A HISTORY OF SCIENCE 



This all-important law, which lies at the very foun- 

 dation of all true conceptions of mechanics, was thus 

 worked out during the first half of the seventeenth 

 century, as the outcome of numberless experiments 

 for which Galileo's experiments with falling bodies fur- 

 nished the foundation. So numerous and so gradual 

 were the steps by which the reversal of view regarding 

 moving bodies was effected that it is impossible to 

 trace them in detail. We must be content to reflect 

 that at the beginning of the Galilean epoch utterly 

 false notions regarding the subject were entertained 

 by the very greatest philosophers by Galileo himself, 

 for example, and by Kepler- whereas at the close of 

 that epoch the correct and highly illuminative view 

 had been attained. 



We must now consider some other experiments of 

 Galileo which led to scarcely less -important results. 

 The experiments in question had to do with the move- 

 ments of bodies passing down an inclined plane, and 

 with the allied subject of the motion of a pendulum. 

 The elaborate experiments of Galileo regarding the 

 former subject were made by measuring the velocity 

 of a ball rolling down a plane inclined at various angles. 

 He found that the velocity acquired by a ball was 

 proportional to the height from which the ball de- 

 scended regardless of the steepness of the incline. 

 Experiments were made also with a ball rolling down 

 a curved gutter, the curve representing the arc of a 

 circle. These experiments led to the study of the curvi- 

 linear motions of a weight suspended by a cord; in 

 other words, of the pendulum. 



Regarding the motion of the pendulum, some very 



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