EXCURSIONS OF AN EVOLUTIONIST 



lecture on " Atoms," and in various passages 

 where he has occasion to allude to the intimate 

 constitution of matter, to solidity, liquidity, 

 quantivalence, and so on. People generally, 

 when they talk about atoms, think only of very 

 little particles, without having in mind anything 

 about their various shapes and modes of be- 

 haviour. Even scientific men, who get on well 

 enough by the aid of established formulas, now 

 and then betray a similar barrenness of concep- 

 tion when some novel point comes up for dis- 

 cussion. But Clifford would describe a cluster 

 of atoms with as much minuteness and as much 

 animation as a fashionable lady would display 

 in describing the gorgeous costumes of last 

 night's ball. Take the air of this room, for ex- 

 ample, which does not fill up all the space in the 

 room, but is composed of a prodigious number 

 of discrete particles of two sorts, one sort 

 called molecules of oxygen, the other sort called 

 molecules of nitrogen. " These small mole- 

 cules," says Clifford, " are not at rest in the 

 room, but are flying about in all directions with 

 a mean velocity of seventeen miles a minute. 

 They do not fly far in one direction ; but any 

 particular molecule, after going over an incredi- 

 bly short distance the measure of which has 

 been made meets another, not exactly plump, 

 but a little on one side ; so that they behave to 

 one another somewhat in the same way as two 

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