Vol. 63.^ ANNIVERSARY ADDEESS OF THE PRESIDENT. llX 



engaged in teaching and research within the walls of his Alma 

 Mater, becoming Assistant Professor in 1 888, and full Professor in 

 1893. Having now thrown himself heart and soul into the 

 prosecution of mineralogical work, and finding the need of more 

 familiarity with the modern methods of optical and microscopical 

 research, he returned to Europe for some months in 1884, in order 

 to work in the Heidelberg Laboratory under Prof. Rosenbusch. 

 He thus admirably equipped himself for attacking mineralogical 

 questions from every side, and for training a school of students in 

 the most advanced modern methods of mineralogical research. His 

 kindly, sympathetic nature, combined with his great scientific 

 attainments, made him a remarkably successful teacher. 



The amount and the quality of his work are alike remarkable. He 

 not only made known the composition and relations of a number of 

 new and interesting minerals, but he was able to throw fresh light 

 on the true chemical constitution and mineralogical affinities of 

 other species which had long been known, and of some which were 

 of familiar occurrence. His analyses of the Branchville minerals 

 led to the recognition of the probable isomorphism of fluorine and 

 hydroxyl which he afterwards completely demonstrated, and thus 

 showed * that the existence of these isomorphous radicals not only 

 explains the structure of many minerals, but that their presence is 

 of the greatest importance in understanding the mode of formation, 

 especially in magmatic processes.' He was not only a chemical 

 analyst of the first order, but was hardly less distinguished as a 

 crystallographer. His ingenuity and skill as a manipulator enabled 

 him to devise and improve methods and instruments of mineral- 

 ogical research. It may be said that, in every department of 

 investigation into which he entered, he left the record of his keen 

 insight, his originality, and his breadth of view. 



Penfield's claims to a high place in the ranks of modern science 

 were recognized in his lifetime by the various honours conferred 

 upon him by scientific institutions in his own country and abroad. 

 He was elected a Corresponding Member of our Society in 1896. 

 His health had not been good for about three years, but the disease 

 from which he suffered took a sudden unfavourable turn, and 

 carried him off on the 12th of August, 1906. 1 



1 This is a brief summary of the memoir by Penfield's f riend and colleague, 

 Prof. L. V. Pirsson, of Yale, in the ' American Journal of Science ' for November 

 1906. 



