Giovanni Alfonso Borelli

...heavy bodies A and B are attached to a rigid and stable rod such as ACB. One can imagine a circular channel AGBF. Suppose it is filled with water or any other fluid where the right side FAG is heavier than the rest of the fluid GBF. For example, if the fluid FAG is mercury Original: "hydrargyrum". A heavy, liquid metal used frequently in early modern scientific instruments. and FBG is common water. In this case, a balance is created in the same way. The center of gravity The point where the total weight of the bodies is balanced in all directions. of both liquids will not lie on the diameter FCG, which is perpendicular to the horizon. Instead, it will lie beyond it between C and A, specifically at some point D. Then C is the center of the entire volume of the fluid. The suspension of the entire fluid occurs precisely at this point C. This is because two opposite motions are produced around it: the descent of fluid A and the ascent of the other, opposite fluid B. Since the common center of gravity D of the two fluids is at a distance from the center of suspension C, a pendulum A weight suspended from a fixed point that swings back and forth under the influence of gravity. is formed. It will move in a circular path through the arc DE.

A circular diagram represents a canal or tube labeled AGBF. A vertical diameter FG and a horizontal diameter AB intersect at the center point C. A point D is marked on the lower-left circumference of the circle. A dotted line connects C to D, and another dotted arc connects D to a point E on the lower vertical axis. The diagram illustrates how the balance of weight and the center of gravity function in a circular vessel containing fluids of different densities.

PROPOSITION III.

At this point, I will use a brief and useful digression. I will point out the impossibility of perpetual motion.