henomenon which he is to study, and then makes his observation on the
developed negative.

The world of astronomy is one of the busiest that can be found to-day,
and the writer proposes, with the reader's courteous consent, to take
him on a stroll through it and see what is going on. We may begin our
inspection with a body which is, for us, next to the earth, the most
important in the universe. I mean the sun. At the Greenwich Observatory
the sun has for more than twenty years been regularly photographed on
every clear day, with the view of determining the changes going on in
its spots. In recent years these observations have been supplemented by
others, made at stations in India and Mauritius, so that by the
combination of all it is quite exceptional to have an entire day pass
without at least one photograph being taken. On these observations must
mainly rest our knowledge of the curious cycle of change in the solar
spots, which goes through a period of about eleven years, but of which
no one has as yet been able to establish the cause.

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. The third requirement is the best of instruments, specially
devised to meet the requirements. In this respect we may be sure tha