Page:In the high heavens.djvu/67

 formerly occupied. We have here to deal with the case that arises not unfrequently in astronomy, in which a fact of broad general truth requires a minute degree of qualification; indeed, it is not too much to say that it is in this qualification of broad general truths that many of the greatest discoveries in physical science have consisted. And such is the case in the present instance. There is a broad general truth and there is the qualification of it. It is the qualification that constitutes the essential discovery which it is my object here to set forth.

Before doing so it will be necessary for me to lay down the broad general truth that the North Pole of the earth as it existed in the time of the Pharaohs appears to be practically the same as the North Pole of the earth now. It seems perfectly certain that at any time within the last 10,000 years the North Pole might have been found within a region on the earth's surface not larger than Hyde Park. Indeed, the limits might be drawn much more closely. It is quite possible that many an edifice in London occupies an area sufficiently great to cover the holes that would be made by all the posts that might be driven to mark the precise sites of the North Pole on the earth not only for the last 5,000 or 10,000 years, but probably for much longer periods. It is very likely that the North Pole at the time of the Glacial Epoch was practically indistinguishable from the North Pole now; in fact, the constancy, or I should, perhaps, rather say, the sensible constancy of the situation of this most critical point in our globe is one of the most astonishing facts in terrestrial physics.

Let us, then, assume this broad general fact of the permanency in the position of the North Pole, and deduce