A quantitative study of pleochroic haloes. IV. New types of haloes

Abstract

The commonest type of pleochroic halo found in nature is that due to the uranium family. A second, rarer, type is recognized as being due to the thorium family. In addition, compound uranium-thorium haloes have been observed. In this paper four further types of haloes are described, three of them for the first time. In order to avoid any premature implication as to their origin they will be referred to simply as types A, B, C and D.* It is further shown that the ring radii of these four new types agree within the limits of experimental error with the ranges of certain α particles emitted by elements belonging to the later portion of the uranium family. It has seemed best to postpone a full discussion of the origin of these haloes until the next paper in this series, and to restrict this paper largely to a consideration of observations and measurements. For the sake of completeness, however, certain results of later discussion have been anticipated in the present paper, which should be read in conjunction with the next.