168 CARNEGIE INSTITUTION OF WASHINGTON. 



(405) An outline of the application of the theory of space groups to the study of the struc- 



ture of crystals. Ralph W. G. Wyckoff. Am. J. Sci., 1, 127-137 (1921). 

 The crystal structure of magnesium oxide. Ibid., pp. 138-152. 



In the first paper are briefly considered such details of the theory of space 

 groups as are of importance in the apphcation of this theory to the determina- 

 tion of the structure of crystals. Point groups, space lattices, and space groups 

 are illustrated by simple examples. A discussion is given of the relations 

 between space groups and crystals and of those modifications in the results 

 of the theory of space groups which are required in order that it may serve as 

 the basis for a general method for the study of the structure of crystals. 



In the second paper the method of studying the structure of crystals which 

 arises from the point of view outhned above is applied to a relatively simple 

 case in the discussion of the structure of magnesium oxide. 



An attempt has been made, using Laue photographs and X-ray spectrum 

 measurements, to get a unique solution for the crystal structure of magnesium 

 oxide. If it possesses holohedral symmetry, then the only simple structure 

 which is possible is the "sodium-chloride arrangement." 



Certain cases of grouping showing tetartohedral symmetry, and two more 

 complicated holohedral arrangements, each with 32 molecules associated 

 with the unit, are in agreement with the existing experiments. These other 

 possibilities, however, differ but slightly from the "sodium-chloride arrange- 

 ment," and can not be positively treated by the experimental faciUties now 

 available. 



(406) The determination of the structure of crystals. Ralph W. G. Wyckoff. J. Franklin 



Inst., 191, 199-230 (1921). (Reprinted, Smithsonian Misc. Coll., 1921.) 



This discussion aims to give a brief survey of the field of the determination 

 of the structure of crystals as it exists at the present time. The most essen- 

 tial events in the development of this work are mentioned, the existing means 

 of experimentation are outlined, and some of its present limitations are dis- 

 cussed, together with some of the kinds of problems to which a knowledge of 

 the arrangement of the atoms in crystals has contributed and may be expected 

 to contribute. 



(407) The compressibility of diamond. Leason H. Adams. J. Wash. Acad. Sci., 11, 



45-50 (1921). 



By the use of pressures up to 10,000 megabars, the compressibility of clear 

 colorless diamond was measured and found to be 0.16 X 10~® per megabar. 

 This is a remarkably low value; indeed, of all substances whose elastic behavior 

 is known, diamond is by far the most incompressible. Its nearest rival, 

 tungsten, is nearly twice as compressible. 



From a consideration of certain formulae connecting various physical prop- 

 erties of solids it is shown that the low compressibility of diamond might be 

 predicted from its high melting-point, its low expansion coefficient, and its 

 high atomic frequency. 



(408) The distribution of scientific information in the United States. Robert B. Sosman. 



J. Wash. Acad. Sci., 11, 69-99 (1921). 



The production of new information in the United States is much better 

 organized than its distribution. It is distributed through five main channels : 



(1) by personal communication or through the "informational middleman;" 



(2) by public lectures; (3) by the museum and public exhibition; (4) by the 

 printed page — books, scientific and technical periodicals, bulletins, general 

 periodicals, newspapers, and separates; (5) by the cinematograph. Ineffec- 

 tive distribution results from disinchnation to use new knowledge, a cause not 

 discussed in this paper, and from the inaccessibility of scientific information 



