Atomic Snapshot

A just-exploded atom bomb is a difficult subject for photography. Its fireball expands so suddenly that no ordinary shutter can act quickly enough to freeze its motion. Last week the Atomic Energy Commission released a picture of a "nuclear device" caught in the very act of vaporizing the tower on which it had stood (see cut).

The picture was taken with a special camera made by Edgerton, Germeshausen & Grier, Inc. of Boston. Its shutter has no moving parts, only two sheets of polarizing material, something like the stuff in the glasses that are used to view 3-D movies. When light passes through the first of them, it is polarized so that its waves vibrate in a single direction. Then it cannot pass through the second sheet, whose plane of polarization is set at right angles to that of the first sheet. In this condition the shutter is closed.

Between the two sheets' is special glass surrounded by a coil of insulated wire. When a powerful current from a condenser is shot through the coil, it creates a magnetic field in the glass which rotates the light waves so that they pass through both of the polarizing sheets and reach the film of the camera. The light can pass only while the current is flowing, so a very short pulse opens the shutter for as little as one millionth of a second. Some such speed was necessary to picture the doomed tower when it was only half-vaporized by the hungry fireball.

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