SCIENCE.— AD VER TISEMENTS. 



RARE MINERALS. 



THAUMASITE, from Paterson, N. J., a sulphate, silicate and 

 carbonate of calcium, pure wliite, 25c. 



EKDEMITE, bright yellow on red wulfenite, Arizona, SOc. 



NATIVE ARSENIC, Japan, 14 to Ji-iuch crsytallized balls, 

 2SC, 3Sc. 



Collections for Schools. 



ALPHA COLLECTION, twenty-five specimens in trays, con- 

 tained in a neat wooden box and accompanied by a he- 

 page guide book (XIII., Guide ior Science Teaching- Bos- 

 ton Society of Natural History), Price, complete, $1.00. 



CABINET COLLECTIONS, 100 specimens, small size, $5.00. 

 100 specimens, large size, $10.00. These specimens are 

 each accompanied by a label giving name, system of 

 crystallization, chemical formula, and locality, and make 

 a good working collection for a student. 



EXCELSIOR COLLECTION for high schools and colleges. 

 200 specimens, nicely mounted on wooden blocks, with 

 beveled fronts for receiving labels. Price, packed, 

 $100.00. JSehool Bulletin just out. 



Loose Crystals. 



Small packages of free crystals for crystallographic study 

 may be sent for inspection by mail at small cost. Ap- 

 proval boxes of cabinet specimens by express or freight. 



ROY HOPPING, 



MINERAL DEALER, 



504-506 Liberty Building, 



Liberty and Greenwich Sts. 



NEW YORK. 



Horsford's Acid Phosphate 



Is the most effective and agreeable 

 remedy in existence for preventing in- 

 digestion, and relieving those diseases^ 

 arising from a disordered stomach. 



D. W. W. Gardner, Springfield, Mass., 

 says : "I value it as an excellent preventive of 

 indigestion, and a pleasant acidulated drink 

 when properly diluted with water and sweet- 

 ened." 



Descriptive pamphlet free on application to 

 Rumford Chemical Worlds, Providence, R. I. 



Beware of Substitutes and Imitations. 



For sale by all Druggists. 



A Great Scientist. 



Life and Letters of William Barton Rogers. 



Edited by liis Wife, with the assistance of WILLIAM T. SEDGWICK, Professor in 

 the Massachusetts Institute of Technology. 



WITH SEVERAL PORTRAITS AND OTHER ILLUSTRATIONS. 2 VOLS., CROWN 8V0, $4.00. 



Professor Rogers was one of the great scientific scholars of America, and held equal 

 rank with the European authorities in science of his time. His life covered a wide and 

 unusuallj' interesting range of experiences, from his bo3'hood in Philadelphia through his 

 life as student and professor at William and Mary College, his labors as head of the Greo- 

 logical Survey of Virginia, his engagement as Professor and Chairman of the Faculty in 

 the University of Virginia, and — as the culmination of his great career — his years of fruitful 

 service as the first President of the Massachusetts Institute of Technolog3^ 



This biography, by Mrs. Rogers, is a judicious and noble tribute to Professor Rogers. 

 It comprises a large number of letters by and to him, his correspondents including nearly 

 all the eminent scientific men of his time, also many distinguished and interesting persons 

 in literary and professional life. 



Sold by Booksellers. Sent, postpaid, by 



HOUGHTON, niFFLIN & CO., Boston, 1 1 East 17th St., New York 



