PHYSICAL SCIENCE 19 



Thus Leonardo and Stevin had placed the science 

 of statics, or the knowledge of the laws of forces in 

 equilibrium, on a sound basis. But no correspond- 

 ing advance had been made in the subject of dynamics, 

 which deals with the phenomena and laws of motion ; 

 though here, too, some signs of progress appear in 

 the notebooks of Leonardo. The ideas current were 

 still held on the authority of the Greek philosopher 

 Aristotle, and it was believed that bodies fell to the 

 earth because each body sought its natural place 

 owing to an intrinsic property of heaviness or light- 

 ness, the " place " of heavy bodies being below and 

 that of light bodies being above. From these ideas 

 it followed that, the heavier a body, the faster it 

 must fall. 



Galileo Galilei (1564-1642), with the instinctive 

 genius of the great man of science, saw that the whole 

 point of view must be changed. Instead of inquir- 

 ing with Greek philosophers and mediaeval school- 

 men why things fell, he set himself, in true modern 

 fashion, to examine experimentally how they fell. 



For two thousand years men had tamely accepted 

 Aristotle's teaching, that heavy bodies fell faster 

 than light ones, when five minutes' experiment by 

 dropping lumps of stone and iron from a cliff or high 

 building would have sufficed to prove it erroneous. 

 Galileo showed his at first incredulous contemporaries 

 that heavy and light bodies, let fall simultaneously 

 from the top of the Leaning Tower of Pisa, reached 



