A HISTORY OF SCIENCE 



measure of success in putting this idea into practice. 

 It remained for the mechanical ingenuity of Huyghens 

 to construct a satisfactory pendulum clock. 



As a theoretical result of the studies of rolling and 

 oscillating bodies, there was developed what is usually 

 spoken of as the third law of motion namely, the law 

 that a given force operates upon a moving body with 

 an effect proportionate to its effect upon the same 

 body when at rest. Or, as Whewell states the law: 

 4 'The dynamical effect of force is as the statical effect; 

 that is, the velocity which any force generates in a 

 given time, when it puts the body in motion, is pro- 

 portional to the pressure which this same force pro- 

 duces in a body at rest. ' ' 2 According to the second law 

 of motion, each one of the different forces, operating 

 at the same time upon a moving body, produces the 

 same effect as if it operated upon the body while at 

 rest. 



STEVINUS AND THE LAW OF EQUILIBRIUM 



It appears, then, that the mechanical studies of 

 Galileo, taken as a whole, were nothing less than rev- 

 olutionary. They constituted the first great advance 

 upon the dynamic studies of Archimedes, and then led 

 to the secure foundation for one of the most important 

 of modern sciences. We shall see that an important 

 company of students entered the field immediately 

 after the time of Galileo, and carried forward the work 

 he had so well begun. But before passing on to the 

 consideration of their labors, we must consider work 

 in allied fields of two men who were contemporaries 

 of Galileo and whose original labors were in some re- 



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