Hero, the elder, was the son of a Greek, settled at Alexandria, who flourished about 130 years before the Christian era. In his work entitled Spiritalia, he describes, among other ingenious machines, three modes in which steam might be employed as a mechanical power; to raise water by its elasticity, to elevate a weight by its expansive force, and to produce a rotary motion by its reaction on the atmosphere. Although these contrivances only took the shape of philosophic toys, we have in them the undoubted germs of the vast power which its present modification permits. Hero in the introduction to his work professes to have made himself acquainted with the works of his predecessors and contemporaries; and, unwilling that they should perish or be overlooked, described them, that they might be better and more generally understood; so that it is probable the properties of expansion and contraction of steam were known long prior to the time in which he flourished.
The following is a brief description of the machine described by Hero for producing a rotary motion; the leading features of which have been the subject of several patents, taken out by uninformed persons; and there are several machines now in use on the same principle.
Hero's engine consisted of a hollow globe, having tubular arms, extending from it radially in opposite directions; and each of these tubes had a small opening on one of its sides near the extremity. The globe was suspended upon horizontal centres, one of which was hollow, and admitted steam, from a caldron situated beneath, with a fire under, into the hollow globe, which passing through the radiating tubular arms, issued laterally against the atmosphere, and produced a rotary motion, in the same manner as water produces that of Barker's mill.
At a is a caldron of water with a fire underneath it. The caldron is closed at the top, except at the pipe b, which is bent horizontally at c, and forms one of the two centres; the other is not visible, as it is behind b c; d is the hollow globe, e e the hollow arms, bent at / into right angles, for the emission of the steam in that direction.
The next proposal for the useful application of steam as a motive power, is to be found in a work by Solomon De Caus, an eminent French mathematician and engineer, published in 1615, entitled, "Les Raisonsdes Forces mouvantes, avec divers Desseins de Fontaines." The following description will explain the principle of his invention. a is a spherical vessel placed over a fire, it is furnished with two pipes b e. The pipe e is open at the top and reaches down to the bottom of the vessel a: the pipe b is furnished with a cock d and funnel c: the vessel being filled with water, and fire applied, steam is speedily generated on the surface of the water, and having no other way to escape, (the cock d being shut,) presses on the surface and so forces the water up the tube e into the air, causing a jet, which varies in proportion to the elasticity of the steam within. It is upon the strength of the above invention, that De Caus has by many been regarded as the inventor of the steam engine; and although we cannot quite concur in this opinion, we certainly regard him as entitled to great credit; for although the arrangement was such as could not be beneficially applied in practice, we have here the distinct announcement of one of the principles upon which Savery, nearly a century afterwards, constructed his engine, which is the first effective one on record.
In 1663 the Marquis of Worcester published a small tract entitled, "A Century of the Names and Scantlings of such Inventions as he had tried and perfected." In the 68th article of this Century he gives an inflated, boastful account of his "fire water-work," and in so obscure and contradictory a manner, that every commentator and writer on the steam engine, who has attempted to make out something reasonable from the pretended description, has been compelled to contrive and arrange what probably never entered into the imagination of the Marquis. Nevertheless, by many writers, implicit credit seems to be given to his assertions, and he is regarded as the inventor of the steam engine!
As far as the principle of his apparatus can be understood from his account, it appears to be the same as that which had been discovered, and much more clearly described, by De Caus fifty years before.
Although various expositions of the properties of steam, and suggestions for their application to move machinery, continued to be made from time to time by various persons, it is to Thomas Savery that we are indebted for the practical introduction of the steam engine as a moving power.
The following figure and description, nearly in Savery's own words, will illustrate the nature of his engine.
The first thing is, to fix the engine in a good double furnace, so contrived that the flame of your fire may circulate round and encompass your boilers, as you do coppers for brewing. Before you make any fire, unscrew G and N, being the two small gauge pipes and cocks belonging to the two boilers; and at the holes fill L, the large boiler, two-thirds full of water, and D, the small boiler, quite full. Then screw on the said pipes again, as fast and as tight as possible. Then light the fire at b, and when the water in L boils, open the cock of the first vessel P, (shown in section,) which makes all the steam rising from the water in L pass with irresistible force through O into P, pushing out all the air before it through the clack R; and when all is gone out, the bottom of the vessel P will be very hot; then shut the cock of the pipe of this vessel, and open the cock of the other vessel P, until that vessel has discharged its air through the clack R up the force-pipe S. In the mean time, a stream of cold water [supplied by a pipe connected with the discharging pipe, but not shown in the cut,] has been made to pass over the outside of the vessel P, which, by condensing the steam within, a vacuum or emptiness is created; so that the water from the well must and will necessarily rise up through the sucking-pipe, (cut off below M,) lifting up the clack M, and filling the vessel P.