THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL 



VOL. XVI. JUNE, 1895. No. 6. 



An Improved Method for the Microscopic Investigation 

 of Crystals. 



By a. E. TUTTON, 

 [Adapted From Nature April 25, 1895.] 

 A memoir of considerable importance to all who 

 are interested in the microscopic determination of the 

 cliaracters of crystals, is contributed by Prof. Klein to 

 the Sitzungshericlite of the Berlin Acadenne ^ der Wisse7i- 

 schaften for January 31, 1895. The two essential points 

 of the communication are that a form of stage goniome- 

 ter is described, which permits of the most comj)lete ex- 

 amination of many of tlie principal zones of the crystal 

 with one and the same setting of the crystal upon its 

 holder, and that the crystal is immersed during the ob- 

 servations in a liquid whose refractive index is about the 

 mean of the refractive indices of the crystal. The idea 

 of the " Universaldrehapparat," as the new stage gonio- 

 meter is termed, appears to have suggested itself almost 

 simultaneously to Prof. Klein and to Herr von Federow, 

 for the former described an earlier form of it in 1891, 

 while the latter described an " Universaltischen " in May 

 of the same year in the Zeitschrift fur Krystallogrtiphie. 

 Federow had previously contributed to the Zeitschrift a 

 remarkable memoir concerning a theololitic universal 

 goniometer, and the application of the principle of that 

 instrument to the microscope goniometer followed nat- 

 urally therefrom. The present memoir of Prof. Klein 



