two single cylinders, placed at some distance from each other, each of which is provided with a piston made to fit air-tight, and connected with a forcing pump.

When steam of considerable elasticity is admitted at the bottom of the first cylinder, it is forced upwards, carrying with it the lever of the pump; at the same time that the steam or air is expelled from the other. On this operation being repeated, or rather reversed, the steam is allowed to enter the second cylinder, which is also connected with the boiler, while the steam in the first cylinder is allowed to escape into the air. From this it will be evident that the process of condensation forms no part of the principle of the high-pressure engine; and that the expansion of gunpowder might be made to produce a precisely similar effect.

The amazing force to be produced by the expansion of highly elastic vapour, did not escape the penetrating notice of that towering genius, which was now directing all its energies towards its improvement. Accordingly, we find in Mr. Watt's first patent, the following clause, which expressly describes this engine: "I intend, in many cases, to employ the expansive force of steam to press on the pistons, or whatever may be used instead of them, in the same manner as the pressure of the atmosphere is now employed in common fire-engines. In cases where cold water cannot be had in plenty, the engines may be

method, however, supposes a capability of blending the business of a distiller with a variety of trades, to which it is totally inapplicable. A scheme somewhat similar to this, and to which we shall afterwards more fully revert, has lately been attempted by Colonel Congreve, in which he proposes to burn a large portion of chalk mixed with the coal, and thus convert the furnace into an

"Since the vapour of alcohol, having the same elastic force as the atmosphere, contains of the latent heat of ordinary steam, and since its elastic force is doubled at the 206th degree (six below the boiling heat of water) with perhaps one-third of additional caloric, might we not, in particular circumstances, employ this vapour for impelling the piston of a steam engine? The condensing apparatus, could be, I imagine, so constructed, as to prevent any material loss of the liquid, while more than a quadruple power would be obtained from the same size of cylinder at 212o, with an expenditure of fuel not amounting to one half of what aqueous vapour consumes; or the power and fuel would be as three to one, calling their relation in ordinary steam one to one. A considerable engine could thus also be brought within a very moderate compass. Possibly, after a few operations of the air pump, the incondensible gas may be so effectually withdrawn, that we might be permitted to detach this mechanism, which, though essential to common engines, takes away one-fourth of their power. In a distillery in this country, or on a sugar estate in the colonies, a trial of this plan might perhaps be made with advantage. While exercising its mechanical functions of grinding, mashing, or squeezing the canes, it would be converting ordinary into strong spirit for rectification, or for the convenience of carriage. Might not such an engine be erected on a small scale, for many purposes of domestic drudgery? It would unquestionably furnish a beautiful illustration in philosophy, to make one small portion of liquid, by the agency of fire, imitate the ceaseless circulation and restless activity of life."-Phil. Tran. vol. cviii. p. 393.

efficient lime-kiln. From this view of the subject, we think it will be seen, that however plausible or ingenious this invention may appear in theory, there are insuperable objections to its general employment. We are still, however, greatly indebted to Mr. Cartwright for the mechanical arrangement of the engine, described in this patent, as it furnishes the first hint for an elastic metal piston, which has since been found of the greatest use in high-pressure engines.

The first Portable Steam Engine appears to have been constructed by Mr. Smeaton, who employed it for draining foundations and other temporary works. It had a pulley, or wheel, to receive the chain which communicated motion from the piston to the pump-rod, instead of a beam. The pivots of the wheel were supported by two inclined beams connected at top, whilst the cylinder and pump were bolted down to the groundsills. Thus, the whole machine being supported by one frame of wood, it could without trouble be set to work in the open air. The boiler, which required no setting in brick work, was in the shape of a tea-kettle, and the fire-place being in the centre, was surrounded on all sides. by water, thus presenting the greatest possible surface to the action of the flame. Portable steam engines are now employed not only in the erection of bridges, and in underground excavations, but are also usefully applied to the purpose of propelling vessels and carriages: the latter appli

a communication both at its top and bottom, with the steam vessel. A communication being also formed between the top of the smaller cylinder and the bottom of the larger cylinder, and vice versa. When the engine is set to work, steam of a high temperature is admitted from the boiler to act by its elastic force on one side of the smaller piston, while the steam which had last moved it, has a communication with the larger or condensing cylinder. If both pistons be placed at the top of their respective cylinders, and steam of a pressure equal to forty pounds the square inch, be admitted, the smaller piston will be pressed down, while the steam below it, instead of being allowed to escape into the atmosphere, or pass into the condensing vessel, as in the common engine, is made to enter the larger cylinder above its piston, which will make its downward stroke at the same time as that in the smaller cylinder; and, during this process, the steam which last filled the larger cylinder, will be passing into the condenser to form a vacuum during the downward stroke.

To perform the upward stroke, it is merely necessary to reverse the action of the respective cylinders; and it will be effected by the pressure of the steam in the top of the small cylinder, acting beneath the piston in the great cylinder; thus alternately admitting the steam to the different sides of the smaller piston, while the steam last admitted into the smaller cylinder, passes regularly to the different sides of the larger piston,

two single cylinders, placed at some distance from each other, each of which is provided with a piston made to fit air-tight, and connected with a forcing pump.

When steam of considerable elasticity is admitted at the bottom of the first cylinder, it is forced upwards, carrying with it the lever of the pump; at the same time that the steam or air is expelled from the other. On this operation being repeated, or rather reversed, the steam is allowed to enter the second cylinder, which is also connected with the boiler, while the steam in the first cylinder is allowed to escape into the air. From this it will be evident that the process of condensation forms no part of the principle of the high-pressure engine; and that the expansion of gunpowder might be made to produce a precisely similar effect.

The amazing force to be produced by the expansion of highly elastic vapour, did not escape the penetrating notice of that towering genius, which was now directing all its energies towards its improvement. Accordingly, we find in Mr. Watt's first patent, the following clause, which expressly describes this engine: "I intend, in many cases, to employ the expansive force of steam to press on the pistons, or whatever may be used instead of them, in the same manner as the pressure of the atmosphere is now employed in common fire-engines. In cases where cold water cannot be had in plenty, the engines may be

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