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result of their skill or industry-microcosms, where men live nearly as unprogressive as the Anthropoids, and little raised above them in intellectual development, living and labouring only to supply their immediate material wants, and dying only to be forgotten.

Among these the engineer has no place; but gradually the stagnant pools of intellectual sleep are being drained, and mankind are being formed into larger masses. In former years this was effected by the rude but ready mode of conquest, or of pilgrimage,-Alexander's glorious raid did more to bring the East and West together, than had been effected by the trade of the Egyptians or Assyrians; and it paved the way for the more systematic conquests of the Romans, who nearly united all the known world into one great empire. When that broke down, as sooner or later all systems based on violence must, it was the Crusades that first awakened Europe from the torpor and isolation of the dark ages; and the pilgrimages to the shrine of St. Peter at Rome, or to the Caaba at Mecca, prevented the two great families of mankind from resolving themselves into a multitude of incoherent atoms. During the last three centuries the tendency has been to combine mankind into a certain number of larger empires; but to define these by strictly marked boundaries, and to prevent intercommunication by custom-house and police regulations. Steam and rail are now tending to sweep away these barriers, and to fuse all the families of the earth together.

This is not the place in which to speculate with the sanguine whether war and international jealousies will cease through this better knowledge and greater familiarity of men with one another, or to attempt to prophesy with the desponding, the greater evils that may arise from this gathering together of the nations. Nothing but a frightful catastrophe, of which we have no suspicion, can now stop the progress of road-making or the development of manufacturing industry. But, accepting that progress and that development as facts, it is well to endeavour to trace how and why the impulse was given, in order that we may more clearly see the direction in which the movement is tending.

The mechanical engineer naturally takes precedence of his road-making brother-in point of time at all events-inasmuch as it requires only one man to make or use a tool, and it requires many to make a road or build a ship; and man's progress in all material or useful arts is measured much more by his power of combination, than by his individual intellectual development. There are besides certain accidental aids placed at man's disposal, which he availed himself of at a very early period. We can

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hardly go back to the time when the hunter and the shepherd had not enlisted the dog to assist him in watching his flocks or in capturing game; or even to the time when the patient ox had not lent his assistance to draw the plough and to thrash out the grain. It was only at a much later stage that the less domestic horse was broken in to work for man, though he became, until the invention of steam, the most useful and the most versatile of all the assistant powers which man had borrowed from nature. He not only did all the work that had formerly been performed by the ox, but carried his master in war or the chase, bearing him or his goods on long journeys by land, or dragging waggons or coaches when roads were made, and turning mills for almost every kind of manufacture. Horse-labour, however, is expensive, and horseflesh heir to many of the ills of humanity; so wind and water were early enlisted to assist it-how early we hardly know-on land at least. On water the wind was in very ancient times entrapped to fill the sail and waft the frail bark of the savage across the lake, and afterwards even on the ocean, and it has since the invention of a keel and the increase in the size of ships done an amount of work in the carrying line far greater than could be done by all the horses in existence. On shore, however, its services have been far less readily available. The most obvious way of using it would evidently be to construct a machine like the paddle-wheel of a steam-boat, and encasing one half of it, to allow the wind to act on the other half. This has been frequently tried, but the exposed surface is so small, and the resistance of the enclosed part so great, that practically a sufficient amount of power cannot be obtained without a great expenditure of means, or unless it is blowing a gale of wind. A far more practical mode is the ordinary screw-mill, which is one of the most ingenious inventions of modern times, though when it was invented, or by whom, is by no means clear. We pride ourselves somewhat on the application of the screw to the propulsion of ships, but the employment of the same instrument to turn a mill, was a far more difficult and less obvious problem, the one being the exact converse of the other. In the windmill the passing air acts on the blades of the screw, and its force is transmitted to the circular mill which it works. In the ship the mill turns the screw, and its action in a fluid at rest forces forward the body containing the machine. Nothing can well be more ingenious than this mode of applying the power of wind; but then calm days frequently occur when the work is most wanted; or gales supervene when it is dangerous to loose the sails, and then all connected with the mill must remain idle. Thus uncertainty is the real defect of wind-power, which no ingenuity

ingenuity can overcome, and which will consequently, in spite of its cheapness, always limit its usefulness. Notwithstanding this a great deal of corn is ground in many parts of the world by wind-power, and much water raised in Holland and other low countries by its agency; but it is too uncertain for the great combinations of manufacturing industry, and therefore will probably never be developed to a greater extent than at present; in fact, it may fall into disuse as other powers become cheaper and handier, in consequence of their more regular and consequently more economical application.

