ATOMS AND MOLECULES 51 



Chemistry and physics, however, bring us to the opposite 

 end of the scale, and we are led to the assumption of bodies 

 that are so exceedingly small and so close together, that we 

 cannot conceive of their dimensions any more clearly than 

 we can conceive of our distance from the sun or from Neptune. 

 The problem of estimating these distances must, therefore, 

 appeal to us as similarly deprived of immediate usefulness. 



There is nevertheless this difference. We are all convinced 

 of the existence of the stars : we follow HerschePs descrip- 

 tion of their multitude with amazement, but we do not for 

 a moment doubt the reality of his statements. The atom 

 and the molecule are every now and then denied reality; that 

 great thinker, Ostwald, who visited us this winter, has emphat- 

 ically expressed the opinion that matter itself is non-existent 

 and that the atom and molecule are conceptions which must 

 sooner or later be abandoned. The permanence of the atom 

 is assailed by the supporters of the new electron theory and is, 

 in a measure, shaken by recent discoveries respecting radium 

 and helium. How about the molecule? It is too small to be 

 seen, too subtle to be handled and weighed as an individual. 

 But we can nevertheless weigh and measure it by different 

 means; and because results attained in various ways agree 

 fairly well with one another, strong evidence is afforded of the 

 reality of the molecule. It would be a very remarkable coinci- 

 dence if three or four different processes gave us an identical 

 measure for a certain thing and the thing itself did not exist. 

 If, in traveling, we noticed a considerable number of rail- 

 roads converging toward a common centre, we should expect 

 to find something interesting and definite at that point. 

 Similarly, I see evidence of the probable existence of the 

 molecule in the fact that many lines of calculation converge 

 upon the same order of magnitude. 



The ancient philosophers who first thought concerning the 



