Chapter 4

In 1833, the French removed the smallest of the two obelisks which stood before the propylon of the temple of Luxor to Paris, and elevated it in the Place de la Concorde. The shaft is 76 feet high, and eight feet wide on the broadest side of the base; the pedestal is 10 feet square by 16 feet high. Permission for the removal of both the obelisks having been granted to the French government by the Viceroy of Egypt, a vessel constructed for the purpose was sent out in March, 1831, under M. Lebas, an eminent engineer, to whom the undertaking was confided, it being previously determined to bring away only one, and M. Lebas found it sufficiently difficult to bring away the smallest of the two. After three months' labor with 800 men, the obelisk was removed on an inclined plane into the vessel, through a hole made in the end for the purpose. It arrived safely up the Seine to Paris, Dec. 23d, 1833. An inclined plane of solid masonry was then constructed, leading from the river up to a platform, also of rough masonry, level with the top of the pedestal. The obelisk, having been placed on a kind of timber car or sledge, was drawn up by means of ropes and capstans. One edge of the base having been brought to its place on the pedestal, it was raised to a perpendicular position by ropes and pulleys attached to the heads of ten masts, five on each side. When all was ready, the obelisk was elevated to its place under the direction of M. Lebas, in three hours, without the least accident, Oct. 25th, 1836. It is said that Lebas had provided himself with loaded pistols, in the firm determination to blow out his brains in case of an accident!

In 1820, the Viceroy of Egypt presented to the English government the monolith lying on the ground at Alexandria, one of the two obelisks called Cleopatra's Needles; the other is still standing. The project of removing it to London and erecting it in Waterloo Square, was entertained for some time by the English government, but seems to have been long abandoned; recently, however, an expedition is being fitted out for the purpose.

CARBURI'S BASE FOR THE EQUESTRIAN STATUE OF PETER THE GREAT.

Milizia gives the following interesting account of the removal of the immense mass of granite, which forms the pedestal or base of the equestrian statue of Peter the Great, from the bogs of the Neva to St. Petersburg, a distance of about fourteen miles. He also cites it as an instance of extraordinary ingenuity and skill in mechanics. It is, however, a much easier task to move a ponderous mass of rough, unhewn rock, than a brittle obelisk, an hundred feet or so in length, requiring the greatest care to preserve it from injury. It is also worthy of mention, that in widening streets in New York, it is no uncommon thing to see a three-story brick house set back ten or fifteen feet, and even moved across the street, and raised an extra story into the bargain--the story being added to the _bottom_ instead of the _top_ of the building. Thus the large free stone and brick school-house in the First Ward, an edifice of four lofty stories, 50 by 70 feet, and basement walls 2½ feet thick, has been raised six feet, to make it correspond with the new grade in the lower part of Greenwich-street. It is also no uncommon thing to see a ship of a thousand tons, with her cargo on board, raised out of the water at the Hydraulic Dock, to stop a leak, or make some unexpected but necessary repairs.

