292 A SHORT HISTORY OF SCIENCE 



Disclaiming any intention of setting up speculative hypotheses, he 

 discusses the observed phenomena of refracted light, speaking of 

 his discovery of the different refrangibility of the rays of light as 

 " in my judgment the oddest if not the most considerable detection 

 which hath hitherto been made in the operations of nature." 

 While he does not insist upon it, he seems always to have the 

 underlying idea that light itself consists of minute particles the 

 degree of fineness corresponding with the color a theory which 

 held the field thanks to his potent authority with his too sub- 

 servient followers against the better undulatory theory of Huy- 

 gens until the nineteenth century. In the experiments on which 

 this work is based Newton not only decomposes light by a refract- 

 ing prism or series of prisms, but also succeeds in recombining the 

 component colors to reproduce the original white. 



The colors of objects, he says, are nothing more than their power 

 to reflect one or another kind of ray. And in the rays again is 

 nothing other than the power to transmit this motion into our organ 

 of sense, in which last finally arises the sensation of these motions in 

 the form of colors. 



He solves at last the problem of the rainbow. All this constitutes 

 an immense advance over the current Aristotelian notions. 



THE THEORY OF GRAVITATION: Principia In 1682 Newton 

 returned to his attempt of 16 years earlier to explain the moon's 

 motion by means of the assumed influence of gravitation. During 

 this long interval French geographers, testing the supposedly spher- 

 ical shape of the earth, had made a new and more precise triangu- 

 lation with the first use of telescopic instruments. Newton's 

 earlier data had led to a determination of the acceleration due 

 to gravity at the distance of the moon as 13 J feet per minute. 

 The new data changed this result to 15, in agreement with his 

 hypothesis that the force varied inversely as the square of the 

 distance. Stirred to the inmost depths of his usually calm nature 

 by his realization that he was approaching a solution of the great 

 problem, he had to beg a friend to complete his calculations. The 

 new astronomy founded by Copernicus, built up byTycho Brahe, 



