### How do polarized sunglasses work?

Who's the next question from? Jamie? What a surprise! "How do polarized sunglasses work?" asks this bartender with a passion for knowledge. He just wasn't satisfied with the answer, "You put 'em on and everything gets darker. Now how's about another Gibson?" So I hadda do some reading.

Polarization is a process whereby waves are restricted so that they have different amplitudes in different planes. It is a phenomenon not restricted to light. Scientists and thinkers such as Isaac Newton, Robert Boyle and Robert Hooke began the useful analysis of the nature of light in the 1600's. Newton believed light consisted of tiny particles, Boyle and Hooke felt light propagated as waves. Hooke published the first wave theory in 1665, after experiments involving interference with thin films.

In 1669 Erasmus Bartholin discovered the polarization of light by double refraction in Iceland spar. This finding had a profound effect on the conception of the nature of light. The effect which Bartholin observed was not easily explained by Newton's particle theory, (although he made a wacky stab at it), nor fully explained by the then current wave theories. It took nearly a century before Thomas Young and Augustin-Jean Fresnel formed a new theory, one that succeeded in explaining all optical phenomenon known at the beginning of the 19th century. It defined light as a transverse wave, in which vibration occurs at right angles to the direction of propagation. These waves can have any vector that is perpendicular to the light's path. Typical non-coherent light, when passed through a polarizing substance, is diminished because one plane of the beam's vibration is removed. Polarizing substances work by either reflection, refraction, or in most man-made polarizers, by absorption. Complex, man-made polarizing crystals are produced in a plastic matrix and oriented by stretching.

The development of man-made polarizers was the result of the genius of none other than Edwin Herbert Land, the inventor of the Polaroid Land Camera. (For a long time I never knew there was a guy named Land. When I was a kid I thought you just couldn't use the damned thing on a plane or a boat.) Land became interested in polarized light when a student at Harvard. He took a leave of absence and, after intensive study and experimentation, succeeded in 1932 in aligning submicroscopic crystals of iodoquinine sulfate and embedding them in a sheet of plastic. The resulting polarizer, named Polaroid sheet J, was an incredible advance, allowing the use of almost any size of polarizer, not to mention reducing the cost of use. By 1936, Land and a partner had opened a laboratory in Boston to exploit the various uses for his Polaroid sheet J, including sunglasses.

Now can I have that drink, Jamie?