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From the Quarterly Review. Irish Sea and of St. George's Channel are not 1. General Description of the Britannia and Con- only everlastingly vibrating backwards and for

way Tubular Bridges on the Chester and Holy- wards, but at the same time, and from the same head Railway. Published, with the permission of Robert Stephenson, Civil Engineer, by cause, are progressively rising or falling from 20

a Resident Assistant. Pp. 34. London. 1849. to 25 feet with each successive tide, which, vary2. An Account of the Construction of the Britannia ing its period of high water every day, forms alto

and Conway Tubular Bridges, with a complete gether an endless succession of aqueous changes. History of their Progress, from the conception The point of the Straits which it was desired of the Original Idea to the conclusion of the to cross-although broader than that about a mile elaborate Experiments which determined the ex- distant, preoccupied by Mr. Telford's Suspensionact Form and Mode of Construction ultimately bridge—was of course one of the narrowest that Adopted. By WILLIAM FAIRBAIRNS, C. E., Memb. Inst. Civil Engineers ; Vice-President could be selected ; in consequence of which the of the Literary and Philosophical Society, ebbing and flowing torrent rushes through it with Manchester, &c. London. 1819.

such violence that except where there is backIn continuation of our sketch of the practical water, it is often impossible for a small boat tó working of the London and North-western Rail- pull against it ; besides which, the gusts of wind way, we now offer to our readers a short descrip-round the sides of the neighboring mountains, are

which come over the tops, down the ravines, and live outline of the aërial passages through which it is proposed, by the directors of the Chester and so sudden, and occasionally so violent, that it is Holyhead Railway, that the public shall, with

as dangerous to sail as it is difficult to row ; in out cuneiform sustentation, ily across the Menai short, the wind and the water, sometimes play

fully, and sometimes angrily, seem to vie with Straits. We shall divide our subject into the following in exhibiting before the stranger the utmost variety

each other-like some of Shakspeare's fairiescompartments :

of fantastic changes which it is in the power of 1. The principle upon which the Britannia

each to assume. Bridge is constructed.

But, in addition to the petty annoyances which 2. The mode of its construction. 3. The floating of its tubes.

air, earth, and water could either separately or 4. The manner in which they were subse- conjointly create, the main difficulty which Mr. quently raised.

Stephenson had to encounter was from a new but

" orbis veteribus 5. Mr. Fairbairns complaint that Mr. Robert irresistible element in nature, an Stephenson has deprived him “ of a considerable incognitus,” termed in modern philosophy The portion of the merit of the construction of the

First Lord, or, generically, The Admiralty. Conway and Britannia Bridges."

The principal stipulation which the require

ments of war, and the interests of commerce, very 1. PRINCIPLE OF THE PROPOSED PASSAGE.—In reasonably imposed upon science was that the the construction of a railway from Chester to proposed passage across the Menai Straits should Holyhead, the great difficulty which its projectors be constructed a good hundred feet above highhad to contend with was to discover by what water level, to enable large vessels to sail beneath means, if

any, long trains of passengers and of it; and as a codicil to this will it was moreover goods could, at undiminished speed, be safely required that, in the construction of the said pastransported across that great tidal chasm which sage, neither scaffolding nor centring should be separates Carnarvon from the island of Anglesey. used—as they, it was explained, would obstruct To solve this important problem the company's the navigation of the Straits. engineer was directed most carefully to reconnoitre Although the latter stipulation, namely, that of the spot; and as the picture of a man struggling constructing a large superstructure without founwith adversity has always been deemed worthy of dation, was generally considered by engineers as a moment's attention, we will endeavor to sketch amounting almost to a prohibition, Mr. Stephena rough outline of the difficulties which one after son, after much writhing of mind, extricated himanother must have attracted Mr. Robert Stephen- self from the difficulty by the design of a most son's attention, as, on the Anglesey side of the magnificent bridge of two cast iron arches, each of Menai Straits, he stood in mute contemplation of which commencing, or, as it is termed, springing, the picturesque but powerful adversaries he was 50 feet above the water, was to be 450 feet broad required to encounter.

