12 APPLICATION OF THE LAWS OF HYDRAULICS the following manner. The column of water h is balanced by the column of kerosene H. The specific weight of water is 1.0 and that of kerosene is 0.80; it follows that : I I J* II l i and the difference in level will be 0.25/i, equivalent to a column of water of 0.25/1 X0.8 = 0.2/i. This experiment may be modified as follows: take a beaker 1' ~T x \ A i — /rv-~>\ - dL^r i i _ - _ <? i i — __ ------ i 1 B-> V FIG. 9. FKI. 10. of water and immerse therein a test-tube filled with kerosene, until the bottom of the test-tube is even with the surface of the water, the test-tube being inverted (Fig. 10), and determine the hydrostatic pressure which it supports. It is evident that at the level B the pressure exerted by the water upon the kerosene and the pressure reciprocally exerted by the kerosene upon the water are equal, because they are in equilibrium. The pressure of the water per unit of surface in millimeters of water column is that given by the height h: -Pwater = h X density of water = AXl = fe mm. The pressure of the kerosene is measured, first, by the weight