342 



NATURE 



[May 13, 1920 



the unilluminated part of the moon as due to reflection 

 from the earth's surface. 



In the search for hidden laws and causes the 

 scientific problem followed hard upon the artistic 

 problem. The study of perspective led to that of light 

 and shade, and so of optics— the study of the structure 

 and functions of the eye, as being the instrument by 

 which light and shade are perceived. He made a 

 model of its parts, and showed how an image is 

 formed on the retina, thus refuting the currently 

 accepted belief of the eye throwing out rays which 

 touch the object it desires to examine. He described 

 also the principle of the camera, obscura ninety years 

 before Porta developed the idea in practice. 



In mechanics he enunciated the theory of inertia, 

 afterwards demonstrated by Galileo, and relegated the 

 theory of perpetual motion then current to the same 

 category as astrology and necromancy. He refound 

 the wisdom of Archimedes, and demonstrated his 

 theorv of oblique forces applied to the arm of the 

 lever," afterwards associated with the name of Galileo. 

 Following on Archimedes 's conception of the pressure 

 of fluids, he showed— a century and a half before 

 Pascal— that liquids stand at the same level in com- 

 municating vessels, while if the two arms are filled 

 by different liquids the heights will vary inversely as 

 their densities. 



Leonardo is at once artist and man of science m 

 his treatment of, and interest in, water. He studies 

 its properties and power of movement under condi- 

 tions varving from the action of the tides of the 

 ocean to 'the laws which regulate the movement of 

 water in siphons— a subject on which he notes his 

 intention of writing a treatise. He follows its trans- 

 formation into vapour, rain, dew, snow, and ice. It 

 winds mysteriously in wonder-working coils through 

 the landscape backgrounds of his pictures. He traces 

 the infinite shapes it assumes, falling in violence of 

 movement in spirals and eddies, circling like the loop 

 of a swallow's flight, something of the artist's sheer 

 delight in the creation of 'beauty of form mingling 

 with the purpose of the man of science to wrest from 

 this variety its underlying principle. Or again, as 

 engineer he harnesses its power, studying to divert 

 its channels either in menace of war or for purposes 

 of commerce or irrigation. t ;a • 



In considering a geological problem his method is 

 entirely deductive. "Since," as he says, "things are 

 far more ancient than letters," he turns from authority 

 to the testimony of things themselves. "Why, he 

 asks, "do we find the bones of great fishes and oysters 

 and 'corals and various other shells and sea-shells on 

 the high summits of mountains by the sea just as we 

 find them in low seas?" The fact that the cockles 

 were living at the time when they became embedded 

 in the strata— this being evident from the shells being 

 found in a row in pairs, while in other places the dead 

 are found separated from their shells and all cast up 

 together bv the waves— is cited as proof that water 

 formerlv covered parts of the earth which are now far 

 above the level of the sea, and that this condition 

 continued for a period of more than the fortv days 

 of the Deluge, because, as the cockle travels along a 

 furrow at the rate of three or four braccia daily, it 

 could not in forty days have proceeded from the 

 Adriatic to Monferrato in Lombardy, a distance ot 

 250 miles. By an investigation of the cuttings formed 

 by the Arno in the successive strata of which the 

 shells are found, he shows the gradual changes in the 

 crust of the earth, and, following on the track of this 

 knowledge, he essays the construction of the map of 

 Italy in days remote beyond record, but of which the 

 earth remains a living witness. 



His special interest in botanical study may be traced 



NO. 2637, VOL. 105] 



back to the earliest period of his artistic work. 

 Vasari tells of a cartoon, intended for tapestry, of the 

 sin of Adam and Eve in Paradise, where was a 

 meadow with innumerable plants and animals, "of 

 which in truth one could say that for diligence and 

 truth to Nature divine wit could not make the like." 

 He mentions a fig-tree as of special excellence for 

 the foreshortening of the leaves and the disposition 

 of the branches, and also a palm in which the round- 

 ness of the fan-like leaves was shown with marvellous 

 art. His description suggests minute attention to 

 detail on the part of the artist based upon a profound 

 study of Nature, and these are the characteristics 

 which find expression in Leonardo's many exquisite 

 studies of plants and flowers, and in the treatment of 

 the herbage in the Virgin of the Rocks in the Louvre. 

 His study of botany was in inception an integral part 

 of his treatise on painting, botany being as necessarv 

 as anatomy, in order that the painter might have the 

 requisite knowledge of form and structure. But here 

 also the artist's power of observation of the varied 

 beauty of earth's raiment of plants and flowers is 

 merged imperceptibly in the mood of the man of 

 science who saw in Nature not only form and colour, 

 but, above all, light, which St. Augustine called " the 

 queen of colours," and uses Nature's profusion as a 

 background whereon to study the incidence of light 

 and shade. 



Leonardo's researches in structure are so exact and 

 so scientific in method as to anticipate the results of 

 subsequent inquiry, as, for instance, in the knowledge 

 his writings reveal of phyllotaxis — the law of quin- 

 cuncial arrangement of the leaves on the stem— pro- 

 mulgated in 1658 by Sir Thomas Browne in his 

 "Garden of Cyrus." In like manner the discovery 

 that the age of a tree may be told from the number 

 of concentric rings visible in a section of its trunk, 

 with which more than a century later the names of 

 Nathaniel Grew and Marcello Malpighi are associated, 

 is contained in a passage in Leonardo's "Treatise on 

 Painting " (Ludvig, 829). Leonardo also states in the 

 same passage that these rings vary in thickness 

 according to the greater or less amount of humidity of 

 each year. 



I have attempted here to summarise a few of the 

 results attained in the course of this investigation. 

 The breadth and variety of their scope may serve to 

 recall the remark of Francis I., who is recorded by 

 Benvenuto Cellini to have said that "he did not 

 believe that any other man had come into the world 

 who had attained so great knowledge as Leonardo." 



Aeronautical Research. 



THE announcement by the Air Ministry of the 

 future arrangements for aeronautical research 

 and education marks an important stage in the his- 

 tory of the subject. The course followed was indicated 

 in a White Paper, noticed in Nature of March 4, 

 p. 14, containing the report of a Committee on 

 Education and Research in Aeronautics. The chair- 

 man of that Committee, Sir Richard Glazebrook, is 

 now head of the new Aeronautical Research Com- 

 mittee and Zaharoff professor at London University. 

 He was for twelve years chairman of the late Advisory 

 Committee for Aeronautics under the presidency of 

 the late Lord Rayleigh, and it may fairly be claimed 

 that the new advance in the direction of the co- 

 ordination of research in a large subject is a conse- 

 quence of the success of the work of the earlier body. 

 The Advisory Committee for Aeronautics had the 

 assistance of such eminent men of science as Sir 

 Horace Darwin, Sir Joseph Petavel, Sir Dugald Clerk, 



