[Footnote 107: J. Barrell: The Origin of the Earth, in Evolution of the Earth and Its Inhabitants, 1918, p. 44, and more fully in an unpublished manuscript.] [Footnote 108: F. W. Clarke: Data of Geochemistry, Fourth Ed., 1920, Bull. No. 695, U. S. Geol. Survey, p. 256.] [Footnote 109: F. W. Clarke: _loc. cit._, pp. 27-34 et al.] [Footnote C: Chas. E. St. John: Science Service Press Reports from the Mt. Wilson Observatory, May, 1922.] [Footnote 110: Abbot and Fowle: Annals Astrophysical Observatory; Smiths. Inst., Vol. II, 1908, p. 163. F. E. Fowle: Atmospheric Scattering of Light; Misc. Coll. Smiths. Inst., Vol. 69, 1918.] [Footnote 111: Abbot and Fowle: _loc. cit._, p. 172.] CHAPTER XIV THE EFFECT OF OTHER BODIES ON THE SUN If solar activity is really an important factor in causing climatic changes, it behooves us to subject the sun to the same kind of inquiry to which we have subjected the earth. We have inquired into the nature of the changes through which the earth's crust, the oceans, and the atmosphere have influenced the climate of geological times. It has not been necessary, however, to study the origin of the earth, nor to trace its earlier stages. Our study of the geological record begins only when the earth had attained practically its present mass, essentially its present shape, and a climate so similar to that of today that life as we know it was possible. In other words, the earth had passed the stages of infancy, childhood, youth, and early maturity, and had reached full maturity. As it still seems to be indefinitely far from old age, we infer that during geological times its relative changes have been no greater than those which a man experiences between the ages of perhaps twenty-five and forty. Similar reasoning applies with equal or greater force to the sun. Because of its vast size it presumably passes through its stages of development much more slowly than the earth. In the first chapter of this book we saw that the earth's relative uniformity of climate for hundreds of millions of years seems to imply a similar uniformity in solar activity. This accords with a recent tendency among astronomers who are more and more recognizing that the stars and the solar system possess an extraordinary degree of conservatism. Changes that once were supposed to take place in thousands of years are now thought to have required millions. Hence in this chapter we shall assume that throughout geological times the condition of the sun has been almost as at present. It may have been somewhat larger, or different in other ways, but it was essentially a hot, gaseous body such as we see today and it gave out essentially the same amount of energy. This assumption will affect the general validity of what follows only if it departs widely from the truth. With this assumption, then, let us inquire into the degree to which the sun's atmosphere has probably been disturbed throughout geological times.