cts by the astronomical telescope.
It is singular that any difficulty should be felt about so simple a
matter, yet I have seen in the writings of more than one distinguished
astronomer, wholly incorrect views as to the nature of the inversion.
One tells us that to obtain the correct presentation from a picture
taken with a telescope, the view should be inverted, held up to the
light, and looked at from the back of the paper. Another tells us to
invert the picture and hold it opposite a looking-glass. Neither method
is correct. The simple correction wanted is to hold the picture upside
down--the same change which brings the top to the bottom brings the
right to the left, _i.e._, fully corrects the inversion.

In the case, however, of a picture taken by an Herschelian reflector,
the inversion not being complete, a different method must be adopted. In
fact, either of the above-named processes, incorrect for the ordinary
astronomical, would be correct for the Herschelian Telescope. The latter
inverts but does not reverse right and left; therefore after inverting
our picture we must interchange right and left because they have been
reversed by the inversion. This is effected either by looking at the
picture from behind, or by holding it up to a mirror.

[Illustration: PLATE II.]

CHAPTER II.

A HALF-HOUR WITH ORION, LEPUS TAURUS, ETC.

Any of the half-hours here assigned to the constellation-seasons may be
taken first, and the rest in seasonal or cyclic order. The following
introductory remarks are applicable to each:--

If we stand on an open space, on any clear night, we see above us the
celestial dome spangled with stars, apparently fixed in position. But
after a little time it becomes clear that these orbs are slowly shifting
their position. Those near the eastern horizon are rising, those near
the western setting. Careful and continuous observation would show that
the stars are all moving in the same way, precisely, as they would if
they were fixed to the concave surface of a vast hollow sphere, and this
sphere rotated about an axis. This axis, in our latitude, is inclined
about 51-1/2 deg. to the horizon. Of course only one end of this imaginary
axis can be above our horizon. This end lies very near a star which it
will be well for us to become acquainted with at the beginning of our
operations. It lies almost exactly towards the north, and is raised from
50 deg. to 53 deg. (according to the season and ho