omputers
make it their duty to provide for the "Berlin Year-Book" detailed
information as to the movements of the minor planets. As soon as a few
complete observations have been obtained, the little object passes into
the secure grasp of the mathematician; he is able to predict its career
for years to come, and the announcements with respect to all the known
minor planets are to be found in the annual volumes of the work referred
to.

The growth of discovery has been so rapid that the necessary labour for
the preparation of such predictions is now enormous. It must be
confessed that many of the minor planets are very faint and otherwise
devoid of interest, so that astronomers are sometimes tempted to concur
with the suggestion that a portion of the astronomical labour now
devoted to the computation of the paths of these bodies might be more
profitably applied. For this it would be only necessary to cast adrift
all the less interesting members of the host, and allow them to pursue
their paths unwatched by the telescope, or by the still more ceaseless
tables of the mathematical computer.

The sun, which controls the mighty orbs of our system, does not disdain
to guide, with equal care, the tiny globes which form the minor planets.
At certain times some of them approach near enough to the earth to merit
the attention of those astronomers who are specially interested in
determining the dimensions of the solar system. The observations are of
such a nature that they can be made with considerable precision; they
can also be multiplied to any extent that may be desired. Some of these
little bodies have consequently a great astronomical future, inasmuch as
they seem destined to indicate the true distance from the earth to the
sun more accurately than Venus or than Mars. The smallest of these
planets will not answer for this purpose; they can only be seen in
powerful telescopes, and they do not admit of being measured with the
necessary accuracy. It is also obvious that the planets to be chosen for
observation must come as near the earth as possible. In favourable
circumstances, some of the minor planets will approach the earth to a
distance which is about three-quarters of the distance of the sun. These
various conditions limit the number of bodies available for this purpose
to about a dozen, of which one or two will usually be suitably placed
each year.

For the determination of the sun's distance this method by the minor
p