140 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1936 



Yet siinspot activity apparently correlates with these terrestrial activ- 

 ities, and the source of the correlation must be sought in other solar 

 phenomena that are correlated in turn with sunspot activity. 



Among the solar phenomena which might possibly have an in- 

 fluence on things terrestrial are the intensity of the solar radiation 

 and the nature of the light which the sun sends earthward. Both 

 of these are found to correlate with sunspot activity. At the times 

 of sunspot maximum the earth's receipt of heat from the sun in- 

 creases over nomal and, when the sunspots are at a minimum, the 

 heat received is below normal. Surely this change in the receipt 

 of warmth by the earth should be noticeable. One would expect 

 that the increased receipt of heat would result in a generally higher 

 terrestrial temperature and a slackened heat input with a generally 

 lower terrestrial temperature, but this is not so. The relationship 

 is exactly the reverse, at least so far as accurate measurements of 

 temperature on the earth are available. The theory commonly 

 given to explain this apparent anomaly is as follows : Increased heat 

 radiation from the sun entails a higher degree of warmth of the earth. 

 High temperatures are, however, conducive of increased evapora- 

 tion from the water-covered areas of the earth with a resulting 

 higher water- vapor content of the earth's atmosphere. Inasmuch as 

 clouds are the results of the condensation of water vapor, its higher 

 percentage should result in the prevalence of clouds as well as in 

 increased rainfall. Both evaporation and rainfall are cooling 

 phenomena. The net result should be that, when the earth is receiv- 

 ing the greatest amount of heat from the sun, svirface temperatures 

 on the earth would be below normal. When the earth's receipt of 

 heat from the sun is at a minimum, the terrestrial effects are the 

 reciprocal of those at sunspot maximum, and terrestrial tempera- 

 tures should be above normal, A number of correlations are sug- 

 gested by this line of reasoning. There should be a correlation be- 

 tween sunspots and the prevalence of clouds on the earth, such that 

 at sunspot maximum, cloudiness should be at a maximum too, while 

 at sunspot minimum, cloudiness should be at a minimum. At sun- 

 spot maximum, rainfall should be at a maximum, at sunspot mini- 

 mum, it should be at a minimum. Of course, it is necessary to inject 

 a word of caution, namely, that terrestrial weather, considered in 

 detail, is such an uncertain affair that to differentiate a strictly solar 

 effect from the multitude of terrestrial effects is not the easiest task 

 imaginable. 



The ideas of the last paragraph would seem to offer a clue to long- 

 range weather forecasting with a somewhat higher degree of validity 

 than that with which it is done in certain almanacs of wide circula- 

 tion. There does seem to be a general agreement among meteor- 



