a pneumatic engine, or syringe, with which a greater quantity of air may be forced into a given space; so that ten or more atmospheres, or ten times as much air as there is at the same time in the same space, under the usual pressure, may be thrown in by means of it; and its egress prevented by valves properly disposed.

It consists of a brass cylinder, in which is a moveable piston, which being drawn out, the air rushes into the cylinder through a hole provided on purpose; and when the piston is again forced into the cylinder, the air is driven into the receiver through an orifice, furnished with a valve to prevent its getting out.

The receiver or vessel containing the condensed air should be made very strong, to bear the increased force of the air; for which reason vessels of this sort are generally made of brass, the orifice being fitted with a female screw to receive the male screw at the end of the condenser.