PREFACE TO yxn REVISED EDITION. 



The present edition of the Smithsonian Physical Tables entails a considerable 

 enlargement. Besides the insertion of new data in the older tables, about 170 

 new tables have been added. The scope of the tables has been broadened to 

 include tables on astrophysics, meteorology, geochemistry, atomic and molecu- 

 lar data, colloids, photography, etc. In the earlier revisions the insertion of 

 new matter in a way to avoid renumbering the pages resulted in a somewhat 

 illogical sequence of tables. This we have tried to remedy in the present edition 

 by radically rearranging the tables; the sequence is now, — mathematical, me- 

 chanical, acoustical, thermal, optical, electrical, etc. 



Many suggestions and data have been received: from the Bureau of Stand- 

 ards, — including the revision of the magnetic, mechanical, and X-ray tables, 

 — from the Coast and Geodetic Survey (magnetic data), the Naval Observ- 

 atory, the Geophysical Laboratory, Department of Terrestrial Magnetism, etc. ; 

 from Messrs. Adams of the Mount Wilson Observatory, Adams of the Geo- 

 physical Laboratory (compressibility tables), Anderson (mechanical tables), 

 DeUinger, Hackh, Humphreys, Mees and Lovejoy of the Eastman Kodak Co. 

 (photographic data). Miller (acoustical data), Van Orstrand, Russell of Prince- 

 ton (astronomical tables), Saunders, Wherry and Lassen (crystal indices of 

 refraction). White, Worthing and Forsythe and others of the Nela Research 

 Laboratory, Zahm (aeronautical tables). To all these and others we are in- 

 debted for valuable criticisms and data. We will ever be grateful for further 

 criticisms, the notification of errors, and new data. 



Frederick E. Fowle. 



astrophysical observatory, 



Smithsonian Institution, 



May, 1919. 



NOTE TO REPRINT OF 7TH REVISED EDITION. 



Opportunity comes with this reprint to insert in the plates a number of correc- 

 tions as well as some newer data. Gratitude is especially due to Messrs. Wherry 

 and Smith of the Bureau of Chemistry, Department of Agriculture, for sugges- 

 tions. 



Frederick E. Fowle. 

 astrophysical observatory, 

 Smithsonian Institution, 



March, 1921. , 



NOTE TO SECOND REPRINT OF 7TH REVISED EDITION. 



Again opportunity is taken to alter the plates for a few corrections. Several 

 tables, especially those connected with molecular physics, have been considerably 

 changed to allow for the rapid advances of the last few years. The data for 



