260 THE WORLD MACHINE 



The identification of the force of attraction with the well-known 

 fact of gravitation constituted a second great step, a second 

 discovery. It was simply an incident that they came together. 

 Either the one or the other would have brought a large meed 

 of fame. 



These two discoveries and the statement of their under- 

 lying Law are the foundation of the Principia. 



It is not easy now to realise the vast stride forward which 

 the publication of this single work represents ; it is equally 

 difficult to separate out what was wholly Newton's own. It 

 was not a large book, five hundred pages or so, so replete with 

 diagrams that it looks like a geometry. The impression is 

 further borne out by the fact that it is written in the style 

 and language of Euclid, proposition succeeding proposition in 

 an unbreakable chain ; it is the application of Euclid to the 

 astronomy of the heavens. It is in no sense historical ; reference 

 to the specific work of others is sparse ; it might readily be 

 used as a textbook in a university. Without a precise know- 

 ledge of the state of the science when it was written, one might 

 readily believe that none, or all of it, was new. 



Newton had a mind that was at once comprehensive and 

 synthetic, a gripping mind that made the whole cohere. It 

 was he first of all who foresaw the consequences that followed 

 from the law he had demonstrated. The moon is held by the 

 earth, the satellites by Jupiter, the earth and other planets 

 by the sun, in virtue of tne force of attraction. This attraction 

 varies directly with the mass of matter contained in each planet. 

 He introduces, therefore, a new conception that of mass as 

 distinguished from mere weight. In the mind of Galileo this 

 separation had not yet taken place. Newton saw and stated 

 the logical inference that is, that between every ultimate 

 particle of matter in the universe there exists an inherent force 

 or power which tends to draw them together, a power that 

 grows less with the square of the distance which separates them. 

 Consider that there was scarce a contemporary, or any one for 

 some time after, who could grasp this simple, central truth 

 not Huyghens, nor Leibnitz, nor Jean Bernouilli, nor Cassini, 

 great mathematicians all the greatest of the time, and you 

 will see how far this single mind outstepped its age. 



Newton was not merely the founder of celestial mechanics 



