THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES. ] 



Art. XLII. — A Microselerometer, for determining the Hard- 

 ness of Minerals ;* by T. A. Jaggak, Jr., Cambridge, 

 Mass. (With Plate XII.) 



Introduction: the definition of "hardness." 



The hardness of minerals and metals has been investigated 

 by the following methods : 



Abrasion-tests. 



Scratching by hand: (Werner, Hatiy, Mohs, Breithaupt, 

 Cohenf, etc.) 



Drawing mineral under a point : 



(a) H. = weight on point — (Seebeck, Franz, Grailich and 



Pekarek,! Exner§). 



(b) H. = weight to draw mineral (inversely) — (Grailich and 



Pekarek). 



(c) H. = number of abrading movements — (Grailich and 



Pekarek). 



* This research has been carried on in the petrographical laboratory of Harvard 

 University, Cambridge, Mass. ; the author is much indebted to Professor J. E. 

 "Wolff, Dr. Charles Palache, Mr. L. W. Page and Professor Victor Goldschmidt, 

 of Heidelberg, for advice and assistance. For the admirable mechanical execu- 

 tion of the instrument, as well as for many valuable suggestions, I have to thank 

 Mr. Sven Nelson, of Cambridge, to whose skill as an instrument maker no words 

 of mine can do justice. f v. Rosenbusch, Mikros. Physiographic I, p. 258. 



\ Sitzungsber. d. k. k. Akad. "Wien, xiii. 1854 (contains complete bibliography 

 of earlier papers). § Preisschrift, Wien, 1873. 



Am. Jour. Sci. — Fourth Series, Yol. IV, No. 24.— Dec, 1897. 

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