[delta] of the stars in a particular manner. We shall
therefore use an abridged notation, so that if for instance [alpha] =
17h 44m.7 and [delta] = +35 deg..84, we shall write

([alpha][delta]) = (174435).

If [delta] is negative, for instance [delta] = -35 deg..84, we write

([alpha][delta]) = (1744{35}),

so that the last two figures are in italics.

[Transcriber's Note: In this version of the text, the last two figures
are enclosed in braces to represent the italics.]

This notation has been introduced by PICKERING for variable stars and is
used by him everywhere in the Annals of the Harvard Observatory, but it
is also well suited to all stars. This notation gives, simultaneously,
the characteristic _numero_ of the stars. It is true that two or more
stars may in this manner obtain the same characteristic _numero_. They
are, however, easily distinguishable from each other through other
attributes.

The _galactic_ coordinates _l_ and _b_ are referred to the Milky Way
(the Galaxy) as plane of reference. The pole of the Milky Way has
according to HOUZEAU and GOULD the position ([alpha][delta]) = (124527).
From the distribution of the stars of the spectral type B I have in L.
M. II, 14[2] found a somewhat different position. But having ascertained
later that the real position of the galactic plane requires a greater
number of stars for an accurate determination of its value, I have
preferred to employ the position used by PICKERING in the Harvard
catalogues, namely ([alpha][delta]) = (124028), or

[alpha] = 12h 40m = 190 deg., [delta] = +28 deg.,

which position is now exclusively used in the stellar statistical
investigations at the Observatory of Lund and is also used in these
lectures.

The galactic longitude (_l_) is reckoned from the ascending node of the
Milky Way on the equator, which is situated in the constellation
_Aquila_. The galactic latitude (_b_) gives the angular distance of the
star from the Galaxy. On plate I, at the end of these lectures, will be
found a fairly detailed diagram from which the conversion of [alpha] and
[delta] of a star into _l_ and _b_ may be easily performed. All stars
having an apparent magnitude brighter than 4m are directly drawn.

Instead of giving the galactic longitude and latitude of a star we may
content ourselves with giving the galactic _square_ in which the star is
situated. For this purpose we assume the sky to be divided into 48
squares, all havin