76 THE HISTORY OF SCIENCE 



experiments, his keen perception for the phenomena of 

 motion led to his making a discovery of great scien- 

 tific moment. He observed a lamp swinging by a long 

 chain in the cathedral of his native city of Pisa, and 

 noticed that, no matter how much the range of the 

 oscillations might vary, their times were constant. 

 He verified his first impressions by counting his 

 pulse, the only available timepiece. Later he invented 

 simple pendulum devices for timing the pulse of pa- 

 tients, and even made some advances in applying his 

 discovery in the construction of pendulum clocks. 



In 1589 he was appointed professor of mathemat- 

 ics in the University of Pisa, and within a year 

 or two established through experiment the founda- 

 tions of the science of dynamics. As early as 1590 

 he put on record, in a Latin treatise Concerning 

 Motion (De Motu), his dissent from the theories of 

 Aristotle in reference to moving bodies, confuting 

 the Philosopher both by reason and ocular demon- 

 stration. Aristotle had held that two moving bodies 

 of the same sort and in the same medium have 

 velocities in proportion to their 

 weights. If a moving body, whose 

 weight is represented by 5, be car- 

 ried through the line c e which 

 is divided in the point cZ, if, also, 

 the moving body is divided accord- 

 ing to the same proportion as line 

 c e is in the point d, it is manifest 

 that in the time taken to carry the 

 whole body through c e, the part 

 will be moved through c d. Gali- 

 leo said that it is as clear as day- 



