POPULAR SCIENCE 



THE STRUCTURE OF MATTER 



By Prof. W. C. McC. LEWIS, D.Sc, 

 University, Liverpool 



Part I 



It is well known that matter is capable of existing in three 

 physical states, the solid, the liquid, and the gaseous, and that 

 transition from one state to another is possible under certain 

 conditions. These physical states correspond to different 

 degrees of spatial distribution of the exceedingly minute dis- 

 crete particles which we call molecules. It is not sufficient, 

 however, simply to know, as a result of observation, that such 

 modes of distribution can exist ; the aim of molecular physics 

 has long been to understand and explain the molecular 

 mechanism which underlies these modes of molecular distribu- 

 tion, and the conditions which determine transition from one 

 to the other. Of course, nothing like finality has been or can 

 be attained in such investigations. It is of interest, however, 

 to review in a very brief manner some of the more important 

 advances which have been made in recent years in this wide 

 and intensely interesting field. 



Evidence for the Real Existence of Molecules 



The concept of discrete particles or molecules, possessing 

 mass and velocity, and therefore kinetic energy, has been 

 employed for the greater part of a century as a satisfactory 

 working hypothesis, by means of which we are able to account 

 for the behaviour of gases, as expressed in the well-known gas 

 laws of Boyle and Gay-Lussac, and to a less degree the be- 

 haviour of liquids. It is only within very recent years, how- 

 ever, that satisfactory evidence for the real existence of mole- 

 cules has been brought forward. This very considerable step 

 we owe to the French physical chemist, Perrin(i) and after 



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