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.
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.