ETHER AND PONDERABLE MATTER 



hitherto formulated. It is only a theory, to be sure; 

 its author would be the last person to claim finality for 

 it. "It is only a dream," Lord Kelvin said to me, in 

 referring to it not long ago. But it has a basis in 

 mathematical calculation and in analogical experiment 

 such as no other theory of matter can lay claim to, and 

 it has a unifying or monistic tendency that makes it, 

 for the philosophical mind, little less than fascinating. 

 True or false, it is the definitive theory of matter of the 

 twentieth century. 



Quite aside from the question of the exact constitu- 

 tion of the ultimate particles of matter, questions as to 

 the distribution of such particles, their mutual rela- 

 tions, properties, and actions, came in for a full share 

 of attention during the nineteenth century, though the 

 foundations for the modern speculations were furnished 

 in a previous epoch. The most popular eighteenth- 

 century speculation as to the ultimate constitution of 

 matter was that of the learned Italian priest, Roger 

 Joseph Boscovich, published in 1758, in his Theoria 

 Philosophic? Naturalis. " In this theory," according 

 to an early commentator, "the whole mass of which 

 the bodies of the universe are composed is supposed to 

 consist of an exceedingly great yet finite number of 

 simple, indivisible, inextended atoms. These atoms 

 are endued by the Creator with repulsive and attractive 

 forces, which vary according to the distance. At 

 small distances the particles of matter repel each other; 

 and this repulsive force increases beyond all limit 

 the distances are diminished, and will consequently 

 forever prevent actual contact. When the particles 

 of matter are removed to sensible distances, the re- 



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