g the same surface. Two of these squares lie at the
northern pole of the Galaxy and are designated GA_1 and GA_2. Twelve lie
north of the galactic plane, between 0 deg. and 30 deg. galactic latitude, and
are designated GC_1, GC_2, ..., GC_12. The corresponding squares south
of the galactic equator (the plane of the Galaxy) are called GD_1, GD_2,
..., GD_12. The two polar squares at the south pole are called GF_1 and
GF_2. Finally we have 10 B-squares, between the A- and C-squares and 10
corresponding E-squares in the southern hemisphere.

The distribution of the squares in the heavens is here graphically
represented in the projection of FLAMSTEED, which has the advantage of
giving areas proportional to the corresponding spherical areas, an
arrangement necessary, or at least highly desirable, for all stellar
statistical researches. It has also the advantage of affording a
continuous representation of the whole sky.

The correspondence between squares and stellar constellations is seen
from plate II. Arranging the constellations according to their galactic
longitude we find north of the galactic equator (in the C-squares) the
constellations:--

Hercules, Cygnus, Cepheus, Cassiopaea, Auriga, Gemini, Canis Minor,
Pyxis, Vela, Centaurus, Scorpius, Ophiuchus,

and south of this equator (in the D-squares):--

Aquila, Cygnus, Lacerta, Andromeda, Perseus, Orion, Canis Major,
Puppis, Carina, Circinus, Corona australis, Sagittarius,

mentioning only one constellation for each square.

At the north galactic pole (in the two A-squares) we have:--

Canes Venatici and Coma Berenices,

and at the south galactic pole (in the two F-squares):--

Cetus and Sculptor.

3. _Changes in the position of a star._ From the positions of a star on
two or more occasions we obtain its apparent motion, also called the
_proper motion_ of the star. We may distinguish between a _secular_ part
of this motion and a _periodical_ part. In both cases the motion may be
either a reflex of the motion of the observer, and is then called
_parallactic_ motion, or it may be caused by a real motion of the star.
From the parallactic motion of the star it is possible to deduce its
distance from the sun, or its parallax. The periodic parallactic proper
motion is caused by the motion of the earth around the sun, and gives
the _annual parallax_ ([pi]). In order to obtain available annual
parallaxes of a star it is usually necessary for