If, now, we draw from the stars α and δ of the Great Bear two lines through the pole, and produce them beyond Cassiopeia, we come to the Square of Pegasus (see Fig. 4), which shows a line of three stars somewhat similar to the tail of the Great Bear. These three stars belong to _Andromeda_, and lead to another constellation, _Perseus_. The last star of the Square of Pegasus is, as we see, the first (α) of Andromeda; the three others are named γ, α, and β. To the north of β of Andromeda is found, near a little star, ν, an oblong nebula, which can be distinguished with the naked eye. In Perseus, α, the brightest—on the prolongation of the three principal stars of Andromeda—appears between two others less brilliant, which form with it a concave arc very easy to distinguish. This arc serves us for a new alignment. Producing it in the direction of δ, we find a very brilliant star of the first magnitude; this is _Capella_ (the Goat). Forming a right angle with this prolongation toward the south we come to the _Pleiades_ (Fig. 5). Not far from that is a variable star, _Algol_, or the _Head of Medusa_, which varies from the second to the fourth magnitude[8] in 2 days, 20 hours, 48 minutes, 51 seconds. We may add, that in this region the star γ of Andromeda is one of the most beautiful double stars (it is even triple). [Illustration: Fig. 7 Fig. 8] If, now, we produce beyond the Square of Pegasus (Fig. 6) the curved line of Andromeda, we reach the Milky Way, and we meet in these parts Cygnus, like a cross; the Lyre, where Vega shines (Fig. 7); the Eagle, and Altair (not Atair, as it is sometimes written) with two companions (Fig. 8). Such are the principal constellations visible in the circumpolar regions on one side; we shall make a fuller acquaintance with them directly. While we are tracing the lines of reference let us still have a little patience and finish our summary review of this part of the sky. [Illustration: Fig. 9] Look now at the side opposite to that of which we have just spoken. Let us return to the Great Bear. Producing the tail along its curve, we find at some distance from that a star of the first magnitude, _Arcturus_ (Fig. 9), or α of Boötes. A little circle of stars which we see to the left of Boötes constitutes the _Northern Crown_ (Corona Borealis). In the month of May, 1866, there was seen shining there a fine star, the brightness of which lasted only fifteen days. The constellation of Boötes is traced in the form of a pentagon. The stars which compose it are of the third magnitude, with the exception of Arcturus, which is of the first. This is one of the nearest to the earth; at least, it is one of a small number whose distance has been measured. It shines with a beautiful golden yellow color. The star ε, which we see above it, is _double_—that is to say, the telescope resolves it into two distinct stars, one yellow, the other blue. [Illustration: Fig. 10.]