This Greenwich system has been extended and improved by an
American. Professor George E. Hale, formerly Director of the
Yerkes Observatory, has devised an instrument for taking
photographs of the sun by a single ray of the spectrum. The light
emitted by calcium, the base of lime, and one of the substances
most abundant in the sun, is often selected to impress the plate.
The Carnegie Institution has recently organized an enterprise for
carrying on the study of the sun under a combination of better
conditions than were ever before enjoyed. The first requirement in
such a case is the ablest and most enthusiastic worker in the
field, ready to devote all his energies to its cultivation. This
requirement is found in the person of Professor Hale himself. The
next requirement is an atmosphere of the greatest transparency,
and a situation at a high elevation above sea-level, so that the
passage of light from the sun to the observer shall be obstructed
as little as possible by the mists and vapors near the earth's
surface. This requirement is reached by placing the observatory on
Mount Wilson, near Pasadena, California, where the climate is
found to be the best of any in the United States, and probably not
exceeded by that of any other attainable point in the world.
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