Public domain
Science and research. Mineral prospecting. A ground comparator will reveal the presence of an ore body under the surface of the earth by measuring the total intensity and the plane of polarization of the secondary electro-magnetic field set up by the ore body. These students are using an adjustable
From the collection of Library of Congress. Free to download, adapt and use — no permission needed.
Credit lineScience and research. Mineral prospecting. A ground comparator will reveal the presence of an ore body under the surface of the earth by measuring the total intensity and the plane of polarization of . 1942-01-01. United States. Office Of War Information, Feininger, Andreas. Farm Security Administration/Office of War Information Collection, Library of Congress. Public domain.
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