the present time is Mr. W. A. Roberts, a resident of South Africa,
whom the Boer war did not prevent from keeping up a watch of the
southern sky, which has resulted in greatly increasing our
knowledge of variable stars. There are also quite a number of
astronomers in Europe and America who make this particular study
their specialty.

During the past fifteen years the art of measuring the speed with
which a star is approaching us or receding from us has been
brought to a wonderful degree of perfection. The instrument with
which this was first done was the spectroscope; it is now replaced
with another of the same general kind, called the spectrograph.
The latter differs from the other only in that the spectrum of the
star is photographed, and the observer makes his measures on the
negative. This method was first extensively applied at the Potsdam
Observatory in Germany, and has lately become one of the
specialties of the Lick Observatory, where Professor Campbell has
brought it to its present degree of perfection. The Yerkes
Observatory is also beginning work in the same line, where
Professor Frost is already rivalling the Lick Observatory in the
precision of his measures.

Let us now go back to our own little colony and see what is being
done to advance our knowledge of the solar system. This consists
of planets, on one of which we dwell, moons revolving around them,
comets, and meteoric bodies. The principal national observatories
keep up a more or less orderly system of observations of the
positions of the planets and their satellites in order to
determine the laws of their motion. As in the case of the stars,
it is necessary to continue these observations through long