Public domain
Dr. N.A. Cobb, technologist of the Dept. of Agric., who has discovered that by the use of a piece of glass he can invoke the aid of the sun in making microscopic studies of minute objects. Until this glass was used, the sun blurred instead of clarified the object
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Subjects
Credit lineDr. N.A. Cobb, technologist of the Dept. of Agric., who has discovered that by the use of a piece of glass he can invoke the aid of the sun in making microscopic studies of minute objects. Until this . 1924-01-01. Harris & Ewing. Harris & Ewing Collection, Library of Congress. Public domain.
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