416 HISTORY OF PHYSICAL ASTRONOMY. 



force as the cause of the celestial motions, had, as we have seen, beer, 

 for some time growing up in men's minds; had gone on becoming 

 more distinct and more general ; and had, in some persons, approached 

 the form in which it was entertained by Newton. Still, in the mere 

 conception of universal gravitation, Newton must have gone far beyond 

 his predecessors and contemporaries, both in generality and distinct- 

 ness ; and in the inventiveness and sagacity with which, he traced the 

 consequences of this conception, he was, as we have shown, without a 

 rival, and almost without a second. As to the facts which he had 

 to include ia his law, they had been accumulating from the very 

 birth of astronomy; but those which he had more peculiarly to take 

 hold of, were the facts of the planetary motions as given by Kepler, 

 and those of the moon's motions as given by Tycho Brahe and Jeremy 

 Horrox. 



We find here occasion to make a remark which is important in its 

 bearing on the nature of progressive science. What Newton thus used 

 and referred to as facts, were the laws which his predecessors had estab- 

 lished. What Kepler and Horrox had put forth as "theories," were 

 now established truths, fit to be used in the construction of other theo- 

 ries. It is in this manner that one theory is built upon another; 

 that we rise from particulars to generals, and from one generalization 

 to another ; that we have, in short, successive steps of induction. As 

 Newton's laws assumed Kepler's, Kepler's laws assumed as facts the 

 results of the planetary theory of Ptolemy ; and thus the theories of 

 each generation in the scientific world are (when thoroughly verified 

 and established, the facts of the next generation. Newton's theory is 

 the circle of generalization which includes all the others ; the highest 

 point of the inductive ascent; the catastrophe of the philosophic 

 drama to which Plato had prologized ; the point to which men's 

 mind's had been journeying for two thousand years. 



Character of Newton. It is not easy to anatomize the constitution 

 and the operations of the mind which makes such an advance in knowl- 

 edge. Yet we may observe that there must exist in it, in an eminent 

 degree, the elements which compose the mathematical talent. It must 

 possess distinctness of intuition, tenacity and facility in tracing logical 

 connection, fertility of invention, and a strong tendency to generalization. 

 It is easy to discover indications of these characteristics in Newton. 

 The distinctness of his intuitions of space, and we may add of force 

 also, was seen in the amusements of his youth ; in his constructing 

 clocks and mills, carts and dials, as well as the facility with which he 



