Polaroid

In the swank Greenbrier Hotel at White Sulphur Springs, W. Va. one day last week, members of the convening Society of Automotive Engineers traipsed into a darkened room, blinked in the glare of a pair of automobile headlights, then, passing behind a clear glass windshield, observed that although the light beams illuminated the room display, they no longer glared into the observer's eye.

This small miracle was made possible, the engineers were soon told, because the "windshield" through which they looked was made of a recently developed material called Polaroid, and the headlight lenses were backed by plates of the same stuff. Polaroid polarizes light. Reduced to simplest terms, polarization is a process of "combing out" a beam of light so that it vibrates in one plane only. Laymen understand polarization more readily if they imagine that a beam of light, vibrating in all directions, is a flight of straws blown along helter-skelter by the wind. If the straws collide with a picket fence, some will pass through if they happen to be aligned vertically with the gaps between the palings. Thus all the straws that get through will be parallel to one another.

In laboratory practice, a light beam's "fence" is a crystal, and the gaps which comb light are a crystal's parallel planes of cleavage. Polaroid is a suspension of crystals. The dazzling headlights at last week's demonstration were dimmed because the Polaroid in the lenses and in the windshield was aligned in conflicting directions. The light could thus pass through one but not through both.

Discovered in the 17th Century, polarization has become an elaborate science using small, costly, natural crystals like Iceland spar. Polaroid's sponsors say that it will do anything expensive crystals will, can be inexpensively manufactured in any size. Actual cost figures will probably not be available until large-scale equipment is set up. Developed by Physicist Edwin H. Land, senior partner of an independent Boston laboratory, Polaroid's synthetic organic crystals are bound in a plastic film of cellulose acetate. The tiny crystals are pulled into parallel alignment by stretching the film. The material polarizes about 99.9% of the transmitted light. Other uses for Physicist Land's discovery: three-dimensional (stereoscopic) movies in color;-- sunglasses which filter out glare without discoloring the view; transparent models of working parts which show up areas of strain; beams permitting dermatologists to see into the nether layers of the skin.

--Leased by Eastman Kodak.

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