Imagine that your eye was placed at the centre of the earth, and that you had a long slender tube from that centre to the surface through which you could look out at the celestial sphere; if that tube be placed in such a way that, when looking from the centre of the earth through this tube your vision was directed exactly to that particular point of the heavens which is the centre of the circle now described by the Pole Star and the other circumpolar stars, then that spot in which the end of the tube passes out through the surface of the earth is the North Pole. Imagine a stake to be driven into the earth at the place named, then the position of that stake is the critical spot on our globe which has been the object of so much scientific investigation and of so much maritime enterprise.
The reader must not think that I am attempting to be hyper-accurate in this definition of the North Pole; no doubt, in our ordinary language we often think of the Pole as something synonymous with the polar regions, an ill-defined and vaguely known wilderness of ice. For scientific purposes it is, however, essential to understand that the Pole is a very definitely marked point, and we must assign its position accurately, not merely within miles, but even within feet. Indeed, it is a truly extraordinary circumstance that, considering that no one, with the possible exception just referred to, has ever yet been within so many hundreds of miles of the Pole, we should be able to locate it so precisely that we are absolutely certain of its position to within an area not larger than that covered by a good-sized church.
We have seen that the North Pole in the sky is in incessant movement, and that the journeys which it
