MECHANICAL PHILOSOPHY. 417 



authority of the " great master," and, to appeal to nature herself, 

 yet the science of motion was not destined to profit by these 

 glimmering lights, and its very foundations remained unlaid until 

 the close of the 16th century. 



Galileo was born at Pisa, in the year 1564, and at an early 

 age devoted the energies of an ardent and powerful mind to the 

 mathematical and physical sciences ; and here was first formed 

 that union of abstract and experimental reasoning, whose force and 

 value in explaining the phenomena of nature is now so well under- 

 stood. While yet pursuing his studies at the university, Galileo 

 had begun to make experiments on the laws of falling bodies; 

 and he then discovered the fact, that all bodies, whether light or 

 heavy (the effect of the air's resistance being abstracted), fall to 

 the ground from the same height in the same time. This im- 

 portant law of gravity was in direct contradiction to the principles 

 of the Aristotelian philosophy, then in full repute ; and, unac- 

 countable as it now seems, it was believed that two unequal 

 weights, if let fall at the same instant, and from the same height, 

 would reach the ground in times inversely proportional to the 

 weights that a weight of 100 Ibs. (for example) would descend 

 in the y^oth part of the time occupied by a weight of 1 Ib. 

 Galileo tried this very case before many witnesses, from the 

 summit of the famous leaning tower of Pisa. The two weights 

 were found to reach the ground in precisely the same time ; and 

 the decisive result of the experiment did more, perhaps, to shake 

 the empire of the Aristotelian philosophy, than any single effort 

 of opposition hitherto made. 



Setting out from the principle that bodies, in their free 

 descent towards the earth, receive equal increments of velocity in 

 equal times, Galileo deduced, by the application of mathematical 

 reasoning, the known laws of falling bodies; and having proved 

 that these laws must hold good also in the case of bodies de- 

 scending on inclined planes, where a portion of the weight is 

 sustained, and where consequently the acceleration is not so rapid, 

 he was enabled to bring the whole theory to the test of experi- 

 ment. He applied himself, in the next place, to the consideration 

 of the motion of a heavy body projected obliquely ; and by the aid 

 of the principle of the composition of motion a principle tacitly 

 assumed in his reasoning he proved that the path traced by a 

 projectile was the well known curve of Appolonius the parabola, 



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