38 



HISTORY OF ASTRONOMICAL DISCOVERY. 



served to render more conspicuous that sublime intelligence by which he unravelled the 

 mechanism of the heavens ; and establish more indisputably his claim to be regarded as 

 the architect of physical astronomy. To determine the motions of the heavenly bodies 

 was the work of Keppler : to explain and demonstrate the causes of those motions was the 

 achievement of Newton. So far however from gaining universal assent when first pro- 

 posed, his theory was ill understood, slightly appreciated, or altogether rejected by 

 numbers of scientific men ; and, especially on the continent, it very slowly won its way to 

 notice and confidence. Newton survived the publication of the Principia forty years, and 

 at the time of his death, according to Voltaire, it had not twenty readers out of the country 

 of its production. It was not until the mutual perturbations of the planets began to 

 occupy the attention of the continental philosophers, that his theory was fully admitted 

 abroad, and the work in which it was developed took the rank it has since occupied, 

 pre-eminent, in the words of Laplace, above all the productions of the human mind. It is a 

 common but vulgar error, to suppose the merit of our countryman to lie in conceiving 

 the idea of the attraction of gravitation. That idea had been suggested to many minds 

 long before his time, and the impression had been created that such a power in nature 

 was the cause of the planetary motions. Thus Keppler surmised an attractive force to 

 reside in the sun, producing these movements, and he even threw out the conjecture, that 

 this force diminishes in proportion to the square of the distance of the body on which it 

 was exerted. Borelli and Hooke also distinctly developed the influence of gravity, and 

 both referred the orbits of the planets to the doctrine of attraction combining with their 

 own proper motions to produce curvilinear movements. What really distinguished 

 Newton, was not the idea of gravity as the principle of attachment between the 

 different members of the solar system, but proving it to be so. He succeeded vague 

 surmise upon the point with mathematical demonstration ; .explained and applied the 

 laws of the force ; an accomplishment which crowns him with honour above all his rivals, 



inasmuch as he who works a mine, and 

 distributes its wealth through society, 

 is incomparably in advance of him who 

 has merely apprehended its existence, bat 

 failed in gaining access to its treasures. 



The manor-house of Woolsthorpe, a few 

 miles from Grantham, seated in a little 

 valley near the source of the Witham, 

 was the scene of Newton's birth. Popular 

 tradition reports, that the fall of an apple 

 from a tree in the orchard belonging to 

 this house was the mustard-seed out of 

 which ultimately grew the grand theory of 

 universal gravitation, and the story is not 

 without a leaven of truth. It is certain 

 that, to avoid the plague which ravaged 

 England in 1666, Newton retired from 

 Cambridge; and, when sitting alone in 

 Newton's Birth-place. his garden at Woolsthorpe, his thoughts 



were directed to that remarkable power which causes all bodies to descend towards 

 the centre of the earth. The supposition presented itself, that as this power extends to 

 the highest altitudes of the earth's surface, it probably extends much farther into space ; 

 so that even the moon may gravitate towards the earth, and be balanced in her orbit by 

 the combined force of attraction and the centrifugal force implied in her motion. If this 



