1920] on Leonardo da Vinci 125 



his particular excellence in mechanics and hydraulics, and the atten- 

 tion 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 heliocentric theory by 

 study at Bologna and Padua — a theory afterwards brought to com- 

 pletion and published in his work, " De Revolutionibus Orbium 

 Ccelestium," 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 Maestlin, who is credited with the dis- 

 covery, he had defined the obscure light of 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 struc- 

 ture 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 necro- 

 mancy. He refound the wisdom of Archimedes, and demonstrated 

 his theory of oblique forces applied to the arm of the lever, after- 

 wards associated with the name of Galileo. Following on Archimedes' 

 conception of the pressure of fluids, he showed— a century and a-half 

 before Pascal — that liquids stand at the same level in communi- 

 cating vessels, while if the two arms are filled by different liquids the 

 heights will vary inversely as their densities. 



He is at once artist and scientist in his treatment of and interest 

 in water. He studies its properties and power of movement under 

 conditions varying from the action of the tides of the ocean to the 

 laws which regulate the movement of water in syphons, a subject on 

 which he notes his intention of writing a treatise. He follows its 

 transformation into vapour, rain, dew. snow and ice. It winds 



