SCIENTISTS OF XVTH AND XVlTH CENTURIES. 99 



justly says, "was almost preternatural," had advanced 

 several branches of science. He had cultivated the MATHE- 

 MATICAL AND PHYSICAL SCIENCES, NATURAL HISTORY, 

 chemistry, ENGINEERING, and MECHANICS. In this last 

 branch, he had anticipated by more than a century Stevinus 

 and Galileo with regard to the laws of the lever and the fall 

 of bodies, and even written on the equilibrium of water. 

 " The progress of the science of mechanics was necessary 

 before the Copernican system could be developed," and it 

 was Leonardo who improved this science. He understood 

 the law regulating the flight of projectiles. He gave a clear 

 exposition of the theory of forces obliquely applied on a 

 lever*; was well acquainted with the earth's yearly 'motion ; 

 understood the LAWS OF FRICTION, and likewise the principle 

 of VIRTUAL VELOCITIES the golden rule of mechanics ; aerial 

 perspective, the nature of coloured shadows, the use of the 

 iris, the effects of the duration of visible impressions on the 

 eye; he INVENTED water-mills, water-engines, canal and 

 river locks, A WATER PUMP, and anticipated Castelli in 

 HYDRAULICS ; he invented a spinning machine, a planing 

 machine, an automatic walking lion ; designed a STEAM 

 CANNON; described the CAMERA OBSCURA before Porta's 

 invention ; he studied the flight of birds ; attempted to make 

 an apparatus for flying ; occupied himself with the " FALL OF 

 BODIES on the hypothesis of the EARTH'S ROTATION on 

 its axis ; " he treated of the TIMES OF DESCENT along in- 

 clined planes and circular arcs, and of the nature of machines. 

 He "considered with singular clearness respiration and 

 combustion, and foreshadowed one of the great hypotheses of 

 geology the UPRISING OF CONTINENTS " after tracing the 

 origin of Fossils. t He also studied chemistry and anatomy : 

 his anatomical designs are the finest in existence. 



* Appendix IV. 



f "The sea," says Leonardo, "alters the equilibrium of the earth ; the 

 shells which are found heaped up in the different layers of soil have 

 necessarily lived in the same place, which was occupied by the sea. The 

 great rivers carry into the ocean the sediment which they roll along in 

 their course. The banks, formed by these deposits, have been covered 

 over by other and later clay layers of various thickness, and what was the 

 bottom of the sea has become the summit of mour. tains." 



H 2 



