POPULAR SCIENCE 637 



an interesting fact in view of the stereochemical principle first 

 enunciated by Le Bel and by van t' Hoff regarding the dis- 

 position of the four valencies of the carbon atom in the forma- 

 tion of carbon compounds. Further, on viewing the structure 

 of the diamond from a certain angle, it is found that an arrange- 

 ment quite analogous to the six-membered ring of the benzene 

 molecule manifests itself, the carbon atoms forming a hexa- 

 gonal figure. 



Before leaving this subject, it may be mentioned that a 

 number of very ingenious applications of Braggs' work have 

 been made by Langmuir (14), in connection with heterogeneous 

 catalysis and absorption of gases upon solid surfaces. 



From the very cursory review of the subject which has 

 been given above, it will be clear that the last decade has 

 advanced our knowledge of the structure of matter in a very 

 decided manner. Many problems, of course, still call for 

 elucidation. We have not yet arrived, for example, at a really 

 satisfactory expression for the temperature — pressure — volume 

 relations of gases and liquids. The same may be said of the 

 problem of the structure of the molecular layer which separates 

 two phases in contact. We are still largely in the dark as 

 regards the connection between capillary effects and the in- 

 fluence of the electric charge upon surfaces, a problem which 

 has a very direct bearing upon the stability of colloids, and 

 through this subject upon many problems in physiology and 

 bio-chemistry. In atomistics itself there is room for almost 

 unlimited research into the problem of what constitutes the 

 chemical reactivity of different atomic structures, the influence 

 of temperature and external conditions upon electronic move- 

 ment and equilibrium states, and finally the still unsolved 

 problem of the constitution of the atomic nucleus. 



Bibliography 



1. J. Perrin, " Brownian Movement and Molecular Reality," translated by F. 



Soddy, 1910. 



2. Millikan, Trans. Amer. Electrochem. Soc. 1912, 21, 185. 



3. GOUY, Journ. de Physique, 1888, [2], 7, 561. 



4. Sutherland, Phil. Mag. 1910, 19, 25. 



5. Dieterici, Annalen der Physik, 1901, [4] 5, 51. 



6. Lewis, Zeitschr. physikal. Chem. 191 1, 78, 24. 



7. Tinker, Phil. Mag. 1917, 33, 449. 



8. J. J. Thomson, " Electricity and Matter," " The Corpuscular Theory of 



Matter." 



