having been above 25,000, or more than all that had before existed in the country. Instead of the erection a single large bridge const.i.tuting, as formerly, an epoch in engineering, hundreds of extensive bridges of novel design were simultaneously constructed. The necessity which existed for carrying rigid roads, capable of bearing heavy railway trains at high speeds, over extensive gaps free of support, rendered it obvious that the methods which had up to that time been employed for bridging s.p.a.ce were altogether insufficient. The railway engineer could not, like the ordinary road engineer, divert his road and make choice of the best point for crossing a river or a valley. He must take such ground as lay in the line of his railway, be it bog, or mud, or shifting sand. Navigable rivers and crowded thoroughfares had to be crossed without interruption to the existing traffic, sometimes by bridges at right angles to the river or road, sometimes by arches more or less oblique. In many cases great difficulty arose from the limited nature of the headway; but, as the level of the original road must generally be preserved, and that of the railway was in a measure fixed and determined, it was necessary to modify the form and structure of the bridge, in almost every case, in order to comply with the public requirements. Novel conditions were met by fresh inventions, and difficulties of the most unusual character were one after another successfully surmounted. In executing these extraordinary works, iron has been throughout the sheet-anchor of the engineer. In its different forms of cast or wrought iron, it offered a valuable resource, where rapidity of execution, great strength, and cheapness of construction in the first instance, were elements of prime importance; and by its skilful use, the railway architect was enabled to achieve results which thirty years ago would scarcely have been thought possible.
In many of the early cast-iron bridges the old form of the arch was adopted, the stability of the structure depending wholly on compression, the only novel feature being the use of iron instead of stone. But in a large proportion of cases, the arch, with the railroad over it, was found inapplicable in consequence of the limited headway which it provided.
Hence it early occurred to George Stephenson, when constructing the Liverpool and Manchester Railway, to adopt the simple cast-iron beam for the crossing of several roads and ca.n.a.ls along that line-this beam resembling in some measure the lintel of the early temples-the pressure on the abutments being purely vertical. One of the earliest instances of this kind of bridge was that erected over Water Street, Manchester, in 1829; after which, cast-iron girders, with their lower webs considerably larger than their upper, were ordinarily employed where the span was moderate; and wrought-iron tie rods below were added to give increased strength where the span was greater.
The next step was the contrivance of arched beams or bowstring girders, firmly held together by horizontal ties to resist the thrust, instead of abutments. Numerous excellent specimens of this description of bridge were erected by Robert Stephenson on the original London and Birmingham Railway; but by far the grandest work of the kind-perfect as a specimen of modern constructive skill-was the High Level Bridge, which we owe to the genius of the same engineer.
The problem was, to throw a railway bridge across the deep ravine which lies between the towns of Newcastle and Gateshead, at the bottom of which flows the navigable river Tyne. Along and up the sides of the valley-on the Newcastle bank especially-run streets of old-fashioned houses, cl.u.s.tered together in the strange forms peculiar to the older cities.
The ravine is of great depth-so deep and so gloomy-looking towards dusk, that local tradition records that when the Duke of c.u.mberland arrived late in the evening at the brow of the hill overlooking the Tyne, on his way to Culloden, he exclaimed to his attendants, on looking down into the black gorge before him, "For G.o.d"s sake, don"t think of taking me down that coal-pit at this time of night!" The road down the Gateshead High Street is almost as steep as the roof of a house, and up the Newcastle Side, as the street there is called, it is little better. During many centuries the traffic north and south pa.s.sed along this dangerous and difficult route, over the old bridge which crosses the river in the bottom of the valley. For about 30 years the Newcastle Corporation had discussed various methods of improving the communication between the towns; and the discussion might have gone on for 30 years more, but for the advent of railways, when the skill and enterprise to which they gave birth speedily solved the difficulty and bridged the ravine. The local authorities adroitly took advantage of the opportunity, and insisted on the provision of a road for ordinary vehicles and foot pa.s.sengers in addition to the railroad. In this circ.u.mstance originated one of the striking peculiarities of the High Level Bridge, which serves two purposes, being a railway above and a carriage roadway underneath.
