ACTUAL MIGRATIONS OF THE POLES 



899 



either to prove or disprove these theories, before the discussion of 

 causes need be undertaken. 



Dctcnuincd Migrations of tlir Poles. 



That the poles, i. c, the points of intersection between the 

 earth's axis of rotation and the surface of the earth, are not 

 actually fixed, but wander about within small limits, was first 

 recognized toward the end of the nineteenth century. From thou- 

 sands of careful observations on latitude made in recent years in 



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Fig. 248. J\Iap showing the ascertained migration of the North Pole from 

 1892 to 1894 (after Mihie) ; the figures indicate the number of 

 large earthquakes in each period. 



Europe and America this wandering has been determined to lie 

 within a circle 40 or 50 feet in diameter. It has a curiously ir- 

 regular, but somewhat spiral path, and completes its erratic circuit 

 in about 428 days. The path described by the North Pole between 

 the years 1892 and 1894 is shown in the above map by Milne, 

 in which each year is divided into ten parts. (Fig. 248.) The 

 figures show the number of earthquakes which occurred in each 

 period, the largest of them, as John Milne has pointed out, coin- 

 ciding with the sharpest curvature in the path of the pole. As 

 Milne suggests, both the abrupt curvature and the sharp earthquake 



