HISTOKICAL NOTK'KS. 21 



icy pull over Llm .l^coIo^'v (•(' tin' liitor tcrtiiiry jtoriodH, is 

 fiist lucltiiii^' away Itcfort! tlu; Hiiiisliinc of tiiitli." 



l'('rlia])s 1 was a little too Haiij^niiiir as to the rapidity 

 (if the )»ro('i!ss, and did not iiiako allowance I'oi' that, 

 chilling current, (»f jiopnlar texL-l>ooks and otlicial 

 intlnence winch has so much retarded the final nudt,iii<i; of 

 the threat continental ^-lacier and the ])iilar ic(! cap. 



Tho followinjj; citations, however, from \ery recent 

 puhlications show thai my forecast of the course of (»]>iin(»n 

 was not altogether wroiiu, and that we may hope foi' .still 

 hetter thin;.f.s in tlm futuie. 



Sir llohert Uall's recent att(Mn)»t to rehahilitiite ('roll's 

 ingenious astronomical theory of the glacial a<i;e will not 

 a.ssist to restore it.s waninj^ fortunes, hut hrin^s out the 

 fact that this in,i,'enious theory was essentially defective.* 

 He shows that (.'roll reasoned on ii mistaken assumjjtifJii 

 that the earth receives e([ual amounts of heat when in 

 periludion and a])helion ])as8ai,'e, whereas the dill'erence is 

 as much as 2G ])er cent., and consequently at lonj^' 

 intervals there nii<fht occur ])erio(ls of ifreut coldness in 

 one lieniis])lune at a time. Tlu; interval of time, however, 

 is too lon,u', even on liall's theory, and the fact that the 

 ice of the glacial period radiated from points consider- 

 al)ly south of the i)<)lar circle, tells of tin; doniinaney of 

 terrestial conditions. This new astronomical theory will 

 therefore fail to all'ect gciological conclusions, and its weak 

 points have already heen ])ointed out hy geological 

 reasoners. It may, in short, he held to have given a 

 death hlow to the theory of astronomical causes of the 

 glacial ])eriod known to us in geology. 



In a recent paper, Mr. Warren Upham, one of the most 



* " The Cause of an Ice Age," London, 1892. 



