282 A CENTURY OF SCIENCE 



apparently was left that could be added to our knowledge 

 of them. New occurrences would still be recorded, new 

 crystal habits would be observed, and an occasional new 

 and small crystal face might be listed, but few facts of 

 great importance seemed undiscovered. This view was 

 not wholly justified because new facts of interest and 

 importance have continuously been brought forward, and 

 the finding of new minerals does not appear to diminish 

 in amount with the years. The work of the investigators 

 on the United States Geological Survey along these lines 

 is especially noteworthy. 



This last of our periods, however, is chiefly signalized 

 by a practically new development along the lines that 

 might be characterized as experimental mineralogy. 

 New ways have been discovered in which to study min- 

 erals. The important but hitherto baffling problems of 

 their genesis, together with their relations to their 

 surroundings, and to associated minerals, have been 

 attacked by novel methods. 



In this pioneer work that of the Geophysical Labora- 

 tory of the Carnegie Institution of Washington has been 

 of the greatest importance. This laboratory was estab- 

 lished in 1905 and, under the directorship of Arthur L. 

 Day, a notable corps of investigators has been assembled 

 and remarkable work already accomplished. While the 

 field of investigation of the laboratory is broader than 

 that of mineralogy, including much that belongs to 

 petrography, vulcanology, etc., still the greater part of 

 the work done can be properly classed as mineralogical in 

 character and should be considered here. Because of its 

 great value, however, it was felt that an authoritative, 

 although necessarily, under existing conditions, a brief, 

 account of it should be given. A concise summary of the 

 objects, methods and results of the investigations of the 

 laboratory has been kindly prepared by a member of its 

 staff, Dr. R. B. Sosman, and is given later. 



During the last few years another line of investigation 

 has been opened by the discovery of the effect of crystal- 

 line structure upon X-rays. Through the refraction or, 

 reflection of the X-ray by means of the ordered arrange- 

 ment of the particles forming the crystalline network, we 

 are apparently going to be able to discover much con- 



