Abstract
LONDON.
Geological Society, December i.-Dr. A. Smith Woodward, president, in the chair.-Dr. J. W. Evans: Petrological methods. The different methods of obtaining the directions-image ("interference figures") of a small mineral in a rock-slice, unaffected by the light from neighbouring minerals, were discussed. The author prefers the use of a diaphragm in the focus of the eyepiece, in conjunction with a Becke lens; he also described the inferences that might be drawn from the form, position, and movement on the rotation of the stage of the isogyres (dark bars or bushes) in the directions-images, both of chance sections and of those cut parallel to planes of optical symmetry or at right-angles to optical axes. He showed how the character or sign of the crystal and its approximate optic axial angle might be determined.
Article PDF
Rights and permissions
About this article
Cite this article
Societies and Academies . Nature 96, 500–502 (1915). https://doi.org/10.1038/096500a0
Issue Date:
DOI: https://doi.org/10.1038/096500a0