(10.)

We have here proceeded upon the supposition that no force acts on the upper surface A D of the lead. If any force presses A D downwards, that force would be transferred to the bottom by the lead, and would produce a pressure on the bottom B C equal to its own amount in addition to the weight of the lead; and if the lead were solid, this would be the only additional mechanical effect which such a force acting on the surface A D of the lead would produce. But if, on the other hand, the lead were liquified, then the force now adverted to, acting on the surface A D, would not only produce a pressure on the bottom B C, equal to its own amount in addition to the weight of the lead, but it would also produce a pressure against every part of the sides of the vessel, equal to that which it would produce upon an equal magnitude of the surface A D.

Thus if we suppose any mechanical cause producing a pressure on the surface A D amounting to ten pounds on each square inch, the effect which would be produced, if the lead were solid, would be an additional pressure on the base B C amounting to ten pounds per square inch. But if the lead were liquid, besides this pressure on each square inch of the base B C, there would likewise be a pressure of ten pounds on every square inch of the sides of the vessel.

All that has been here stated with respect to a square or a cubical vessel will be equally applicable to a vessel of any other form. [Pg027]