182 HISTORY OF PHYSICAL ASTRONOMY. 



first to think of the mutual attraction of matter, we 

 cannot help noticing Francis Bacon ; for his notions 

 were so far from being chargeable with the loose- 

 ness and indistinctness to which we have alluded, 

 that he proposed an experiment 21 which was to 

 decide whether the facts were so or not ; whether 

 the gravity of bodies to the earth arose from an 

 attraction of the parts of matter towards each other, 

 or was a tendency towards the center of the earth. 

 And this experiment is, even to this day, one of the 

 best which can be devised, in order to exhibit the 

 universal gravitation of matter : it consists in the 

 comparison of the rate of going of a clock in a deep 

 mine, and on a high place. Huyghens, in his book 

 De Causa Gravitatis, published in 1690, showed 

 that the earth would have an oblate form, in conse- 

 quence of the action of the centrifugal force ; but 

 his reasoning does not suppose gravity to arise from 

 the mutual attraction of the parts of the earth. The 

 influence of the moon upon the tides had long been 

 remarked; but no one had made any progress in 

 truly explaining the mechanism of this influence ; 

 and all the analogies to which reference had been 

 made, on this and similar subjects, as magnetic and 

 other attractions, were rather delusive than illus- 

 trative, since they represented the attraction as 

 something peculiar in particular bodies, depending 

 upon the nature of each body. 



81 Nov. Org. Works, vol. viii. p. 148. 



