In the second section, which treats first of the artist’s studio, the construction of a suitable window forms the object of careful investigations; the special importance attached to this by Leonardo is sufficiently obvious.  His theory of the incidence of light which was fully discussed in a former part of this work, was to him by no means of mere abstract value, but, being deduced, as he says, from experience (or experiment) was required to prove its utility in practice.  Connected with this we find suggestions for the choice of a light with practical hints as to sketching a picture and some other precepts of a practical character which must come under consideration in the course of completing the painting.  In all this I have followed the same principle of arrangement in the text as was carried out in the Theory of Painting, thus the suggestions for the Perspective of a picture, (Nos. 536-569_), are followed by the theory of light and shade for the practical method of optics (Nos._ 548—­566_) and this by the practical precepts or the treatment of aerial perspective (567—­570)._

In the passage on Portrait and Figure Painting the principles of painting as applied to a bust and head are separated and placed first, since the advice to figure painters must have some connection with the principles of the treatment of composition by which they are followed.

But this arrangement of the text made it seem advisable not to pick out the practical precepts as to the representation of trees and landscape from the close connection in which they were originally placed—­unlike the rest of the practical precepts—­with the theory of this branch of the subject.  They must therefore be sought under the section entitled Botany for Painters.

As a supplement to the Libro di Pittura I have here added those texts which treat of the Painter’s materials,—­as chalk, drawing paper, colours and their preparation, of the management of oils and varnishes; in the appendix are some notes on chemical substances.  Possibly some of these, if not all, may have stood in connection with the preparation of colours.  It is in the very nature of things that Leonardo’s incidental indications as to colours and the like should be now-a-days extremely obscure and could only be explained by professional experts—­by them even in but few instances.  It might therefore have seemed advisable to reproduce exactly the original text without offering any translation.  The rendering here given is merely an attempt to suggest what Leonardo’s meaning may have been.

LOMAZZO tells us in his Trattato dell’arte della Pittura, Scultura ed Architettura (Milano 1584, libro II, Cap.  XIV):  “Va discorrendo ed argomentando Leonardo Vinci in un suo libro letto da me (?) questi anni passati, ch’egli scrisse di mano stanca ai prieghi di LUDOVICO SFORZA duca di Milano, in determinazione di questa questione, se e piu nobile la pittura o la scultura; dicendo che quanto piu un’arte porta seco fatica di corpo, e sudore, tanto piu e vile, e men pregiata”. But the existence of any book specially written for Lodovico il Moro on the superiority of Painting over sculpture is perhaps mythical.  The various passages in praise of Painting as compared not merely with Sculpture but with Poetry, are scattered among MSS. of very different dates.