navigation, and the observations
have from the first been specially arranged with the object of
determining with the greatest accuracy the positions of the principal
fixed stars, the sun, the moon, and the planets. In recent years,
however, great developments of the work of the Observatory have been
witnessed, and the most modern branches of the science are now
assiduously pursued there.

The largest equatorial at Greenwich is a refractor of twenty-eight
inches aperture and twenty-eight feet long, constructed by Sir Howard
Grubb. A remarkable composite instrument from the same celebrated
workshop has also been recently added to our national institution. It
consists of a great refractor specially constructed for photography, of
twenty-six inches aperture (presented by Sir Henry Thompson) and a
reflector of thirty inches diameter, which is the product of Dr.
Common's skill. The huge volume published annually bears witness to the
assiduity with which the Astronomer Royal and his numerous staff of
assistant astronomers make use of the splendid means at their disposal.

The southern part of the heavens, most of which cannot be seen in this
country, is watched from various observatories in the southern
hemisphere. Foremost among them is the Royal Observatory at the Cape of
Good Hope, which is furnished with first-class instruments. We may
mention a great photographic telescope, the gift of Mr. M'Clean.
Astronomy has been greatly enriched by the many researches made by Dr.
Gill, the director of the Cape Observatory.

[Illustration: Fig. 9.--The Great Bear.]

It is not, however, necessary to use such great instruments to obtain
some idea of the aid the telescope will afford. The most suitable
instrument for commencing astronomical studies is within ordinary reach.
It is the well-known binocular that a captain uses on board ship; or if
that cannot be had, then the common opera-glass will answer nearly as
well. This is, no doubt, not so powerful as a telescope, but it has some
compensating advantages. The opera-glass will enable us to survey a
large region of the sky at one glance, while a telescope, generally
speaking, presents a much smaller field of view.

Let us suppose that the observer is provided with an opera-glass and is
about to commence his astronomical studies. The first step is to become
acquainted with the conspicuous group of seven stars represented in Fig.
9. This group is often called the Plough, or Charles