Scientific American Magazine

The increased number of college graduates in the U.S. has altered the composition of its work force. Professionals and managers now hold one out of four of the nation's jobs

They are asteroidlike bodies whose orbits cross the orbit of the earth. Some 30 of them are now known. They may be nuclei of comets that have lost their volatile components

Metastasis, and not the primary tumor, is usually the threat in cancer. Apparently only certain very malignant cells possess characteristics that enable them to travel through the body and establish new tumors

For almost a century light emitted by the simplest of atoms has been the chief experimental basis for theories of the structure of matter. Exploration of the hydrogen spectrum continues, now aided by lasers

What shade of gray a surface appears is related to the perceived distribution of light and shadow, which in turn depends on the perceived spatial relation between the surface and its neighbors

The nerve impulse is generated by the flow of sodium and potassium ions through molecular channels embedded in the nerve membrane. The operation of these ion channels is now being intensively studied

These descendants of land mammals that took to sea have a large brain, learn quickly and exhibit a rich vocal repertory. Yet lack of evidence leaves open the question of how intelligent they are

Surviving Greek and Roman texts reveal the remarkable level of mathematical and engineering skill that went into the development of these early ballistic-missile launchers