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If, however, there is no great scope for mechanical ingenuity, and no great power to be obtained from so impalpable and so uncertain an element as wind, water forms a far more stable and more tangible agent for assisting man in his labours. It is uncertain how far the Romans ever used water as a power. they had mills, they were probably only wheels supported on two boats anchored in the current, such as are seen on the Rhine or Danube at the present day. To throw a dam across a stream, and conduct a regulated quantity of water to a fixed wheel in a house, required a mechanical organisation which the Romans had not apparently reached, and may also have been unsuited to the 'fiumaras' of Italy. Very early, however, in the Middle Ages corn-mills became common on the more constant streams of Northern Europe, and soon superseded hand-grinding as completely as the spinning-frame and the power-loom have done away with hand-spinning or weaving in this country. At the present day an immense quantity of hard work is done by waterwheels. Some of vast diameter have been erected where the fall of water is great, and others of great breadth where the stream is heavy and the fall small. Practically almost all our corn is still ground by water-power, and a great deal of forging and many mining operations are carried on with its assistance. The great inconvenience is that in most cases the manufacture must be taken to the power, as local circumstances generally prevent the power being conveyed to the spots most suitable for its application. The convenience of transport and the facility of subsistence generally limit the localities of large centres of manufacturing industry to fertile plains, and in these water-power is seldom available to any great extent.

Recently a new application of water-power has been effected by the inventive genius of Sir W. Armstrong. He first applied it at Newcastle, where the general level of the town is very much above that of the wharves of the harbour, and the waterworks in consequence provided a very tall column of water at the lower levels. Of this he availed himself by applying the pressure so

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obtained to force a piston along a watertight cylinder, and with a simple multiplying gear the cranes on the quays were made, by the mere turning of a cock, to raise any weight their construction could support. By applying the water-power alternately on both sides of the piston, and acting on a cranked axle—as done in the steam-engine-a water-engine was next invented, capable of exerting any amount of power that could be obtained from the height of the column of water and the amount of supply. When a sufficient head of water is available, or where the work is intermittent, this is certainly one of the most successful applications of water-power yet invented. At Great Grimsby Dock and at Birkenhead pipes are laid under the pavement from a reservoir at the top of a tall tower, to every part of the dock premises. At the foot of every crane, under the piston of every hoist, at every dock-gate, unseen and noiseless the power lies dormant; but a woman's hand applied to a small handle will set in motion a force sufficient to raise a mass weighing fifty or one hundred tons, and either to place it in the hold of a ship, or deposit it in any spot within reach of the arms of the crane. With equal ease the gates of locks one hundred feet in width are opened or shut, and the smallest as well as the heaviest works of the dockyard done without a stranger being able to perceive what it is that sets everything in motion.

As an accumulator of power Bramah's hydraulic press surpasses anything that has yet been invented, and may be carried to any extent that the strength of the metal will stand. The presses which were used to raise the tubes of the Menai Bridge when worked by a 40-horse power engine were capable of exerting a power equal to that of 14,200 horses, and raised one-half the tube, or 900 tons, slowly but steadily, through the 100 feet at which they were to be placed above the level of the water.

Air is, perhaps, too elastic to be ever practically used as an accumulator, but as a transmitter of power it nearly succeeded in the Atmospheric Railway in superseding the locomotive, and might have done so if engineers had been able to make a durable air-tight valve; and if they ever do so now it may again come into play. In the meanwhile a most ingenious combination of the working and transmitting power of air is employed to carry out the great tunnel through the Alps, which, without its aid, would be difficult in the extreme.

The tunnel under Mount Cenis is to be rather more than seven miles and a half in length, and as it is one English mile below the summit of the mountain, no air-shafts could be sunk from above; and the first difficulty was to ventilate a cul-de-sac that at one time, at least, must be nearly four miles in length. This has been accomplished

accomplished most successfully by M. Sommeiller the engineer, availing himself on the Italian side-of a stream of water eighty feet above the mouth of the tunnel. This is used to force air into a chamber, where it is kept at a constant pressure of six atmospheres by a stand-pipe 165 feet (50 metres) in height. From this it is conveyed in pipes to the innermost end of the excavation, where it is set to work to bore holes in the face of the rock for blasting purposes. There are eight perforators, each of which sinks ten holes three feet deep in the face of the rock in six hours. It takes some time to dry each of these, and to charge it with gunpowder; and it takes four hours to clear away the débris and to make all ready for commencing another set of perforations. So that practically only two sets are bored in twentyfour hours, and the progress is consequently six feet per day. At each blow on the head of the jumper a portion of the compressed air escapes, as steam does in a high-pressure engine. Its expansion is sufficient to cause a draft outwards, and keep the place perfectly ventilated; and even immediately after a blast the tunnel is freed from the products of the explosion very rapidly, and no inconvenience felt. By improvements in the machinery the engineer hopes to bore one set of holes in eight hours; and as the more work it does the more air it blows off, not only will the work be expedited, but the ventilation improved by the more rapid working.

There are numberless other methods by which air and water can be and are applied either separately or together, according to the locality or the nature of the work to be performed. They are invaluable assistants in mechanical operations as transmitters or accumulators, and when certain mechanical difficulties are conquered, will no doubt be much more used for these purposes than they have been hitherto; but as workers they are daily sinking into insignificance as compared with steam, which, whether used for locomotive purposes at sea or on land, or in stationary engines, bids fair to perform most of the heavy work of the world.

Without doubt the invention of the steam-engine is the greatest mechanical triumph which man has yet achieved. The use of horse-power, or of wind or water, was merely catching a portion of those forces which were already in motion on the face of the earth, and putting them into harness in order to extract as much work out of them as their inconstant nature would admit of; but the steam-engine owes its power to forces which were absolutely dormant till called into action by processes in its own interior, and which can be stopped or regulated at the will of those who have charge of it. The nearest approach

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