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 coil of copper wire which acts as an electrical transformer, and may be tilted to determine the minimum and maximum intensity of the field. They are conducting an experiment in electronics, taught in the department of geophysics at a famous mining engineering school. They will apply the knowledge they are acquiring to airplane detection and anti-submarine warfare. Colorado School of Mines, Golden, Colorado. Sourced from the Library of Congress.