UNITED STATES DEPARTMENT OF COMMERCE, Charles Sawyer, Secretary U.S. NATIONAL BUREAU OF STANDARDS, E. U. Condon, Director

The publication of International Critical Tables in 1926 provided the world with a comprehensive and critical selection of the then existing scientific data. Scientists of many nations cooperated in its compilation. Since then, the immense growth and refinement of scientific data have made much of it obsolete and incomplete, but its revision would be an enterprise even more tremendous than the original collection. A cooperative effort has therefore been established among the National Research Council, the International Union of Pure and Applied Chemistry, the International Union of Pure and Applied Physics, the National Bureau of Standards, and other interested institutions to compile separate critical tables of data in selected fields. The selection is governed by the apparent need in particular fields and the availability of experts thoroughly familiar with the subjects to undertake the work.

The tables presented in this volume represent one of these cooperative efforts sponsored by the National Bureau of Standards, the Committee on Tables of Constants of the National Research Council, and Princeton University.

E. U. CONDON, Director.