NO. 9 PERIODICITY IN SOLAR VARIATION AllBOT AND BOND 3 



standard calories per square centimeter per minute. We improved the 

 recording spectrobolometer of Langley so that in less than lo minutes 

 it could furnish an excellent record of the intensities of all wave lengths 

 in the solar spectrum from about 0.35 micron in the ultra-violet to 

 about 2.5 microns in the infra-red. We devised graphical methods 



196 



1 95 



192 



191 



1.90 



NOV. JAN. MCH. MAY JULY SEPT. NOV. JAN MCH. MAY JULY SEPT. 



1920 1921 1922 



Fig. 2. — Solar variation 1920-1922 showing great change in 1922. 



operated by instrumental appliances whereby we were able to compute 

 the intensity and distribution in the spectrum of the solar radiation as 

 it is outside the atmosphere, whenever we determined the intensity and 

 distribution of it as it reached the surface observatory at different solar 

 altitudes. We devised an instrument for measuring the brightness 



