JEROME WEXLER / SCIENCE PHOTO LIBRARY JEROME WEXLER / SCIENCE PHOTO LIBRARY
Polarising filters. Two light-polarising filters overlapping. In normal white light the vibrations in the light waves are perpendicular to the direc- tion of flow but can point in any direction through 360 degrees. In polarised light the vibra- tions are confined to a specific plane. These two filters are rotated so that they both transmit light polarised in the same plane. If one filter was rotated 90 degrees, however, no light could pass through both filters and the overlap would appear dark. See photograph A200/323 for same filters after rotation of handle through 90 degrees.
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