Among other important improvements in the steam engine are those for replenishing the water in the boiler, and the Giffard Injector is the simplest and most ingenious of all boiler feeds. It was invented in 1858 and covered by French patent No. 21,457, May 8, 1858, and U. S. patent No. 27,979, April 24, 1860. Prior to the Giffard Injector, steam boilers were supplied with water usually by steam pumps, which forced the water into the boiler against the pressure of the steam. The Giffard Injector takes a jet of steam from the boiler, and causes it to lift the water in an external pipe, and blow it directly into the boiler against its own pressure. So paradoxical and inoperative did this seem at first that it was met with incredulity, and not until repeated demonstrations established the fact was it accepted as an operative device. Its construction is shown in Fig. 82. A is a steam pipe communicating with the boiler, B another pipe receiving steam from A through small holes and terminating in a cone. C is a screw rod, cone-shaped at its extremity, turned by the crank M, and serving to regulate and even intercept the passage of steam. D is a water suction pipe. The water that is drawn up introduces itself around the steam pipe and tends to make its exit through the annular space at the conical extremity of the latter steam pipe. This annular space is increased at will by means of the lever L, which acts upon a screw whose office is to cause the pipe B and its attached parts to move backward or forward. E is a diverging tube which receives the water injected by the jet of steam that condenses at I, and imparts to the water a portion of its speed in proportion to the pressure of the boiler. F is a box carrying a check valve to keep the water from issuing from the boiler when the apparatus is not at work. G is a pipe that leads the injected water to the boiler. H is a purge or overflow pipe, K a sight hole which permits the operation of the apparatus to be watched, the stream of water being distinctly seen in the free interval. Fig. 83 shows the application of the injector to locomotives, which are now almost universally supplied with this device. [Illustration: FIG. 82.--GIFFARD INJECTOR.] [Illustration: FIG. 83.--INJECTOR ON LOCOMOTIVE.]