Why is water spherical? The order of the elements
Why the heavy element lies below the light, and why water does not press on its bed
In two dense columns Leonardo reasons about the natural order of the four elements. He asks why water forms a sphere, argues that the heavier element always lies beneath the lighter, and that no part of water's sphere can stand permanently higher than the surrounding air. He also asks why water does not weigh upon its own bed, and why a free heavy body descends to the centre of the world by the shortest path, not from attraction but because the medium cannot support it. A small drawing of a cylinder rising from a round basin appears at the top, with the word 'Domo' jotted in the upper margin.
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Why is water spherical?
The right column opens with the question 'Why is water spherical?' Leonardo answers geometrically: all lines from the centre to the circumference are equal, so free water settles into a sphere and no part can stand permanently higher than the air surrounding it.
The heavier element lies beneath the lighter
He states as a rule that the heavier thing always lies beneath the lighter, and that a thing is 'higher' the more remote it is from the centre of the world. Free water is therefore always lower than air, along whatever line it lies.
Why water does not press upon its bed
Leonardo asks why water does not weigh upon its own bottom, reasoning that it does not rest on an element lighter than itself, since earth is heavier than water. He adds the maxim that a body weighs more where it meets weaker resistance.
Descent of a heavy body to the centre of the world
The left column concludes that a free heavy body descends to the centre of the world by the shortest path, not because the centre attracts it nor because the body desires to join it, but only because the medium through which it passes cannot support it.
The sphere of water and the centre of the world
The reasoning treats water as forming a sphere about the centre of the world, the elemental bodies ordered by weight around that centre. No part of the water's sphere can rise permanently to the height of the air that encircles it.