These improvements were combined in a very masterly manner, in what were called his single reciprocating Engines. The lever-beam, boiler, pumprod, and the use of a plug-frame to act by its pins or tappets on the hand-gear, or contrivances for opening and shutting the valves, with some improvements in their arrangement, were retained; the valves were, however, on a different and a better construction. In the Twenty-sixth Figure the pipe d, conducts steam from a boiler (which is omitted in order to have the principal parts of the apparatus on a larger scale); e, is the nozle, or square box, containing a valve, which in its rise or fall opens or shuts the passage between one side of the piston and the boiler, and also between the pipe o, l, and the cylinder a. Y Y is the interstice between the casing and its cylinder: the casing was called the jacket. This interval was sometimes filled with charcoal, or some other slow conducting substance; or steam from the boiler might be admitted into it: by any of these means the radiation of heat from the steam cylinder, and its conduction by the air, was very perfectly prevented. b, is the steam piston attached to the lever-beam by the rod x. The pins or tappets n, n, fixed on the plug-frame (or tappet rod,) which in our Figure also serves for the rod of the pump, attached to the condensing apparatus: at the ascent or descent of these pins, they strike on the ends of the levers or spanners m, m, m, connected with the valves, e, f, c, and open or shut them, as they may be adjusted. The condenser h, is connected with the steam cylinder by the pipes u, and g. The air-pump barrel is attached to this vessel by the pipe s, which is furnished with a valve opening from the condenser: the piston is similar to those usually employed in water-pumps, with the exception of the joints of the valves being made of metal instead of leather; the condensing pump, i, has a short pipe proceeding from near its top, on the end of which is a valve, k, opening outwards, and into a vessel of water, r: the condenser and its pump are placed in a cistern of water, kept as cold as possible, by allowing the heated water to escape, and renewing the supply from the mine or some reservoir by a pump, q, which is worked by a rod attached to the lever-beam. The short pipe k, opens into a cistern generally separated from that in which the condenser is placed, in the manner shewn in the Figure. From this cistern water is pumped into the boiler through the pipe p, by the pump A, to supply its waste from evaporation. B, is a foundation of masonry or wood, on which the cylinder is fixed; o, a post or beam to receive the spanner fulcrum-in some engines it is supplied by brackets fixed to the cylinder; w, is a stuffing-box, first used by Mr. Watt, to keep the aperture in which the piston-rod slides steam-tight; the rod of the mine pump is suspended at the opposite end of the lever to the steam piston-rod, as in the Figures of the Atmospheric Engine; (the limits of our page not permitting a greater extension, it is not shewn in the engraving). This end of the lever, or the rods attached to it, are made so much heavier than those on the other side of the axis, as to be sufficient to act as a counterpoise to raise the steam-piston from the bottom to the top of the cylinder. The steamcylinder is closed at top, and the rod slides through the stuffing-box; so that all communication with the atmosphere, and any part either of the cylinder or the condenser, is completely prevented. If we now suppose the apparatus to be in the position shewn in the Figure, and a proper supply of steam in the boiler, the valves c, e, f, are to be opened, and N is shut. Steam then enters above and below the piston into the pipe o, and the condenser h; when the cylinder becomes sufficiently heated, the steam will descend into the condenser, and from its less gravity occupying the upper portion, will expel all the air through the blowing valve, f, which may have collected in those vessels, or which may have been produced by the condensation of the steam in heating the apparatus. The cock e, is now to be shut, and the injection-cock opened; the jet of cold water will condense the steam in the condenser, and the steam under the piston in the cylinder, a, rushing through the pipe u, g, to restore the equilibrium, will also be condensed by the jet which is kept playing; and a vacuum is formed in the cylinder and condenser. This condensation in the largest engines is prodigiously rapid; in practice it may be considered quite instantaneous. The communication between the boiler and the upper side of the piston remaining open, the elasticity of the vapour having no now resistance from that on the other side, presses the piston downwards into the vacuous space until it reaches the bottom of the cylinder. At this instant the descent of the tappets in the plug-frame strikes the end of the spanners m, m, connected with |