A Treatise on Painting, by Leonardo da Vinci
Senex and Taylor, London
A Painter ought to have his Mind continually at work, and to make Remarks on every Object worthy of notice, that he meets. He ought even to stand still in order to view them with the greater attention; and afterwards to Form rules on what he has observ'd, with regard to Lights, Shadows, Place and other Circumstances. Let him make himself a Master of the Theory, before he meddle with the Practice, and be very curious in comparing the Limbs and Jonctures of different Animals with one another: taking Minutes of every thing he learns, the better to fix them in his Memory.