552 E. HUNTINGTON SOLAR HYPOTHESIS OF CLIMATIC CHANGES 



of the trees of California as given in figure 14. There it will be seen that 

 the fourteenth century was a period of peculiarly rapid growth. It was 

 the last great epoch when the growth of the trees approximated that of 

 earlier centuries, such as the periods centering about 1000 A. D. and at 

 the time of Christ. The high position of the curve in the middle of the 

 fourteenth century is the condition which we should naturally expect at 

 a time of many sun-spots. In this respect it agrees exactly with the con- 

 ditions in Europe. 



The Probability of geeat Changes in Sun-spots in the Past 



PETTER880N'8 SUN-SPOT HYPOTHESIS 



The importance of the data collected by Pettersson is not yet exhausted. 

 He definitely connects sun-spots with the climatic vicissitudes which he 

 describes : 



"In Europe the sun-spots were discovered as recently as in 1610, but in China 

 they were observed 1,500 years earlier, and are recorded in Chinese annals 

 from the first century. In these Chinese records, of course, only such years as 

 were marked by a great number of spots are registered; and it is remarkable 

 that those years occur in groups with long intervals, and that certain centuries 

 are noted by an unusual frequency of spots. Thus in the fourteenth century 

 the years from 1370 to 1385 are noted for sun-spot maxima. So long a period 

 of maxima had not occurred since the end of the fourth century, and Wolf 

 therefore considers that an absolute maximum of spots occurred about 1372." 



The importance of Pettersson's connection of sun-spots with changes 

 of climate scarcely needs to be pointed out. It is completely in accord 

 with what we should expect. The agreement with expectation pertains 

 even to details. For example, the curve of the storm frequency in the 

 main area of northward shifting in North America (figure 9) led us to 

 suspect that the apparently connected phenomena of the sun and the earth 

 reach their maxima at slightly different times. We concluded, it will be 

 remembered, that the conditions look as if a certain force sets the atmos- 

 pheres of both the earth and the sun in motion at the same time, but 

 that the earth^s atmosphere reaches its maximum activity sooner than 

 that of the sun and falls into quiescence sooner. The fact that the Cali- 

 fornia curve reaches its maximum a few decades earlier than the date 

 assigned by Wolf for the absolute maximum of sun-spots harmonizes with 

 this idea. I do not lay much stress on- this, however, partly because we 

 are as yet so totally in the dark as to the real cause of both sun-spots and 

 storms and partly because of the considerations advanced in the next 

 paragraph. 



