For more than 100 years, the National Academies have provided independent advice on issues of science, technology, and medicine that underlie many questions of national importance. The National Academies - comprising the National Academy of Sciences, the National Academy of Engineering, the Institute of Medicine, and the National Research Council - work together to enlist the nation's top scientists, engineers, health professionals, and other experts to study specific issues. The results of their deliberations have inspired some of America's most significant and lasting efforts to improve the health, education, and welfare of the nation. To learn more about Academies' activities,check the Web site at www.nationalacademies.org.

The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee whose work this report summarizes were chosen for their special competences and with regard for appropriate balance.

This project was supported by the National Aeronautics and Space Administration under Grant No.NAG5-6916, the National Science Foundation under Grant No. AST-9800149, and the Keck Foundation.

Copies of this report are available from:
Board on Physics and Astronomy
National Research Council
HA 562,2101 Constitution Avenue, N.W.
Washington, DC 20418;
Internet www.nationalacademies.org/bpa.

Copyright 2001 by the National Academy of Sciences. All rights reserved.