It is required to know the effect of the form of the orifice from which a liquid is flowing on the velocity of the efflux. With an orifice of the same diameter as the pipe, the liquid escapes at the same speed as that at which it travels in the pipe. If the orifice is contracted, the same quantity has to pass through the smaller aperture, and to do this the speed must increase so that it issues with greater force, and, if pointed vertically, would be driven to a greater height. On the other hand, if the orifice is increased as a trumpet, the speed of the issuing water is lowered at the point where it enters the open air, and the water will not rise to such a great height, but will be broken into spray by the resistance of the air acting on a larger surface. A trumpet-mouth orifice is used only when it is desired that the issuing liquid shall spread, and a jet orifice is used when the water is to be forced a considerable distance, as illustrated by some kinds of fountains and also by the hose jets used for extinguishing fires in buildings, etc.