But the telescope is out of focus, therefore we must turn the small
focussing screw. Observe the charming chromatic changes--green, and
red, and blue light, purer than the hues of the rainbow, scintillating
and coruscating with wonderful brilliancy. As we get the focus, the
excursions of these light flashes diminish until--if the weather is
favourable--the star is seen, still scintillating, and much brighter
than to the naked eye, but reduced to a small disc of light, surrounded
(in the case of so bright a star as Sirius) with a slight glare. If
after obtaining the focus the focussing rack work be still turned, we
see a coruscating image as before. In the case of a very brilliant star
these coruscations are so charming that we may be excused for calling
the observer's attention to them. The subject is not without interest
and difficulty as an optical one. But the astronomer's object is to get
rid of all these flames and sprays of coloured light, so that he has
very little sympathy with the admiration which Wordsworth is said to
have expressed for out-of-focus views of the stars.

We pass to more legitimate observations, noticing in passing that Sirius
is a double star, the companion being of the tenth magnitude, and
distant about ten seconds from the primary. But our beginner is not
likely to see the companion, which is a very difficult object, vowing to
the overpowering brilliancy of the primary.

Orion affords the observer a splendid field of research. It is a
constellation rich in double and multiple stars, clusters, and nebulæ.
We will begin with an easy object.

The star [delta] (Plate 3), or _Mintaka_, the uppermost of the three
stars forming the belt, is a wide double. The primary is of the second
magnitude, the secondary of the seventh, both being white.