ider lines the telescope is properly sighted. We use the word sighted
designedly, because we wish to suggest a comparison between the sighting
of a rifle at the target and the sighting of a telescope at a star.
Instead of the ordinary large bull's-eye, suppose that the target only
consisted of a watch-dial, which, of course, the rifleman could not see
at the distance of any ordinary range. But with the telescope of the
meridian circle the watch-dial would be visible even at the distance of
a mile. The meridian circle is indeed capable of such precision as a
sighting instrument that it could be pointed separately to each of two
stars which subtend at the eye an angle no greater than that subtended
by an adjoining pair of the sixty minute dots around the circumference
of a watch-dial a mile distant from the observer.

This power of directing the instrument so accurately would be of but
little avail unless it were combined with arrangements by which, when
once the telescope has been pointed correctly, the position of the star
can be ascertained and recorded. One element in the determination of the
position is secured by the astronomical clock, which gives the moment
when the object crosses the central vertical wire; the other element is
given by the graduated circle which reads the angular distance of the
star from the zenith or point directly overhead.

Superb meridian instruments adorn our great observatories, and are
nightly devoted to those measurements upon which the great truths of
astronomy are mainly based. These instruments have been constructed with
refined skill; but it is the duty of the painstaking astronomer to
distrust the accuracy of his instrument in every conceivable way. The
great tube may be as rigid a structure as mechanical engineers can
produce; the graduations on the circle may have been engraved by the
most perfect of dividing machines; but the conscientious astronomer will
not be content with mere mechanical precision. That meridian circle
which, to the uninitiated, seems a marvellous piece of workmanship,
possessing almost illimitable accuracy, is viewed in a very different
light by the astronomer who makes use of it. No one can appreciate more
fully than he the skill of the artist who has made that meridian circle,
and the beautiful contrivances for illumination and reading off which
give to the instrument its perfection; but while the astronomer
recognises the beauty of the actual machine he is