If we now draw, from the stars α and δ in _Ursa Major_, two lines meeting at the Pole, and afterwards extend them beyond _Cassiopeia_, they will abut on the square of _Pegasus_, which is bounded on one of its sides by a group, or series, of three stars resembling the triangle in _Ursa Major_. These three belong to the constellation of _Andromeda_ (α, β, and γ), and themselves abut on another three-orbed group, that of _Perseus_. The last star in the square of _Perseus_ is also the first α of _Andromeda_: the other three are named, Algenib, γ; Markab, α; and Scheat, β. To the north of _Andromeda_ β, and near a small star, ν, the Arctic traveller will discern an oblong nebula, which may be compared to the light of a taper seen through a sheet of horn; this is the first nebula to which any allusion occurs in the annals of astronomy. In _Perseus_ α, an orb of great brilliancy, on the prolonged plane of the three principal stars of _Andromeda_, shines with steady lustre between two less dazzling spheres, and forms in conjunction with them a concave arc very easily distinguished. Of this arc we may avail ourselves as a new point of departure. By prolonging it in the direction of δ, we come to a very bright star of the first magnitude, the _Goat_. By forming a right angle to this prolongation in a southerly direction we come to that glorious mass of stars, not very frequently above the Polar horizon, the _Pleiads_. These were held in evil repute among the ancients. Their appearance was supposed to be ominous of violent storms, and Valerius Flaccus speaks of them as fatal to ships. [Illustration: NEBULA IN ANDROMEDA.] Algol, or Medusa’s Head, known to astronomers as Perseus β, belongs to the singular class of Variable Stars. Instead of shining with a constant lustre, like other orbs, it is sometimes very brilliant, and sometimes very pale; passing, apparently, from the second to the fourth magnitude. According to Goodricke, its period of variation is 2 days 20 hours 48 minutes. This phenomenal character was first observed by Maraldi in 1694; but the duration of the change was determined by Goodricke in 1782. For two days and fourteen hours it continues at its brightest, and shines a glory in the heavens. Then its lustre suddenly begins to wane, and in three hours and a half is reduced to its minimum. Its weakest period, however, does not last more than about fifteen minutes. It then begins to increase in brightness, and in three hours and a half more it is restored to its full splendour; thus passing through its succession of changes in 2 days 20 hours 48 minutes. This singular periodicity suggested to Goodricke the idea of some opaque body revolving around the star, and by interposing between it and the Earth cutting off a portion of its light. Algol is one of the most interesting of the welcome stars which kindle in the long Arctic darkness.