Announcement Concerning Publications of the National Research Council The Proceedings of the National Academy of Sciences is partly supported by the National Research Council which is represented officially on its Editorial Board and Executive Committee. It is open for the publication of papers to members of the National Research Council on the same terms as to members of the National Academy of Sciences. Subscription rate for the "Proceedings" is $5 per year. Business address: Home Secretary, National Academy of Sciences, Smithsonian Institution, Washington, D. C. The Bulletin of the National Research Council presents contributions from the National Research Council, other than proceedings, for which hitherto no appropriate agencies of publication have existed. The "Bulletin" is published at irregular intervals. The subscription price, postpaid, is $5 per volume of approximately 500 pages. Numbers of the "Bulletin" are sold separately at prices based upon the cost of manufacture. The Reprint and Circular Series of the National Research Council renders available for purchase, at prices dependent upon the cost of manufacture, papers published or printed by or for the National Research Council. Orders for the "Bulletin " or the "Reprints and Circulars" of the National Research Council, accompanied by remittance, should be addressed: Publication Office, National Research Council, Washington, D. C. This monograph is part of the report of the National Research Council Com- mittee on X-Rays and Radioactivity. The Committee consists of the following |