250 PERSONAL PREPAKATION FOE RESEARCH. 



improbable but positively ridiculous. His single-minded 

 devotion to truth, howeyer, led him to abandon each of 

 these hypotheses in its turn, so soon as he had proved its 

 fallacy by submitting it to the test of its conformity to 

 observed facts ; while his fertile ingenuity furnished him 

 with a continual supply of new guesses, which presented 

 themselves in turn as creations of his imagination, to be 

 successively dismissed when they proved to be nothing else 

 than imaginary. But he was at last rewarded by the dis-^ 

 co very of that relation between the times and the distances 

 of the planetary revolutions, which, with the discovery of 

 the ellipticity of the orbits, and of the passage of the 

 ' radius vector" over equal areas in equal times, has given 

 him immortality as an astronomical discoverer. But these 

 discoveries cannot be regarded as based on any higher 

 mental attribute than persevering ingenuity ; ' 'for so far 

 was he from divining the true rationale of the planetary 

 revolutions, that we learn from his own honest confessions 

 that he was led to the discovery of the elliptic orbit of 

 Mars by a series of happy accidents, which turned his 

 erroneous guesses into a right direction, and to that of the 

 " equal areas " by the notion of a whirling force emanating 

 from the sun ; whilst his discovery of the relation between 

 the times and distances was the fortunate guess which 

 closed a long series of it^fortunate ones, many of which 

 were no less ingenious.' ' Now it was by a grand exertion 

 of Newton's constructive imagination, based on his won- 

 derful mastery of geometrical reasoning, that, starting with 

 the conception of two forces, one of them tending to 

 produce continuous uniform motion in a straight line, the 

 other tending to produce a uniformly accelerated motion 

 towards a fixed point, he was able to show that if these 

 dynamical assumptions be granted, Kepler's phenomenal 

 " laws " being consequences of them, must be universally 



