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Features

Particle-Beam Weapons

It is said that missiles could be shot down by accelerator. Even if such a weapon could be built, which is questionable, it would be ineffective because it would be vulnerable to countermeasures

By John Parmentola and Kosta Tsipis

A Timekeeping Enzyme in the Pineal Gland

The activity of the enzyme N-acetyltransferase in the pineal gland of some animals provides a natural timing mechanism: a biological clock that may regulate both physiological and behavioral processes

By Sue Binkley

The Evolution of Disk Galaxies

A spiral galaxy can evolve into a smooth disk without spiral arms. Whether or not it does so depends on its environment: the galaxy most ilkely to evolve into a smooth disk belongs to a rich cluster

By Karen M. Strom and Stephen E. Strom

Clay

It has myriad uses principally because it consists of fine particles, which result from the nature of clay minerals. These minerals are created and destroyed and created again in a long geological cycle

By Georges Millot

Teratomas and Chimeras

Teratomas are tumors composed of a jumble of differentiated cells and tissues. Their malignant stem cells can differentiate normally in the mouse embryo and give rise to chimeras, or genetic mosaics

By Karl Illmensee and Leroy C. Stevens

Chinese Oracle Bones

In the Shang dynasty of 3,000 years ago aristocrats liked to seek the advice of their ancestors. The questions, engraved on bone or on turtle shell, are clues to the origins of Chinese civilization

By Hung-Hsiang Chou

The Physics of Karate

A close examination of how the karate expert can break wood and concrete blocks with his bare hand reveals the remarkable capacity of the unaided human body for exerting physical force

By Michael S. Feld, Ronald E. McNair and Stephen R. Wilk

Ink-Jet Printing

Minute drops of ink, squirted from a nozzle and steered in flight, can be made to form printed characters. The ink-jet technology is particularly well suited to printing at the command of a computer

By Larry Kuhn and Robert A. Myers

Departments

  • 50 and 100 Years Ago, April 1979

  • Science and the Citizen, April 1979

  • Letters

    Letters to the Editors, April 1979

  • Recommended

    Books, April 1979

  • Mathematical Recreation

    Mathematical Games, April 1979

  • Amateur Scientist

    The Amateur Scientist, April 1979

  • Departments

    The Authors, April 1979

  • Bibliography, April 1979

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April 1979