418 RISE AND PROGRESS OF 



All these results were confirmed by observation, and thus the 

 nature and laws of terrestrial gravity were fully established. 



Galileo seems to have turned his attention at an early period 

 to the motions of pendulous bodies ; and he is said to have been 

 conducted to the knowledge of the fact that all the vibrations 

 of the same pendulum, whether great or small, are performed in 

 the same time by observing the swinging of the lamps in the 

 Cathedral of Pisa. The tautochronism of the pendulum, however, 

 seems to have been noticed, and even applied, at a much earlier 

 period. The astronomers of Arabia employed the instrument in 

 some of their observations, patiently counting the number of its 

 oscillations during the period of an eclipse, and renewing the 

 motion with a slight push of the finger, when the arcs of vibration 

 became too small. The same mode of observation was practised 

 in more recent times by Gassendi, Biccioli, and other astronomers 

 of Europe, when the attention of the scientific world was again 

 drawn to the principle of tautochronism. 



By these important discoveries, Galileo has justly earned the 

 title of " father of dynamical science." But to estimate duly the 

 merits of this great man, we must consider the age in which he 

 lived, and the darkness with which he was encompassed. Alone 

 and unsupported, he assailed the Aristotelian philosophy with all 

 the weapons of sound argument and caustic ridicule ; and the 

 inveterate spirit of hostility which he thus excited, the rancour 

 of rivals, and the intolerant persecution of the Church, ended 

 only with his life. Notwithstanding all this opposition, however, 

 truth was progressive. The proofs which the astronomical dis- 

 coveries of Galileo brought in support of the Copernican system 

 roused the attention of philosophers; and it may be fairly ques- 

 tioned whether the discoveries of the Florentine philosopher have 

 not had as great an influence on the progress of physical science, 

 as the works of his immortal contemporary Lord Bacon. 



While to Galileo we owe the foundation of the doctrine of 

 motion, to his pupil Torricelli we are indebted for the first step 

 which was made in that branch of the doctrine which relates to 

 fluids. The fundamental problem of hydraulics that which de- 

 termines the velocity of efflux of a fluid through an aperture in 

 the bottom or side of a vessel was first solved by this writer, in 

 his work de motu gravium. 



As the terrestrial mechanics of Aristotle were overthrown by 



