Samuel Lewis Penfield. 359 



Penfield ? s work as a crystallographer is scarcely of less 

 importance than that which he performed on the chemical 

 side of mineralogy. He handled mathematical relations with 

 ease and clearness and his work was both rapid and accurate. 

 His perception of crystal forms and symmetry seemed almost 

 intuitive and in practical .operations he was greatly aided by 

 the same manual dexterity that he showed in chemical manip- 

 ulation ; thus he made measurements on the goniometer of 

 crystals of such a degree of minuteness, as in the case of 

 sperrylite, that it seemed almost impossible that they could be 

 handled. 



Besides establishing the crystallization of the new minerals 

 already mentioned, Penfield determined that of the following 

 species : Amarantite, Argyrodite, jBertrandite, Herderite, 

 Zansfordite, Metacinnabarite, Penfieldite, Polybasite, Sjper- 

 rylite, Tiemannite, Willemite. 



In addition to his contributions to the crystallography of 

 minerals we also owe to Penfield the determination of the other 

 physical properties of many species, especially the optical ; a 

 work which he first took up in Rosenbush's laboratory and after- 

 wards accurately and skillfully carried out whenever possible 

 upon all of the species which he investigated. 



His labors as a crystallographer were not, however, confined 

 to minerals. For a number of years he spent much time in the 

 determination of the crystallization and optical properties of 

 compounds prepared in the chemical laboratory of the Sheffield 

 Scientific School. As may be seen by reference to the appended 

 bibliography, this work was done either directly by himself 

 or under his care and supervision by the assistants and advanced 

 students in the laboratory whom he had trained. Among these 

 compounds studied there maybe mentioned as of special import- 

 ance the large series of new double salts, particularly the double 

 halides, prepared by his colleague Prof essor Wells or under his 

 direction. During the later years of his life Penfield gave much 

 time and thought to the perfecting -of practical methods for the 

 solution of problems in crystallography. He was led to a study 

 of the stereographic projection as a means of expression and in 

 1901 published an important paper on this subject, showing 

 how it could be used for solving problems, not only in crystallog- 



