Comets and Problems of Cosmogony


    THE presidential address at the British Astronomical Association was delivered on October 27 by the Rev. Dr. M. Davidson. He discussed comets, especially in connexion with the light that they throw on problems of cosmogony. Considering that comets move in orbits of such a diverse nature, direct and retrograde orbits being nearly equal in number, taking comets on the whole, he showed that there are difficulties in reconciling this fact with the tidal theory of the origin of the solar system. He referred to the families of comets which are associated with the major planets, stating that it is quite impossible to explain these on the capture theory. There is, he considers, some basis for the view that they were expelled by the planets, though there are certain objections here also. Various theories for the origin of both the short-period and long-period comets were dealt with in turn ; but, Dr. Davidson pointed out, none of these can be considered satisfactory. Bobrovinokoff's conjecture that the sun captured comets when it was passing through diffuse clouds of obscuring matter less than a million years ago would appear to be mere speculation, and great difficulties arise when we inquire how bodies of such diverse sizes as are found in the nuclei of comets should appear in diffuse clouds of obscuring matter. The whole subject is full of difficulties, and Dr. Davidson contented himself with expressing the hope that posterity would be able to solve the problem. At the close of his address, he presented the Walter Goodacre Gold Medal and Gift to Dr. A. C. D. Crommelin, whom the Council selected this year for this award, in consideration of the very valuable work that he has done for the Association, more especially in connexion with comets and minor planets, on which he is a recognized authority.

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    Comets and Problems of Cosmogony. Nature 140, 799–800 (1937).

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