INDUCTIVE EPOCH OF NEWTON. 403 



celestial motions as distinctly as the motions which took place close to 

 him ; considered them as of the same kind, and applied the same 

 rules to each, without hesitation or obscurity. But so far, this thought 

 was merely a guess : its occurrence showed the activity of the thinker ; 

 but to give it any value, it required much more than a " why not ?'' 

 a " perhaps." Accordingly, Newton's " why not ?" was immediately 

 succeeded by his " if so, what then ?" His reasoning was, that if 

 gravity reach to the moon, it is probably of the same kind as the 

 central force of the sun, and follows the same rule with respect to the 

 distance. What is this rule? We have already seen that, by calcu- 

 lating from Kepler's laws, and supposing the orbits to be circles, the 

 rule of the force appears to be the inverse duplicate proportion of the 

 distance ; and this, which had been current as a conjecture among the 

 previous generation of mathematicians, Newton had already proved by 

 indisputable reasonings, and was thus prepared to proceed in his train 

 of inquiry. If, then, he went on, pursuing his train of thought, the 

 earth's gravity extend to the moon, diminishing according to the in- 

 verse square of the distance, will it, at the moon's orbit, be of the 

 proper magnitude for retaining her in her path ? Here again came in 

 calculation, and a calculation of extreme interest ; for how important 

 and how critical was the decision which depended on the resulting 

 numbers ? According to Newton's calculations, made at this time, the 

 moon by her motion in her orbit, was deflected from the tangent 

 every minute through a space of thirteen feet. But by noticing the 

 space through which bodies would fall in one minute at the earth's 

 surface, and supposing this to be diminished in the ratio of the inverse 

 square, it appeared that gravity would, at the moon's orbit, draw a 

 body through more than fifteen feet. The difference seems small, the 

 approximation encouraging, the theory plausible ; a man in love with 

 his own fancies would readily have discovered or invented some prob- 

 able cause of this difference. But Newlon acquiesced in it as a dis- 

 proof of his conjecture, and " laid aside at that time any further 

 thoughts of this matter ; thus resigning a favorite hypothesis, with a 

 candor and openness to conviction not inferior to Kepler, though his 

 notion had been taken up on far stronger and sounder grounds than 

 Kepler dealt in ; and without even, so far as we know, Kepler's regrets 

 and struggles. Nor was this levity or indifference ; the idea, though 

 thus laid aside, was not finally condemned and abandoned. When 

 Hooke, in 1079, contradicted Newton on the subject of the curve 

 described by a falling body, and asserted it to be an ellipse, Newton 



