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pand to about five, ten, twenty, thirty, and forty times its volume respectively; its elastic force, when thus dilated, being in each case equal to the ordinary pressure of the atmosphere.

One pound of Newcastle coal converts seven pounds of boiling water into steam; and the time required to convert a given quantity of boiling water into steam, is six times that required to raise it from the freezing to the boiling point.

To shew by direct experiment the great expansive force of vapour from water when converted into steam, by the application of heat, it will only be necessary to take a glass tube, at one end of which is a bulb of two inches in diameter, and dropping into it a single spherule of water, the diameter of which will scarcely exceed one tenth of an inch, or about the eighteen hundredth part of the size of the glass bulb, we shall find, that it may very readily be expanded by the application of heat, so as to expel the air from the vessel. That this is actually the case, may be shewn by merely plunging the mouth of the tube into cold water, and suffering the steam to return to its original state, which being effected by the abstraction of a portion of its artificial heat, the water will rush in from the external vessel, and occupy the place of the steam thus condensed, which could not have taken place had any portion of the air remained in the tube or its bulb.

From these data, it will be evident, that when steam is merely employed to displace the air in a

close vessel, and afterwards produce a vacuum by condensation, no more heat is necessary than what will raise the water for this purpose to 212°; but if, on the contrary, high pressure steam is required, a very considerable increase of heat will be essential; and of this kind was the elastic vapour employed in all the early steam engines to which we may now more immediately direct the

reader's attention.

Among the numerous competitors for the honour of having first suggested steam as a moving power in mechanics, we must certainly place Brancas and the Marquis of Worcester in the foremost rank. The former of these was an Italian philosopher, of considerable eminence, and who, in 1629, published a treatise entitled, "Le Machine, &c." which contained a description of a machine

for this purpose. The apparatus employed by

Brancas, was in fact nothing more than a large æolipile, similar to the blow-pipe invented by M. Pictet of Geneva, with this difference, that the aperture in the pipe connected with the body of the æolipile instead of being directed to the lamp, (or in this case, the furnace that heated the machine,) was made to strike against the floats or vanes of a wheel, by which means a rotatory motion was produced.

After the publication of this scheme, which it is probable was never put in practice with any useful effect, nearly thirty years elapsed ere the farther consideration of this important subject

was resumed by the Marquis of Worcester. The mode of employing steam recommended by the Marquis, and which he describes in his "Century of Inventions" to have completely carried into effect, was entirely different from that of his predecessor; and it is evident that the noble author had received no previous hint of Brancas' invention, as he expressly states in another part of the above work, that he "desired not to set down any other mens' inventions ;" and if he had in any case acted on them, "to nominate likewise the inventor."

It is said that the Marquis, while confined in the

* This work was written about the middle of the seventeenth century, and considered as a description of the united discoveries of one individual, is certainly one of the most extraordinary scientific productions which has yet issued from the press in any age or nation. In addition, however, to its value, as containing the first tangible suggestion for the employment of steam, as an hydraulic and pneumatic force, it has unquestionably formed the foundation of a large portion of the patent inventions, which make so prominent a feature in the present day. The praiseworthy labours, however, of this indefatigable nobleman, shared the fate which usually attends on projections; and it was left to the slow though certain march of scientific improvement, to award to his memory a posthumous praise. The Marquis also published a work, entitled, "An exact and true Definition of the most stupendous Water-commanding Engine, invented by the Right Honourable (and deservedly to be praised and admired) Edward Somerset, Lord Marquis of Worcester, and by his Lordship himself presented to his most excellent Majesty Charles the Second, our most gracious Sovereign." This was published in a small quarto volume of only twenty-two pages, and consists of little more than an enumeration of the wonderful

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