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THE POPULAR SCIENCE MONTHLY.

present positions as far as they were moved forward in our second diagram. The result is a figure having no resemblance to either of the others. It is a sort of cross, with Beta at the point of intersection, Alpha marking the extremity of the left arm, and Gamma that of the right; Beta the top, Epsilon, Zeta, and Eta, the stem. Eta was, properly speaking, not yet in association with the other six. For the rest, on analyzing the movement of these stars, we see that five of them, Beta, Gamma, Delta, Epsilon, and Zeta, are associated together by a common tie. They are a group of friends: they move on with one accord, and, as will be seen, maintain the same relative position to one another. Alpha and Eta are only intruders, and, though they happen just at present to be with the group, they really have nothing to do with it. Look at Fig. 2: Alpha, which is evermoving toward the right, will, in time, quit the group for good. On the other hand, Fig. 3 shows Eta coming in on the left; previously that star had no relation at all to the five.

Fig. 3.
PSM V04 D308 Ursa major 100K years ago.jpg
Ursa Major 100,000 Years ago.

The remarks just made with regard to the secular transformation of Ursa Major might be applied to all the other constellations. We have selected that one, because it is the best known of all, and one of the most characteristic. To sum up: we find that a knowledge of the proper movements of the stars completely transforms our common notions about the fixity of the heavens. The stars move in all directions through the endless realms of space, and as the aspect of the heavens changes, so does the constitution of the universe also change from age to age, undergoing innumerable metamorphoses.—Revue Scientifique