The breadth of the river at the point of crossing is 515 feet, but the length of the bridge and viaduct between the Gateshead station and the terminus on the Newcastle side is about 4000 feet. It springs from Pipewell Gate Bank, on the south, directly across to Castle Garth, where, nearly fronting the bridge, stands the fine old Norman keep of the _New_ Castle, now nearly 800 years old, and a little beyond it is the spire of St. Nicholas Church, with its light and graceful Gothic crown; the whole forming a grand architectural group of unusual historic interest. The bridge pa.s.ses completely over the roofs of the houses which fill both sides of the valley; and the extraordinary height of the upper parapet, which is about 130 feet above the bed of the river, offers a prospect to the pa.s.sing traveller the like of which is perhaps nowhere else to be seen. Far below are the queer chares and closes, the wynds and lanes of old Newcastle; the water is crowded with pudgy, black, coal keels; and, when there is a partial dispersion of the great smoke clouds which usually obscure the sky, the funnels of steamers and the masts of shipping may be seen far down the river. The old bridge lies so far beneath that the pa.s.sengers crossing it seem like so many bees pa.s.sing to and fro.
The first difficulty encountered in building the bridge was in securing a solid foundation for the piers. The dimensions of the piles to be driven were so huge, that the engineer found it necessary to employ some extraordinary means for the purpose. He called Nasmyth"s t.i.tanic steam-hammer to his aid-the first occasion, we believe, on which this prodigious power was employed in bridge pile-driving. A temporary staging was erected for the steam-engine and hammer apparatus, which rested on two keels, and, notwithstanding the newness and stiffness of the machinery, the first pile was driven on the 6th October, 1846, to a depth of 32 feet, in four minutes. Two hammers of 30 cwt. each were kept in regular use, making from 60 to 70 strokes a minute; and the results were astounding to those who had been accustomed to the old style of pile-driving by means of the ordinary pile-frame, consisting of slide, ram, and monkey. By the old system, the pile was driven by a comparatively small ma.s.s of iron descending with great velocity from a considerable height-the velocity being in excess and the ma.s.s deficient, and calculated, like the momentum of a cannon-ball, rather for destructive than impulsive action. In the case of the steam pile-driver, on the contrary, the whole weight of a heavy ma.s.s is delivered rapidly upon a driving-block of several tons weight placed directly over the head of the pile, the weight never ceasing, and the blows being repeated at the rate of a blow a second, until the pile is driven home. It is a curious fact, that the rapid strokes of the steam-hammer evolved so much heat, that on many occasions the pile-head burst into flames during the process of driving. The elastic force of steam is the power that lifts the ram, the escape permitting its entire force to fall upon the head of the driving block; while the steam above the piston on the upper part of the cylinder, acting as a buffer or recoil-spring, materially enhances the effect of the downward blow. As soon as one pile was driven, the traveller, hovering overhead, presented another, and down it went into the solid bed of the river, with almost as much ease as a lady sticks pins into a cushion. By the aid of this powerful machine, pile-driving, formerly among the most costly and tedious of engineering operations, became easy, rapid, and comparatively economical.
When the piles had been driven and the coffer-dams formed and puddled, the water within the enclosed s.p.a.ces was pumped out by the aid of powerful engines, so as, if possible, to lay bare the bed of the river.
Considerable difficulty was experienced in getting in the foundations of the middle pier, in consequence of the water forcing itself through the quicksand beneath as fast as it was removed, This fruitless labour went on for months, and many expedients were tried. Chalk was thrown in in large quant.i.ties outside the piling, but without effect. Cement concrete was at last put within the coffer-dam, until it set, and the bottom was then found to be secure. A bed of concrete was laid up to the level of the heads of the piles, the foundation course of stone blocks being commenced about two feet below low water, and the building proceeded without further difficulty. It may serve to give an idea of the magnitude of the work, when we state that 400,000 cubic feet of ashlar, rubble, and concrete were worked up in the piers, and 450,000 cubic feet in the land-arches and approaches.
