INFORMATION TO CONTRIBUTORS 
Thk Prockbdings is the official organ of the Nationai, Academy of 
Sciences and of the NationaIv Research Council for the pubHcation of 
brief accounts of important current researches of members of the Academy 
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PubHcation in the Proceedings will supplement that in journals devoted 
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to secure prompt publication of original announcements of discoveries 
and wide circulation of the results of American research among investi- 
gators in other countries and in all branches of science. 
ArTIcIvES should be brief. The viewpoint should be comprehensive 
in giving the relation of the paper to previous publications of the author 
or of others and in exhibiting, where practicable, the significance of the 
work for other branches of science. Elaborate technical details of the 
work and long tables of data should be avoided, but authors should be 
precise in making clear the new results and should give some record of 
the methods and data upon which they are based. 
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References to literature, numbered consecutively, will be placed at the 
end of the article and short footnotes should be avoided. It is suggested 
that references to periodicals be furnished in some detail and in general 
in accordance with the standard adopted for the Subject Catalogue of the 
International Catalogue of Scientific Literature, viz., name of author, 
with initials following (ordinarily omitting title of paper), abbreviated name 
of Journal, with place of publication, series (if any), volume, year, inclusive 
pages. For example: Montgomery, T. H., Morph., Boston, 22, 1911 
(731-815); or, Wheeler, W. M., Konigshurg, Schr. physik. Ges., 55, 1914 
(1-142). 
Papers by members of the Academy may be sent to Edwin Bidwell 
Wilson, Managing Editor, Mass. Institute of Technology, Cambridge, 
Mass. Papers by non-members should be submitted through some 
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Proof will not ordinarily be sent; if an author asks for proof, it will be 
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correct obvious minor errors. 
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SCHEDULE OF RATES FOR REPRINTS, CARRIAGE CHARGES EXTRA. 
No. copies 
4 PP- 
8 pp. 
12 pp. 
16 pp. 
Covers 
50 
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$1.35 
100 
1.60 
3.20 
4.80 
6.40 
1.65 
150 
1.80 
3 -60 
5.40 
7.20 
1.95 
200 
2.00 
4.00 
6.00 
8.00 
2.25 
250 
2.20 
4.40 
6.60 
8.80 
2.52 
Copyright, 1920, by the National Academy Sciences 
