steam, so as to obtain the use of the enormous expansive force for our own purposes, it is evident that we could produce most powerful effects by it. To do this-to catch water in the act of passing into steam, and turn the expansive force to account-is the purpose of steam-engines properly so called.

Even this use of the expansive force of steam was in some degree known to the ancients. Often, as M. Arago observes, in casting the fine metal statues for which ancient art is so famous, a drop of water or other liquid would be left enclosed in the plaster or clay moulds when the molten metal was poured in; and the consequence would be an explosion, and, in many cases, a fearful accident from the instantaneous conversion of the enclosed drop of liquid into steam. Arguing from such instances, the ancient naturalists accounted for earthquakes and submarine explosions on a similar principle, by supposing the sudden vaporisation of a mass of water by volcanic heat. Nor were the ancients afraid of handling the power which they thus recognised. In the images of the ancient gods were concealed crevices containing water with the means of heating it; and tubes proceeding from these crevices conducted the steam, so as to make it blow out plugs from the mouths and foreheads of the images with loud noise and apparent clouds of smoke. A more ingenious device still, and which represents the utmost extent to which the ancients carried their use of the expansive force of steam, is one described by Hero, the purpose of which seems likewise to have been priestly imposition. To accomplish this trick, Hero directs vessels halffull of wine to be concealed inside of two figures, in the shape of men standing on each side of an altar. From these vessels tubes, in the form of bent siphons, with the short end in the wine, proceed along the extended arms of the figures to the tips of their fingers, which are held over the flame of the sacrifice. Other tubes proceed from the same vessels downwards, through the feet of the figures, communicating through the floor with the altar and the fire. "When, therefore," says Hero, "you are about to sacrifice, you must pour into the tubes a few drops, lest they should be injured by heat, and attend to every joint lest it leak; and so the heat of the fire, mingling with the water, will pass in an aërial state through these tubes to the vases inside the figures, and, pressing on the wine, make it to pass through the bent siphons, until, as it flows from the hands of the living creatures, they will appear to sacrifice as the altar continues to burn." Here we have the expansive force of steam employed directly to raise a liquid, by pressure, above its natural height.

From the time of Hero down to the beginning of the seventeenth century, no advance appears to have been made in the application of steam-power. Passing over one or two casual notices of persons who, about this time, are said to have conceived the use of steam for mechanical purposes, it may be stated that the process of discovery was taken up exactly at the point where

Hero left it by Solomon de Caus, a Frenchman of Normandy, who, after a residence in England, where he was employed in designing grottos, fountains, &c. for the palace of the Prince of Wales, afterwards Charles I., at Richmond, returned to the continent, and published an account of these and other inventions at Frankfort in the year 1615. De Caus's steam invention is a modification, in a more patent and distinct form, of the lastmentioned artifice of Hero. A hollow copper globe is filled to the extent of two-thirds or thereby with water, through a funnelshaped pipe, which enters it, and which is furnished with a stopcock. Besides this pipe, another descends nearly to the bottom of the globe, so as to have its termination beneath the water. It is likewise furnished with a stopcock, and its nozzle is small. If now the vessel be placed over a fire, with the stopcock of the first pipe shut, and that of the other open, it is evident that when the water begins to boil, the steam being enclosed, will press down the water, and compel it to rush up the second pipe, forming a jet.

an

Such is the steam toy of De Caus, upon which many French writers have founded the claim that steam should be considered a French invention. If, however, the merit of a man, with regard to an invention with the origin of which he is concerned, is to be measured by his own perception of its importance, the merit of Solomon de Caus, with regard to steam machinery, cannot be compared with that of the Marquis of Worcester (known in political history as the Earl of Glamorgan), who, in his "Century of Inventions," published in 1663, describes " admirable and most forcible way to drive up water by fire, not by drawing or sucking it upward," but by a method according to which 66 one vessel of water rarefied by fire driveth up forty vessels of cold water." What value the marquis attached to this invention, appears from the striking language he uses with regard to other modifications of it. Of one he says, "I call this a semi-omnipotent engine, and do intend that a model thereof be buried with me." He also describes a water-work capable, he says, of raising water with the utmost facility to the height of a hundred feet, and which will, therefore, "drain all sorts of mines, and furnish cities with water though never so high seated." This he pronounces "the most stupendous work in the whole world-an invention which crowns his labours, rewards his expenses, and makes his thoughts acquiesce in the way of further inventions."

It is ascertained that the Marquis of Worcester had actually constructed an apparatus such as he describes. Although, however, it would thus seem that steam-power, in one of its most imposing forms, was in actual operation so early as 1656, the invention does not appear to have taken root; and it is not till 1699, upwards of thirty years after the Marquis of Worcester's death, that we find the steam-engine again pressed on public

notice. In that year Captain Thomas Savary exhibited to the Royal Society a model of an engine for draining mines, and raising water to great heights. The difference between the Marquis of Worcester's invention and Savary's consisted in this, that whereas "the Marquis's model appears to have been placed on or below the level of the water to be raised, so that the water was forced up solely by the elastic force of the steam, Savary, on the other hand, erected his engine at a height of nearly thirty feet above the level of the water."

The improvement of Savary consists in combining the force of atmospheric suction, as it is usually called, with that of steam pressure; using the first to raise the water thirty feet, and then the other to raise it thirty feet or more additional; and when it is considered that, in the actual working engine, there was not only one receiver, but two, which could be alternately filled with steam and cooled, so as to prevent the loss of time, the value of the improvement will be seen to be very great. Savary called his machine the "Miner's Friend;" it seems, however, to have been used only for the purpose of raising water in houses.

