334 



PAST CLIMATES AND CLIMAXES. 



McKcimum and minimum years, 1 610-1913. 



Nature of sun-spots. — ^Huntington (1914 : 2: 555) has briefly summarized the 

 evidence as to the nature of sun-spots, of which the following is a condensed 

 abstract. Recent studies seem to indicate that sun-spots are cyclonic vortices 

 somewhat of the nature of volcanoes and somewhat of the nature of cyclonic 

 storms. like both volcanoes and cyclones, the sun-spots appear to carry 

 material from lower to higher levels. It is thought by Hale and others that 

 the material carried out is cooled somewhat, and consequently acts as a cloud 

 and appears dark. Humphreys suggests that some solar radiation is actually 

 cut off in this way. Sun-spots also resemble cyclones in seeming to have a 

 spiral motion like that of the inblowing winds of our own storms. They 

 neither travel rapidly like cyclones, nor are they stationary like volcanoes, but 

 resemble both in being highly electric in quality. They also seem to be allied 

 to solar prominences, which may be roughly likened to clouds in our own 

 atmosphere, though such prominences may be more analogous to clouds of 

 volcanic dust. Like volcanoes and cyclonic storms, sun-spots appear to relate 

 only to the outer layer of the sun. Their activity varies in much the same 

 irregular way as that of cyclonic storms, as well as that of volcanoes. In 

 general, they are periodic, but the intervals may be longer or shorter. Finally, 

 there is some reason for thinking that, although the mean temperature of the 

 sun as a whole may remain unchanged, the activity of its surface as shown 

 in spots may vary as greatly as has the activity of volcanoes on the earth's 

 surface. 



Effects of sun-spots upon climate. — ^As already indicated, the effect of the 

 sun-spot cycle is felt ia temperature, rainfall, and cyclones. As Harm makes 

 clear (1908:356), the conclusions of investigators as to temperature and 

 rainfall are often contradictory, especially when different regions are compared. 

 In general, temperatures are higher during a sun-spot Tninim iiTn, and lower 

 during a sun-spot maximum, in spite of the fact that the solar constant is 

 higher during the maximum. This contradiction, as well as the contradictory 

 results as to rainfall, seems to be explained by Kullmer's theory of the shift 

 of the storm-track. According to this, it is the track of cyclonic areas which 



