334 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 52 



the atmosphere, the determination of the correction to be appHed to 

 eHminate the loss by absorption becomes the most important and, at 

 the same time, the most difficult part of this investigation. It is in 

 this connection that the transparency and the uniformity of the at- 

 mosphere on Mount Wilson have proved to be so great an advantage 

 in the work of the Smithsonian expeditions. The results already 

 obtained by Mr. Abbot show^ that the heat radiation of the Sun 

 ranges in value from 1.93 to 2.14 calories per square centimeter per 

 minute, and seem to indicate a real variability outside of the Earth's 

 atmosphere. 



Nevircomb. in his recent paper on "A Search for Fluctuations in the 

 Sun's Thermal Radiation through their Influence on Terrestrial 

 Temperature," is inclined to believe that such apparent variability 

 must be due to changes in the absorption of our atmosphere, rather 

 than in the heat radiation of the Sun. He was led to this conclusion 

 by the fact that short-period temperature changes, such as would 

 result from a change in the Sun's heat, are not shown to exist in an 

 extensive examination of the Earth's mean temperature as recorded 

 during a period of 34 years at 13 stations. Langley and Abbot, on 

 the contrary, maintain that the method employed in their observa- 

 tions eliminates the effect of atmospheric absorption so completely 

 that the observed variations must be due to changes within the Sun. 

 The fact that the thermometer records employed by Newcomb were 

 all made at seacoast stations, where the steadying effect of the ocean 

 might tend to eliminate short period fluctuations, leads Abbot to 

 doubt the validity of Newcomb's conclusions. His method having 

 proved capable of showing the small progressive differences in the 

 solar heat due to the change in the Earth's distance from the Sun 

 during the period of observation, he sees no reason to dispute the 

 solar origin of the larger differences. Since variations in the Sun's 

 heat radiation could not fail to be accompanied by changes in other 

 solar phenomena, investigations on the nature of these phenomena, 

 and on their relationship to the so-called "solar constant," may yield 

 reliable information as to the origin of such differences as Abbot 

 has observed. The possibility of predicting variations in the mean 

 temperature of the Earth caused by the influence of the Sun must 

 depend upon the acquirement of much more complete knowledge 

 than we now possess of the solar constitution. We thus perceive the 

 intimate connection which unites the work of the Smithsonian As- 

 trophysical Observatory with that of the Mount Wilson Solar Ob- 

 servatory, and recognize the importance, from this standpoint, of 

 continuing and greatly extending solar research in all its phases. 



