Encyclopedia Of Inorganic [14309grr694j]
Points E and F being at same level, p + h = H,, the net pressure is p = H – h. The product (H – h1) is calculated. Now raise the open tube CD, the levels F and G again, say it is h; then net pressure will be (H– h1) or H + h1 according as level of mercury in the open tube is lower or higher than that of mercury in the closed tube.