8io THE POPULAR SCIENCE MONTHLY. 



of rapid and minute scintillations. Inquiry in this direction, I think, 

 has never been made; nor is an analysis necessary for our present pur- 

 pose. For, if we regard the light either as the result of slow combus- 

 tion, or catch the vivid flash of the electric spark in this reproduction 

 (itself the product of decay), we are met by the same inexorable per- 

 manent 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. 



CEOLL'S "CLIMATE AND TIME."* 



By W. J. McGEE. 



THE recent publication in " The Popular Science Monthly " of a 

 paper on " The Age of Ice," and its apparently favorable recep- 

 tion and republication elsewhere, prompt the writer to submit the 

 following incomplete notice of a work in which the field barely en- 

 tered by the author of that paper is most thoroughly and exhaustively 

 examined. 



In addition to a convenient abstract of the line of argument pur- 

 sued, 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 aeons 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,f which may be considered as supple- 

 mentary 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 ge- 

 ologists, physicists, and mathematicians, that the vai'ious cataclysmic 

 theories of geological climate are alike untenable. Telluric causes 

 being thus shown to be incompetent, no alternative remains but to 



* Climate and Time in their Geological Eelations : 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. xvL-S^I, with Plates. New York : 

 D. Appleton & Co., 1875. 



f "Geological Magazine," September, IS'/S. 



