IX. The Practice of Painting: 493.
493.
OF THE LIFE OF THE PAINTER IN THE COUNTRY.
The artist's private life and choice of company (493-494).A painter needs such mathematics as belong to painting. And the absence of all companions who are alienated from his studies; his brain must be easily impressed by the variety of objects, which successively come
before him, and also free from other cares 237 . And if, when considering and defining one subject, a second subject intervenes--as happens when an object occupies the mind, then he must decide which of these cases is the more difficult to work out, and follow that up until it becomes quite clear, and then work out the explanation of the other 238 . And above all he must keep his mind as clear as the surface of a mirror, which assumes colours as various as those of the different objects. And his companions should be like him as to their studies, and if such cannot be found he should keep his speculations to himself alone, so that at last he will find no more useful company [than his own].