THE SOLAR HYPOTHESIS. 253 



ation in the eleven-year cycle is quite sufficient to cause appreciable meteorological results, 

 though the effect of either extreme is largely neutralized by a speedy change to the other. 

 Finally, the great objection to the solar hypothesis has been that while abundant 

 indications of an eleven-year cUmatic cycle have been found, it has rarely been possible 

 to point to specific terrestrial phenomena as the result of specific solar phenomena. The 

 work of Arctowski, Abbott, Fowle, and Humphreys supplies this deficiencj^ and suggests 

 that the constantly varying conditions of the earth's surface may induce a given solar 

 variation to produce its chief effect sometimes at one point and sometimes at anothei', 

 or that the obstructive action of volcanic dust may shut out solar radiation for a time in 

 certain areas or even in all parts of the world. Moreover, effects which appear to be due 

 to solar variation seem to be transmitted in the foim of waves or by means of winds and 

 currents and thus may not reach a given point until after a delay of more or less duration. 

 All things considered, the solar hypothesis seems to fit the facts better than anj^ other, 

 so far as the changes of climate indicated by our tree curves are concerned. The theories 

 of precession, elevation, and carbon dioxide seem too slow and ponderous to account for 

 changes which last only 1,000 years or less and are geologically very rapid and small. 

 On the other hand, from the standpoint of man's history, a change whose duration is 1,000 

 years is relatively slow and important, and is probably too large to be due to purely 

 terrestrial causes, such as accidental perturbations in the atmosphere. Volcanic activity, 

 on the other hand, may vary either in long or short intervals, and thus meets all the 

 requirements in this respect, but the actual curves which record its variations fail to 

 show any marked agreement with the general course of cUmatic phenomena, although 

 they show marked agreement at selected periods. The sun, however, seems to meet 

 all the requirements. It is known to vary on a small scale, it is certainly adequate to 

 produce the observed effects, and there is no reason why its variations should not in the 

 past have been on a larger scale than at present. Wliether the sun could vary sufficiently 

 to produce all the climatic variations of geological times, and whether it was the only cause 

 of those variations, is another question, which will be discussed in the next chapter. 



NOTE. 



The completion of the new work of Professor KuUmer mentioned on p. 205 furnishes strong 

 confirmation of the conclusious reached in this chapter. In an address before the Association 

 of American Geographers at Princeton, January 1, 1914, he has shown that in the belt of the 

 northern United States and southern Canada where storms on the average are most numerous, 

 the number of storms varies almost directly in harmony with the number of sun-spots, just as is 

 the case witli tropical hurricanes. In other areas, however, the reverse appears to be true, and 

 there is a decrease in storminess. The general conclusion seems to be that when sun-spots are 

 few in number cyclonic storms move in a great variety of tracks, but when spots are numerous 

 the storms tend to confine themselves to a few well-defined tracks, so that storminess is more or 

 less restricted to certain areas within which it is highly concentrated. Under such conditions it 

 is possible for pronounced climatic changes to occur witli only a minimum variation in the mean 

 temperature of the earth as a whole. 



Kullmer's work has led the present author radically to revise the conclusions set forth in this 

 chapter. While the general conclusions are not changed they are greatly amplified, and thus 

 lead to a wholly new form of the solar hypothesis, and to a new conception of such phenomena as 

 the formation of loess during glacial periods, or the localization of glaciation during the Permian 

 era. These new conclusions are fully set forth in a paper entitled " The Cyclonic Solar Hypothesis 

 of Climatic Changes," which will probably appear in the Bulletin of the Geological Society of 

 America during 1914. 