The most novel feature of the structure is the use of cast and wrought iron in forming the double bridge, which admirably combines the two principles of the arch and suspension; the railway being carried over the back of the ribbed arches in the usual manner, while the carriage-road and footpaths, forming a long gallery or aisle, are suspended from these arches by wrought-iron vertical rods, with horizontal tie-bars to resist the thrust. The suspension-bolts are enclosed within spandril pillars of cast iron, which give great stiffness to the superstructure. This system of longitudinal and vertical bracing has been much admired, for it not only accomplishes the primary object of securing rigidity in the roadway, but at the same time, by its graceful arrangement, heightens the beauty of the structure. The arches consist of four main ribs, disposed in pairs with a clear distance between the two inner arches of 20 feet 4 inches, forming the carriage-road, while between each of the inner and outer ribs there is a s.p.a.ce of 6 feet 2 inches, const.i.tuting the footpaths. Each arch is cast in five separate lengths or segments, strongly bolted together. The ribs spring from horizontal plates of cast iron, bedded and secured on the stone piers. All the ab.u.t.ting joints were carefully executed by machinery, the fitting being of the most perfect kind. In order to provide for the expansion and contraction of the iron arching, and to preserve the equilibrium of the piers without disturbance or racking of the other parts of the bridge, it was arranged that the ribs of every two adjoining arches resting on the same pier should be secured to the springing-plates by keys and joggles; whilst on the next piers on either side, the ribs remained free and were at liberty to expand or contract according to temperature-a s.p.a.ce being left for the purpose. Hence each arch is complete and independent in itself, the piers having simply to sustain their vertical pressure. There are six arches of 125 feet span each; the two approaches to the bridge being formed of cast-iron pillars and bearers in keeping with the arches.
[Picture: High Level Bridge-Elevation of one Arch]
The result is a bridge that for ma.s.sive solidity may be p.r.o.nounced unrivalled. It is perhaps the most magnificent and striking of all the bridges to which railways have given birth, and has been worthily styled "the King of railway structures." It is a monument of the highest engineering skill of our time, with the impress of power grandly stamped upon it. It will also be observed, from the drawing placed as the frontispiece of this book, that the High Level Bridge forms a very fine object in a picture of great interest, full of striking architectural variety and beauty. The bridge was opened on the 15th August, 1849, and a few days after the royal train pa.s.sed over it, halting for a few minutes to enable her Majesty to survey the wonderful scene below. In the course of the following year the Queen opened the extensive stone viaduct across the Tweed, above described, by which the last link was completed of the continuous line of railway between London and Edinburgh.
Over the entrance to the Berwick station, occupying the site of the once redoubtable Border fortress, so often the deadly battle-ground of the ancient Scots and English, was erected an arch under which the royal train pa.s.sed, bearing in large letters of gold the appropriate words, "_The last act of the Union_."
The warders at Berwick no longer look out from the castle walls to descry the glitter of Southron spears. The bell-tower, from which the alarm was sounded of old, though still standing, is deserted; the only bell heard within the precincts of the old castle being the railway porter"s bell announcing the arrival and departure of trains. You see the Scotch express pa.s.s along the bridge and speed southward on the wings of steam.
But no alarm spreads along the border now. Northumbrian beeves are safe.
Chevy-Chase and Otterburn are quiet sheep-pastures. The only men at arms on the battlements of Alnwick Castle are of stone. Bamborough Castle has become an asylum for shipwrecked mariners, and the Norman Keep at Newcastle has been converted into a Museum of Antiquities. The railway has indeed consummated the Union.
CHAPTER XVII.
