Chap. XVII.

OF THE MOTION OF FLUIDS.

1157

The bottom, PQ, of the vessel C forms a cover to the lower vessel, C /x , the two onlycommunicating by the opening A, which is closed by a plug when the vessel C" is fulL of

Fig. 1756.

IMERO’S FOUNTAIN.

water : the vessel C ,f communicates with the external air by a tube, K L, which traversesthe bottom, P Q, of the vessel C, and is open at both ends.

To put this machine into play, the cock, Z, of the tube, B Z D D, is opened ; the waterfrom the vessel C flows through D', fills the vessel C', and compresses the air contained init, which compression transmits itself by the tube F E II to the liquid in the vessel CV, andobliges it to rise by the tube, KL ; the vessels C, C" are emptied, and C' is filled ; N I, ni,Ii S being the levels of the water in the three vessels; the air comprised between the levels11S and ni is more compressed than the atmospheric air, and this increase of pressure, whichwe may call p , is measured by a column of water whose vertical height is the distance betweenthe levels N 1 and It S, which is variable, the vertical distance being continually diminished.The pressure at K, the extremity of the tube KL, open at both ends, is evidently the sum ofthe two pressures, of which one is equal to p, and the other p! is measured by a column ofwater of the variable height K K, K K, being the vertical distance from the extremity, Kof the tube to the level of the water, n i, in the vessel C ,f ; therefore the pressure at K, whichelevates the water in the tube KL, is variable, because it depends on two other pressures pand p' which decrease every moment. If the level ni descended to K, the water wouldrise in the tube KL, to a height equal to the vertical distance of the two levels, N I and11 S, corresponding to the level ni, which we suppose has descended to K ; but at themoment when the machine is put into play, the water would elevate itself in the tube K Lto a height equal to the vertical distance of the extremity D' of the tube 15 D', from thefirst level N I ; then the force which elevates the water in the tube K L would decrease;

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