and 100 feet high-the necessity for centring Immediately in his front, and gradually rising being very ingeniously dispensed with by connect towards the clouds above him, were the lofty ing together the half arches on each side of the snow-capped mountains of Snowdon, along the centre pier, so as to cause them to counterbalance sides of which, or through which, the future each other like two boys quietly seated on the railroad, sometimes in bright sunshine and some opposite ends of a plank supported only in the times in utter darkness, was either to meander or middle. This project, however, which on very: to burrow.

competent authority has been termed “one of the Beneath him were the deep Menai Straits, in most beautiful structures ever invented," the Ado length above 12 miles, through which, imprisoned miralty rejected, because the stipulated height of between precipitous shores, the waters of the 100 feet would only be atlained under the crown of

000I.

LIVING AGE.

VOL. XXIV.

23

the arch, instead of extending across the whole of It need hardly be stated that, whatever mighi the water-course. It was also contended that such be the result of Mr. Stephenson's abstract calcuvast cast iron arches would take the wind out of lations on these points, his practical decision was vessels' sails, and, as a further objection, that they one that necessarily involved the most painful would inevitably be much affected by alternations responsibility; which, indeed, if possible, was inof temperature.

creased by the reflection that the directors of the Although this stern and unanticipated demand, Chester and Holyhead Railway placed such imthat the passage throughout its whole length should plict confidence in his judgment and caution that be of the specified heiglit, appeared to render they were prepared to adopt almost whatever success almost hopeless, it was evidently useless expedient he might, on mature consideration, recto oppose it. The man of science had neither the ommend. power nor the will to contend against men of war, In war, the mangled corpse of the projector of and accordingly, Mr. Stephenson felt that his best, an enterprise is usually considered a sufficient and indeed only, course was

-like

poor

little Oliver atonement for his want of success ; indeed, the Twist when brought before his parish guardians leader of the forlorn-hope, who dies in the breach, "TO BOW TO THE BOARD ;” and we beg leave is not only honorably recollected by his survivors, to bow to it too, fur, gnarled as were iis require- but by a glorious resurrection occasionally lives in ments, and flat as were its refusals, it succeeded, the history of his country; but when a man of at a cost to the company to which we will subse- science fails in an important undertaking involvquently refer, in effecting two great objects ;-ing the capital of his employers and the lives of first, the maintenance forever, for the purposes the public, in Josing his reputation he loses that of war and commerce, of an uninterrupted passage which never can be revived ! for vessels of all nations sailing through the Unawed, however, by these reflections, Mr. Menai Straits ; and, secondly, the forcing an eri- Stephenson, asier mature calculations-in which nent engineer to seek until he found that which his practical experience of iron ship-building must was required ; in fact, just as a collision between have greatly assisted him-confidently announced, a rough flint and piece of highly-lernpered steel first to his employers and afterwards to a commitelicits from the latter a spark which could not tee of the House of Commons, by whom he was otherwise have appeared, so did the rugged stip- rigidly examined, that he had devised the means ulations of the Admiralty elicit from science a of accomplishing that which was required ; and, most brilliant discovery, which possibly, and in- further, that he was ready to execute his design. deed probably, would never otherwise have come The great difficulty had been in the conception to light.

and gestation of his project ; and thus his sever But to return to the Anglesey shore of the est mental labor was over before the work was Menai Siraits.

commenced, and while the stream, as it hurried When Mr. Stephenson, after many weary hours through the Menaj Straits, as yet saw not on its of rumination in his London study, beheld vividly banks a single workman. portrayed before him the physical difficulties The outline or principle of his invention was, with which he had to contend in the breadth and that the required passage of passengers and goods rapidity of the stream ; when he estimated not across the Conway and Menai Straits should be only the ordinary violence of a gale of wind, effected through low, long, hollow, straight lubes but the paroxysms or squalls, which, in the chasm -one for up-trains, the other for down ores before him, occasionally like the Erle King ter- composed of wrought iron “boiler-plates," firmly rifying the

