LEONARDO AND MODERN SCIENCE 71 



to pathological anatomy: the hardening of the arteries; tubercu- 

 lous lesions of the lungs; a very searching study of the symptoms 

 of senility. 



On the other hand his activity as a practical engineer led him 

 to study, or we might almost say to found, geology: he set to 

 wonder at the various layers of sand and clay which the cutting of 

 a canal did not fail to display; he tried to explain the fossils which 

 he found embedded in the rocks and his explanations were sub- 

 stantially correct. Moreover, he clearly perceived the extreme 

 slowness of most geological transformations, and figured that the 

 alluvial deposits of the river Po were two hundred thousand years 

 old. He well understood the geological action of water and its 

 meteorological cycle. 



His work as a sculptor, or as a military engineer (for instance, 

 when he had to supervise the casting of bombards) , caused him 

 to study metallurgy, particularly the smelting and casting of 

 bronze, the rolling, drawing, planing, and drilling of iron. On all 

 these subjects he has left elaborate instructions and drawings. He 

 undertook in various parts of northern Italy a vast amount of 

 hydraulic work : digging of canals, for which he devised a whole 

 range of excavating machines and tools; building of sluices; estab- 

 lishment of water wheels and pipes, and his study of hydro- 

 dynamics was so continuous that notes referring to it are found in 

 all his manuscripts. He also studied the tides, but did not under- 

 stand them. 



In fact, it is impossible to give even a superficial account of all 

 his scientific and technical investigations, and the reader must for- 

 give me if the magnitude of the subject obliges me to limit myself 

 to a sort of catalogue, for the adequate development of any single 

 point would take many a page. Leonardo's manuscripts contain a 

 great number of architectural drawings, sketches of churches and 

 other buildings, but also more technical matters; he studied the 

 proportion of arches, the construction of bridges and staircases; 

 how to repair fissures in walls; how to lift up and move houses 

 and churches. There is also much of what we would call town- 



