The upper cyhnder acts as a steamengine, and receives its steam from a boiler under its piston, which is then carried up to the top of the cylinder by the steam (at the same time, the piston of the lower cyUnder is brought up to its top, from its connection M-ith the upper piston, by the aforesaid bolt,) they then shut the communication from the boiler, and open another to discharge the steam for condensation j by this means the atmosphere acts upon the piston of the upper

1. Qu. Cliargir-ijT

KAVIGATION. 1019

conveyed to the piston in the lower cylinder, by the aforesaid connecting bolt, which forces the water, then in the lower cylinder, through the trunk, with considerable velocity ; the re-action of which, on the other end of the trunk, is the power that propels the boat forward.

To prove the use of the Trunk.

It is well known that a heavy body falling near the earth wull pass through a space of about fifteen feet in the first second of time ; if the same body was acted upon in a horizontal direction, by an impulse equal to its weight, it would move in that direction tlie same distance in an equal time; it follows, then, that the water in the trunk, will have the effect proportionable to its weight, of retarding the water from being discharged from the cylinder in too short a time.

Near the cylinder, on the top of the trunk, there is a valve to admit air, which follows the water that is then in motion, and gives time for the water to rise gradually into the trunk through valves, at its bottom, for that purpose ; this water has but little motion with respect to the boat and is therefore capable of resisting the next stroke of the engine.