poor baby'-convulsed even the riveled together. He conceived that, in order to tempest in its career; and, lastly, when he return aside the force of the wind, these tubes ought, flected that, in constructing a passage so high like common waier-pipes, to be made oval or above the water, he was to be allowed neither elliptical, and that they should be constructed at centrings, scaffoldings, nor arches, it occurred to their final elevation on temporary platforms, upheld him, almost as intuitively as a man when his by chains, which-notwithstanding the evident house is on fire at once avails himself of the objection, in theory as well as in practice, to an means lest hiin for escape, that the only way in adınixture of movable and inmovable parts which he could effect his object was by construct might of course subsequently be allowed to give ing, in some way or other, at the height re-to the bridge an auxiliary support, although Mr. quired, a straight passage, which, on the principle Stephenson's experience enabled him to deelare of a common beam, would be firm enough 10 to the committee of the House of Commons very allow railway trains to pass and repass without positively that no such extra assistance would be oscillation, danger, or even the shadow of risk ; required. He proposed that the extremities of the and it of course followed that an aërial road of tubes should rest on stout abutments of masonry. this description should be composed of the strong-terminating the large embankment by which from est and lightest material ; that its form should be either side of the country each was to be ap that best suited for averting the wind; and, lastly, proached ; the intermediate portions of the aërial that no expense should be spared to protect the passage reposing at the requisite elevation upon public from the awful catastrophe that would result three massive and lufty towers. or these one was from the rupture of this " baseless fabric" dur-lo be constructed at high-water mark on each sido ing the passage over it of a train.

of the Straits. The third, no less than 210 feet

a

472

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in heigkt, was to be erected as nearly as possible be " distinguished as the first scientific authority in the middle of the stream, on a tiny rock, which, on the strengih of iron beams.” To these two covered with 10 feet of water at high tide, although competent authorities Mr. Stephenson subsequently at low water it protruded above the surface, had added one of his own confidential assistants, Mr. long been considered as a grievance by boatmen Edwin Clark, a practical engineer of the highest and travellers incompetent to foresee the important mathematical altainments, who regularly recorded service it was destined to perform.

and reported to Mr. Stephenson the result of every · The four lengths of each of the twin tubes, experiment to whom the construction and listing. when supported as described, were to be as fuld of the Britannia galleries were eventually solely lows:

intrusted—and by whom an elaborate description Feet.

of that work is about to be published. * From Carnarvon embankment, terminating

The practicability of Mr. Stephenson's hollowin its abutment, to the tower at high-water beam project having thus, at his own suggestion, mark

274 been subjected to a just and rigid investigation, we From the latter tower to Britannia tower,

shall have the pleasure of briefly detailing a few situated upon Britannia rock in the middle

of the most interesting and unexpected results ; of the stream From Britannia tower to that at high-water

previous, however, to doing so, we will endeavor mark on the Anglesey shore

472 to offer to those of our readers who may not be From the Anglesey tower to the abutment conversant with the subject a short practical ex

terminating the embankment which ap- planation of the simple principle upon which proaches it

274 beam, whether of wood or iron, is enabled :0 sup

port the weight inflicted upon it. Total length of each tube

1492

If human beings can but attain what they desire, Total length of both tubes

2984

they seldom alloy the gratification they receive by

reflecting-even for a moment on the sufferings Notwithstanding the bare proposal of this mag- which their fellow-creatures may have undergone nificent conception was unanswerable evidence of in procuring for them the luxury in question. the confidence which the projector himself enter- Dives soinetimes extols his coals, his wine, his tained of its principles, yet, in justice to his pro food, his raiment, his house, his carriages, and his fession, to his employers, to the public, as well horses, and yet how seldom does he either allude as to himself, Mr. Stephenson deemed it proper to to or ruminate on the bardships and misery which, recommend that, during the construction of the for his enjoyment, have been endured in coal-pits, towers and other necessary preparations, a series lead-mines, sugar-plantations, cotton-fields, manuof searching experiments should be made by the factories, smelling-houses, in horticultural and most competent persons that could be selected, agricultural labor, by the sons and daughters of in order lo ascertain the precise shape and thick- Lazarus !--and if this heartless apathy characterness of the immense wrought-iron aërial galler-izes human beings with reference to each other, ies that were to be constructed, as also the ex- it may naturally enough be expected that, provided act amount of weight they would practically inanimate objects answer our purpose, we think bear. In short, the object of the proposed exper- not of them at all. For instance, if a beam withiments was to insure that neither more nor less out bending or cracking bears—as it usually does materials should be used than were absolutely - the weight which the builder has imposed upon requisite, it being evident that every pound of it

