looking (at it) there remain in the eye images of intense
brightness, that make any less brilliant spot seem dark until the
eye has lost the last trace of the impression of the stronger light.

_II.

Linear Perspective.

We see clearly from the concluding sentence of section 49, where the
author directly addresses the painter, that he must certainly have
intended to include the elements of mathematics in his Book on the
art of Painting. They are therefore here placed at the beginning. In
section 50 the theory of the "Pyramid of Sight" is distinctly and
expressly put forward as the fundamental principle of linear
perspective, and sections 52 to 57 treat of it fully. This theory of
sight can scarcely be traced to any author of antiquity. Such
passages as occur in Euclid for instance, may, it is true, have
proved suggestive to the painters of the Renaissance, but it would
be rash to say any thing decisive on this point.

Leon Battista Alberti treats of the "Pyramid of Sight" at some
length in his first Book of Painting; but his explanation differs
widely from Leonardo's in the details. Leonardo, like Alberti, may
have borrowed the broad lines of his theory from some views commonly
accepted among painters at the time; but he certainly worked out its
application in a perfectly original manner.

The axioms as to the perception of the pyramid of rays are followed
by explanations of its origin, and proofs of its universal
application (58--69). The author recurs to the subject with endless