I.j THE THAMES. 9 



Wain, forming part of the Grea( Bear (Fig. i ). A line drawn 

 through two of these stars (/3, a) will, if prolonged to about 

 five times its length, pass very close to the famous Fole-star?- 

 On a clear night, all the groups of stars appear to move 

 slowly round a certain fixed point in the sky, which is the 

 north pole of the heavens. That point of the earth 

 immediately beneath the celestial north pole is the north 

 pole of the earth. If the explorers in the Alert and 

 Z>iscove?-y could have reached the north pole, they would 

 have found the pole star almost directly overhead. It must 

 be remembered, however, that the pole-star is not exactly at 

 the north pole of the heavens, although very near to it. By 

 observing the position of the pole-star, the north can be 

 determined on a clear night as readily as the south may be 

 determined by the sun at noon. 



If, however, the sky is beclouded so that the heavenly 

 bodies are not visible, there is yet another easy means of 

 finding the direction of the cardinal points. Let a thin bar 

 of steel, or even a needle, be nicely balanced upon a pivot, 

 or suspended by a thread, or floated upon a cork in water, 

 so that it can turn freely in all directions horizontally ; it 

 will be found that the bar may be brought to rest in any 

 desired position. If, however, the bar be rubbed with a 

 rnagnet, a peculiar change is wrought in the steel, and it 



* It is the practice of astronomers to distinguish the several stars of 

 a particular group, or constellation, by means of Greek letters. Thus 

 the two stars in the Great Bear, known as the Pointers, since a line 

 joining them points towards the pole-star, are distinguished in Fig. I by 

 the letters o and /3. The first of these stars would be technically 

 described as a Ursa Majoris, or the alpha star of the Great Bear. 

 This constellation contains several stars of which only seven conspicuous 

 ones are represented in the figure. The pole-star, known also as 

 Polaris, is the brightest of a group called the Little Bear, and is con- 

 sequently described as a Ursa Minoris. 



