174 CARNEGIE INSTITUTION OF WASHINGTON. 



(44) The relation between birefringence and stress in various types of optical glass. L. H. 



Adams and E. D. Williamson. J. Wash. Acad. Sci., 9, 609-623 (1919). (Papers 

 on Optical Glass, No. 21.) 



In the examination of optical glass, the internal strains caused by poor 

 annealing are detected by means of the birefringence which accompanies 

 stress or strain. Since no adequate measurements of the quantitative 

 relation between stress aad birefringence were known, it was necessary to 

 determine this relation in order to know the precise magnitude of the stresses 

 commonly met with in unannealed glass. In this paper data are presented 

 for nine different kinds of American-made optical glass. 



(45) The nature of the forces between atoms in sohds. Ralph W. G. Wyckoff. J. Wash. 



Acad. Sci., 9, 565-592 (1919). 



The structure of the atom, as we now know it, is discussed with reference 

 to the nature of the forces operating between atoms, and it is emphasized 

 that the arrangement of only the outside electrons has a bearing on the 

 phenomena usually included under the term "chemistry," The arrange- 

 ment of the inner electrons can not be deduced from chemical data alone. 

 The outstanding fact is the tendency, still unexplained, to form "closed 

 clusters" of eight or twice-eight electrons. 



Several typical compounds are considered with reference to the nature of 

 the forces producing them. All compounds lie between the two extremes of 

 "polar" and "non-polar" compounds. A simplified method of representing 

 the type of combination in a given compound is suggested. 



Solid substances are classified, according to the nature of the forces of 

 combination, into molecule-forming, polar, and valency compounds. 



The phenomena of adsorption, solubility, ionization in solution, formation 

 of complex ions, and molecular complexes are discussed from this point of 

 view. 



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