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of rapid and minute scintillations. Inquiry in this direction, I think, has never been made; nor is an analysis necessary for our present purpose. For, if we regard the light either as the result of slow combustion, or catch the vivid flash of the electric spark in this reproduction (itself the product of decay), we are met by the same inexorable permanent law, that there is not a leaf that rots by the roadside, nor a spear of pale club-moss, that is not in itself a reservoir of recreative power throwing back its faint, pulsing light or its equivalent of heat into that quickening flood which the great heart of Nature sends down through the illimitable and unknown.

By W. J. McGEE.

THE recent publication in "The Popular Science Monthly" of a paper on "The Age of Ice," and its apparently favorable reception and republication elsewhere, prompt the writer to submit the following incomplete notice of a work in which the field barely entered by the author of that paper is most thoroughly and exhaustively examined.

In addition to a convenient abstract of the line of argument pursued, and a statement of some fundamental principles of geology, it is pointed out in an introductory chapter that the earlier theories framed to account for climatal variations during the geological æons are utterly inadequate; that the earth could not pass through hotter or colder portions of space without seriously deranging the mechanism of the solar system; that a diminution of heat from this or any other cause could never inaugurate a glacial epoch; that considerable changes in the obliquity of the ecliptic have never occurred, and could not have caused glacial periods if they had; and, finally, here as well as in a more recently published paper,[2] which may be considered as supplementary to this chapter, that material changes in the position of the terrestrial axis can never have taken place: in short, he shows, by bringing together the independent results arrived at by eminent geologists, physicists, and mathematicians, that the various cataclysmic theories of geological climate are alike untenable. Telluric causes being thus shown to be incompetent, no alternative remains but to

  1. Climate and Time in their Geological Relations: A Theory of Secular Changes of the Earth's Climate. By James Croll, LL.D., F.R.S., etc., of Her Majesty's Geological Survey of Scotland. American edition, 12mo, pp. xvi.-577, with Plates. New York: D. Appleton & Co., 1875.
  2. "Geological Magazine," September, 1878.