Ford— Growth of Mineralogy, 1818 to 1918. 251 



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- 

 rate use of this projection in solving problems in 

 crystallography. 



Penfield was born in 1856, was graduated from the 

 Sheffield Scientific School in 1877 and immediately 

 became an assistant in the chemical laboratory of that 

 institution. At this time he, together with his colleague 

 Horace L. Wells, made the analyses of the minerals from 

 the newly discovered Branchville locality. He spent the 

 years 1880 and 1881 in studying chemistry in Germany, 

 returning to Yale as an instructor in mineralogy in the 

 fall of 1881. Except for another semester in Europe at 

 Heidelberg he continued as instructor and professor of 

 mineralogy in the Sheffield Scientific School until his 

 early death in 1906. 



It is difficult to choose for mention the names of other 

 investigators in Mineralogy during this period. Toward 

 its end a great many writers contributed to the pages of 

 this Journal, more than fifty different names being 

 counted for the volumes 41 to 50 of the Third Series. 

 Many of these are still living and still active in scientific 

 research. Mention should be made of Frank W. Clarke, 

 who contributed many important articles concerning 

 the chemical constitution of the silicates. His work on 

 the mica and zeolite groups is especially noteworthy. 

 The work of W. H. Hillebrand, particularly in regard to 

 his analytical investigations of the minerals containing 

 the rarer elements, was of great importance. The name 

 of W. E. Hidden should be remembered, because, with 

 his keen and discriminating eye and active search for new 

 mineral localities, he was able to make many additions to 

 the science. 



In glancing over the indices to this Journal the close 

 interrelation of mineralogy to the other sciences is strik- 

 ingly shown by the fact that so many scientists whose 



