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on a pole of the earth, with a flagstaff fastened in the ground, we should be carried round the flagstaff by the earth's rotation once in twenty-four hours. We should become aware of the motion by seeing the sun and stars apparently moving in the opposite direction in horizontal circles by virtue of the diurnal motion. Now, the great discovery of the variation of latitude is this: The point in which the axis of rotation intersects the surface is not fixed, but moves around in a somewhat variable and irregular curve, contained within a circle nearly sixty feet in diameter. That is to say, if standing at the north pole we should observe its position day by day, we should find it moving one, two, or three inches every day, describing in the course of time a curve around one central point, from which it would sometimes be farther away and sometimes nearer. It would make a complete revolution in this irregular way in about fourteen months.

Since we have never been at the pole, the question may arise: How is this known? The answer is that by astronomical observations we can, on any night, determine the exact angle between the plumb line at the place where we stand and the axis on which the earth is rotating on that particular day. Four or five stations for making these observations were established around the earth in 1900 by the International Geodetic Association. One of these stations is near Gaithersburg, Md., another is on the Pacific coast, a third is in Japan, and a fourth in Italy. Before these were established observations having the same object were made in various parts of Europe and America. The two most important stations