_Experimental researches_.--All experiments referred to in this paper were made by jets of water under an actual vertical head of 45 ft., but as the supply came through a considerable length of ½ in. bore lead piping, and many bends, a large and constant loss occurred through friction and bends, so that the actual working head was only known by measuring the velocity of discharge. This was easily done by allowing all the water to flow into a tank of known capacity. The stop cock had a clear circular passage through it, and two different jets were used. One oblong measured 0.5 in. by 0.15 in., giving an area of 0.075 square inch. The other jet was circular, and just so much larger than ¼ in. to be 0.05 of a square inch area, and the stream flowed with a velocity of 40 ft. per second, corresponding to a head of 25 ft. Either nozzle could be attached to the same universal joint, and directed at any desired inclination upon the horizontal surface of a special well-adjusted compound weighing machine, or into various bent tubes and other attachments, so that all pressures, whether vertical or horizontal, could be accurately ascertained and reduced to the unit, which was the quarter of an ounce. The vertical component _p_ of any pressure P may be ascertained by the formula-- _p_ = P sin alpha, where alpha is the angle made by a jet against a surface; and in order to test the accuracy of the simple machinery employed for these researches, the oblong jet which gave 71 unit when impinging vertically upon a circular plate, was directed at 60 deg. and 45 deg. thereon, with results shown in Table I., and these, it will be observed, are sufficiently close to theory to warrant reliance being placed on data obtained from the simple weighing machinery used in the experiment. _Table I.--Impact on Level Plate._ --------------+--------------------+----------+----------+---------- | Inclination of jet | | | Distance. | to the horizonal. | 90 deg. | 60 deg. | 45 deg. --------------+--------------------+----------+----------+---------- | | Pressure | Pressure | Pressure | | | | / | Experiment \ | / | 61.00 | 49.00 1½ in. < | > | 71.00 < | | \ | Theory / | \ | 61.48 | 50.10 | | | | | | | | / | Experiment \ | / | 55.00 | 45.00 1 in. < | > | 63.00 < | | \ | Theory / | \ | 54.00 | 45.00 | | | | --------------+--------------------+----------+----------+---------- In each case the unit of pressure is ¼ oz.