"In 1769, the Count Marino Carburi, of Cephalonia, moved a mass of granite, weighing three million pounds, to St. Petersburg, to serve as a base for the equestrian statue of Peter the Great, to be erected in the square of that city, after the design of M. Falconet, who discarded the common mode of placing an equestrian statue on a pedestal, where, properly speaking, it never could be; and suggested a rock, on which the hero was to have the appearance of galloping, but suddenly be arrested at the sight of an enormous serpent, which, with other obstacles, he overcomes for the happiness of the Muscovites. None but a Catherine II., who so gloriously accomplished all the great ideas of that hero, could have brought to perfection this extraordinary one of the artist. An immense mass was accidentally found buried 15 feet in a bog, four miles and a half from the river Neva and fourteen from St. Petersburg. It was also casually that Carburi was at the city to undertake the removal of it. Nature alone sometimes forms a mechanic, as she does a sovereign, a general, a painter, a philosopher. The expense of this removal was only 70,000 rubles and the materials left after the operation were worth two-thirds of that sum. The obstacles surmounted do honor to the human understanding. The rock was 37 feet long, 22 high, and 21 broad, in the form of a parallelopipedon. It was cleft by a blast, the middle part taken away, and in the cavity was constructed a forge for the wants of the journey. Carburi did not use cylindrical rollers for his undertaking, these causing an attrition sufficient to break the strongest cables. Instead of rollers he used balls composed of brass, tin, and calamina, which rolled with their burden under a species of boat 180 feet long, and 66 wide. This extraordinary spectacle was witnessed by the whole court, and by Prince Henry of Prussia, a branch from the great Frederick. Two drums at the top sounded the march; forty stone-cutters were continually at work on the mass during the journey, to give it the proposed form--a singularly ingenious idea. The forge was always at work: a number of other men were also in attendance to keep the balls at proper distances, of which there were thirty, of the diameter of five inches. The mountain was moved by four windlasses, and sometimes by two; each required thirty-two men: it was raised and lowered by screws, to remove the balls and put them on the other side. When the road was even, the machine moved 60 feet in the hour. The mechanic, although continually ill from the dampness of the air, was still indefatigable in regulating the arrangements; and in six weeks the whole arrived at the river. It was embarked, and safely landed. Carburi then placed the mass in the square of St. Peter's, to the honor of Peter, Falconet, Carburi, and of Catherine, who may always, from her actions, be classed among illustrious men. It is to be observed, that in this operation the moss and straw that was placed underneath the rock, became by compression so compact, that it almost equalled in hardness the ball of a musket. Similar mechanical operations of the ancients have been wonderfully exaggerated by their poets."

COMPARATIVE SKILL OF THE ANCIENTS AND MODERNS IN MECHANICS.

Many persons suppose, and maintain, that the grandeur of the monuments of the ancients, and the great size of the stones they employed for building purposes, prove that they understood mechanics better than the moderns. The least knowledge in mechanics, however, will show this opinion to be erroneous. The moderns possess powers which were unknown to the ancients, as the screw, and the hydraulic press, the power of which last is only limited by the strength of the machinery. The works of the ancients show that they expended a vast deal of power and labor to gratify the pride and ambition of kings; but the moderns can do all these things much easier, and in far less time, whenever they deem it proper. There was nothing in ancient times to be compared with that daring, ingenious, and stupendous monument of engineering skill--the Britannia Tubular Bridge, across the Menai straits--projected, designed, and built by Robert Stephenson, the famous English engineer. He had previously built a similar but smaller structure--the Conway Tubular Bridge.

THE BRITANNIA TUBULAR RAILWAY BRIDGE.

Had this stupendous fabric existed in ancient times, it would have been regarded as the _first_ of the seven wonders of the world. Greater and more expensive structures have been raised, but none displaying more science, skill, and ingenuity, and none requiring such tremendous mechanical power to execute.

The Britannia Tubular Bridge was built to conduct the Chester and Holyhead Railway across the Menai Straits, to the island of Anglesea, in the Irish Sea.

The difficulties which the engineer had to overcome, were greatly augmented by the peculiar form and situation of the straits. Sir Francis Head says, "The point of the straits which it was desired to cross, although broader than that about a mile distant; preoccupied by Mr. Telford's suspension bridge--was of course one of the narrowest that could be selected, in consequence of which the ebbing and flowing torrent rushes through it with such violence, that, except where there is back water, it is often impossible for a small boat to pull against it; besides which, the gusts of wind which come over the tops, down the ravines, and round the sides of the neighboring mountains, are so sudden, and occasionally so violent, that it is as dangerous to sail as it is difficult to row; in short, the wind and the water, sometimes playfully and sometimes angrily, seem to vie with each other--like some of Shakspeare's fairies--in exhibiting before the stranger the utmost variety of fantastic changes which it is in the power of each to assume." The Menai Straits are about twelve miles long, through which, imprisoned between the precipitous shores, the waters of the Irish Sea and St. George's Channel are not only everlastingly vibrating, backwards and forwards, but at the same time and from the same causes, are progressively rising and falling 20 to 25 feet, with each successive tide, which, varying its period of high water, every day forms altogether an endless succession of aqueous changes.

