THE WANDERINGS OF THE NORTH POLE. 77 



star is describing is becoming less and less. Tlie time will come when 

 the circle which this star performs will have reached its lowest dimen- 

 sions, but still the pole will be moving on its way, and then, of course, 

 the dimensions of the circle traversed by the Pole-star will undergo a. 

 corresponding increase. As hundreds of years and thousands of years 

 roll by the i)ole will retreat farther and farther from the Pole star, so 

 that in the course of a i)eriod as far on in the future as the foundation 

 of l\ome was in the past, the pole will be no longer sufiticiently near 

 the Pole-star to enable the latter to render to astronomers the peculiar 

 services which it does at |)resent. 



Looking still fiirther ahead, we find that in the course of about twelve 

 thousand years the pole will have gained a position as remote as it 

 j)ossibly can from that position which it now occupies. This most criti- 

 cal point in the heavens will then lie not far from the star Vega, tlie 

 brightest point in the northern sky, and then it will commence to return, 

 so that after the lapse of about twenty-five thousand years the pole 

 will be found again in the same celestial neighborhood where it is 

 to-night, having, in the meantime, traversed a mighty circle through the 

 constellations. In all this there is no novelty; these movements«of the 

 pole are so conspicuous that they were detected long before the intro- 

 duction of accurate instruments. They were discovered so far back as 

 the time of Hipparchus, and the cause of theju was assigned by New- 

 ton as one of the triumphs of his doctrine of universal gravitation. In 

 giving the title of " The Wanderings of the North Pole" to this paper 

 I did not however intend to discourse of the movements to which I 

 have hitherto referred. They are so familiar that every astronomer has 

 to attend to them practically in the redaction of almost every observa- 

 tion of the place of the celestial body. It was however necessary to 

 make the reference which I have done to this subject in order that the 

 argument on which we are presently to enter should be made suffi- 

 ciently clear. It must be noted that the expression "the North Pole " 

 is ambiguous. It may mean either of two things, which are quite dis- 

 tinct. In the case we have already spoken of, I understand by the 

 North Pole that point on the celestial sphere which is the center of the 

 system of concentric circles described by the circumpolar stars. The 

 other sense in which the North Pole is used is the terrestrial one; it 

 denotes that point on this earth which has been the goal of so many 

 expeditions, and to reach which has been the ambition of so many illus- 

 trious navigators. We have a general notion that the terrestrial North 

 liole lies in a desolate region of eternal ice, somewhat relieved by the 

 circumstance that for six months of the year the frozen prospect is 

 brightened by perpetual day, though on the other hand, during the 

 remaining six months of the year this region is the abode of perpetual 

 night. 



The North Pole is that hitherto unattainable point on our globe on 

 which, if an observer could take his station, he would find that the 



