Huyghens' Gunpowder and Air Engine, consisting of a hollow cylinder A, well polished within and of uniform size throughout. B, a movable piston inserted into the top of the cylinder, the upper portion of which is surrounded by a small quantity of water. C, C, two apertures, each one-half the diameter of the cylinders which are fastened to the main cylinder at the apertures, (one of the tubes being shown extended, the other hanging). E, E, holdfasts, by which the cylinder is joined to the case in which it sits, which is not shown in the figure. F, F, a cord attached to the piston and passing over a pulley G, for the purpose of raising whatever is attached to it. H, a small box for receiving the charge of gunpowder, attached to the bottom of the cylinder by means of a screw, a leather ring being employed to aid in making the joint air-tight.