66 DIVISIBILITY OF MATTER ATOMIC THEORY. 



tions of other matter, sometimes not exceeding a 

 millionth part of their weight ? l 



Nor are questions of this kind limited to what we 

 may regard as simple atoms. They apply alike to 

 those endless atomic compounds, of the same or differ- 

 ent kinds of matter which make up the natural world 

 around us. These compound atoms, now distinctively 

 termed molecules, we may assume to be larger and of 

 less simple figure than the atoms composing them, 

 though this conclusion is one rather of inference than 

 of experimental knowledge. Appreciation by mea- 

 surement, or other direct means, of these infinitesimal 

 parts is as impossible as to conceive them by effort of 

 thought. There are, indeed, some recent experiments 

 (made by subjecting simple and compound gases re- 

 spectively to equal increments of heat and pressure) 

 which tend to show that all gases, under similar con- 

 ditions, contain equal numbers, and therefore equal 

 sizes, of constituent atoms or molecules. But this is 

 one of the many questions alluded to as awaiting 

 solution. 



The glory of chemistry as a science depends espe- 

 cially upon its researches into molecular properties and 

 combinations. The endless number and variety of 

 chemical compounds, their tendency to types and de- 

 terminate series, and the mastery now obtained over 

 them by synthesis as well as analysis, show how vast 



1 Sir W. Thomson (1870) assigns four physical proofs of limits to 

 the smallness of atoms and molecules one derived from the contact and 

 electricity of metals, the others from the doctrine of capillary attraction 

 and the kinetic theory of gases, giving the certainty that there is a limit 

 to the molecular size, however exceeding all conception in minuteness. 



