80 REPORT OF THE SECRETARY. 



description of the apparatus and methods employed for the various kinds of 

 research, and the sources and magnitude of the errors attending their use. 



The work thus summarized seems definitely to fix the approximate average 

 value of the intensity of solar radiation at about 2.1 calories per square 

 centimeter per minute, and to show decisively that there is a marked fluctuation 

 about this mean value, sufficient in magnitude to influence very perceptibly the 

 climate, at least of inland stations, upon the earth. This being so, there is 

 good reason for making the series of measurements of solar radiation as com- 

 plete and continuous as possible for some years to come, in order to determine 

 more thoroughly the causes and limits of the solar changes, and their precise 

 effects upon climate. The former part of the study will involve further solar 

 measurements, and the latter part a more complete study of meteorological 

 records in connection with the solar measurements. Thus far no other observa- 

 tory has been so well equipped as this one for the special kinds of measurement 

 involved, and it will naturally be our task for some time to come to continue 

 the work along the lines stated. 



Respectfully submitted. 



C. G. Abbot, 

 Director of the Astrophysical Observatory. 



Dr. Ohables D. Waxcott, 



Secretary of the Smithsonian Institution. 



