[1] In the words of J. Burckhard, cited by Alexandra Konstantinowa, Die Entwicklung des Madonnentypus by Leonardo da Vinci, Strassburg, 1907.
[2] Vite, etc. LXXXIII. 1550-1584.
[3] Traktat von der Malerei, new edition and introduction by Marie Herzfeld, E. Diederichs, Jena, 1909.
[4] Solmi. La resurrezione dell' opera di Leonardo in the collected work; Leonardo da Vinci. Conferenze Florentine, Milan, 1910.
[5] Scognamiglio Ricerche e Documenti sulla giovinezza di Leonardo da Vinci. Napoli, 1900.
[6] W. v. Seidlitz. Leonardo da Vinci, der Wendepunkt der Renaissance, 1909, Bd. I, p. 203.
[7] W. v. Seidlitz, l. c. Bd. II, p. 48
[8] W. Pater. The Renaissance, p. 107, The Macmillan Co., 1910. "But it is certain that at one period of his life he had almost ceased to be an artist."
[9] Cf. v. Seidlitz, Bd. I die Geschichte der Restaurations—und Rettungsversuche.
[10] Müntz. Léonard de Vinci, Paris, 1899, p. 18. (A letter of a contemporary from India to a Medici alludes to this peculiarity of Leonardo. Given by Richter: The literary Works of Leonardo da Vinci.)