Page:In the high heavens.djvu/70

 qualification. Complete examination of this subject is desirable, not only on account of its natural importance, but also because it illustrates the refinements of which modern astronomical processes are susceptible.

I have stated that the position of the terrestrial Pole undergoes no large or considerable fluctuation. But while we admit that no large fluctuation is possible, it is proper to consider whether there may not be a small fluctuation. It is certain that the position of the Pole as it would be marked by a post driven into the earth to-day cannot differ by a mile from the position in which the same point would be marked last year or next year. But does it differ at all? Is it absolutely exactly the same? Would there be a difference not indeed of miles but of yards or of feet between the precise position of the Pole on the earth determined at successive intervals of time? Would it be the same if we carried out our comparisons not merely between one year and another, but day after day, week after week, month after month? No doubt the more obvious phenomena proclaim in the most unmistakable manner that the position of the Pole is substantially invariable. If, therefore, there be any fluctuations in its position, these can only be disclosed by careful scrutiny of minute phenomena which are too delicate to be detected by the coarser methods of observation. There is indeed a certain presumption in favour of the notion that absolute constancy in the position of the Pole need not be expected. Almost every statement of astronomical doctrine requires its qualification, and it would seem indeed unlikely that when sufficient refinement was introduced into the measurements the position of the Pole in the earth should appear to be absolutely unalterable.