It may now be adviseable to trace the history of the steam-engine through some of its earlier modifications; and we shall find that, although the present form of this stupendous machine almost deserves the title of an invention, yet that many steps have been taken, and much labour and much ingenuity expended, before it was brought to that point from which the more modern improvements may be said to have begun. And whilst we admire the genius of those who have perfected the application of a mighty power, let us not refuse the tribute of praise to those, who first pointed out that such a power existed. [Illustration] The first apparatus of this description, of which any authentic account has been preserved, was suggested by Hero of Alexandria, and consisted of a vessel F in which steam was generated by the application of external heat. The ball G was supplied with the elastic vapour thus procured, by means of the bent pipe E B, a steam tight joint being provided for that purpose. Two tubes bent to a right angle at A and D, are the only parts open to the air, and as the steam rushes out from very minute apertures, a rotatory motion is produced. An account of this apparatus is preserved in Hero's _Spiritalia_, published by the Jesuits in 1693; and a copy of this highly curious work, with a Latin translation prefixed, is now in the Library of the London Institution. A modification of Hero's apparatus is represented beneath: It was constructed by Mr. Styles for the use of the Editor in his public lectures. The circular tube _a_ is in this case supported by the upright pillar _c d_; and the flame of alcohol in the trough _b_, by generating high pressure steam, which rushes from the apertures _e_, produces a rotatory motion. [Illustration] [Illustration] Brancas's revolving apparatus, as will be seen by reference to the diagram in the preceding page, was still more simple than that contrived by Hero. A copper vessel filled with water, (in the original figure made in the form of an ornamental head,) was furnished with a pipe _c_, through which the steam was propelled, and striking against the vanes of the float wheel _d_, readily gave motion to a pestle and mortar, which was employed in the alchemist's laboratory. The only work in which a description of this engine has been preserved, was published in 1629; it is exceedingly rare, and the above diagram is engraved from a copy in the possession of Major Colby. A slight examination of the principle upon which this simple apparatus is constructed, will shew that no very considerable force could have been obtained; as the steam passing through the atmosphere in its passage to the wheel, must, to a certain extent at least, be converted into water.