THE THEORIES OF ISAAC NEWTON. 437 



And thus both Gilbert and Newton agree that earth and 

 moon attract one another, and in proportion to the quan- 

 tity of matter in each. So much for similarities which 

 are certainly striking enough. 



But Gilbert regarded the earth as emitting a magnetic 

 virtue, and the moon (which he does not suppose to be a 

 magnet) also as emitting a virtue, but of a different nature. 

 Here Newton differs and moves ahead. The attractive 

 power in the members of the solar system, he declares, is 

 no different, but of the same nature in all, for it acts in 

 each in the same proportion to the distance and in the 

 same manner upon every particle of matter. 



Not even is this power new or unfamiliar. It is "one 

 no different from that existing on earth which we call 

 gravity." With what was then called gravity, Gilbert 

 was well acquainted, for he tells how the earth not only 

 attracts magnetic bodies but also "all others in which the 

 primary force is absent by reason of material." u And - 

 this inclination," he adds, "in terrene substances is com- 

 monly called 'gravity.' " It must not be forgotten, how- 

 ever, that Gilbert had never assumed that the gravity of 

 the earth could control aught but earthly things. It could 

 make a stone fall to the ground to "the source, the mother 

 where all (parts of the. earth) are united and safely kept." 

 The idea that mother earth could govern by her gravity ^x 

 attraction "th* inconstant moon" never entered his head. 



The magnetic attraction of that great magnet, the earth, 

 on the other hand, was to him a different attribute alto- 

 gether; and it was not at all difficult to imagine the colos- 

 sal enclosing sphere of magnetic virtue as sufficiently 

 enormous to "pervade the regions of the moon." 



But that was imagination, which rigorous proof pushed 

 aside as a great steamer displaces fog. Then it was grav- 

 ity which became colossal, and, under the mighty concep- 

 tion of Newton, grew into an attraction as broad as the 

 universe itself existing between all masses, all sorts of 

 matter, always, everywhere; between worlds as well as be- 



