Petrological Abstracts and Reviews 



Edited by ALBERT JOHANNSEN 



Arschinow, Wladimir. "Ueber die Verwendung einer Glashalb- 



kugel zu quantitativen optischen Untersuchungen am Polari- 



sationsmikroskope," Zeitschr. Kryst., XL VIII (1910), 225-29. 



Fig. 1. 



A simple apparatus for making quantitative measurements by 



tilting a thin section under the microscope. The author claims to be 



able to make measurements with as great a degree of accuracy as may 



be made with Fedorow's or Klein's Universaltisch. 



The instrument consists of a glass hemisphere, 50-60 mm. in diameter, 

 which is centered upon the stage of the microscope and rotated by hand. 

 The section is fastened to the flat side of the hemisphere with cedar oil 

 or glycerin, and with the cover-glass down. The determination of 

 planes of extinction and so on are made as with the Fedorow Univer- 

 saltisch, and the angle of rotation is measured by means of two grad- 

 uated metal strips, attached 90 apart, to a movable ring around the 

 equator of the glass hemisphere, and themselves capable of being moved 

 on pivots. By raising the tube of the microscope above these rings, the 

 angles at which they cross may be read, and this determines the amount 

 of rotation of the glass hemisphere. For certain measurements a small 

 glass hemisphere, 8-15 mm. in diameter, is attached to the upper sur- 

 face of the slide. 



Albert Johannsen 



Bastin, Edson S. "Geology of the Pegmatites and Associated 

 Rocks of Maine," Bull. U.S. Geol. Survey No. 445, Washington, 

 1911. Pp. 152, pi. 18, figs. 8, map 1. 

 In this bulletin on the pegmatites of Maine, Doctor Bastin has 

 given not only local descriptions but has made an important contribu- 

 tion to the general literature of the pegmatites as well. The work is 

 divided, practically, into three parts: a general discussion of pegmatites 



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