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A mass-spectrographic study of the isotopic constitution of Sr, Ba, Bi, and Tl has been made. Although the sensitivity and resolving power of the apparatus were sufficient to detect extremely rare isotopes, no new ones were found. Relative abundances of the isotopes of Sr, Ba, and Tl were determined. It was possible to show that if Hg^203 exists it must be with an abundance less than one-tenth of that at one time assigned to it by Aston.
A. O. Nier (Mon,) studied this question.