and the atmospheric pressure forces down the piston to the bottom of its
stroke, during which work may be obtained.

On the board I have made a sketch of this engine. Some years previous to
Huyghens' proposal, the Abbe Hautefeuille (1678) proposed a gunpowder
engine without piston for pumping water. It is similar to Savery's steam
engine, but using the pressure of the explosion instead of the pressure of
steam. This engine, however, had no piston, and was only applicable as a
pump. The Savery principle still survives in the action of the well-known
pulsometer steam pump.

Denys Papin, the pupil and assistant of Huyghens, continued experimenting
upon the production of motive power, and in 1690 published a description
of his attempts at Leipzig, entitled "A New Method of Securing Cheaply
Motive Power of Considerable Magnitude."

He mentions the gunpowder engine, and states that "until now all
experiments have been unsuccessful; and after the combustion of the
exploded powder there always remains in the cylinder one-fifth of its
volume of air."

For the explosion of the gunpowder he substituted the generation and
condensation of steam, heating the bottom of his cylinder by a fire; a
small quantity of water contained in it was vaporized, and then on
removing the fire the steam condensed and the piston was forced down. This
was substantially the Newcomen steam engine, but without the separate
boiler.

Papin died about the year 1710, a disappointed man, about the same time as
Newcomen. Thomas Newcomen, ironmonger and blacksmith, of Dartmouth,