XXVI 



whom he went for instruction in "special mathematics " was the crys- 

 tallographer Levy : by him the young Des Cloizeaux was initiated 

 into the mysteries of that science, and was advised to enter upon the 

 mineralogical course then being given by Dufrenoy, at the ficole des 

 Mines. At that institution he later made the acquaintance of 

 Senarmont, through whose influence it was that he afterwards came 

 to devote himself so closely to the optical investigation of crystals. 

 His first paper dealt with the crystallisation of JEschynite, and 

 appeared in 1842 ; for the next half-century scarcely a year passed 

 without the issue of one or more papers recording the results of some 

 mineralogical research. In 1843 he was appointed Repetiteur at the 

 Ecole Centrale, and in 1857 Maitre des Conferences at the ficole 

 Normale ; from 1873 to 1876 he took the place of Delafosse at the 

 Sorbonne, and, on the retirement of that professor from his office at 

 the Paris Natural History Museum, Des Cloizeaux was appointed 

 (1876) to the Curatorship of that important mineral collection. 

 This office was particularly congenial to his tastes, for he was always 

 more happy in the laboratory than in the lecture-room ; he retained 

 it till 1892, when the rules of the Civil Service necessitated his 

 retirement at the age of seventy- five. 



Though his life-work related almost wholly to the morphologj- 

 and optics of crystals, his inquiries were not limited to the examina- 

 tion of museum specimens ; he was much interested in modes of 

 origin and of occurrence, and in the geological relations of minerals ; 

 and he was always ready to seek an opportunity for seeing in its 

 native home any mineral to the determination of the characters of 

 which he had been devoting his attention. He went on two missions 

 to Iceland (1845-6) to investigate the mode of occurrence of the 

 well-known spar, about the scarcity of which physicists had already 

 become anxious, and he brought back from that island many 

 specimens of its minerals and rocks useful to him in his later 

 researches ; in 1868 he was sent on another special mission, on this 

 occasion to Norway, Sweden, and Russia ; and in the course of a long 

 life he found it practicable to visit all the more important mineral 

 localities of the Continent. 



Two characteristics specially manifest in the work of Professor 

 Des Cloizeaux are accuracy and perseverance : he would spare no 

 pains to obtain the best values for the crystallographic constants of 

 the material he was investigating, while, a problem once started 

 upon, he would persist in its investigation for years, and return to it 

 again and again as new specimens or new methods became available. 

 For the first twelve or thirteen years his work was almost wholly 

 morphological, and consisted in the determination of the crystallo- 

 graphic constants of rare or new specimens and in the description of 

 the minerals associated together at new localities. To this epoch 

 belongs his memoir on the crystallisation of quartz ; to the thirty- 



