ii4ii6] The Pendulum : Falling Bodies 147 



chiefly at home, where he continued to read and to think 

 on scientific subjects. In the year 1586 he wrote his first 

 known scientific essay,* which was circulated in manuscript, 

 and only printed during the present century. 



116. In 1589 he was appointed for three years to a 

 professorship of mathematics (including astronomy) at Pisa. 

 A miserable stipend, equivalent to about five shillings a 

 week, was attached to the post, but this he was to some 

 extent able to supplement by taking private pupils. 



In his new position Galilei had scope for his remarkable 

 power of exposition, but far from being content with giving 

 lectures on traditional lines he also carried out a series of 

 scientific investigations, important both in themselves and 

 on account of the novelty in the method of investigation 

 employed. 



It will be convenient to discuss more fully at the end 

 of this chapter Galilei's contributions to mechanics and to 

 scientific method, and merely to refer here briefly to his 

 first experiments on falling bodies, which were made at this 

 time. Some were performed by dropping various bodies 

 from the top of the leaning tower of Pisa, and others by 

 rolling balls down grooves arranged at different inclinations. 

 It is difficult to us nowadays, when scientific experiments 

 are so common, to realise the novelty and importance at 

 the end of the i6th century of such simple experiments. 

 The mediaeval tradition of carrying out scientific investiga- 

 tion largely by the interpretation of texts in Aristotle, Galen, 

 or other great writers of the past, and by the deduction 

 of results from general principles which were to be found 

 in these writers without any fresh appeal to observation, 

 still prevailed almost undisturbed at Pisa, as elsewhere. 

 It was in particular commonly asserted, on the authority 

 of Aristotle, that, the cause of the fall of a heavy body 

 being its weight, a heavier body must fall faster than a 

 lighter one and in proportion to its greater weight. It may 

 perhaps be doubted whether any one before Galilei's time 

 had clear enough ideas on the subject to be able to give 

 a definite answer to such a question as how much farther 

 a ten-pound weight would fall in a second than a one-pound 



* On an instrument which he had invented, called the hydrostatic 

 balance. 



