Inventions in the Century. Doolittle William Henry

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СКАЧАТЬ it is at the bottom of mines, a thousand feet below the earth's surface; it is in the mills and in the workshops of the trades. It rows, it pumps, it excavates, it carries, it draws, it lifts, it hammers, it spins, it weaves, it prints. It seems to say to men, at least to the class of artisans: 'Leave off your manual labour, give up your bodily toil; bestow but your skill and reason to the directing of my power and I will bear the toil, with no muscle to grow weary, no nerve to relax, no breast to feel faintness!' What further improvement may still be made in the use of this astonishing power it is impossible to know, and it were vain to conjecture. What we do know is that it has most essentially altered the face of affairs, and that no visible limit yet appears beyond which its progress is seen to be impossible."

      CHAPTER VIII.

      ENGINEERING AND TRANSPORTATION

      The field of service of a civil engineer has thus been eloquently stated by a recent writer in Chambers's Journal:

      "His duties call upon him to devise the means for surmounting obstacles of the most formidable kind. He has to work in the water, over the water, and under the water; to cause streams to flow; to check them from overflowing; to raise water to a great height; to build docks and walls that will bear the dashing of waves; to convert dry land into harbours, and low water shores into dry land; to construct lighthouses on lonely rocks; to build lofty aqueducts for the conveyance of water, and viaducts, for the conveyance of railway trains; to burrow into the bowels of the earth with tunnels, shafts, pits and mines; to span torrents and ravines with bridges; to construct chimneys that rival the loftiest spires and pyramids in height; to climb mountains with roads and railways; to sink wells to vast depths in search of water. By untiring patience, skill, energy and invention, he produces in these several ways works which certainly rank among the marvels of human power."

      The pyramids of Egypt, the roads, bridges and aqueducts built by the Chinese and by Rome; the great bridges of the Middle Ages, and especially those built by that strange fraternal order known as the "Brothers of the Bridge"; the ocean-defying lighthouses of a later period – these, and more than these, attest the fact that there were great engineers before the nineteenth century.

      But the engineering of to-day is the hand-maid of all the Sciences; and as they each have advanced during the century beyond all that was imagined, or dreamed of as possible in former times, so have the labours of engineering correspondingly multiplied. No longer are such labours classified and grouped in one field, called Civil Engineering, but they have been necessarily divided into great additional new and independent fields, known as Steam Engineering, Mining Engineering, Hydraulic Engineering, Electrical Engineering and Marine Engineering. Within each of these fields are assembled innumerable appliances which are the offspring of the inventive genius of the century just closed.

      We have seen how one discovery, or the development of a certain art, brings in its train and often necessitates other inventions and discoveries. The development and dedication of the steam engine to the transportation of goods and men called for improvements in the roads and rails on which the engine and its load were to travel, and this demand brought forth those modern railway bridges which are the finest examples in the art of bridge making that the world has ever seen.

      The greatest bridges of former ages were built of stone and solid masonry. Now iron and steel have been substituted, and these light but substantial frameworks span wide rivers and deep ravines with almost the same speed and gracefulness that the spider spins his silken web from limb to limb. These, too, waited for their construction on that next turn in the wheel of evolution, which brought better processes in the making of iron and steel, and better tools and appliances for working metals, and in handling vast and heavy bodies.

      The first arched iron bridge was over the Severn at Coalbrookdale, England, erected by Abraham Darby in 1777. In 1793 one was erected by Telford at Buildwas, and in the same year Burden completed an arch across the weir at Sunderland. The most prominent classes of bridges in which the highest inventive and constructive genius of the engineers of the century are illustrated are known as the suspension, the tubular and the tubular arch, the truss and cantilever.

      Suspension bridges consisting of twisted vines, of iron chains, or of bamboo, or cane, or of ropes, have been known in different parts of the world from time immemorial, but they bear only a primitive and suggestive resemblance to the great iron cable bridges of the nineteenth century. The first notable structure of this kind was constructed by Sir Samuel Brown, across the Tweed at Berwick, England, in 1819. Brown was born in London in 1776 and died in 1852. He entered the navy at the age of 18, was made commander in 1811, and retired as captain in 1842. We have alluded to the spider's web, and Smiles, in his Self Help, relates as an example of intelligent observation that while Capt Brown was occupied in studying the character of bridges with the view of constructing one of a cheap description to be thrown across the Tweed, near which he lived, he was walking in his garden one dewy autumn morning when he saw a tiny spider's web suspended across his path. The idea immediately occurred to him of a bridge of iron wires. In 1829 Brown also was the engineer for suspension bridges built over the Esk at Montrose and over the Thames at Hammersmith. Before that time, a span in a bridge of 100 feet was considered remarkably long. Suspension bridges are best adapted for long spans, and have been constructed with spans more than twice as long as any other form. Sir Samuel Brown's bridge had a span of 449 feet. This class of bridges is usually constructed with chains or cables passing over towers, with the roadway suspended beneath. The ends of the chains or cables are securely anchored. The cables are then passed over towers, on which they are supported in movable saddles, so that the towers are not overthrown by the strain on the cables. Nice calculations have to be made as to the tension to be placed on the cables, the allowance for deflection, and the equal distribution of weight. The floor-way in the earlier bridges of this type was supported by means of a series of equidistant vertical rods, and was lacking stiffness, but this was remedied by trussing the road bed, using inclined stays extending from the towers and partially supporting the roadway for some distance out from the tower.

      The next finest suspension bridge was constructed by Thomas Telford and finished in 1826, across the Menai Strait to connect the island of Anglesea with the mainland of Wales. Telford was born in Dumfriesshire, Scotland, in 1757, and died in Westminster in 1834. Beginning life as a stone mason, he rose by his own industry to be a master among architects and a prince among builders of iron bridges, aqueducts, canals, tunnels, harbours and docks.

      The Menai bridge was composed of chains or wire ropes, each nearly a third of a mile in length, and which descended 60 feet into sloping pits or drifts, where they were screwed to cast-iron frames embedded in the rocks. The span of the suspended central arch was 560 feet, and the platform was 100 feet above high water. Seven stone arches of 52½ feet span make up the rest of the bridge.

      But a suspension bridge was completed in 1834 by M. Challey of Lyon over the Saane at Fribourg, Switzerland, which greatly surpassed the Menai bridge. The span is 880 feet from pier to pier, and the roadway is 167 feet above the river. It is supported by four iron wire cables, each consisting of 1056 wires. It was tested by placing 15 pieces of artillery, drawn by 50 horses and accompanied by 300 men crowded together as closely as possible, first at the centre, and then at each extreme, causing a depression of 39½ inches, but no sensible oscillation was experienced.

      Isambard K. Brunel was another great engineer, who constructed a suspension bridge at the Isle of Bourbon in 1823, and the Charing Cross over the Thames at Hungerford in 1845, which was a footbridge, having a span of 675 feet, the longest span of any bridge in England. Then followed finer and larger suspension bridges in other parts of the world. It was across the Niagara in front of the great falls that in 1855 British America and the United States were joined by a magnificent suspension bridge, one of the finest in the world, and the two English speaking countries were then physically and commercially united. At the opening of the bridge, one portion of which was for a railway, the shriek of the locomotive and the roar of the train mingled with the roar of the wild torrent 250 feet below. The bridge, 800 feet long, СКАЧАТЬ