34 GREAT MEN OF SCIENCE 



which appeared in 1605: 'Take, as Professor Jan Cornets de 

 Groot and I have done, two lead balls, one ten times larger 

 and heavier than the other, and allow them to fall from a 

 height of thirty feet on to a plate or other object, upon which 

 they strike with sufficient noise, and it will then be found 

 that they strike the plate at the same moment, so that both 

 sounds seem like one.' With this he goes considerably be- 

 yond questions of equilibrium (statics) and engages upon an 

 investigation of the process of motion (dynamics), wherein 

 Galileo then followed him with decisive results. What here 

 distinguishes Stevin and Galileo from Aristotle in a very 

 fundamental way, is their obvious inborn and lively feeling 

 for the supreme importance of simple processes of motion 

 such as the mere fall of bodies, these being roads to the 

 understanding of all phenomena of motion. Aristotle must 

 have been quite devoid of this feeling. For him the motion 

 of falling was of no particular interest; he dealt with it as 

 with the mass of other matters which he undertakes, without 

 having properly examined any one of them, although Pythag- 

 oras already existed as an example of how investigation 

 begins with simple things, which nevertheless must be 

 treated with quantitative exactness. 



GALILEO GALILEI 



1^64-1642 



Here we come to a man of the highest genius, who was able 

 to exert in many directions such an influence on science as 

 to change the whole position. Above all, he was the founder 

 of the doctrine of the motion of matter (dynamics), which 

 he turned from scattered small beginnings and suppositions 

 into a finished science. Since all that happens to tangible 

 and weighable bodies as far as they are without life, from 



