From the circumstance of the nature of the machinery having been concealed, it is impossible to say in what this machine consisted; but as a boiler was used, it is probable, though not certain, that steam was the agent. There have been various machines proposed, of which a furnace and boiler form a part, and in which the agency of steam is not used. The machine of Amontons furnishes an example of this. It is most probable that the contrivance of Garay was identical with that of Hero. The low state of the arts in Spain in the sixteenth century would be incompatible with the construction of any machine requiring great precision of execution. But the simplicity of Hero's contrivance would have rendered its construction and operation quite practicable. As to the claims to the invention of the steam engine advanced by the advocates of De Garay, founded on the above document, a refutation is supplied by the admission, that though he was rewarded and promoted by the government of the day, in consequence of the experiment, and although the great usefulness of the contrivance in towing ships out of port, &c., was admitted, yet it does not appear that a second experiment was ever tried, much less that the machine was ever brought into practical use. SOLOMON DE CAUS, 1615. (5.) Solomon De Caus was engineer and architect to Louis XIII., king of France, before the year 1612. In that year he entered the service of the Elector Palatine, who married the daughter of King James I., with whom he came to England. He was there employed by the Prince of Wales in ornamenting the gardens of his house at Richmond. [Pg018] During his sojourn in England he composed and published at London, in the same year, a Treatise on Perspective. This person was the author of a work entitled, "_Les Raisons des Forces Mouvantes, avec diverses Machines tant utiles que plaisantes_," which was apparently composed at Heidelburg, but published at Franckfort, in 1615. The same work was subsequently republished in Paris in 1623. The treatise commences with definitions of what were then considered the four elements: earth, air, fire, and water. Air is defined to be a cold, dry, and light element, capable of compression, by which it may be rendered very violent. He says, "The violence will be great when water exhales in air by means of fire, and that the said air is enclosed: as, for example, take a ball of copper of one or two feet diameter, and one inch thick, which being filled with water by a small hole, which shall be strongly stopped with a peg, so that neither air nor water can escape, it is certain that if we put the said ball upon a great fire, so that it will become very hot, that it will cause a compression so violent, that the ball will burst in pieces, with a noise like a petard."