What Is Heavy and Light: Gravity, Water and Trapped Air
Elements pressing on elements, the pyramidal fall of water, and bubbles rising under water
Both faces of this dense sheet argue a theory of gravity as one element being unable to sustain a heavier one that rests upon it. Leonardo shows that heavy liquid descends into a lighter medium in a pyramidal figure, and that air trapped under water is not fleeing upward of its own will but is squeezed out by the water pressing around it, spreading its base into an opposite pyramid. Small marginal figures label the three cases fire-in-air, water-in-air, and air-under-water; further columns argue that equal weights resist one another at the center of the world, and a note in another hand and two upside-down memoranda fill spare corners.
On this page
What is heavy and what is light
Gravity is defined as an action by which one part of an element, being heavier, cannot be sustained by another, or being lighter cannot bear the heavier parts resting on it. A continuous heavy liquid descending into a lighter medium takes a pyramidal shape whose opposite parts intersect to form an inverted pyramid, gaining width of base at every degree of descent.
Why trapped air rises through water in a pyramid
Air by its nature does not flee from beneath water; rather the water leaning around it presses and drives it out. The water capping the air rests upon it and, being heavier, dilates its edges evenly from the center, so that at each degree of rise the enclosed air spreads its base into a pyramidal form opposite to that of falling water. Three marginal sketches label the cases: fire in air, water in air, and air under water.
Why a heavy body descends in a straight line
A weight falls not because the center of the world draws it, nor from any desire to reach that center, but only because the air cannot sustain a thing heavier than itself. It goes straight down not by any choice of straight over oblique motion, but because it presses the air beneath it harder than the lateral and upper air, and the more compressed air yields most quickly.
Equal weights resist one another at the center of the world
A heavy body never ceases to descend until an equal power opposes it; equal things do not overcome one another, but unequal things do. A light support is driven from its place by a heavy body, whereas a heavy equal to another heavy neither drives it nor is driven, so that two things of equal weight and lowness come to rest resisting one another at the center of the world.
Memoranda jotted upside down
In a corner, with the sheet inverted, stand two brief reminders: the manganese for glass, and the crab of Francesco da Lusanna. They are unconnected jottings among the physics.