THE PROGRESS OF PHYSICS. 135 



possible, from the metaphysical obscurities which 

 lurk even in their apparent lucidity.* But all will 

 agree that ^Newton supplied the firm foundation on 

 which, especially during the last hundred years, phys- 

 ical science has gradually grown into a stately edifice. 



It is doubtless' true that Newton stood on the 

 shoulders of Galilei, but his genius in discerning the 

 unity amid multiplicity was none the less great, and 

 there is no finer instance of a unifying idea than the 

 gravitation-formula. At the same time, it must be 

 recognised that, like other big scientific generalisa- 

 tions, the gravitation-theory raised problems which it 

 did not answer. 



What we have is a general formula: that 

 every particle or atom or body in the universe at- 

 tracts every other with a force proportional to their 

 masses taken conjointly, and inversely proportional 

 to the square of their distances apart. This may be 

 called the law of gravitation, but is there no theory 

 of the law ? In this respect there has been little ad- 

 vance since the beginning of the nineteenth century. 



It was then that Lesage of Geneva suggested that 

 in addition to the gross particles of tangible or sensi- 

 ble matter, " infinite as these are in number, there 

 is an infinitely greater number of much smaller ones 

 darting about in all directions with enormously great 

 velocities. Lesage showed that, if this were the case, 

 the effects of their impacts upon the grosser particles 

 or atoms of matter would be to make each two of 

 these behave as if they attracted one another with a 

 force following exactly the law of gravity. In fact, 

 when two such particles are placed at a distance from 

 one another, each, as it were, screens the other from 



* Grammar of Science, Chapter VIIL, "The Laws of 

 Motion." 



