Government discovers method to preserve film. (2) Expansion and contraction, like paper and other sheet materials made from cellulose, films expand as they take up moisture and contract as they lose it, and the extent of the change is different in the two directions of them. This may cause some distortion of the image, and therefore is of particular importance where the image must be true to scale, such as in aerial photography. C.O. Pope is shown with a type of expansiveity tester used and which was designed by the Bureau of Standards. Long strips of film are suspended under constant tension in the [cabinet?] in which the humidity is varied by means of [...] solutions. The change in length is indicated [...continuously?] on a scale by means of an optical-level arrangement, 7/8/38
Summary
Public domain photograph of people, building, free to use, no copyright restrictions image - Picryl description
Tags
Date
1938
Contributors
Harris & Ewing, photographer
Location
Washington, District of Columbia, United States, 38.90719, -77.03687
Source
Library of Congress
Copyright info
No known restrictions on publication.