526 e. huntington solar hypothesis of climatic changes 



The Climate of historic Times 

 general di8cvssi0x 



Having completed our survey of present climatic conditions, we are 

 prepared to consider the climate of the past. The first period to claim 

 attention is the few thousand years covered by written history. Strangely 

 enough, the conditions during this time are known with less accuracy 

 than are those of geological periods hundreds of times more remote. Yet 

 if pronounced changes have occurred since the days of the ancient Baby- 

 lonians and since the last of the post-Glacial stages, they are of great im- 

 portance not only because of their possible historic effects, but because 

 they bridge the gap between the little variations of climate which are 

 observable during a single lifetime and the great changes known as Gla- 

 cial epochs. Only by bridging the gap can we determine whether there 

 is any genetic relation between the great changes and the small. A full 

 discussion of the climate of historic times is not here advisable, for it has 

 been considered in detail in numerous other publications. Our most 

 profitable course would seem to be to consider first the general trend of 

 opinion and then to take up the chief objections to each of the main 

 hypotheses. 



THE TREND OF OPINION AS TO THE CLIMATE' OF THE PAST 



In the hot debate over this problem during the last decade or two the 

 ideas of sfeosrraphers seem to be sroins: throusrh much the same metamor- 

 ■ pilosis as nave tnose of seoiosrists in resrard to the climate of times far 

 aLiLccedont to tiie historic period. It is scarcelv necessarv to remind 

 e;ooi()a:iRts of tiie wav m which oninion has chansred in rearard to the cli- 

 mate of sreolosrical times. An admirable summarv of the subject may be 

 found in !Seliuchert\s naner on "Climates of Geolosric Times," which 

 forms The conciuclinsr nart of "The Climatic Factor." nublication 192 of 

 Ihe CnT7ioo-ie institution of Washinsfton. As everv ^eolosfist well knows, 

 at ihe dawn of sfeoJoorv people believed in climatic uniformity — that is, 

 it was snpDosed that since the completion of an orisrinal creative act there 

 liad been no important changes. This view quickly disappeared and was 

 sinx'rscded bv the hypothesis of progressive cooling and drying, an hy- 

 pothesis which had much to do with the develonment of the nebular 

 hypoth(»sis. and which has in turn been srreatly strensrthened by that hy- 

 iJULutjsis. The discovery of evidence of wide-spread continental glaciation, 

 however, necessitated a modification of this view, and succeeding years 

 have brought to light a constantly increasing number of glacial, or at 

 least cool, periods distributed throughout almost the whole of geological 



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