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need not say to understand, but even to accept the notion of, the commonest and most elementary phenomena. Aristotle had already noticed that if a square hole were cut in a window shutter, the beam of light thrown through it by the sun nevertheless described a circle on the wall; absorbed by the anomaly, he omits to push his investigations into its cause.1 Eighteen centuries were to pass before anything more was to be known. Leonardo says that if you place yourself in a hermetically closed room, facing a building, landscape, or any other object directly lighted by the sun, and then cut a small circular hole in the shutter, images of the objects outside will be thrown on any surface facing the hole and will be reversed. The principle of the "camera obscura" was found. Perhaps one Don Papnuzio may have had something to do with the discovery; but of the latter we find no mention until after 1521, when Leonardo was already dead. On the other hand we know for certain that Da Vinci's discovery was at least half a century in advance of that of Cardan, and seventy-five years before that of G. B. Porta, to whom the credit has hitherto been "given. Cardan's Dc Subtilitate did not appear until 1550, nor Porta's treatise on natural magic until 1589. Leonardo's contrivance was not, of course, complete, for it omitted the use of the glass lens, by which the size and definition of the image could be increased. This was to be Cardan's contribution to the invention. Thus we see that even a sovereign intellect cannot dispense with the help of time, which, in carrying an idea to complete fruition, often makes use of the most humble students.
The theory of complementary colours, so indissolubly connected with the name of Chevreul, z is to be found, in germ, in the Trattato della Pittura (cap. 190): "If you wish that the neighbourhood of one colour should lend charm to the colour near it, observe what happens when the sun's rays form the rainbow, or iris ; the colours are begotten by the movement of the rain, for each drop changes, in falling, into each of the colours of this rainbow, as will be proved in its proper place." A few lines farther on Leonardo advises the juxtaposition of green and red.l
1 Problems, § 6.
"Chevreul, De la Loi du Contraste simultane des Couleurs. Paris, 1839. The same: Expose d'un Moyen de d'efinir et de nommer les Couleurs tfapres une Methode precise et experimentale. (Mcmoires de I'Amdemie des Sciences, vol. xxxiii. Paris, 1861.)
I may compare this theory with that of Chevreul, as epitomised by Charles Blanc: "If we combine two primary colours, yellow and blue, for instance, in order to make a secondary colour, green, this secondary colour will reach its maximum of intensity when we bring it into the immediate neighbourhood of.its complementary, which is red. So, too, if we combine yellow and red to form orange, this secondary colour will be enhanced by the juxtaposition of blue. Finally, if we combine red and blue to form violet, this secondary tint will have its brilliancy increased when set against yellow." 2
All this is most significant. Without depriving Chevreul of any part of his credit, for he was certainly ignorant of Leonardo's teachings, our quotations secure priority for the Florentine in a capital discovery in the science of colours.
A few more isolated remarks may be noted. "Black clothes make the complexion look whiter than it is, white clothes make it look darker; yellow clothes heighten people's colour, red clothes make them seem pale" (cap. 238).
Leonardo enumerates six colours (against three admitted by the ancients, and seven by Newton), namely, blue, yellow, green; the colour of a lion, tan or ochre; red, and the colour of mulberries. 3 "As for black and white," he says, "they are not colours, for one corresponds to the absence of colour, and the other is the genesis of colour (cap. 213; cf. cap. 247)." a Elsewhere (cap. 254) he counts among the simple colours white, black, (including these two, as he explains, simply out of regard for the special needs of painters), yellow, green, and red. "White," he says, "corresponds to light, yellow to earth, green to water, blue to air, red to fire, and black to shadows."
1 L. B. Alberti had already caught a glimpse of this law, but his ideas were still very indefinite. "The colour red," he says, "set between sky-blue and green, communicates a mutual nobleness to them. The colour white set between an ashy grey and yellow, enriches them with a certain gaiety, as it does, indeed, most colours. Dark colours receive a notable accessicn of dignity when placed among light ones, and light colours produce the best effects when placed among dark ones." Cardan advises that in a picture dark colours should be alternated with light ones; that red should be placed between blue (" cseruleus") and green, white between grey ("cinereus") and yellow. (De Subtilitate, ed. of 1550, p. 130.)