ROBERT STEPHENSON"S TUBULAR BRIDGES AT MENAI AND CONWAY.
We have now to describe briefly another great undertaking, begun by George Stephenson, and taken up and completed by his son, in the course of which the latter carried out some of his greatest works-we mean the Chester and Holyhead Railway, completing the railway connection with Dublin, as the Newcastle and Berwick line completed the connection with Edinburgh. It will thus be seen how closely Telford was followed by the Stephensons in perfecting the highways of their respective epochs; the former by means of turnpike-roads, and the latter by means of railways.
George Stephenson surveyed a line from Chester to Holyhead in 1838, and at the same time reported on the line through North Wales to Port Dynllaen, proposed by the Irish Railway Commissioners. His advice was strongly in favour of adopting the line to Holyhead, as less costly and presenting better gradients. A public meeting was held at Chester, in January, 1839, in support of the latter measure, at which he was present to give explanations. Mr. Uniacke, the Mayor, in opening the proceedings, said that Mr. Stephenson was present, ready to answer any questions which might be put to him on the subject; and it was judiciously remarked that "it would be better that he should be asked questions than required to make a speech; for, though a very good engineer, he was a bad speaker." One of the questions then put to Mr.
Stephenson related to the mode by which he proposed to haul the pa.s.senger carriages over the Menai Suspension Bridge by horse power; and he was asked whether he knew the pressure the bridge was capable of sustaining.
His answer was, that "he had not yet made any calculations; but he proposed getting data which would enable him to arrive at an accurate calculation of the actual strain upon the bridge during the late gale.
He had, however, no hesitation in saying that it was more than twenty times as much as the strain of a train of carriages and a locomotive engine. The only reason why he proposed to convey the carriages over by horses, was in order that he might, by distributing the weight, not increase the wavy motion. All the train would be on at once; but distributed. This he thought better than pa.s.sing them, linked together, by a locomotive engine." It will thus be observed that the practicability of throwing a rigid railway bridge across the Straits had not yet been contemplated.
The Dublin Chamber of Commerce pa.s.sed resolutions in favour of Stephenson"s line, after hearing his explanation of its essential features. The project, after undergoing much discussion, was at length embodied in an Act pa.s.sed in 1844; and the work was brought to a successful completion by his son, with several important modifications, including the grand original feature of the tubular bridges across the Menai Straits and the estuary of the Conway. Excepting these great works, the construction of this line presented no unusual features; though the remarkable terrace cut for the accommodation of the railway under the steep slope of Penmaen Mawr is worthy of a pa.s.sing notice.
About midway between Conway and Bangor, Penmaen Mawr forms a bold and almost precipitous headland, at the base of which, in rough weather, the ocean dashes with great fury. There was not s.p.a.ce enough between the mountain and the strand for the pa.s.sage of the railway; hence in some places the rock had to be blasted to form a terrace, and in others sea-walls had to be built up to the proper level, on which to form an embankment of sufficient width to enable the road to be laid. [Picture: Penmaen Mawr. (By Percival Skelton.)] A tunnel 10 chains in length was cut through the headland itself; and on its east and west sides the line was formed by a terrace cut out of the cliff, and by embankments protected by sea walls; the terrace being three times interrupted by embankments in its course of about 1 mile. The road lies so close under the steep mountain face, that it was even found necessary at certain places to protect it against possible accidents from falling stones, by means of a covered way. The terrace on the east side of the headland was, however, in some measure protected against the roll of the sea by the ma.s.s of stone run out from the tunnel, and forming a deep shingle bank in front of the wall.
