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[Dark visions and adaptation in Danish ophthalmology 1889-1940].

The scotopticometer is a small, light and handy instrument from 1935, which was developed in Denmark by Carsten Edmund Zeuthen (1897-1973) and Hans Ulrik Møller (1894-1954) for the measurement of dark vision without the use of a dark chamber. The prerequisites are Jannik Bjerrum's contrast letters from 1889 and Marius Tscherning's photometric neutral-gray filter-glasses with a logaritmic scale (Ph 1-8); both Bjerrum (1851-1920) and Tscherning (1854-1939) were Danish ophthalmologists. Tescherning's basic experiments and theories are reported, based on a study of his scientific publications, scientific protocols, letters and scrapbook. Tscherning inspired many young Danish scientists to further studies of dark adaptation, which is still an important topic (traffic, military, art, illumination, gerontology).