250 A CENTURY OF SCIENCE 



The geologists in carrying out their studies also observed 

 the rocks as they saw them in the field and made inci- 

 dental reference to them, but investigations of the rocks 

 themselves was very little attempted. An inspection of 

 the first two series of the Journal shows relatively little 

 of importance in petrology published in this country; 

 a few analyses of rocks, occasional mention of mineral 

 composition, of weathering properties, and notices of 

 methods of classification proposed by French and Ger- 

 man geologists nearly exhaust the list. 



Introduction of the Microscope. 



The beginnings of a particular branch of science are 

 generally obscure and rooted so imperceptibly in the 

 foundations on which it rests that it is difficult to point 

 to any particular place in its development and say that 

 this is the start. There are exceptions of course, like the 

 remarkable work of Willard Gibbs in physical chemistry, 

 and it may chance that the happy inspiration of a single 

 worker may give such direction to methods of investiga- 

 tion as to open the gates into a whole new realm of 

 research, and to thus create a separate scientific field, as 

 happened in Eadiochemistry. 



This is what occurred in petrology when Sorby in 

 England, in 1858, 3 pointed out the value of the micro- 

 scope as an instrument of research in geologic investiga- 

 tions, and demonstrated that its employment in the study 

 of thin sections of rocks would yield information of the 

 highest value. Others beside Sorby had made use of the 

 microscope, as pointed out by Zirkel, 4 but, as he indi- 

 cates, no one before him had recognized its value. Dur- 

 ing the next ten years or so, however, its recognition was 

 very slow and the papers published by Sorby himself 

 were mainly concerned in settling very special matters. 



As Williams 5 has suggested, the greatest service of 

 Sorby was, perhaps, his instructing Zirkel in his ideas 

 and methods, for the latter threw himself whole-heart- 

 edly into the study of rocks by the aid of the microscope 

 and his discoveries stimulated other workers in this field 

 in Germany, his native country, until the dawning science 

 of petrology began to assume form. A further step for- 