The part of the work which lies on the westward of the headland penetrated by the tunnel, was exposed to the full force of the sea; and the formation of the road at that point was attended with great difficulty. While the sea wall was still in progress, its strength was severely tried by a strong north-westerly gale, which blew in October, 1846, with a spring tide of 17 feet. On the following morning it was found that a large portion of the rubble was irreparably injured, and 200 yards of the wall were then replaced by an open viaduct, with the piers placed edgeways to the sea, the openings between them being spanned by ten cast-iron girders each 42 feet long. This accident induced the engineer to alter the contour of the sea wall, so that it should present a diminished resistance to the force of the waves. But the sea repeated its a.s.saults, and made further havoc with the work; entailing heavy expenses and a complete reorganisation of the contract. Increased solidity was then given to the masonry, and the face of the wall underwent further change. At some points outworks were constructed, and piles were driven into the beach about 15 feet from the base of the wall, for the purpose of protecting its foundations and breaking the force of the waves. The work was at length finished after about three years"
anxious labour; but Mr. Stephenson confessed that if a long tunnel had been made in the first instance through the solid rock of Penmaen Mawr, a saving of from 25,000 to 30,000 would have been effected. He also said he had arrived at the conclusion that in railway works engineers should endeavour as far as possible to avoid the necessity of contending with the sea; {324} but if he were ever again compelled to go within its reach, he would adopt, instead of retaining walls, an open viaduct, placing all the piers edgeways to the force of the sea, and allowing the waves to break upon a natural slope of beach. He was ready enough to admit the errors he had committed in the original design of this work; but he said he had always gained more information from studying the causes of failures and endeavouring to surmount them than he had done from easily-won successes. Whilst many of the latter had been forgotten, the former were indelibly fixed in his memory.
But by far the greatest difficulty which Robert Stephenson had to encounter in executing this railway, was in carrying it across the Straits of Menai and the estuary of the Conway, where, like his predecessor Telford when forming his high road through North Wales, he was under the necessity of resorting to new and altogether untried methods of bridge construction. At Menai the waters of the Irish Sea are perpetually vibrating along the precipitous sh.o.r.es of the strait; rising and falling from 20 to 25 feet at each successive tide; the width and depth of the channel being such as to render it available for navigation by the largest ships. The problem was, to throw a bridge across this wide chasm-a bridge of unusual span and dimensions-of such strength as to be capable of bearing the heaviest loads at high speeds, and at such a uniform height throughout as not in any way to interfere with the navigation of the Strait. From an early period, Mr. Stephenson had fixed upon the spot where the Britannia Rock occurs, nearly in the middle of the channel, as the most eligible point for crossing; the water-width from sh.o.r.e to sh.o.r.e at high water there being about 1100 feet. His first idea was to construct the bridge of two cast-iron arches, each of 350 feet span. There was no novelty in this idea; for, as early as the year 1801, Mr. Rennie prepared a design of a cast-iron bridge across the Strait at the Sw.i.l.l.y rocks, the great centre arch of which was to be 450 feet span; and at a later period, in 1810, Telford submitted a design of a similar bridge at Inys-y-Moch, with a single cast-iron arch of 500 feet. But the same objections which led to the rejection of Rennie"s and Telford"s designs, proved fatal to Robert Stephenson"s, and his iron-arched railway bridge was rejected by the Admiralty. The navigation of the Strait was under no circ.u.mstances to be interfered with; and even the erection of scaffolding from below, to support the bridge during construction, was not to be permitted. The idea of a suspension bridge was dismissed as inapplicable; a degree of rigidity and strength, greater than could be secured by any bridge constructed on the principle of suspension, being considered an indispensable condition of the proposed structure.
[Picture: Britannia Bridge]
Various other plans were suggested; but the whole question remained unsettled even down to the time when the Company went before Parliament, in 1844, for power to construct the proposed bridges. No existing kind of structure seemed to be capable of bearing the fearful extension to which rigid bridges of the necessary spans would be subjected; and some new expedient of engineering therefore became necessary.
Mr. Stephenson was then led to reconsider a design which he had made in 1841 for a road bridge over the river Lea at Ware, with a span of 50 feet,-the conditions only admitting of a platform 18 or 20 inches thick.