Is the Earth Shrinking?


FOR a quantitative discussion of the effects of secular cooling on the earth's crust, Mr. Birrell may be referred to a couple of papers by Dr. C. Davison and Sir George Darwin in the Philosophical Transactions of the Royal Society for 1887. He will find that though the speculative nature of the assumption is frankly confessed, yet the observed phenomena are shown to be consistent with the theory of contraction and secular cooling. On the whole, students of cosmogony (as opposed to geology), arguing to some extent from the analogy of other celestial bodies, are in agreement in accepting the hypothesis of secular cooling. A notable exception is Prof. F. R. Moulton, of Chicago. In conjunction with Prof. T. C. Chamberlin, he has developed a “planetesimal hypothesis”, according to which the earth was built up by a series of solid accretions. The hypotheses of secular cooling and initial high velocity of rotation for the earth have no place in his theory. For details Mr. Birrell may be referred to “The Tidal and other Problems” (Carnegie Institution of Washington, 1909).

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