Another account[41] states that a draft of Savery’s engine having come under Newcomen’s notice, he proceeded to make a model of it, which he fixed in his garden, and soon found out its imperfections. He entered into a correspondence on the subject with the learned and ingenious Dr. Hooke, then Secretary to the Royal Society, a man of remarkable ingenuity, and of great mechanical sagacity and insight. Newcomen had heard or read of Papin’s proposed method of transmitting motive power to a distance by creating a vacuum under a piston in a cylinder, and transmitting the power through pipes to a second cylinder near the mine. Dr. Hooke dissuaded Newcomen from erecting a machine on this principle, as a waste of time and labour; but he added the pregnant suggestion, “could he (meaning Papin) make a speedy vacuum under your piston, your work were done.”
[40] Switzer, ‘Introduction to a System of Hydrostatics and Hydraulics,’ p. 342.
The capital idea thus cursorily thrown out--of introducing a moveable diaphragm between the active power and the vacuum--set Newcomen at once upon the right track. Though the suggestion was merely that of a thoughtful bystander, it was a most important step in the history of the invention, for it contained the very principle of the atmospheric engine. Savery created his vacuum by the condensation of steam in a closed vessel, and Papin created his by exhausting the air in a cylinder fitted with a piston, by means of an air-pump. It remained for Newcomen to combine the two expedients--to secure a sudden vacuum by the condensation of steam; but, instead of employing Savery’s closed vessel, he made use of Papin’s cylinder fitted with a piston. After long scheming and many failures, he at length succeeded, in the year 1705,[42] in contriving a model that worked with tolerable precision; after which he sought for an opportunity of exhibiting its powers in a full-sized working engine. It ought to be mentioned, that in the long course of experiments conducted by Newcomen with the object of finding out the new motive power, he was zealously assisted throughout by one John Calley, a glazier of Dartmouth, of whom nothing further is known than that he was Newcomen’s intimate friend, of the same religious persuasion, and afterwards his partner in the steam-engine enterprise.