NOTICE: The project that is the subject of this report was approvedby the Governing Board of the National Research Council, whose membersare drawn from the councils of the National Academy of Sciences,the National Academy of Engineering, and the Institute of Medicine.The members of the panel responsible for the report were chosen fortheir special competences and with regard for appropriate balance.

This report has been reviewed by a group other than the authors accordingto procedures approved by a Report Review Committee consisting ofmembers of the National Academy of Sciences, the National Academyof Engineering, and the Institute of Medicine.

The National Academy of Sciences is a private, nonprofit, self-perpetuatingsociety of distinguished scholars engaged in scientific and engineeringresearch, dedicated to the furtherance of science and technologyand to their use for the general welfare. Upon the authority of thecharter granted to it by Congress in 1863, the Academy has a mandatethat requires it to advise the federal government on scientific andtechnical matters. Dr. Bruce Alberts is president of the NationalAcademy of Sciences.

The National Academy of Engineering was established in 1964, underthe charter of the National Academy of Sciences, as a parallel organizationof outstanding engineers. It is autonomous in its administrationand in the selection of its members, sharing with the National Academyof Sciences the responsibility for advising the federal government.The National Academy of Engineering also sponsors engineering programsaimed at meeting national needs, encourages education and research,and recognizes the superior achievements of engineers. Dr. HaroldLiebowitz is president of the National Academy of Engineering.

The Institute of Medicine was established in 1970 by the NationalAcademy of Sciences to secure the services of eminent members ofappropriate professions in the examination of policy matters pertainingto the health of the public. The Institute acts under the responsibilitygiven to the National Academy of Sciences by its congressional charterto be an advisor to the federal government and, upon its own initiative,to identify issues of medical care, research, and education. Dr.Kenneth I. Shine is president of the Institute of Medicine.

The National Research Council was established by the National Academyof Sciences in 1916 to associate the broad community of science andtechnology with the Academy's purposes of furthering knowledge andadvising the federal government. Functioning in accordance with generalpolicies determined by the Academy, the Council has become the principaloperating agency of both the National Academy of Sciences and theNational Academy of Engineering in providing services to the government,the public, and the scientific and engineering communities. The Councilis administered jointly by both Academies and the Institute of Medicine.Dr. Bruce Alberts and Dr. Harold Liebowitz are chairman and vicechairman, respectively, of the National Research Council.

This project was supported by the National Aeronautics and SpaceAdministration (NASA) under Grant No. NAGW-3304.

Front Cover: The anisotropy of the temperature of the cosmic microwave backgroundradiation, as mapped by the Differential Microwave Radiometer onNASA's Cosmic Background Explorer satellite. Red shades representhotter fluctuations, and blue and black shades represent cooler fluctuations.(Courtesy of the COBE team and NASA.)

Back Cover: Looking back in time with NASA's Hubble Space Telescope (HST). The HST's Wide-Field Planetary Camera (WFPC2) captured this image of galaxiesas they were billions of years ago. Many objects are irregular andill-formed compared to nearby galaxies, showing the evolution offorms of galaxies between the distant past and times closer to thepresent. The size of the image is 75 arc seconds, and the total exposuretime is 15 hours. (Courtesy of Edward Groth, Jerome Kristian, andmembers of the WFPC2 team.)

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