CHAPTER VIII 



MATTER, SPACE, AND TIME 



Oh, dear ! what can the matter be ? 



— Old Song. 



Our primary conception of matter as continuous 

 In time and space fails to correspond with phe- 

 nomena which are perceived as soon as inquiry 

 passes beyond the most elementary stages. The 

 expansion of a quantity of gas without assignable 

 limit can hardly be represented mentally if the 

 gas is thought of as a homogeneous substance 

 filling completely the space in which It exists. 

 We cannot imagine that the same amount of 

 substance fills equally at different times volumes 

 different from each other. The immediate 

 difficulty disappears if we suppose the gas to 

 consist of a number of discrete particles, which 

 can be pressed nearer together or allowed to move 

 farther apart. 



The phenomena of diffusion, too, clearly 

 indicate that liquids and gases must consist of 

 particles in motion relatively to each other, 

 capable of penetrating the interspaces between 

 the similar particles of contiguous bodies. A 

 vessel filled with hydrogen and a vessel filled 

 with oxygen, when opened into each other, soon 

 contain an equal mixture of the two gases, while 

 two solutions in contact gradually become of 

 uniform concentration throughout. Nor are such 



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