GALILEO GALILEI 27 



while all the problems of motion which he dealt with - simple 

 free fall, vertical and inclined projection with its peculiar 

 path, the pendulum - were no doubt taken up during his 

 time in Pisa, their true solution was only found later, and in 

 the connection between all these problems. At the various 

 intermediate stages of his knowledge, he met with ideas al- 

 ready put forward by Hipparchus, but still incomplete, and 

 from time to time he imagined that he had conquered the 

 difficulties, but only to find that he was wrong. This gradual 

 development is of high interest;^ we cannot follow it here in 

 detail, but we may point to this case as an example of the 

 erroneous assumption of peculiar inborn gifts.^ 



The key to all this was a knowledge of the law of inertia, 

 and of the fact that the velocities attained under the influence 

 of a force must be regarded as dependent upon time and not 

 upon distance; that is to say, it was necessary to form the 

 concept of acceleration in its quantitative aspect, as, familiar 

 to us to-day. Publication followed late in the famous Discord 

 {Dialogues); in the meantime other discoveries engaged his 

 attention. There can be no doubt that observations on fall- 

 ing and projected bodies and pendulums already attracted 

 his attention during his stay in Pisa. But we have very 

 little accurate information of the details of this, much less 



^ The best description of Galileo's scientific life based upon recent re- 

 search will be found in E. Wohlwill's Galilei undsein Kampffiir dieKoper- 

 nikanische Lehre (1909 and 1926). See also Galileo, by W. W. Bryant, 

 in the S.P.C.K. series 'Pioneers of Progress' (1918); also J. J. Fahie, 

 Galileo: His Life and Work (London, 1903). 



2 The phrase so often met with of the 'intuition of genius' as peculiar 

 to great investigators, is erroneous; only persons without understanding 

 can have originated it. It may of course appear to the outsider as if im- 

 portant discoveries and great steps forward are the outcome of a special 

 gift for guessing the secrets of nature. But enough scientific investigation, 

 observation and thought have always been performed by others pre- 

 viously, and thus sufficient insight into the actual behaviour of nature is 

 already available, and only requires to be worked upon further. This is 

 often a comparatively easy matter for someone who has hitherto taken no 

 part, and approaches the matter with a fresh mind. The earliest workers 

 in science found little store of such knowledge; they had to make their 

 own provision for it. 



