Note 1657 — Chapter VI · (continued 2)

Of the manifold reasons which have been assigned for these great climatic changes (Lubbock, Prehistoric Times, 391, and Croll, Discussions, enumerates the principal reasons) there is at least some considerable credence given to the one of which James Croll has been the most prominent advocate, and which points to that reduction of the eccentricity of the earth’s orbit which in 22,000 years will be diminished from the present scale to one sixth of it, or to about half a million miles. This change in the eccentricity induces physical changes, which allow a greater or less volume of tropical water to flow north. In this way the once mild climate of Greenland is accounted for (Wallace’s Island Life). Croll first advanced his views in the Philosophical Mag., Aug., 1864; but he did not completely formulate his theory till in his Climate and time in their geological relations, a theory of secular changes of the earth’s climate (N. Y., 1875). It gained the acquiescence of Lyell and others; but a principal objector appeared in the astronomer Simon Newcomb (Amer. Jl. of Sci. and Arts, April, 1876; Jan., 1884; Philosoph. Mag., Feb., 1884). Croll answered in Remarks (London, 1884), but more fully in a further development of his views in his Discussions on Climate and Cosmology (N. Y., 1886). Whitney’s Climatic Changes argues on entirely different grounds.