26 OPTICAL INSTRUMENTS AND COMPONENTS-NAMELY, TELESCOPES; LENSES AND LENS HOUSINGS; MIRRORS AND MIRROR CELLS; WINDOW AND WINDOW FRAMES; INTERFEROMETERS; AUTOCOLLIMATORS; TELEVISION PROJECTION EQUIPMENT AND OPTICAL AND PHOTOGRAPHIC SYSTEMS COMPRISED OF FILTERS, LIGHT SOURCES, MIRRORS AND WINDOWS FOR RECORDING WIND TUNNEL TESTS AND OTHER SUBJECTS NOT VISIBLE TO THE NAKED EYE