Water Pressure

“Suppose the cistern a to be capable of holding one hundred gallons, and into its bottom there be fitted the tube b, bent, as seen in the figure, and capable of containing one gallon. The top of the cistern, and that of the tube, being open, pour water into the tube at c, and it will rise up through the perpendicular bend into the cistern, and if the process be continued, the cistern will be filled by pouring water into the tube. Now it is plain, that the gallon of water in the tube presses against the hundred gallons in the cistern, with a force equal to the pressure of the hundred gallons, otherwise, that in the tube would be forced upwards higher than that in the cistern, whereas, we find that the surfaces of both stand exactly at the same height.” —Comstock, 1850

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