138 Wychoff — Crystal Structure of Magnesium Oxide, 



Art. IX. — The Crystal Structure of Magnesium Oxide; 

 by Ralph W. G. Wyckoff. 



Previous measurements on powdered magnesium 

 oxide^ have led to the conclusion that this compound has 

 the same crystal structure as sodium chloride. Such a 



Fig. 1. The Lane photograph obtained by passing the X-rays in a direc- 

 tion roughly normal to the (lOU) face of magnesium oxide. 



study did not, however, furnish a unique solution. The 

 following determination is based upon the general method 

 for studying the structures of crystals which has been 

 developed from the theory of space groups and which 

 is given in a very general form in the preceding article. - 



In the case of a cubic crystal there is no uncertainty 

 as to the choice of those coordinate axes which will give 

 the simplest unit of structure. The number of chemical 



^ W. p. Davey and E. O. Hoffman, Phys. Eev., (2), 15, 333, 1920. 

 ^ Kalph W. G. Wyckoff, see the preceding article in this number. 



