The point, the surface, and the elements
First book of the waters: the indivisible point, the surface dividing water from air, and the elements
Headed 'First book of the waters', these pages continue Leonardo's meditation on continua. He insists the point has no middle yet is itself the middle of everything, that it is the common boundary of nothing with the line, and that points, lines and surfaces in mere contact cannot compose line, surface or body. He then treats the surface as an incorporeal common boundary of two bodies in contact, illustrated by the surface between water and air, which is part of neither, and closes with the elements, in which gravity and levity arise only from mixture, restating that line, surface and body are generated by successive motions. A marginal drawing shows a new tower founded partly upon the old.
On this page
The point as common boundary of nothing and the line
The point has no middle yet is itself the middle of everything, and nothing can be smaller; it is the common boundary of nothing with the line, in contact but not joined. Leonardo concludes that many points in continuous contact do not compose a line, nor lines a surface, nor surfaces a body, since bodies are not composed of incorporeal things.
Point, line, surface and body generated by motion
Under 'Of the elements', the line is defined as a length made by the motion of the point, the surface as an extension made by the transverse motion of the line, and the body as a quantity made by the motion of a face of the surface. The point, having no middle, has no width, length or depth and is indivisible in every aspect.
The incorporeal surface dividing water from air
A single surface is the common boundary of two bodies in contact, as the surface of water is part neither of water nor of air. What divides air from water must be incorporeal, for a body interposed would prevent their contact; so they are joined, and one cannot be moved without the other. In the elements themselves there is neither gravity nor levity until they are mixed.
A new tower founded partly on the old
A marginal drawing is labelled as a new tower founded in part upon the old, a note on the settling behaviour of construction raised over an existing structure. It sits among the geometric text as a built illustration of foundations.