THE TUBES.

The tubes forming the viaducts, rest upon two abutments and three piers, called respectively the Anglesea abutment and pier, the Carnarvon abutment and pier, and the Britannia or central pier, built upon the Britannia rock in the middle of the straits, which gives name to the bridge. The Anglesea abutment is 143 feet 6 inches high, 55 feet wide, and 175 feet long to the end of the wings, which terminate in pedestals, supporting colossal lions on either side, 25 feet 6 inches in length, 12 feet 6 inches high, and 8 feet broad, carved out of a single block of Anglesea marble. The space between the Anglesea abutment and pier is 230 feet. This pier is 196 feet high, 55 feet wide, and 32 feet long. The Carnarvon abutment and pier are of the same dimensions as those above described, on the opposite shore. The Britannia pier is 240 feet high, 55 feet wide, and 45 feet long. This pier is 460 feet clear of each of the two side piers. The bottom of the tubes are 124 feet above low water mark, so that large ships can pass under them, under full sail.

There are two tubes, to accommodate a double track (one would have done in this country, but in England they do nothing by halves), and each is 1513 feet long. The total length of the bridge is 1841 feet. These tubes are not round or oval, but nearly square at the termini; the bridge being constructed on the principle of the arch. A section of one of the tubes at the Britannia pier is in the form of a parallelogram, where it is 30 feet high, gradually diminishing towards each end to 20 feet. The tubes are riveted together into continuous hollow beams; they are of the uniform width of 14 feet 8 inches throughout; they are constructed entirely of iron, and weigh about 12,000 tons, each tube containing 5000 tons of wrought iron, and about 1000 tons of cast iron. The tubes were constructed each in four sections; the sections extending from the abutments to their corresponding piers, each 250 feet long, were built _in situ_, on immense scaffolding, made of heavy timbers for the purpose, even with the railway; but the middle sections, each 470 feet long, were built on piers on the Carnarvonshire shore, then floated into the stream, and elevated to their position; each of these sections weighed 1800 tons.

CONSTRUCTION OF THE TUBES.

The sides, bottom, and top of these gigantic tubes are formed of oblong wrought iron plates, varying in length, width, and thickness, according to circumstances, but of amazing size and weight. They are so arranged as to obtain the greatest possible strength, the whole being riveted together in the strongest manner. In addition to the 1600 tons of wrought iron in each of the four large pieces, an additional 200 tons was used to form lifting frames, and cast iron beams for the purpose of attaching the tube to those huge chains by which they were elevated. The construction of the tubes is thus described in the London Illustrated News, from which this account is derived:

"In order to carry out this vast work (the construction of the tubes), eighty houses have been erected for the accommodation of the workmen, which, being whitewashed, have a peculiarly neat and picturesque appearance; among them are seen butcher's, grocer's, and tobacconist's shops, supplying the wants of a numerous population. A day school, Sunday school, and meeting-house also conspicuously figure. Workshops, steam-engines, store-houses, offices, and other buildings meet the eye at every turn; one is led to conclude that a considerable time has elapsed since the works were commenced, yet it is little more than two years ago. A stranger, on coming to the ground, is struck with wonder when for the first time he obtains a near view of the vast piles of masonry towering majestically above all the surrounding objects--strong as the pillars of Hercules, and apparently as endurable--his eyes wander instinctively to the ponderous tubes, those masterpieces of engineering constructiveness and mathematical adjustment; he shrinks into himself as he gazes, and is astonished when he thinks that the whole is the developed idea of one man, and carried out, too, in the face of difficulties which few would have dared to encounter."

FLOATING OF THE TUBES.

