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NOTICE: The project resulting in this report was approved by the Governing Board of the National Research Council, whose members come from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the board responsible for the project were chosen for their special competencies and with regard for appropriate balance.
This publication was supported by the National Aeronautics and Space Administration and the National Science Foundation. Support for preparing the industry studies cited in this report was provided by Department of Energy Office of Information Technologies, Alfred P. Sloan Foundation, Ralph Landau, and Lockheed Martin Corporation. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the organizations or agencies that provided support for the project.
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Cover: The emblem appearing on the cover of this publication is an illustration of the bronze medallion in the floor of the Great Hall in the National Academy of Sciences building in Washington, D.C. The medallion is the wellhead placed in the floor when the spectroscopic case over which the Foucault pendulum swings is lowered below floor level. The design is based on a map of the solar system published in 1661 by Andreas Cellarius Palatinus. The array of the planets is the Copernican system as known to Galileo.
Copyright 1999 by the National Academy of Sciences. All rights reserved.
Printed in the United States of America
First Printing, May 1999
Second Printing, September 1999