SCIENTIFIC METHOD 77 



light that this view is ridiculous, for who would be- 

 lieve that when two lead spheres are dropped from a 

 great height, the one being a hundred times heavier 

 than the other, if the larger took an hour to reach 

 the earth, the smaller would take a hundred hours? 

 Or, that if from a high tower two stones, one twice 

 the weight of the other, should be pushed out at the 

 same moment, the larger would strike the ground 

 while the smaller was still midway? His biography 

 tells that Galileo in the presence of professors and 

 students dropped bodies of different weights from 

 the height of the Leaning Tower of Pisa to demon- 

 strate the truth of his views. If allowance be made 

 for the friction of the air, all bodies fall from the 

 same height in equal times : the final velocities are 

 proportional to the times ; the spaces passed through 

 are proportional to the squares of the times. The 

 experimental basis of the last two statements was 

 furnished by means of an inclined plane, down a 

 smooth groove in which a bronze ball was allowed to 

 pass, the time being ascertained by means of an 

 improvised water-clock. 



Galileo's mature views on dynamics received ex- 

 pression in a work published in 1638, Mathematical 

 Discourses and Demonstrations concerning Two 

 New Sciences relating to Mechanics and Local 

 Movements. It treats of cohesion and resistance to 

 fracture (strength of materials), and uniform, ac- 

 celerated, and projectile motion (dynamics). The dis- 

 cussion is in conversation form. The opening sentence 

 shows Galileo's tendency to base theory on the em- 

 pirical. It might be freely translated thus : " Large 

 scope for intellectual speculation, I should think, 



