Hero's Aeolipile
In the same treatise of Hero mentioned previously, there is a drawing and description of another Steam Machine, more ingenious than the preceding, and forming one of the various forms of an ancient apparatus called an aeolipile, which is still used by lecturers on Natural Philosophy, to illustrate the nature and the properties of steam. This machine, which is represented in Figure 2, consists of a pot or vessel of water AB, placed over a fire as before, and covered with a lid, CD, into which, at one side, is fixed the one end D, of a tube EFG, bent at right angles, and having it's other end G fitted into a hollow sphere, in the direction of it's axis. At the other extremity of this axis, there is placed a pivot, which is fixed on a rod LM, fastened to the lid, at the other side. From the sphere, two tubesm H and K, proceed in the direction of a diameter, at right angles to the axis, and bent at right angles to this diameter, in opposite directions.
When the vessel is heated, the steam will pass through the upright tube into the sphere, and thence issuing through the tubes bent at right angles, will cause the sphere to revolve with a velocity proportioned to the force of the steam. The representation of this apparatus is copied from an old edition of Hero's work, and, from it's shape, it is evidently of great antiquity.
With respect to this machine, it may be observed, that if the steam were made to issue from straight tubes placed in the direction of the radii of the sphere, no motion would be produced; but, when these tubes are bent at right angles, the steam cannot issue from them without creating a certain reaction, in a direction opposite to that from which the steam proceeds. This reaction producs a motion of rotation whose velocity increases in proportion to the intensity of the steam which issues through the tubes. The greatest effect, is, of course, produced when the orifices of the bent tubes are in opposite directions, and perpendicular to the same diameter.