CLIMATE OF HISTORIC TIMES 



545 



How far do the changes which have taken place in historic times agree 

 with those which now take place during the sun-spot cycle? In the 

 second place, Is there any reason to think that the activity of sun-spots 

 may have varied more in the past than at present ? In answering these 

 questions we shall confine ourselves to the United States and Europe, 

 with only brief consideration of western Asia, since these are the only 

 regions where sufficient data have as yet been worked up. 



i 



Over -f- 28 per cent. 

 •y to + 28 per cent. 

 to —14 per cent. 

 Less than —14 per cent. 



iJi 



LEGEND 



The figures indicate the percentages by which 

 the average storminess of the years of 7naxi- 

 itiiim sun-spots exceeds or falls short of the 

 average storminess of the years of minimum 

 sun-spots. The mean storminess for 30 years 

 is taken as 100 per cent. 



Figure 16. — Comparative Storminess of Nine Years of Maximum Sun-spots and Twelve 

 Tears of Minimum Sun-spots in the United States in Percentages of mean Storminess 

 for Thirty Years. 



This diagram is the same as figure 7, except that it has been calculated in percentages, 

 and covers only the United States 



The United States. — The United States is probably the best of all 

 areas for the study of the problem now before us, for nowhere else is so 

 large a body of reliable and homogeneous observations easily available. 

 On the basis of the observations of the United States Weather Bureau, 

 the maps of figures 16 and 17 have been compiled. Figure 16 shows the 



