May 13, 1920] 



NATURE 



341 



destruction of that instrument of which he has him- 

 self become the living principle and the propeller." 



In the analogy thus drawn from Nature to the 

 problem before him, Leonardo has anticipated the 

 attitude of modern research. 



In his construction of the instrument he finally 

 attempted to combine the type of the lark soaring 

 with its wings open with that of the bat as it 

 descends. He does this by the introduction of sportelli 

 (trap-doors or shutters) in the surface of the wings, 

 whereby, as he says, " the wing is full of holes as it 

 rises and closes up when it falls." The shutters 

 should have rims of cane and be covered with starched 

 taffeta to render them airtight. Perhaps it was after 

 the Monte Ceceri attempt that he wrote on a page of 

 MS. B of the Paris manuscripts, "Try the actual 

 instrument in the water, so that if you fall you will 

 not do yourself any harm." It may also have been 

 the failure of this attempt that caused him to search 

 for a fresh source of motive power to take the place 

 of that exerted by the muscles of a man. On 83 verso, 

 MS. B of the Paris manuscripts, there is a drawing 

 of a large screw constructed to revolve round a vertical 

 axis, and a note explains its intended use: "If this 

 instrument made with a screw is well made — that is to 

 say, made of linen of which the pores are stopped up 

 with starch — ^and is turned swiftly, the said screw 

 will make its spiral in the air, and it will rise high." 

 Leonardo adds that a small model may be made of 

 cardboard, with the axis formed of fine steel wire 

 bent by force, and that this when released will turn 

 the screw. To his drawing of this instrument the 

 architect Luca Beltrami has — to me, as it seems, 

 justlv — applied the word "aeroplane." 



Another page in the Codice Atlantico (311 v. d.) 

 of unique interest contains three studies of artificial 

 wings, a name, and a note that the machine is to be 

 made, not with sportelli— that is, shutters— but united. 

 The natural interpretation is that the note refers to a 

 commission for the construction of a machine for flight, 

 with regard to which the patron, Gian Antonio de 

 Mariolo, has expressed a desire that the wings should 

 be such that no wind would be able to pass through 

 them as it would if they had shutters, i.e. should be 

 like the wrings of the bat. 



Leonardo's researches in natural and applied science 

 cover so wide a field, and specialisation in these days 

 has so divided knowledge into watertight compart- 

 ments, that properlv to gauge the value of his con- 

 tributions to scientific research would require a com- 

 bination of many trained intelligences. But it is not 

 possible to devote a number of years to the close 

 studv of all that concerns Leonardo without becoming 

 imbued with the conviction of the complete oneness 

 of his work and method. The dominant purpose 

 which animates him, whatever the nature of the 

 problem, is to investigate, to examine, and to define 

 primary causes. His pen reinforces his practice. 

 "Nature," he says, "is constrained by the order of 

 her own law, which lives and works within her." 

 Again, "There is no result in Nature without a 

 cause ; understand the cause, and you will have no 

 need of the experiment"; and "Nature is full of 

 infinite causes which were never set forth in 

 experience." 



With Leonardo the latter end of this search forgot 

 the beginning. His intellectual curiosity into the 

 origins and causes of all created things is revealed in 

 infinite variety in the thousands of pages of his manu- 

 scripts, compact, as has been said, "of observation, 

 of prophecy, of achievement," and in his triple legacy 

 forming a record probably unequalled, certainly un- 

 surpassed, bv that of any other man in the history of 

 the world. For consider what he was ! Painter, 



NO. 2637, VOL. 105] 



sculptor, engineer, architect— all these to the wonder 

 of his contemporaries. His manuscripts reveal that 

 he was no less distinguished as physicist, biologist, 

 and philosopher. But in the field of science he was 

 essentially a forerunner. The results that he achieved 

 must be reckoned as small compared with his grasp of 

 basic principles, with the vistas that he opened up, 

 and with the unerring instinct which he displayed in 

 choosing the true method of investigation. 



AH Leonardo's writings connected with science seem, 

 as it were, fragments of a larger purpose, charted, 

 defined, explored, but never fulfilled, of v^^hich his 

 researches in anatomy, zoology, physiology, embryo- 

 logy, and biology are the allied and component parts. 

 Discerning the essential unity of man and the animals 

 —■"because," as he says, "all land animals have 

 similar members^ — that is to say, muscles, nerves, and 

 bones — and these members do not vary at all except 

 in length and thickness " (MS. G, 5 verso) — he may 

 be said to have founded comparative anatomy. Draw- 

 ings now at Windsor show^ the gradations of the 

 human type merging into that of various animals. 

 Leonardo tracks the mystery of life from the concep- 

 tion and the foetus through growth to maturity, and 

 so to the gradual wasting of the tendons and all the 

 physical phenomena of death. 



"I have dissected," he says, "more than ten human 

 bodies, destroying all the various members, and remov- 

 ing even the very smallest particles of the flesh which 

 surrounded these veins without causing any effusion 

 of blood other than the imperceptible bleeding of the 

 capillary veins. And, as one single body did not suffice 

 for so long a time, it was necessary to proceed by 

 stages with so many bodies as would render my know- 

 ledge complete; and this I repeated twice over in 

 order to discover the differences." 



The drawings made in the course of these investiga- 

 tions, now in the Royal Collection at Windsor, were 

 examined in the time of George III. by the famous 

 surgeon William Hunter, who, approaching them with 

 natural professional distrust, thus made the amende 

 honorable : — 



" I expected," he says, " to see little more than such 

 designs in anatomy as might be useful to a painter 

 in his own profession. But I saw, and indeed w^ith 

 astonishment, that Leonardo had been a general and 

 deep student. When I consider what pains he has 

 taken upon every part of the body, the superiority of 

 his universal genius, his particular excellence in 

 mechanics and hydraulics, and the attention with 

 which such a man would examine and see objects 

 which he has to draw, I am fully persuaded that 

 Leonardo was the best anatomist at that time in the 

 world." Although he does not fully explain its 

 mechanism, he evidently knew of the circulation of 

 the blood a hundred years before Harvey gave the 

 knowledge to the world. "The heart," he wrote, "is 

 a muscle of great strength ; the blood which returns 

 when the heart opens again is not the same as that 

 which closes the valve." 



The depth and variety of his researches in other 

 branches of natural science may be inferred from the 

 citation of a few instances in which he anticipated the 

 results of investigations associated with other names. 

 Either before, or at latest during such time as 

 Copernicus was laying the foundations of his helio- 

 centric theory by studv at Bologna and Padua — a 

 theory afterwards brought to completion and published 

 in his work, " De Revolutionibus Orbium Coelestium," 

 in 1543 — Leonardo had enunciated the ruling principle 

 of it in a line in the manuscripts now at Windsor, 

 "II sole non si muove " ("The sun does not move"). 



A hundred years before MaestUn, who is credited 

 with the discovery, he had defined the obscure light of 



