Scientific American

The heart of the chick embryo begins to beat on the second day of development. New chemical techniques now make it possible to investigate the formation of the heart at an even earlier stage

In his time certain species of moths were light in color. Today in many areas these species are largely dark. If he had noticed the change occurring, he would have observed evolution in action

Seismologists are tuning their instruments to record earth motions with periods of one minute to an hour and amplitudes of less than .01 inch. These waves tell much about the earth's crust and mantle

They are now recognized as reflecting a fourth force of nature. The other three are gravity, electromagnetism and the "strong" force which holds together the particles of the atomic nucleus

The discovery of this substance which can raise the blood pressure has shed new light on the causes of hypertension and on the role of the kidney in the control of circulation

A case history of a schizophrenic child who converted himself into a "machine" because he did not dare be human. His story sheds light on emotional development in a mechanized society

At the bottom of a Guatemalan lake skin divers have found objects sacrificed to the lake spirits as early as 2,500 years ago. These finds help trace the history of a little-known branch of the Maya

Instruments borne aloft by artificial satellites and lunar probes indicate that our planet is encircled by two zones of high-energy particles, against which space travelers will have to be shielded