The tubes were floated to the places whence they were elevated to their positions on eight huge pontoons, fitted with valves and pumps to exhaust the water from them, when all was ready to float the prodigious iron beams. These pontoons or boxes were each 90 feet long, 25 feet wide, and 15 feet deep. The pontoons having been placed under one of the tubes (sections), the floating was easily effected, and the operation is thus described by the "Assistant Engineer."

"The operation of floating the tubes (the four sections, and one only at a time), will be commenced by closing the valves in the pontoons at low water; as the tide rises, the pontoons will begin to float, and shortly afterwards to bear the weight of the tube, which will at last be raised by them entirely off its temporary supporting piers; about an hour and a half before high water, the current running about four miles an hour, it will be dragged out into the middle of the stream, by powerful capstans and hawsers, reaching from the pontoons at each end, to the opposite shore. In order to guide it into its place with the greatest possible certainty, three large hawsers will be laid down the stream, one end of two of them being made fast to the towers (piers) between which the tube is intended to rest, and the other to strong fixed points on the two shores, near to and opposite the further end of the tube platforms; in their course, they will pass over and rest upon the pontoons, being taken through 'cable-stoppers' which are contrivances for embracing and gripping the hawser extended across the stream, and thereby retarding, or if necessary entirely destroying, the speed induced by the current."

RAISING THE TUBES

The tubes of the Britannia bridge were raised by means of three hydraulic presses of the most prodigious size, strength, weight, and power; two of which were placed in the Britannia pier, above the points where the tubes rest, and the other alternately on the Anglesea and Carnarvon piers.

In order that all who read these pages may understand this curious operation, it is necessary to describe the principle of the hydraulic press. If a tube be screwed into a cask or vessel filled with water, and then water poured into the tube, the pressure on the bottom and sides of the vessel will not be the contents of the vessel and tube, but that of a column of water equal to the length of the tube and the depth of the vessel. This law of pressure in fluids is rendered very striking in the experiment of bursting a strong cask by the action of a few ounces of water. This law, so extraordinary and startling of belief to those who do not understand the reasoning upon which it is founded, has been called the _Hydrostatic paradox_, though there is nothing in reality more paradoxical in it, than that one pound at the long end of a lever, should balance ten pounds at the short end. This principle has been applied to the construction of the Hydrostatic or Hydraulic press, whose power is only limited by the strength of the materials of which it is made. Thus, with a hydraulic press no larger than a common tea-pot, a bar of iron may be cut as easily as a slip of pasteboard. The exertion of a single man, with a short lever, will produce a pressure of 1500 atmospheres, or 22,500 pounds on every square inch of surface inside the cylinder. By means of hydraulic presses, ships of a thousand tons burthen, with cargo on board, are lifted out of the water for repairs, and the heaviest bodies raised and moved, without any other expense of human labor beyond the management of the engine.

The tubes on the Anglesea side were raised first. The presses in the Britannia tower were each capable of raising a weight of 1250 tons; that in the Anglesea tower, larger than the others, 1800 tons, or the whole weight of the tube. These presses were worked by two steam engines of 40 horse power each, which forced the water into the cylinders, through a tube half an inch in diameter. These steam engines were placed in the Britannia and Anglesea piers. The press in the Anglesea pier is thus described, the others being constructed in the same manner. The hydraulic press stands on massive beams of wrought iron plates constructed on the principle of the arch, placed in the tower above the points where the tubes rest. The press consists of a huge cylinder, 9 feet 2 inches in length, 3 feet 6 inches outside diameter, and the ram 1 foot 8 inches in diameter, making the sides and bottom of the cylinder 11 inches thick; it was calculated that it would resist a pressure of 8000 or 9000 pounds to the square inch. The ram or piston was attached to an exceedingly thick and heavy beam of cast iron, called the cross-head, strengthened with bars of wrought iron. To the cross-head were attached the huge chains that descended to the tubes far below, to which they were secured, so that, as the ram was forced up 6 feet at each stroke, the tube was raised the same distance. "The power of the press is exerted on the tube by aid of chains, the links of which are 6 feet in length, bolted together in sets of eight or nine links alternately.--The ram raises the cross-head 6 feet at each stroke, and with it the tube, when that height is attained, a lower set of chains on the beams grip the next set of links, and thus prevent them from slipping down, whilst the clamps on the cross-heads are unscrewed, the upper links taken off, and the ram and cross-head lowered to take another stroke." To guard against all chances of injury to the tubes in case of accident to the machinery, a contrivance was adopted by which the tubes were followed up with wedges. The importance of this precaution was fully proved on the very first attempt to raise the tube on the Anglesea side, when the huge cylinder broke, almost at the commencement of the operations. The following is the engineer's interesting report of the accident:

