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 periods of time in order that everything possible to learn
may be discovered.

Our own moon is one of the enigmas of the mathematical astronomer.
Observations show that she is deviating from her predicted place, and
that this deviation continues to increase. True, it is not very great
when measured by an ordinary standard. The time at which the moon's
shadow passed a given point near Norfolk during the total eclipse of
May 29, 1900, was only about seven seconds different from the time
given in the Astronomical Ephemeris. The path of the shadow along the
earth was not out of place by more than one or two miles But, small
though these deviations are, they show that something is wrong, and no
one has as yet found out what it is. Worse yet, the deviation is
increasing rapidly. The observers of the total eclipse in August, 1905,
were surprised t