GROWTH OF MINERALOGY 279 



in which all the various aspects of mineral investigation 

 received more nearly equal prominence. While the 

 chemical composition of minerals still held rightly its 

 prominent place, the investigation of the crystallographic 

 and optical characters and the relationships existing 

 between all three were of much more frequent occurrence. 

 Edward S. Dana commenced his scientific work by pub- 

 lishing in 1872 an article on the crystals of datolite which 

 was probably the first American article concerned wholly 

 with the description of the crystallography of a mineral. 

 Samuel L. Penfield began his important investigations in 

 1877 and the first articles by Frank W. Clarke appeared 

 during this period. The first edition of the Text Book 

 of Mineralogy by Edward S. Dana with its important 

 chapters on Crystallography and Optical Mineralogy 

 was published in 1877 and his revision of the System of 

 Mineralogy (sixth edition) appeared in 1892. 



Unquestionably the foremost figure in American min- 

 eralogy during this period was that of Samuel L. Pen- 

 field. He embodied in an unusual degree the characters 

 making for success in this science, for few investigators 

 in mineralogy have shown, as he did, equal facility in all 

 branches of descriptive mineralogy. He was a skilled 

 chemist and possessed in a high degree that ingenuity in 

 manipulation so necessary to a great analyst. He was 

 also an accurate and resourceful crystallographer and 

 optical mineralogist. His contributions to the science of 

 mineralogy can be partially judged by the following 

 brief summary of his work. He published over eighty 

 mineralogical papers, practically all of which were 

 printed in the Journal. These included the descriptions 

 of fourteen new mineral species, the establishment of the 

 chemical composition of more than twenty others, and 

 the crystallization of about a dozen more. By a series 

 of brilliant investigations he established the isomorphism 

 between fluorine and the hydroxyl radical. He first 

 enunciated the theory that the crystalline form of a min- 

 eral was due to the mass effect of the acid present rather 

 than that of the bases. He contributed also a number of 

 articles on the stereographic projection and its use in 

 crystallographic investigations, devising a series of pro- 

 tractors and scales to make possible the rapid and accu- 



