The study of our own planet can hardly be said to belong to the realm of astronomy. Nevertheless, it is through astronomical observation that the motion of the North Pole has been discovered. For many years it has been a problem whether there is a variation of latitude resulting from the motion of the pole. Euler had declared, from theoretical investigation, that, were there such a motion, the period must be 10 months. The question was revived in 1885 by the observations of _Seth Carlo Chandler_ (born 1846) at Cambridge, Mass., with his newly-invented instrument, the “almucantar,” which indicated an appreciable variation of latitude. This was confirmed by _Friedrich Küstner_ (born 1856), now director of the Observatory at Bonn. The idea now occurred to Chandler to search through the older records to discover if there was any trace of the variation of latitude, with the result that he brought out a period of 14 months instead of 10. This aroused much interest, and many prominent astronomers denied Chandler’s results, which were announced in 1891. As a well-known astronomer has expressed it, “Euler’s work had shown what period the motion must have, and any appearance of another period must be due to some error in the observations. Chandler replied to the effect that he did not care for Euler’s mathematics: the observations plainly showed 14 months, and if Euler said 10, _he_ must have made the mistake. I do not exaggerate the situation in the least; it was a deadlock: Chandler and observation against the whole weight of observation and theory.” It was now shown by Newcomb that Euler had assumed the Earth to be an absolutely rigid body, while modern investigations show that it is not so. Chandler’s discovery is now accepted, and proves that the North Pole is not fixed in position, but has a small periodic motion, though never twelve yards from its mean position. That the small resulting variation in the position of the stars has been noticed at all is a striking illustration of the accuracy of astronomical observation.