The engine is shown in Fig. 15, which is copied from the "Experimental Philosophy" of Desaguliers. [Illustration: FIG. 15.--Engine built by Desaguliers in 1718.] The receiver, _A_, is connected to the boiler, _B_, by a steam-pipe, _C_, terminating at the two-way cock, _D_; the "forcing-pipe," _E_, has at its foot a check-valve, _F_, and the valve _G_ is a similar check at the head of the suction-pipe. _H_ is a strainer, to prevent the ingress of chips or other bodies carried to the pipe by the current; the cap above the valves is secured by a bridle, or stirrup, and screw, _I_, and may be readily removed to clear the valves or to renew them; _K_ is the handle of the two-way cock; _M_ is the injection-cock, and is kept open during the working of the engine; _L_ is the chimney-flue; _N_ and _O_ are gauge-cocks fitted to pipes leading to the proper depths within the boiler, the water-line being somewhere between the levels of their lower ends; _P_ is a lever safety-valve, as first used on the "Digester" of Papin; _R_ is the reservoir into which the water is pumped; _T_ is the flue, leading spirally about the boiler from the furnace, _V_, to the chimney; _Y_ is a cock fitted in a pipe through which the rising-main may be filled from the reservoir, should injection-water be needed when that pipe is empty. Seven of these engines were built, the first of which was made for the Czar of Russia. Its boiler had a capacity of "five or six hogsheads," and the receiver, "holding one hogshead," was filled and emptied four times a minute. The water was raised "by suction" 29 feet, and forced by steam pressure 11 feet higher. Another engine built at about this time, to raise water 29 feet "by suction," and to force it 24 feet higher, made 6 "strokes" per minute, and, when forcing water but 6 or 8 feet, made 8 or 9 strokes per minute. Twenty-five years later a workman overloaded the safety-valve of this engine, by placing the weight at the end and then adding "a very heavy plumber's iron." The boiler exploded, killing the attendant. Desaguliers says that one of these engines, capable of raising ten tons an hour 38 feet, in 1728 or 1729, cost £80, exclusive of the piping. Blakely, in 1766, patented an improved Savery engine, in which he endeavored to avoid the serious loss due to condensation of the steam by direct contact with the water, by interposing a cushion of oil, which floated upon the water and prevented the contact of the steam with the surface of the water beneath it. He also used air for the same purpose, sometimes in double receivers, one supported on the other. These plans did not, however, prove satisfactory. Rigley, of Manchester, England, soon after erected Savery engines, and applied them to the driving of mills, by pumping water into reservoirs, from whence it returned to the wells or ponds from which it had been raised, turning water-wheels as it descended.