In the "Handbook of Physical Constants," Special Paper Number 36, published by The Geological Society of America in 1942, the editors sought to compile for the first time a wide variety of physical constants needed for geological and geophysical calculations. The choices of data were necessarily arbitrary; the compilations were contributed by the labors of volunteers with little bibliographical assistance. Nevertheless, the usefulness of the Handbook has been demonstrated, both by the exhaustion of several editions and by many citations in subsequent literature.
For at least ten years, the desirability of a revised edition has been recognized: many sections are now badly out of date, and new kinds of measurements have appeared. As the amount of material has increased, however, so has the labor of dealing with it. A preliminary selection of chapters and compilers was drawn up in 1955, and a few manuscripts eventually appeared. It was apparent, however, that a vigorous effort was needed to push the work to completion, and Prof. Sydney P. Clark, Jr., agreed to assume the editorship. The present volume is the result.
A primary consideration has been brevity, on the assumption that a volume of moderate size would be most generally useful. The introductory sections of the chapters have consequently been kept to the minimum length consistent with clarity and usefulness. A critical attitude toward measurements has been encouraged by the inclusion, in many cases, of measurements of ostensibly the same physical property by different observers. Without this confrontation, the real uncertainties of