The proving of the hose is of very considerable importance, and the method of doing so which I have mentioned is greatly superior to the old plan of proving them on an engine or fire-cock. By the latter method, no certain measure can be obtained by which the pressure can be calculated. In the first place it must depend on the relative height of the reservoir from whence the water is obtained and that of the fire-cock where the experiment is made; and as the supply of water drawn from the pipes by the inhabitants may be different on different days of the week and even in different hours of the day, it is quite evident that by this method no certain rule can be formed for the purpose required, the pressure being affected by the quantity of water drawn at the time. The method of proving by an engine is considerably better than this; but when a proving-pump can be obtained it is infinitely better than either. One disadvantage of an engine is, that it requires a considerable number of men; but even the proof, that of throwing the water to a given height on the gable of a house or other height, is not always a test of the sufficiency of the hose. As the temperature is low or high, the wind fresh or light, the degree of pressure on the hose in throwing the water to the required height will be greater or less. Indeed, in high winds it is a matter of extreme difficulty to throw the water to any considerable height. With an engine of 7-inch barrels and 7-inch stroke, fitted with eighty feet of 2-3/8-inch hose, I have found from several experiments that when the water is thrown seventy-five feet high, the pressure on the hose is equal to one hundred feet. The same engine, with 160 feet of hose, and the branch-pipe raised fifty feet above the level of the engine, when the water was thrown fifty-six feet from the branch, occasioned a pressure equal to 130 feet on the hose. From these experiments, I am convinced that the pressure will not be equal to 200 feet, except in very extreme cases, or when some obstacle gets into the jet pipe. I tried the extreme strength of a piece of riveted hose 4 feet long and 2-3/8 inches diameter, and found that it did not burst till the pressure increased to 500 feet; and when it gave way the leather was fairly torn along the rivet-holes.