, who cares how it suffers or where it suffers ? unnecessary weight that could be abstracted would, For want, therefore, of a few moments' reflecpro tanto, add to the strength and security of the lion on this subject, most people, in looking up at structure.

a common ceiling-girder, consider that the correAlthough it was foreseen, and very candidly sponding upper and lower parts thereof must at all foretold, that these experiments would be exceed-events, pari passu, suffer equally ; whereas these ingly expensive, the directors of the company upper and lower strata suffer from causes as diareadily acceded to the requisition, and accord-metrically opposite to each other as the climates ingly, without loss of time, the proposed investi- of the pole and of the equator of the earth ; that gation was, at Mr. Stephenson's recommendation, is to say, the top of the beam throughout its whole solely confided to Mr. William Fairbairn, a ship length suffers from severe compression, the bottom builder and boiler-maker, who was justly supposed from severe extension, and thus, while the partito possess more practical experience of the power

* With the sanction and under the immediate supervisand strength of iron than any other person that ion of Robert Stephenson, Civil Engineer. A Descrip could have been selected. Mr. Fairbairn, how- tion of the Britannia and 'Conway Tubular Bridges : 1never, after having conducted several very impor- and Details of the Preliminary Experiments, with the

cluding an Historical Account of the Design and-Erection, tant investigations, deemed it necessary to apply to Theories deduced from them. Also, General Inquiries Mr. Stephenson for permission “to call in the aid on Beams, and on the Application of Riveted Wroughtand assistance of Mr. Hodgkinson," a powerful Rules and Deductions, illustrated ly Experiments. By

iron Plates 10 Purposes of Construction ; with Practical mathemnatician, now professor in the University of Edwin Clark, Assistant Engineer. Willi Diagrams and London, and whom Mr. Stephenson, in his report Progress of the Works.

a folio volume of Plates and Drawings, illustrative of the

London Published for the to the directors, dated Feb. 9, 1846, declared to Author, by Johu Weale, 59, High Holborn, 1849.

cles of the one are violently jammed together, the haps a startling exemplification of the truth of his particles of the other are on the point of separa- theory, it may be stated that although his platetion ; in short, the difference between the two is iron galleries, suspended by the tension as well as precisely that which exists between the opposite supported by the compression of their materials, punishments of vertically crushing a man to death have, on mature calculations, been constructed to under a heavy weight, and of horizontally tearing bear nearly nine times the amount of the longest him to pieces by horses !

railway train that could possibly pass through Now this theory, confused as it may appear in them, (namely, one of their own lengih,) yet if, words, can at once be simply and most beautifully instead of being hollow, they had been a solid illustrated by a common small straight stick freshly iron beam of the same dimensions, they would not cut from a living shrub.

