PETROLOGICAL ABSTRACTS AND REVIEWS 475 
WRIGHT, FRED. EUGENE. ‘‘The Measurement of the Refractive 
Index of a Drop of Liquid,” Jour. Wash. Acad. Sct., IV 
(1914), 269-79, figs. 14. 
Describes various methods for measuring the refractive index of 
liquids, five of them new methods for the petrographic microscope. 
WRIGHT, FRED. EUGENE. “The Determination of the Relative 
Refringence of Mineral Grains under the Petrographic Micro- 
scope,” Jour. Wash. Acad. Sci., IV (1914), 389-92. 
Describes a new diaphragm for observing relative refractive indices. 
WRIGHT, FRED. EUGENE. ‘“‘The Optical Character of the Faint 
Interference Figure Observed in High Power Objectives be- 
tween Crossed Nicols,”’ Jour. Wash. Acad. Sci., IV (1914), 
301-09. 
Explains the positive character of the interference figure produced 
by the rotation of the vibration plane of the transmitted light. 
Wricut, FreD. Eucene. “A New Half-Shade Apparatus with 
‘Variable Sensibility,’ Wash. Acad. Sci., IV (1914), 309-13. 
Describes a device for varying the sensibility of a half-shade appa- 
ratus. 
WRIGHT, FRED. EuGENE. “A Simple Method for the Accurate 
Measurement of Relative Strain in Glass,” Jour. Wash. Acad. 
Sci., IV (1914), 594-08. 
Describes a wedge with which it is possible to measure path- 
differences of less than typ. 
WRIGHT, FRED. EUGENE. ‘Measurements of Refractive Indices 
on the Principal Optical Sections of Birefracting Minerals in 
Convergent Polarized Light,” Jour. Wash. Acad. Sci., IV 
(1914), 534-42. 
Two refractive indices are measured by the immersion method, the 
third by measurements made on the rings in the interference figure. 
