rvatory, with which
pictures of the sky are systematically taken, but had remained
unnoticed, or had been taken for an ordinary star among the thousands of
star images surrounding it. From these telltale plates it was
ascertained that in 1894 it had been in perihelion very near the earth,
and had shone with the brilliance of a seventh-magnitude star.

It will, unfortunately, be a long time before Eros comes quite as near
us as it did on that occasion, when we failed to see it, for its close
approaches to the earth are not frequent. Prof. Solon I. Bailey selects
the oppositions of Eros in 1931 and 1938 as probably the most favorable
that will occur during the first half of the twentieth century.

We turn to the extraordinary fluctuations in the light of Eros, and the
equally extraordinary conclusions drawn from them. While the little
asteroid, whose diameter is estimated to be in the neighborhood of
twenty or twenty-five miles, was being assiduously watched and
photographed during its opposition in the winter of 1900-1901, several
observers discovered that its light was variable to the extent of more
than a whole magnitude; some said as much as two magnitudes. When it is
remembered that an increase of one stellar magnitude means an accession
of light in the ratio of 2.5 to 1, and an increase of two magnitudes an
accession of 6.25 to 1, the significance of such variations as Eros
exhibited becomes immediately apparent. The shortness of the period
within which the cycle of changes occurred, about two hours and a half,
made the variation more noticeable, and at the same time suggested a
ready explanation, viz., that the asteroid was rapidly turning on its
axis, a thing, in itself, quite in accordance with the behavior of other
celestial bodies and naturally to be expected.

But careful observation showed that there were marked irregularities in
the light fluctuations, indicating that Eros either had a very strange
distribution of light and dark areas covering its surface, or that
instead of being a globular body it was of some extremely irregular
shape, so that as it rotated it presented successively larger and
smaller reflecting surfaces toward the sun and the earth. One
interesting suggestion was that the little planet is in reality double,
the two components revolving around their common center of gravity, like
a close binary star, and mutually eclipsing one another. But this theory
seems hardly competent to explain th