(3.)

The discovery of the fact, that a mechanical force is produced when water is evaporated by the application of heat, [Pg013] must be considered as the first capital step in the invention of the steam engine. It is recorded in a work entitled Spiritalia seu Pneumatica, that Hero of Alexandria contrived a machine, 120 years before the Christian era, which was moved by the mechanical force of the vapour of water. The principle of this machine admits of easy explanation: When a fluid issues from any vessel in which it is confined, that vessel suffers a force equal to that with which the fluid escapes from it, and in the opposite direction. If water issues from an orifice, a pressure is produced behind the orifice corresponding to the force with which the water escapes. If a man discharge a gun, the gases produced by the explosion of the powder issue with a certain force from the muzzle, and his shoulder is driven backwards by the recoil with a corresponding force. If the muzzle, instead of being presented forwards, were turned at right angles to the length of the gun, then, as the gases of explosion would escape sideways, the recoil would likewise take place sideways, and the shooter, instead of being driven backward, would be made to spin round as a dancer pirouettes. This was the principle of Hero's steam engine. A small globe or ball was placed on pivots at A and B ( fig. 1.), on which it was capable of revolving: steam was supplied through one of these pivots from one of the tubes D C E F, which communicated with the boiler. This steam filled the globe A I B K, and also the arms I H and K G. A lateral orifice, represented at G, near the end of these arms, allowed the steam to escape in a jet, and the reaction, producing a recoil, had a tendency to drive the arm round. A small orifice at H, on the other side of the tube, produced a like effect. In the same manner, any convenient number of arms might be provided, surrounding the globe and communicating with its interior like the spokes of a wheel. Thus these arms, having lateral orifices for the escape of the steam, all placed so that the recoil may [Pg014] tend to turn the globe in the same direction, a rotatory motion might be communicated to any machinery which it was desired to move.

After having been allowed to slumber for nearly two thousand years, this machine has recently been revived, and engines constructed similar to it are now working in these countries. In the proper place we shall describe Avery's Rotatory Engine, which it will be seen is, not only in its principle, but almost in its details, the machine of Hero of Alexandria.

Although the elastic force of steam was not reduced to numerical measure by the ancients, nor brought under control, nor applied to any useful purpose, yet it appears to have been recognised in vague and general terms. Aristotle, Seneca, and other ancient writers, accounted for earthquakes by the sudden conversion of water into steam within the earth. This change, according to them, was effected by subterranean heat. Such tremendous effects being ascribed to steam, it can scarcely be doubted that the Greeks and Romans were acquainted with the fact, that water in passing into vapour exercises considerable mechanical power. They were aware that the earthquakes, which they ascribed to this cause, exerted forces sufficiently powerful to extend the natural limits of the ocean; to overturn from their foundations the most massive monuments of human labour; to raise islands in the midst of seas; and to heave up the surface of the land of level continents so as to form lofty mountains.

Such notions, however, resulted not as consequences of any exact or scientific principles, but from vague analogies derived from effects which could not fail to have been manifested in the arts, such as those which commonly occurred in the process of casting in metal the splendid statues which adorned the temples, gardens, and public places of Rome and Athens. The artisan was liable to the same accidents to which modern founders are exposed, produced by the casual presence of a little water in the mould into which the molten metal is poured. Under such circumstances, the sudden formation of steam of an extreme pressure produces, as is well known, explosions attended with destructive effects. The Grecian [Pg015] and Roman artisans were subject to such accidents; and the philosopher, generalising such a fact, would arrive at a solution of the grander class of phenomena of earthquakes and volcanoes.

Before natural phenomena are rendered subservient to purposes of utility, they are often made to minister to the objects of superstition. The power of steam is not an exception to this rule. It is recorded in the Chronicles, that upon the banks of the Weser the ancient Teutonic gods sometimes marked their displeasure by a sort of thunderbolt, which was immediately succeeded by a cloud that filled the temple. An image of the god Busterich, which was found in some excavations, clearly explains the manner in which this prodigy was accomplished by the priests. The head of the metal god was hollow, and contained within it a pot of water: the mouth, and another hole, above the forehead, were stopped by wooden plugs; a small stove, adroitly placed in a cavity of the head under the pot, contained charcoal, which, being lighted, gradually heated the liquid contained in the head. The vapour produced from the water, having acquired sufficient pressure, forced out the wooden plugs with a loud report, and they were immediately followed by two jets of steam, which formed a dense cloud round the god, and concealed him from his astonished worshippers.[1]

Among other amusing anecdotes showing the knowledge which the ancients had of the mechanical force of steam, it is related that Anthemius, the architect of Saint Sophia, occupied a house next door to that of Zeno, between whom and Anthemius there existed a feud. To annoy his neighbour, Anthemius placed on the ground floor of his own house several close digesters, or boilers, containing water. A flexible tube proceeded from the top of each of these, which was conducted through a hole made in the wall between the houses, and which communicated with the space under the floors of the rooms in the house of Zeno. When Anthemius desired to annoy his neighbour, he lighted fires under his boilers, and the steam produced by them rushed in such quantity and with [Pg016] such force under Zeno's floors, that they were made to heave with all the usual symptoms of an earthquake.[2]

Blasco de Garay, A. D. 1543.