The next great contribution to the steam-engine came from a French engineer, Denis Papin, known for other important mechanical inventions. His important service to steam-power consisted in the idea of making it act through the cylinder and piston. In De Caus's and in Savary's apparatus, the steam pressed directly upon the surface of the water; but Papin-conceived the idea of introducing the steam into the bottom of the receiver, so as to force up, by its elasticity, a tightly-fitting plate or piston, which would again descend by the pressure of the atmosphere as soon as the steam beneath was condensed. The importance of this modification can hardly be overrated, when it is considered that it amounts to the application of steam-power to produce the motion of a rod up and down in a cylinder. This was the great step, the conciliation of steam, as it were, into a regular moving power at the command of man; and, as M. Arago observes, the procuring afterwards, from the strokes of the piston, the power to turn millstones, or the paddles of a steamboat, or to uplift the massy hammer, or to move the huge clipping shears-these were but secondary problems. Papin, however, did not work out his own conception-did not perceive all its consequences.

The next modification of the steam-engine, and its ultimate one before it came into the hands of Watt, consisted, it may be said, in the union of Savary's idea with that of Papin. The authors of this invention-which may, in reality, be considered as the first working steam-engine-were Thomas Newcomen, an ironmonger, and John Cawley, a glazier, both of Dartmouth in Southampton. In the year 1705, these two individuals " constructed a machine which was meant to raise water from great depths, and in which there was a distinct vessel where the steam was generated. This machine, like the small model of Papin,

consisted of a vertical metallic cylinder, shut at the bottom and open at the top, together with a piston accurately fitted, and intended to traverse the whole length, both in ascending and descending. In the latter, as in the former apparatus also, when the steam was admitted into the lower part of the cylinder, so as to fill it, and counterbalance the external atmospheric pressure, the ascending movement of the piston was effected by means of a counterpoise. Finally, in the English machine, in imitation of Papin's, so soon as the piston reached the limit of its ascending stroke, the steam which had impelled it was refrigerated; a vacuum was thus produced, and the external atmosphere forced the piston to descend."* The only novelty in Newcomen's engine, over and above what had existed either in Papin's or in Savary's model, was the mode of condensing the steam in the cylinder. This was effected not by simply withdrawing the heat from the bottom of the cylinder, as Papin had done, nor by dashing cold water on the outside of it, as in Savary's apparatus, but in directing a stream of cold water into the inside of the cylinder at every rise of the piston. This improvement—an important one at the time-is said to have been made by accident, from the circumstance of water once finding its way into the cylinder through a hole in the piston, and astonishing the onlookers by its results. The en

tire action of Newcomen's engine will be understood from the annexed cut, representing a section of it. B is the boiler, built over a furnace, and kept about two-thirds full of water; the quantity of water being regulated by means of two vertical tubes with stopcocks (GG), which descend into the boiler, the one to a greater depth than the other, so that when the boiler contains its proper quantity of water, the longer tube shall dip into it, while the shorter does not reach

it. When the boiler is heated, the pressure of the steam in its

* Arago's Life of Watt.

upper part will, if the proper quantity of water be in the boiler, force the water up the longer pipe, while only steam issues from the shorter. Should both pipes emit water, then it is known that the boiler is too full; should both emit steam, that it is not full enough; and the supply can be regulated accordingly. Besides these gauge pipes, there is in the boiler a safety valve (Š V), loaded so as to lie tight until the steam in the boiler accumulates to a degree sufficient to force it up. From the boiler the steam passes through the connecting tube, guarded by the regulating valve (V), made so as to open and shut easily, into the cylinder (C). Up and down in this cylinder, which is open at the top, moves the piston (P), attached by means of the piston-rod (M) to a flexible chain, which is fastened to the top of the arch at the end of a beam, moving on the pivot (I). The end of the beam to which the pistonrod is attached is made lighter than the other end, so that when the engine is at rest, it ascends and pulls up the piston to the top of the cylinder. The piston thus lying at the top of the cylinder, lets the steam from the boiler be admitted through the regulating valve (V). The steam rushing in expels the air which was in the cylinder through the snifting valve (H), which is at the bottom of the cylinder, and so constructed, that although it permits the escape of the air, it allows none to enter. The whole space of the cylinder underneath the piston being now filled with steam, the next operation is to condense it. This is done by turning a cock (R) in the tube (A), which descends from a cistern kept constantly full of cold water. The water, tending to rise to the height from which it has fallen, spouts into the cylinder, striking against the bottom of the piston, and falling down in a shower of drops, which cool the cylinder and condense the steam. This condensation of the steam produces a vacuum in the cylinder; and the piston, pressed down by the weight of the atmosphere outside, rapidly descends-the water which was thrown into the cylinder being carried off by the long eduction pipe which, having a valve at its extremity opening only outwards, leads to a cistern (S), whence the boiler is supplied. The descent of the piston pulls down the piston-rod and chain, and the end of the beam to which they are attached. The other end of the beam accordingly rises, pulling up a chain which is attached to the pump-rod (N), working the pump by which the mine is to be drained. The purpose of the smaller pump-rod working parallel to N, is, by the action of the engine, to raise a portion of the water through the tube (E E) to the cistern from which the water is sent into the cylinder. The piston is now at the bottom of the cylinder, and would remain there by the pressure of the atmosphere on its upper surface; but by opening the valve (V), the steam from the boiler is admitted under it, and the pressure of the atmosphere being thus counterbalanced, the superior weight of the pump-rod end of the beam causes it to descend, elevating the other end with the piston attached to it.