MENTAL EVOLUTION 129 



remember, however, that a considerable body of thoughtful 

 investigators do not yet accept the view here presented. 



One of the most firmly established of all facts about the earth 

 and the sun is that when the sun is especially active, as indicated 

 by sunspots, the average temperature of the earth is lower than 

 usual. This conclusion is based chiefly on the work of Koppen, 

 who tabulated the results of over twenty million meteorological 

 observations covering all available parts of the earth and dis- 

 tributed through a century. With it must be coupled another 

 fact. Although the sun as a whole probably changes its tem- 

 perature very slowly, the temperature of the surface may change 

 rapidly. Superheated gases appear to be shot up from below, 

 much as the earth pours out lavas. Thus the amount of heat 

 received by the earth changes constantly. Abbot's measurements 

 show that when sunspots are numerous the sun gives out more 

 than the usual amount of heat. Thus we have the strange anomaly 

 of a hotter sun and a cooler earth. 



How is this possible.'* The answer is apparently found in the 

 movements of the earth's atmosphere. When the sun's surface 

 is disturbed by eruptions from below, some force, perhaps electri- 

 cal, causes the earth's atmosphere to be correspondingly dis- . 

 turbed. The terrestrial disturbances take the form of changes \ 

 of atmospheric pressure which give rise to stronger winds and 

 more intense storms. All storms are more or less cyclonic in 

 nature. That is, they may be compared with inverted whirlpools. 

 From every side the winds blow spirally inward toward the center 

 of the storm. In the center the air moves upward. The area of 

 the upward movement may have a diameter of only a few hundred 

 yards as in a summer dust-whirl, or of hundreds of miles as in an 

 ordinary storm. The rate of upward movement may be so rapid 

 that roofs are lifted bodily as in a tornado, or so gentle that it is 

 not noticed except through the cooling of the air. Everyone knows 

 that a warm wave commonly precedes a storm, especially in winter. 

 The wind blows from a southerly direction, and brings air from 



