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Accidents

Engine to nautical purposes. are now, however, of but rare occurrence; and it is more than probable, that the great improvements that have been made in the boiler and safety-valve, will effectually secure these parts of the engine from a recurrence of those tremendous explosions, which unfortunately characterized the first introduction of Steam Navigation.

And, lastly, the political economist must hail with the most heartfelt gratification, the introduction of so able and efficient a substitute for animal labour as the Steam Engine. It has been calculated that there are at least ten thousand of these machines at this time at work in Great Britain; performing a labour more than equal to that of two hundred thousand horses, which, if fed in the ordinary way, would require above one million acres of land for subsistence; and this is capable of supplying the necessaries of life to more than fifteen hundred thousand human beings.

HISTORICAL ACCOUNT

OF THE

STEAM ENGINE.

CHAP. I.

Nature of Steam-Application of it as a moving power Brancas-Marquis of Worcester-Sir Samuel Morland-Papin-Savery—NewcomenHulls Falck-Amontons-Deslandes-Francois.

As the whole power of the Steam Engine depends on the employment of elastic vapour, produced from water at different temperatures, varying from 212°, or the boiling point of Fahrenheit's thermometer, to 300° of the same scale, it may be advisable in the first instance to examine some of the principal phenomena connected with the formation of vapour in its most simple form, and its application to the steam engine will then be sufficiently obvious.

B

Steam is highly rarefied water, the particles of which are expanded by the absorption of caloric, or the matter of heat. Water rises in vapour at all temperatures, though this is usually supposed to take place only at the boiling point: when, however, the evaporation occurs below 212°, it is confined to the surface of the fluid acted upon, but at that heat, steam is formed at the bottom of the water, and ascends through it, preventing its elevation to a higher temperature, by carrying off

the heat in a latent form. At the common pressure of the atmosphere, one cubic inch of water produces about 1700 cubic inches of aqueous vapour or steam; but the boiling point, as we have already stated, varies very considerably, and these anomalies materially effect the density of the va pour produced. Thus, in a vacuum water boils at about 70°, under common pressure, at 212°; and when pressed by a column of mercury, five inches in height, water does not boil until it is heated to 217°; each inch of mercury producing by its pressure, a rise of about 1° in the thermometer.

According to Dr. Ure's elaborate experiments, the elastic force of this vapour at 212° is such, that it is equivalent to the pressure of a column of mercury 50 inches in height; at 226.3°, to that of 40 inches; at 238.5°, to 50.3 inches; at 257.5°, to 69.8 inches; at 273.7°, to 91.2 inches; at 285.2°, to 112.2 inches; at 312°, to 166 inches; and Mr. Woolf has ascertained that at these temperatures, omitting the last, a cubic foot of steam will ex

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