Abstract
THE star-system best known to us is the Galactic system, which is bounded by the Milky Way. About two million such systems of stars can now be observed; they are known as extra-galactic nebulæ. A random collection of extra-galactic nebulæ seems at first to show a bewildering variety of size, shape, brightness, and constitution, but a scientific study soon reduces them to law and order. Rejecting all those which are not seen edge on, we find that by far the greater number of the remainder can be arranged in a single continuous sequence, beginning with spheres and ending with flat discs. Since the speed of rotation of a body increases as it shrinks, it seems likely that we may interpret this sequence of nebulæ as one of different stages of development or evolution. If this conjecture is sound, a nebula starting with little rotation at first and shrinking in size would gradually increase its speed of rotation as it shrank, and would move steadily along the sequence as it did so.
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Beyond the Milky Way*. Nature 128, 592–594 (1931). https://doi.org/10.1038/128592a0
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DOI: https://doi.org/10.1038/128592a0