Word: flintglass
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Dates: during 1888-1888
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There has been invented a new form of telescope object glass which can be transformed at will from a "photographic" to a "visual" lens by simply turning over the crown-glass lens and changing its distance from the flintglass lens. The Clarks have made for Professor Pickering a lens of this construction with an aperture of thirteen inches and a focal length of fifteen feet...
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