Where the painter should stand to the light; blow and voice notes
Positioning to a window's light, and how repeated blows and small voices fail to equal a single one
A perspective diagram places the painter between a window's light (point m, between the jambs a and b) and his subject, so that his eye falls on the boundary of light and shadow on a modelled sphere; a companion note prefers a light that is large, high, and gentle for rendering detail. Leonardo then warns that a painter unconsciously reproduces his own bodily defects in the limbs he draws, urging long study as a guard. Two physical queries close the page: whether ten one-pound blows drive a nail as far as a single ten-pound weight (they do not), and whether many small voices can equal one large voice.
On this page
How the painter should stand to light and relief
Let a b be the window and m the point of light. The painter stands well wherever his eye lies between the shaded and lighted parts of the body portrayed; he finds this position by placing himself between point m and the division of shadow and light on the body. The diagram shows rays converging through m, two half-lit spheres, and painter positions n and o.
On the quality of light for painting
A light that is large and high and not too powerful will render the details of bodies in a very pleasing way.
The painter reproduces his own defects in limbs
A painter with ungainly hands makes similar hands in his works, and the same holds for any limb unless long study prevents it. Leonardo urges the painter to examine the ugliest part of his own person and guard against it, since one's good or unfortunate features are shown in one's figures.
On the blow: repeated blows versus a single weight
Will ten blows of one pound each, falling from one braccio, drive in a nail as much as a united weight of ten pounds? Leonardo says no: one could not drive a nail with the weight of another like nail even by ten thousand blows, whereas twenty such weights would give a blow of the right proportion.
On the voice: many small voices versus one large
Do many small voices joined together make a noise like a large voice? Leonardo says not: the voices of ten thousand flies together would not carry as far as a man's voice, and a man's voice divided into ten thousand parts would leave none equal to a fly's.