2 Grammaire des Arts du Dessin, p. 597-598.
3 To appreciate the independence of Leonardo in his studies of colours, it will be enough to compare his conclusions with those of the Neapolitan, S. Portio, who published at Florence, in 1548, a De Coloribus Libellus, full of antiquated Aristotelian ideas. Leonardo's notes on the subject have been analysed and properly appreciated by E. Brucke in Sitzungs Berichte der Wiener Akademie der IVissenschaften (1852), in his Physiologie der Farben (Leipsic, 1866), and in his Bruchstiicke aus der Theorie der bild. Kiinsle (Leipzig, 1877).
The study of acoustics gave Leonardo materials for curious experiments in echoes, in vibratory movements, etc. He notes that a blow struck on one bell produces a sympathetic effect on another bell of the same kind; "that when the string of a lute is struck it corresponds with and conveys a movement to a similar string of the same tone on another lute, as one may convince one's self by placing a straw on the string similar to the one struck. Who would believe, asks Govi, that these notes and observations anticipated those of Galileo, Mersenne, and others, which, however, they did by more than a century ? 2
A method suggested by Leonardo for perceiving distant sounds has a certain analogy with suggestions made in our own time for the same purpose, before the invention of the electric telephone. Here is the passage in which it is set out:—" If you bring your ship to, and put one end of a tube (" sarbacane ") in the water and the other end to your ear, you will hear ships which are quite a long way off; and if you do the same thing on land, you will hear what is going on far away from where you are." 3
He has left but few notes on the conduct of the loadstone, but those notes show a wonderful grasp of his subject; he established the fact that, given an equality of weight, the loadstone and iron attract in the same proportion.4
1 L. B. Alberti had already excluded black and white from the catalogue of colours (Mancini, p. 138).
2 Saggio, p. 16.
3 Charles Ravaisson-Mollien, Comptes-rendus de I'Acadbnie des Sciences, 18Si, vol. ii., p. 497.
4 Saggio, p. 15.
To chemistry he felt no more than a passing attraction; it interested him chiefly by its connection with the preparation of pigments.1
He had, nevertheless, a good idea of the conditions of combustion. "Fire," he says, "continually destroys the air by which it is nourished. It would create a vacuum if more air did not rush in to fill the space. When air is not in a proper condition to receive flame, neither flame nor any animal, terrestrial or aerial, can live in it. No animal can live where a flame cannot live." 2
Does not this give a complete definition of the part played by oxygen, and that two centuries and a half before Lavoisier made his immortal discoveries? Nothing is wanting but the name of the gas and the idea of employing scales to weigh the products of calcination, before and after. (M. Berthelot, however, reminds me that similar ideas are to be found in the works of Aristotle and Cicero.)
That Leonardo shared in many of the delusions of his time has been proved lately by examination of his treatise on animals, the manuscript of which is preserved in the Institut de France. This treatise contains a long dissertation on the mysterious virtues of all kinds of quadrupeds, birds, reptiles, and fishes. A leading historian of art, Anton Springer,3 has demonstrated that the treatise in question is nothing more than an extract from a famous work of the middle ages, the Physiologus or Bestiarius. We are therein told, for instance, that if the bird known as the " callendrino" is placed before a sick person, it will turn away its head if the latter is going to die; if, on the other hand, he is going to get better, the bird will look him straight in the face, and will take the disease upon himself. When the Bestiarii failed Leonardo in his study of animal habits, he had recourse to Brunetto Latini's Tesoro. Here again Springer has removed all doubt as to the borrowings of the fifteenth century Florentine from his fellow-countryman of the thirteenth. Even Pliny—the credulous Roman naturalist —was drawn upon. How an intellect so independent as Leonardo's could take the trouble to analyse—I will not say to receive—so many absurd beliefs, in which the basilisk, the phoenix, and the sirens are accepted as real beings, it is difficult to explain. His only excuse is to be found in the example set by the most eminent men among his contemporaries.
1 Richter, vol. i., pp. 320, et seq.
2 Codex Atlanticus, fols. 234, 236.
3 Berichte der k. Sachs. Gesellschaft der Wissenschaften, 1884, p. 244-271.
He did not always confine himself to mere compilation. Many a
comparison or maxim reveals a personal note. Thus he says of the lion: "We may compare him to the children (or disciples) of virtue, who awake at the call of glory and raise themselves by honourable studies, thanks to which they continually mount higher and higher. As for those who are deaf to this appeal, they stand apart and separate from virtuous men."
In the domain of natural science, Leonardo was a student of anatomy, botany, and geology.