(28.)

Let us now return to the proceedings of Papin. How great a power would result from such a machine as he conceived, will be apparent, if it be considered that the unresisted atmosphere exercises a pressure of about fifteen pounds on [Pg045] each square inch of surface exposed to it, and that if the piston in the cylinder imagined by Papin, had a diameter of only one foot, its superficial magnitude would be about 114 square inches. The pressure of the atmosphere upon it, therefore, would be 114 times fifteen pounds, or 1710 pounds. Papin first proposed to produce the vacuum under the piston by means of common air pumps, worked by a water-wheel; and by such means he conceived that the power of a river, stream, or waterfall might be conveyed by pipes to a distance. While he was in England, in 1687, he laid his contrivance before the Royal Society of London, but was met by objections and difficulties, the nature of which he does not explain.

It is, however, apparent, from what has been already explained, that such a method of proceeding would amount to a mere transfer of power, and would not, properly speaking, be itself a moving force: the moving power would, in reality, be the force of the water by which the water-wheel would be driven; and the air-pumps, tubes, together with the piston and cylinder, would be merely means of conveying the power of the water-wheel to the objects to be moved, or the machinery to be driven. Papin states, that, long before this, he had attempted to expel the air from his cylinder by means of gunpowder; but, notwithstanding all the precautions which he could take, there always remained a considerable quantity; so much, indeed, as to deprive the vacuum of more than half its proper force. At length he adopted an expedient for the production of a vacuum which forms a most important step in the progressive invention of the steam engine, and which gives to Papin's name a high place in the history of that machine. This method is explained in the following paragraph of a work published by Papin in 1695, at Cassel, entitled "Recueil de diverses Pièces touchant quelques nouvelles Machines", p. 53.

"I have endeavoured," says he, "to attain this end (viz. the production of a vacuum in the cylinder) in another way. As water has the property of elasticity, when converted into steam by heat, and afterwards of being so completely recondensed by cold, that there does not remain the least [Pg046] appearance of this elasticity, I have thought that it would not be difficult to work machines in which, by means of a moderate heat and at a small cost, water might produce that perfect vacuum which has vainly been sought by means of gunpowder."

This remarkable passage is given in the work just cited, as an extract from the "Leipsic Acts," of August, 1690.

Let us pause here to explain more fully this important discovery.