In Fig. 26, the steam passes from the boiler through the pipe _d_ and the valve _c_ to the cylinder-casing or steam-jacket, _Y Y_, and above the piston, _b_, which it follows in its descent in the cylinder, _a_, the valve _f_ being at this time open, to allow the exhaust into the condenser, _h_. The piston now being at the lower end of the cylinder, and the pump-rods at the opposite end of the beam, _y_, being thus raised and the pumps filled with water, the valves _c_ and _f_ close, while _e_ opens, allowing the steam which remains above the piston to flow beneath it, until, the pressures becoming equal above and below, the weight of the pump-rods overbalancing that of the piston, the latter is rapidly drawn to the top of the cylinder, while the steam is displaced above, passing to the under-side of the piston. The valve _e_ is next closed, and _c_ and _f_ are again opened; the down-stroke is repeated. The water and air entering the condenser are removed at each stroke by the air-pump, _i_, which communicates with the condenser by the passage _s_. The pump _q_ supplies condensing-water, and the pump _A_ takes away a part of the water of condensation, which is thrown by the air-pump into the "hot-well," _k_, and from it the feed-pump supplies the boiler. The valves are moved by valve-gear very similar to Beighton's and Smeaton's, by the pins, _m m_, in the "plug-frame" or "tappet-rod," _n n_. The engine is mounted upon a substantial foundation, _B B_. _F_ is an opening out of which, before starting the engine, the air is driven from the cylinder and condenser. The inventions covered by the patent of 1769 were described as follows: "My method of lessening the consumption of steam, and consequently fuel, in fire-engines, consists in the following principles: "1st. That the vessel in which the powers of steam are to be employed to work the engine--which is called 'the cylinder' in common fire-engines, and which I call 'the steam-vessel'--must, during the whole time that the engine is at work, be kept as hot as the steam which enters it; first, by inclosing it in a case of wood, or any other materials that transmit heat slowly; secondly, by surrounding it with steam or other heated bodies; and thirdly, by suffering neither water nor other substances colder than the steam to enter or touch it during that time. "2dly. In engines that are to be worked, wholly or partially, by condensation of steam, the steam is to be condensed in vessels distinct from the steam-vessel or cylinder, though occasionally communicating with them. These vessels I call condensers; and while the engines are working, these _condensers_ ought at least to be kept as cold as the air in the neighborhood of the engines, by application of water or other cold bodies.