THE DETERMINATION OF THE STRUCTURE OP 



CRYSTALS. 1 



By Ralph W. G. Wyckoff, Ph. D., 

 Geophysical Laboratory, Carnegie Institution of Washington. 



[With 7 plates.] 

 OUTLINE. 



introduction. 



An Outline of the Development of the Means Employed in Studying the 

 Structures of Crystals : 



The experiment of Laue. 



The " reflection " of X rays. 



Powder reflections. 



The structure of sodium chloride. 



The wave lengths of X rays. 



The general method of studying the structures of crystals. 



A Brief Discussion of the Methods of Obtaining Diffraction Effects Prom 

 Crystals : 

 The spectrometer method. 

 Spectrometer data. 

 The " laws " of reflection. 

 The method of powders. 

 The method of Laue photographs. 

 R6sum6. 



A Discussion of Some of the Structures Thus Far Studied and Some of the 

 Information Which They Seem to Yield Concerning the Nature of Crys- 

 talline Solids : 



Metals. 



Compounds of the type AB. 



Other simple compounds. 



Information to be derived from the structure of the atom. 



INTRODUCTION. 



The following discussion aims to give a brief survey of the field of 

 the determination of the structures of crystals as it exists at the 

 present time. The most essential events in the development of this 



1 Reprinted by permission from the Journal oi the Franklin Institute, February, 1921. 



199 