"On Friday last (August 17, 1849), at a quarter to twelve o'clock, we commenced lifting the tube at the Anglesea end, intending to raise it six feet, and afterwards to have raised the opposite end the same height.

"The tube rose steadily to the height of two feet six inches, being closely followed up by inch wooden boards packed beneath it, when suddenly, and without any warning, the bottom of the hydraulic press gave way, separating completely from the body of the press.

"The ram, cross-head, and chains descended violently on the press, with a tremendous noise, the tube sinking down upon the wooden packing beneath it. The bottom of the press, weighing nearly two tons and a half, fell on the top of the tube, a depth of eighty feet.

"A sailor, named Owen Parry, was ascending a rope ladder at the time, from the top of the tube into the tower; the broken piece of press in its descent struck the ladder and shook him off; he fell on to the tube, a height of fifty feet, receiving a contusion of the skull, and other injuries, of so serious a nature that he died the same evening. He was not engaged in the raising, and had only chosen to cross the tube, as being the nearest road from one tower to the other. An inquest was held on the following day, and a verdict of accidental death returned. No one actually engaged in the operation was injured, although Mr. Edwin Clark, who was superintending the operation, on the top of the cross-head, and his brother, Mr. L. Clark, who was standing beneath it, had both a very narrow escape.

"The tube is not at all injured, but some portions of the cast iron lifting frames are broken, and require repairing; some weeks must elapse before a new cylinder is made, and the operation continued."

Sir Francis Head, when he saw one of the tubes raised, and in its place, observed, "It seemed surprising to us that by any arrangement of materials, it could possibly be made strong enough to support even itself,--much less heavily laden trains of passengers and goods, flying through it, and actually passing each other in the air at railway speed. And the more we called reason and reflection to our assistance, the more incomprehensible did the mystery practically appear; for the plate iron of which the aërial gallery is composed is literally _not so thick_ as the lid, sides, and bottom which, by heartless contract, are _required_ for an elm coffin 6½ feet long, 2¼ wide, and 2 deep, of strength merely sufficient to carry the corpse of an emaciated pauper from the workhouse to his grave! The covering of this iron passage, 1841 feet in length, is literally not thicker than the hide of an elephant; lastly, it is scarcely thicker than the bark of the good old English oak,--and if this noble sovereign, notwithstanding 'the heart' and interior substance of which it boasts, is, even in the well-protected park in which it has been born and bred, often prostrated by the storm, how difficult is it to conceive that an attenuated aërial hollow beam, no thicker than its mere rind, should, by human science, be constructed strong enough to withstand, besides the weights rushing through it, the natural gales and artificial squalls of wind to which, throughout its entire length, and at its fearful height, it is permanently to be exposed."

Notwithstanding these "incomprehensible" speculations, the tubes are abundantly strong to sustain the pressure of the heaviest trains, even were they to stand still in the middle of the bridge. It is calculated that each tube, in its weakest part, would sustain a pressure of four or five thousand tons, "support a line of battle ship, with all her munitions and stores on board," and "bear a line of locomotives covering the entire bridge." The bridge was completed, and the first train passed through it March 5th, 1850. The total cost of this gigantic structure was only £601,865.

GLORY OF ANCIENT ROME.