PHILADELPHIA Charles R. Alcock, an astrophysicist at the University of Pennsylvania, has been elected to membership in the National Academy of Sciences. Alcock is one of 72 researchers nationwide inducted into the Acad-emy this year.

Election to the Academy is considered one of the highest honors accorded American scientists and engineers. Alcock induction brings to 35 the number of Penn researchers in the 1,874-member body.

Alcock joined the Penn faculty in 2000 as the Reese W. Flower Professor of Astronomy and Astrophysics. Previously, he directed the Institute of Geo-physics and Planetary Physics at the Lawrence Livermore National Laboratory in California.

Alcock serves as lead researcher on the MACHO Project, an international dark matter experiment. Astronomers have suspected for several decades that the universe contains far more mass than is visible; this "missing mass" is referred to as dark matter because it is imperceptible using current techniques.

Together with his peers, Alcock has found evidence of approximately 20 compact but weighty objects, nicknamed MACHOs, or Massive Compact Halo Objects. The discovery of these invisible MACHOs in just one small slice of the universe has led Alcock and others to believe that they may account for a significant percentage of our galaxy mass.

Alcock was educated at the University of Auckland, in his native New Zealand, and the California Institute of Technology, which granted him a Ph.D. in 1978.

The National Academy of Sciences is a private organization of scientists and engineers dedicated to the furtherance of science and its use for the general welfare. Established in 1863 by a congressional act signed by Abraham Lincoln, the Academy acts as an official adviser to the federal government, upon request, in any matter of science or technology.