only have been unable to sustain the load required, In its natural form, the bark or rind around the but would actually have been bent by—or, metastick is equally smooth or quiescent throughout; phorically, would have fainted under-their own whereas, if the little bough firmly held in each weight. hand be bent downwards, so as to form a bow, or, Experiments.—One of the most interesting and in other words, to represent a beam under heavy important results of the preliminary investigations pressure, two opposite results will instantly ap- so ably conducted by Mr. Fairbairn and his friend pear-namely, the rind in the centre of the upper and associate Mr. Hodgkinson, was the astonishhalf of the stick will, like a smile puckering on ing difference found to exist between the power of an old man's face, be crumpled up; while on the cast and that of wrought iron to resist compresopposite side, immediately beneath, it will, like sion and extension. From the experience which the unwrinkled cheeks of Boreas, be severely dis- engineers and builders had obtained in imposing tended—thus denoting, or rather demonstrating, weights upon cast iron girders of all shapes and what we have stated, namely, that beneath the rind sizes, it had long been considered almost a methe wood of the upper part of the stick is severely chanical axiom, that iron possessed greater power compressed, while that underneath it is as vio to resist compression than extension; whereas Jently stretched ; indeed, if the little experiment Mr. Fairbairn's experiments, to his surprise as be continued by bending the bow jill it breaks, the well as to that of all who witnessed them, most splinters of the upper fracture will be seen to clearly demonstrated that, after bearing a certain interlace or cross each other, while those beneath amount of weight, the resisting properties of cast will be divorced by a chasm.

and of wrought iron are diametrically opposite ; in But it is evident on reflection that these oppo- short, the results in figures proved to be nearly as site results of compression and extension must, as follows :they approach each other, respectively diminish in Cast iron can resist per square inchdegree, until in the middle of the beam, termed Compression of from 35 to 49 tons. by mathematicians, “its neutral axis,” the two Extension of

7 " antagonist forces, like the anger of the Kilkenny Wrought iron can resist per square inchcats, or, rather, like still-water between tide and

Compression of from 12 to 13 tons. back-stream, become neutralized, and, the laminæ Extension of

16 " 18 of the beam consequently offering no resistance The unexpected results thus obtained were of either to the one power or to the other, they are incalculable practical value; for, if the preliminary literally useless.

experiments proposed by Mr. Stephenson had not As, therefore, it appears that the main strength been made, he, Mr. Fairbairn, Mr. Hodgkinson, of a beam consists in its power to resist compres- Mr. Clark, and indeed all the eminent engineers sion and extension, and that the middle is com- and mathematicians of the present day, wouldparatively useless, it follows that, in order to ob- on the correct principle of everywhere adjusting tain the greatest possible amount of strength, the the thickness of iron 1o the force it has to resistgiven quantity of material to be used should be have erroneously concurred in recommending that accumulated at the top and bottom, where the the proposed wrought iron tubes for crossing the strain is the greatest ; or, in plain terms, the mid- Conway and Menai Straits should be constructed dle of the beam, whether of wood or iron, should stronger at bottom than at lop, instead of, as it be bored out. All iron girders, all beams in appears they ought to be, stronger at top than at houses, in fact all things in domestic or naval ar-bottom-in consequence of which error the aërial chitecture that bear weight, are subject to the gallery would have been improperly weakened in same law.

one part by an amount of iron which would have The reader has now before him the simple phil- unscientifically overloaded it at another, and thus, osophical principle upon which Mr. Stephenson, like Falstaff's " increasing belly and decreasing when he found that he was to be allowed neither legs," the huge mass, with diminished strength, scaffolding, centring, nor arches, determined to would have labored under unnecessary weight. undertake to convey at undiminished speed the By continuing, with great patience and ability, Chester and Holyhead Railway's passenger and the experiments above referred to, it was finally gonds traffic across the Conway and Menai Straits ascertained that the relative strength of wrought through hollow tubes, instead of attempting to do iron in the top and bottom of the lubes should be so vpen solid beams; and as a striking and per-in the proportion of about 5 to 4; and whereas,

