Injec′tor, an instrument used to force water into a boiler by using the energy in a jet of steam taken from the boiler into which the water is to be forced. It is simply an instrument for allowing steam to escape from a boiler through a suitable nozzle and to suck up and mix with a stream of cold water, by which it imparts so much of its own energy that the combined mass of cold water and condensed steam enters and feeds the boiler. The injector takes many special forms given by different makers and for special conditions. The injector was invented in 1858 by H. J. Giffard, a French mathematician and engineer. It is used universally on locomotives. It is said that “it is without doubt better than any device hitherto used for feeding boilers and the best that can be employed, and also is the simplest and the most ingenious.”