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and incompletely developed halos


Fig. 35.—Thorium and Radium Halos in Biotite. ( x 150 diameters.)
(cropped from page; border reconstructed)
ex Frederick Soddy. The Interpretation of Radium; and the Structure of the Atom. Fourth edition, revised and enlarged. 1920
University of California copy, digitized September 27, 2007

epigram from p 166, from which —

Now, occurring in various natural micas, there are sometimes found microscopic halos of darkening of perfect circular outline, called pleochroic halos. These have been exhaustively studied by Professor Joly, and the microphotographs shown in Figs. 35 and 36 are taken from a paper by him and Mr. Fletcher in the Philosophical Magazine for 1910...

24 March 2014

pleochroic halos; rounds
F. Soddy, The Interpretation of radium (1920)