Pagina:Scientia - Vol. VIII.djvu/42
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principal results arrived at. One of the two streams is moving (relatively to the sun) towards the point E. A. 93° Dec. -7°; this is generally called Stream I. The other, Stream II, is moving towards E. A. 246° Dec. -64°. The velocity of Stream 1 is to that of Stream II in the ratio 3:2; the actual velocities are in fact about 40 and 26 kilometres per second. It will be noticed that the two streams are proceeding in widely diverging directions, being inclined at about 110° to one another; but this angle entirely depends on the point of reference (in this case the sun) to which the relative motions are referred. Looked at from some other star the angle would be altered, so that from the cosmical standpoint the apparent inclination of the two streams has no particular significance. The stars appear to be fairly equally divided between the two streams, a result which holds not only when all the stars are considered together, but for the different parts of the sky separately. Moreover the mean distances of the stars of the two streams from the sun are everywhere nearly equal. This means that the streams completely interpenetrate one another. It is as though two systems of stars were passing through the same part of space entirely ignoring the presence of one another. It is important to grasp this very essential part of the theory because several attempts to explain the phenomenon have broken down at this point. A rotating motion of the stellar universe seen from an eccentric point would perhaps account for two streams, the one passing behind the other; but it does not explain the two streams permeating each other. As regards the number of stars coming within the scope of this theory, we have of course no knowledge of the motions of the many millions of faint stars visible in the great telescopes: but, so far as can be learnt from the samples available, the stars down to the ninth magnitude and even fainter appear to conform to this arrangement. We may estimate that each stream has at least a quarter of a million members.
We may regard the two streams as two independent systems of stars travelling through space, and at the present time passing through one another, perhaps brought together by their mutual attraction; or it may be possible to explain
- The numerical results adopted in this paragraph have generally been taken from Prof. Dyson’s papers.