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They indicated a marked deficiency of thermal radiations, implying for coronal light, in Professor Langley's opinion, an origin analogous to that of the electric glow-discharge, which, at low pressures, was found by K. Ångström in 1893 to have no invisible heat-spectrum. The corona was photographed by Professor Barnard, at Wadesborough, North Carolina, with a 61-1/2-foot horizontal "coelostat."
The "coelostat," in the form given to it by Professor Turner, has proved an invaluable adjunct to eclipse-equipments. It consists essentially of a mirror rotating in forty-eight hours on an axis in its own plane, and parallel to the earth's axis. In the field of a telescope kept rigidly pointed towards such a mirror, stars appear immovably fixed.
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