If we take the seven stars as representing the characteristic points of a chariot, the four stars of the quadrilateral will represent the four wheels, and the three others will represent the three horses. Above the centre of the three horses any one with clear sight may perceive a small star of the fifth or sixth magnitude, called the Cavalier. Each of these several stars is indicated, as is usual with all the constellations, by a Greek letter, the largest being denoted by the first letter. Thus the 4 stars in the quadrilateral are [Greek: a], [Greek: b], [Greek: g], [Greek: d], and the 3 tail stars [Greek: e], [Greek: x], [Greek: e]. The Arabs give to each star its special name, which in this case are as follows:--Dubhe and Merak are the stars at the back; Phegda and Megrez those of the front; Alioth, Mizat, and Ackiar the other three, while the little one over Mizat is Alcor. Another name for it is Saidak, or the Tester, the being able to see it being a mark of clear vision. There is some little interest in the Great Bear on account of the possibility of its being used as a kind of celestial time-keeper, and its easy recognition makes it all the more available. The line through [Greek: a] and [Greek: b] passes almost exactly through the pole. Now this line revolves of course with the constellation round the pole in 24 hours; in every such interval being once, vertical above the pole, and once vertical below, taking the intermediate positions to right and left between these times. The instant at which this line is vertical over the pole is not the same on any two consecutive nights, since the stars advance each day 4 minutes on the sun. On the 21st of March the superior passage takes place at 5 minutes to 11 at night; on the following night four minutes earlier, or at 9 minutes to 11. In three months the culmination takes place 6 hours earlier, or at 5 minutes to 5. In six months, _i.e._ on Sept. 22, it culminates at 10.55 in the morning, being vertically below the pole at the same hour in the evening. The following woodcut exhibits the positions of the Great Bear at the various hours of September 4th. It is plain from this that, knowing the day of the month, the hour of the night may be told by observing what angle the line joining [Greek: a] and [Greek: b] of this constellation makes with the vertical. [Illustration: FIG. 4.]