Sight unseen: vision and perception in Leonardo's Madonnas: in the first of two articles on Leonardo da Vinci, Larry J. Feinberg explains how the artist's interest in the way the eyes work influenced his realistic depictions of the Christ Child as a baby learning to see

Apollo, July, 2004 by Larry J. Feinberg

(18) These early optical sketches would seem to be the less evolved predecessors of the diagrams concerning binocular vision that appear on sheets at Windsor (fols. 19102r, 19117r, and 19147v) and in Manuscript D (fols. 4r and 8v). See Clark and Pedretti, op. cit., vol. III, pp. 40, 46 (reproduced upside-down), and 56-57; and Strong, op. cit., pp. 58-59 and 80-81. The two drawings beside the optical diagrams on the British Museum sheet--a design for Some sort of instrument with wires or strings that (by means of a sliding mechanism?) can be manipulated to form various angles, and a crude sketch that resembles half of a spoked wheel (with a complete central circle)--are similar to small studies on one of the Windsor sheets (tel. 19117r). Because those Windsor diagrams illustrate Leonardo's understanding of physiological diplopia, or double vision, one must wonder if the study for the variable-angle contraption and 'spoked half-wheel' (eye emitting rays?) sketch relate to Leonardo's optical investigations as well. See Keele, op. cit., pp. 208-10, and for other optical diagrams similar to the 'spoked haft-wheel', see Codice Atlantico/Marinoni. fol. 331r, vol. I, pp. 572-73; and A. Philip McMahon (ed.), Leonardo da Vinci, Treatise on Painting, translated by the editor, Princeton, 1956, vol. I, pp. 95-96, and vol. II, fol. 70v.

(19) Jean Paul Richter, The Literary Works of Leonardo da Vinci, London, 1883, vol. I, p. 20, no. 25; and Codice Atlantico/Marinoni, fol. 380, vol. II, p. 662.

(20) The 'transparency effect' is described in Manuscript D (fol. 6v); see MacCurdy, op. cit., vol., I, p. 239, and Kemp, op. cit. in n. 1 above, pp. 326-27, fig. 92. The problem of objects appearing too small at very close range is noted by Leonardo in the margin of tel. 4r of Manuscript D. See Strong. op. cit., p, 59.

(21) For the 'blurred-edge' effect, discussed In Manuscript D (fol. 10v) and in the Trattato della Pittura, see Kemp, op. cit. in n. 13 above, p. 147; Strong, op. cit., pp. XXXV and 92-93; and Kemp, op. cit. In n. 1 above, pp. 326-27, fig. 93. For the 'moving-needle' effect (MS D, fol. 6v), see MacCurdy, op. cit., vol. I, p. 240, and Kemp, op, cit. in n, 1 above, pp, 327-28, fig. 94. In Manuscript A (c. 1492), Leonardo presented other examples of optical distortions caused by close viewpoints. See Ackerman, op. cit., pp. 110-t4.

(22) Brian Bowers, Sir Charles Wheatstone FRS, 1802-1875, London, 2001, pp. 45-54.

(23) Earle R. Galley and John F.C. Richards, Theophrastus on Stones, Columbus, Ohio, 1956, lines 23-24, pp. 50, and 97-100; and see Georgia L Irby-Massie and Paul T. Keyser, Greek Science of the Hellenistic Era: A Sourcebook, London and New York, 2002), p. 229. The faint, muddied appearance of the green stones in Leonardo's Madonnas is probably due to the Painter's use of a copper-green pigment, which has changed with age. Of the green pigments available in the renaissance, Leonardo in his Treatise on Painting discusses only copper green, emphasising its fugitive nature. See McMahon (ed.), op. cit., vol. I, pp. 91-92 and vol. II, pp. 67v-68v. Neither the Hermitage nor the Munich museum have conducted pigment analyses of the Madonnas, and se our speculation concerning the chemical composition of the paint has not been confirmed.