“Painting, says Leonardo, depends on ‘l’armonica proporzionalita della parti che compongono il tutto, che contenta il senso’.  Here Leonardo shows himself touched by the predominant Platonism of his time, for the idea that the visual arts were a sort of frozen music was familar to many theorists of the Renaissance, and had been given superb expression by Leon Battista Alberti, to whose treatise on painting, written in 1435, Leonardo was greatly indebted.”

Kenneth Clark, “Leonardo da Vinci: An Account of His Development as an Artist.” Cambridge: 1939
Kenneth Clark, “Leon Battista Alberti on Painting.” London: G. Cumberlege,1945