. The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology. Biophysics. Chap. xix.] HYDROSTATIC PARADOX. 191 worked by a lever. Of course the upward movement of the press is correspondingly slow. It arises further from the principle of Pascal that the pressure exerted on the bottom of a vessel depends upon the extent of surface of the bottom of the vessel, and the height of the liquid column which it supports. Thus, let AB'C' (Fig. 94) be a glass vessel with the tube-shaped portion AA', and let it be fil
. The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology. Biophysics. Chap. xix.] HYDROSTATIC PARADOX. 191 worked by a lever. Of course the upward movement of the press is correspondingly slow. It arises further from the principle of Pascal that the pressure exerted on the bottom of a vessel depends upon the extent of surface of the bottom of the vessel, and the height of the liquid column which it supports. Thus, let AB'C' (Fig. 94) be a glass vessel with the tube-shaped portion AA', and let it be filled with some liquid. Consider the area be of the bottom of the vessel. It is manifest that it sustains not only the pressure of the column of liquid A'6c, but of the column AA' as well, so that its pressure is conditioned by its area Fig. 94. —. 7 ,i i • 1 , r? ,1 i drostatic Para- 6c, and the height ot the column of liquid it supports, viz. Ac. But by Pascal's law, the column AA' transmits its pressure equally in all directions, and not only, therefore, on the small section of the bottom be, but on the whole bottom B'C'. So that every portion of the surface B'C' of area equal to be bears not only the pressure of the liquid column up to the level of A', but also the pressure of the column AA'. Thus the pressure on the bottom B'C' is equal to the pressure of a column of liquid whose base is equal to B'C', and whose height is equal to AC ; and so the pressure on B'C' is as great as it would be if the vessel had had the shape BB'C'C, the shape indicated by the dotted lines. Thus the pressure on the bottom of a vessel is independent of the shape of the vessel, but is determined by the area of the bottom, and the height of the column of liquid it supports. This must not be misunderstood. If two vessels, one represented by BB'C'C (Fig. 94), and the other repre- sented by AB'C', were filled with water, the pressure on the bottom of each would be the same ; but if they. Please not
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