A Canal Lock, Pyramid Sections, and Notes on Shadows
A stone gate to fill a lock quickly; proportions of a cut pyramid; why shadows blur
On the left a canal-lock (conca) is drawn with a hinged stone slab, a b, five braccia long and one wide, that opens like a chest-lid to close the mill-canal mouth and fill the basin quickly; the same could serve the Santa Maria lock and make a first lock without gates. A second sketch is labelled 'the lock of the works'. To the right are columns of arithmetical operations. Turning the sheet, a circular sector and semicircle show that a pyramid cut parallel to its base yields proportional sections, and inverted notes observe that shadows are never sharply terminated, the edges growing more confused the larger the light and the more remote the wall.
On this page
A hinged stone gate to fill a lock quickly
The slab a b uncovers the mouth of the outflow and closes the mouth of the mill-canal so the lock fills quickly; it is five braccia long and one wide and opens like the lid of a chest, giving the water entry into the lock. The same device could be applied to the lock of Santa Maria.
A first lock without gates; the lock of the works
With this method one can make the first lock without gates ('finestre'), perfect and safe, filling quickly. A second lock figure is simply labelled 'lock of the works'.
Proportional sections of a cut pyramid
A sector and semicircle carry the letters b, a, c, d, e, f, p, o. Such proportion has c d to a b as c e has to a e; if a pyramid is cut parallel to its base, the cut is to the base as the side of the cut-off part is to the side of the remainder, and as the second pyramid is to the whole entire pyramid.
Shadows that are never terminated
The greater the light is than the shadowed body, the more confused the edges of that body's shadows. A derivative shadow has the more confused edges of percussion on the wall the more remote it is from its shadowed body, and it is impossible that two shadows created by one and the same light should ever intersect.