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had they been constructed of cast iron, these pro-two; and as every successive test confirmed the portions would have been reversed in the higher fact, he continued his search with an energy that proportion of nearly 5 to 1, it may reasonably be has only since been equalled by the American asked why, if the latter material bears compres- judge, who, it is said, on arriving at California, sion so much better than the former, it was not deserted the bench for “ the diggings." selected for the top of the tube? In theory, this The following is an abstract of the important adjustment of the two metals to the force which result of about forty experiments made by Messrs. each was peculiarly competent to resist, would Fairbairn, Hodgkinson, and Clark, on the comparhave been perfectly correct. It, however, could ative strength of circular, elliptical, and rectannot practically be effected, from the difficulty of gular tubes :- Circular, 13; Elliptical, 15; Reccasting as well as of connecting together plates ten tangular, 21. and twelve feet in length of the very slight thick- As soon as the rectangular was, by the investi nesses required. Mr. Stephenson, therefore, ad- gation recommended by Mr. Stephenson, clearly hered to his determination to make the whole of ascertained to be the best form of hollow tube that his aërial galleries of wrought iron ; and we may could be selected, the next important problem to here observe that, to ensure the public from acci- be determined by experiment was what amount of dent, ne further resolved that the amount of the strength should be given to it; or, in other words, force of extension upon them should be limited to what should be the thickness of its top and botonly one third of their power of resistance, that of tom, in which, as we have shown, consisted its compression to one half-the reason of the differ- main power. ence being that, inasmuch as any little flaw in the The investigations on this subject soon demoniron would infinitely more impair its power to strated that if, instead of obtaining this thickness resist extension than compression, it was evidently by riveting together two or three layers of plates, safer to approximate the limits of the latter than they were, on the principle of the beam itself, of the former.

placed in horizontal strata a foot or two asunder As the exact strength of a hollow wrought iron the included hollow space being subdivided by cube, such as was proposed, was unknown to en- small vertical plates into rectangular passages or gineers, it was deemed necessary by Mr. Stephen- fues extending along the whole top as well as son that its form as well as the disposition of its bottom of the tube-an immense addition of materials should be correctly ascertained. This strength, with very nearly the same weight of portion of the investigation Mr. Fairbairn and his material, would be obtained. colleagues with great care and ability conducted This adaptation proving highly advantageous, by subjecting tubes of different shapes to a series it was deemed advisable by Mr. Stephenson that of experiments, the results of which were briefly further experiments should be made by Mr. Fairas follows:

bairn and his colleagues to determine finally, the 1. Cylindrical tubes, on being subjected to nine precise form and proportions of the great tubes. very severe trials, failed successively by collapsing For this object an entirely new model tube, one at the top ; or, in other words, by evincing inabil- sixth of the dimensions of the intended Britannia ity to resist compression. The tube, losing its Bridge, was very carefully constructed ; and the shape, gradually became elongated or lantern- cellular tops and bottoms thereof, as well as the jawed, while the two extremities were observed to sides, were subjected to a series of experimento flatten or bulge out sideways-besides which the until the exact equilibrium of resistance to comends, which, for precaution sake, rested on con- pression and extension, as also the variations in centric wooden beds, invariably bent inwards. the thicknesses of the plates in the several parts

2. Elliptical tubes, with thick plates riveted to of the tube as they approached or receded from the top and bottom, had been particularly recom- different points of support, were most accurately mended for experiment by Mr. Stephenson. These ascertained. tubes, under heavy pressure, displayed greater

In these as well as in all the previous experistiffiiess and strength than round or cylindrical ments the trial tubes were loaded till they gave ones; but, after being subjected to a variety of way—the results being accurately recorded and torturing experiments of a most ingenious descrip- transmitted by Mr. Clark to Mr. Stephenson, who tion, they all evinced comparative weakness in in return confidentially assisted Mr. C. with his the top lo resist compression. They likewise ex- opinion and advice. From the fibrous nature of hibited considerable distortions of form.

wrought iron, as compared with the crystalline 3. A faraily weakness in the head having been composition of the cast metal, the tendency to thus detected in all models circular at bottom and rupture in most of these experiments was slow top, rectangular tubes were in their turn next sub- and progressive. Destruction was never instanjected to trial. As they at once appeared to in- taneous, as in cast iron, but it advanced gradually ; dicale greater strength than either of the other two the inaterial, for some time before absolute rupforins bad done, a very elaborate and interesting ture took place, emitting an unmistakable warninvestigation was pursued by Mr. Fairbairn, who, ing noise ; just as a camel, while kneeling on the by the light of his experiments, soon satisfied him- burning sandy desert, and while writhing his head self of the superiority of this form over the other from one side to the other, snarls, grunts, grumbles

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