WITH the development of powerful magnets for physics research, industrial uses and even transportation, increasing numbers of people are being exposed to magnetic fields thousands of times stronger than those in which humans evolved.

In the neighborhood of the giant magnets in some laboratories visitors can feel the pull on nails in their shoes. Japan is developing a magnetically levitated vehicle which will subject both passengers and crew to strong magnetic fields.

Magnetism is not felt by the human senses in any obvious way, nor is there any substantial evidence that it is harmful. Yet it does have subtle effects on vision and heart performance. Consequently, researchers at the Lawrence Berkeley Laboratory of the University of California are conducting a long-term study of magnetic influences on body functions.

Probably the best-known sensory effect of magnetism is shown in total darkness, when the head of a person whose eyes are fully adapted to the dark is put between the poles of an alternating current magnet. As the field strength is increased, the person will begin to see a faint glow around the visual periphery. When the field is reduced, the glow vanishes.