H2 SCIENCE AND THE HUMAN MIND 



There must have been changes in the crust of the 

 earth, and mountains have raised themselves in new 

 places. But no catastrophic action is needed ; " in 

 time the Po will lay dry land in the Adriatic in the 

 same way as it has already deposited a great part of 

 Lombardy " Hutton's uniformitarian theory three 

 hundred years before its time ! 



i As a painter and sculptor, da Vinci felt the need of 

 an accurate knowledge of anatomy. In the face of 

 ecclesiastical tradition, he procured many bodies and 

 dissected them, making anatomical drawings which 

 are works of art as well as most accurate in all detail. 

 Many of them still exist in his manuscripts preserved 

 at Windsor. " And you who say that it would 

 be better to look at an anatomical demonstration 

 than to see these drawings," he observes, " you would 

 be right, if it were possible to observe all the details 

 shown in these drawings in a single figure, in which, 

 with all your ability, you will not see nor acquire a 

 knowledge of more than some few veins, while, in 

 order to obtain an exact and complete knowledge of 

 these, I have dissected more than ten human bodies." 

 From anatomy the next step is physiology, and here 

 too Leonardo is found in possession of the field. He 

 describes how the blood makes and remakes con- 

 tinually the whole body of man, bringing material 

 to the parts and carrying off the waste products, as 

 a candle or furnace is fed. He studies the muscles 

 of the heart, and makes drawings of the valves which 

 in the opinion of Knox show a knowledge of their 

 functions. He compares the flow of blood with the 

 circulation of water from the hills to the rivers, from 



v the rivers to the sea, from the sea to the clouds and 



