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 produce a diminution of the distance between the Pole and Greenwich, that is to say, there must be an increase in the distance from Greenwich to the Equator. This corresponds to a change in the latitude of Greenwich; in fact it would diminish by three-tenths of a second, which is a magnitude quite large enough to be recognisable by the observations I have already indicated as proper for the determination of latitude. A shift of the Pole to a distance of sixty feet would be a conspicuous alteration announced in every observatory in Europe provided with instruments of good modern construction.

Until the last few years there was not much reason to think that the Pole exhibited any unequivocal indications of movement. No doubt, displacements resembling those which have now been definitely ascertained have existed for many years, but they were too small to produce any appreciable effect, except on instruments of a more refined description than those with which the earlier observatories were equipped. It was obvious that the Pole did not make movements of anything like a hundred yards in extent; had it done so the resulting variations in latitude would have been conspicuous enough to have obtained notice many years ago. The actual movements which the Pole does make are of that small character which require very minute discussion of the observations to establish them beyond reach of cavil. There is, however, one striking method of confirming such observations as have been made which leaves no doubt of the accuracy of the results to which they point.

If the observatories in Europe indicated at a certain time that their latitudes had all increased; this would imply that the Equator had receded from them, and