"So novel an apparatus excited the curiosity of all Rome, and of foreigners also, who came from distant countries to see what effect would be produced by this ma.s.s of beams, mingled with ropes, windla.s.ses, levers, and pulleys. In order to prevent confusion, Sixtus V. issued one of his mandates, that on the day of its being worked, no one, except the workmen, should enter the enclosure, on pain of death, and that no one should make the least noise, nor even speak loud. Accordingly, on the 30th of April, 1586, the first to enter the barrier was the chief justice and his officers, and the executioner to plant the gibbet, not merely as a matter of ceremony. Fontana went to receive the benediction of the pope, who, after having bestowed it, told him to be cautious of what he did, for a failure would certainly cost him his head. On this occasion, Sixtus felt the difference between his regard for his own glory, and his affection for the architect. Fontana, in terror, secretly placed horses at every gate, ready to convey him from the papal anger, in case of an accident. At the dawn of day, two ma.s.ses of the Holy Ghost were celebrated; all the artificers made their communion, and received the papal benediction, and before the rising of the sun all entered the barrier. The concourse of spectators was such, that the tops of the houses were covered, and the streets crowded. The n.o.bility and prelates were at the barriers, between the Swiss guards and the cavalry: all were fixed and attentive to the proceedings; and, terrified at the sight of the inexorable gibbet, every one was silent.
"The architect gave an order that, at the sound of the trumpet, each should begin working, and at that of the bell, placed in the castle of wood, each should desist; there were more than 900 workmen, and 75 horses. The trumpet sounded, and in an instant, men, horses, windla.s.ses, cranes, and levers were all in motion. The ground trembled, the castle cracked, all the planks bent from the enormous weight, and the pyramid, which inclined a foot towards the choir of St. Peter, was raised perpendicularly. The commencement having prospered so well, the bell sounded a rest. In twelve more movements the pyramid was raised almost two feet from the ground, in such a situation that it could be placed on the rollers, and it remained firmly fixed by means of wedges of iron and wood. At this happy event the castle of St. Angelo discharged all its artillery, and a universal joy pervaded the whole city.
"Fontana was now convinced that the ropes were better than iron bands, these being most broken or distorted, or expanded by the weight. On the 7th of May the pyramid was placed on the sledge--a more difficult and tedious operation than that of raising it, it being necessary to convey it over the piazza to the situation intended for it, which was 115 rods from where it then stood. The level of the piazza being about 30 feet lower, it was necessary to throw up an earthen embankment from one place to the other, well secured by piles, &c. This being done, on the 13th of June, by means of four windla.s.ses, the pyramid was removed with the greatest facility on the rollers, to the place of its destination. The pope deferred its erection to the next autumn, lest the summer heats should injure the workmen and spectators.
"In the meantime the pedestal, which was interred 30 feet, was removed: it was composed of two parts, the ogee and bas.e.m.e.nt being of the same ma.s.s, and the plinth of white marble. All the preparations were made for this last operation on the 10th of September, with the same solemnities; 140 horses and 800 men were employed. The pope selected this day for the solemn entrance of the duke of Luxembourg, amba.s.sador of ceremony from Henry III. of France, and caused the procession to enter by the Porta Angelica, instead of the Porta del Popolo. When this n.o.bleman crossed the Piazza of St. Peter"s, he stopped to observe the concourse of workmen in the midst of a forest of machines, and saw, admiring, Rome rising again by the hand of Sixtus V. In fifty-two movements the pyramid was raised, and at the setting of the sun it was placed firm upon its pedestal. The castle disappeared, and the artificers, intoxicated with joy, carried Fontana on their shoulders in triumph to his own house, amidst the sound of drums and trumpets, and the plaudits of an immense crowd.
"In placing it upright on the pedestal, Fontana considered the method adopted by the ancients as the least difficult; which was to rest one end on two globes, then draw the point round, raising it at the same time, afterwards letting it fall perpendicularly on the pedestal. It is conjectured that this was the practice adopted by the ancients, because two dies alone were always covered with lead for a foot or more, and were moreover crushed at the extremities. Sixtus V. placed a cross 7 feet high at the top of the obelisk, which was carried in procession, and which made the whole height 132 feet.
"For this undertaking, Fontana was created a knight of the Golden Spur, and a Roman n.o.bleman; he had a pension of 2000 crowns, transferable to his heirs, ten knighthoods, 5000 crowns of gold in ready money, and every description of material used in the work, which was valued at more than 20,000 crowns. Two bronze medals of him were struck; and the following inscription was placed on the base of the pyramid by order of the pope:--"
Dominicvs Fontana, Ex. Pago. Agri. Novocomensis.
Transtvlit. Et. Erexit.
REMOVAL OF AN OBELISK FROM THEBES TO PARIS.
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 ma.s.s 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 ma.s.s 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 bas.e.m.e.nt walls 2 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 ma.s.s 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 ma.s.s 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 b.a.l.l.s composed of bra.s.s, 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 ma.s.s 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 b.a.l.l.s at proper distances, of which there were thirty, of the diameter of five inches. The mountain was moved by four windla.s.ses, and sometimes by two; each required thirty-two men: it was raised and lowered by screws, to remove the b.a.l.l.s 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 ma.s.s in the square of St. Peter"s, to the honor of Peter, Falconet, Carburi, and of Catherine, who may always, from her actions, be cla.s.sed among ill.u.s.trious 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 a.s.sume." The Menai Straits are about twelve miles long, through which, imprisoned between the precipitous sh.o.r.es, 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 s.p.a.ce 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 sh.o.r.e. 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 pa.s.s 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 sh.o.r.e, 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 circ.u.mstances, 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 Ill.u.s.trated 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 "a.s.sistant 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 sh.o.r.e. 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 sh.o.r.es, near to and opposite the further end of the tube platforms; in their course, they will pa.s.s 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 r.e.t.a.r.ding, 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.