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ALTHOUGH the elastic power of the vapour of water must have been familiar to man from the ear liest period of his history, the first recorded observation of the fact, and the application of Steam to generate motion, appear to have been made by a Greek mechanic, about one hundred and thirty years before the Christian era.

Hero the Elder, who flourished at Alexandria in the reign of Ptolemy Philadelphus, was eminently distinguished in that age and region of refinement, not only for the extent of his attainments in the learning of the time, but also for the number and ingenuity of his mechanical inventions. In one of his books, he deduced all the laws of what are called the mechanical powers from the properties of the lever. His Spiritalia, or Pneumatica, contains the 3 first account of the forcing pump: of a fountain, still

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known by his name, in which water is elevated in a jet by the elasticity of condensed air. Among other contrivances in the same treatise, he describes two machines of his invention; in one of which a rotatory motion is produced by the emission of heated air; and a similar movement is imparted to the other by the reaction of vapour rising from boiling water.

A pipe, a, is directed by Hero to be inserted under the hearth of an altar, (our vignette,) on which a fire is burning. This pipe, placed in a vertical position, is moveable on a pivot, b, resting on the base of the altar. Two other pipes, c, d, of smaller diameter, proceed from the vertical one in a horizontal direction, having their extremities, e, f, open, and turned upwards. A base, or drum, g, is attached to the pipes, on which are placed small figures in various attitudes. The air at the upper extremity of the vertical pipe being heated by contact with the under side of the altar hearth, is expanded, and descends into the pipe, and proceeding along the horizontal arms, is expelled at their orifices, e, f. This causes them to revolve round the pivot b, so that the figures which are placed on the base g, are carried round with it, and appear "to lead the dance, as if they were animated beings."

It is scarcely necessary to notice the identity of this elegant apparatus with that of Barker's mill; and that the rotatory motion would be produced, as stated by Hero, though not by the emission of warm, but through the admission of cold air at the orifices in the horizontal arms, in consequence of the rarefaction at the upper end of the vertical pipe under the hearth of the altar.

The second machine is constructed on a similar principle ;—a globe moved on a pivot, by means of steam conducted into it from a boiling caldron.

The caldron or heated vase, p, in the Second Figure, is to be closely covered with a lid; into which a pipe, o, is inserted at one side of its circumference. This pipe, after rising vertically for a short distance, is bent at right angles. On its horizontal end is placed a small globe, x, kept in its position by a pipe, s, also bent at right angles and fixed to the lid opposite to o, but terminating in a pivot, q, on which the little globe revolves. This globe is furnished with two small pipes, %, w, bent at their extremities and open. The steam from the boiling water in p, rising through the pipe o, is admitted at s into the globe; and issuing through the bent tubes z, w, causes the sphere to revolve as if it were "actuated from within by a spirit.

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This simple and effective apparatus, though described but as a philosophical toy, is curious, as being the primitive mode in which steam was applied to produce motion, and as conferring on Hero the honour of having invented and constructed the FIRST STEAM ENGINE.†

*The Spiritalia was first edited by Commandine, in 1571. It is also printed in the splendid folio collection of the works of the Ancient Mathematicians, published at Paris in 1693. The Greek text is accompanied with a Latin translation. The descriptions of the two machines, we have described, are in page 202 of that edition.

It is a remarkable circumstance, too, that this Greek scheme should be revived as an improvement upon the almost