2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



The longer wave-length portion of the Hartley band ( i) has been 

 used by Fabry and Buisson ' and others to measure the amount of 

 ozone in the atmosphere. On June /, 1920, they found an equivalent 

 layer of a little more than 3 mm. at normal temperature and pressure 

 (ntp). They estimated that at 0.2800/X the ozone absorption would 

 reduce the incident solar energy to lO"^'' of its entering value. Ozone, 

 therefore, by its absorption in this band, limits the solar spectrum 

 at its violet end as observable at the surface of the earth. Dr. 

 Dobson ^ uses this band for measures both of the amount and the 



Fig. I. — Atmosplieric absorption coefficients showing ozone band (Fowle). 



height of atmospheric ozone. He found a height of 30 to 40 km. 

 above sea-level. 



The Huggins band (2) was used by Cal^annes and Dufay ' for 

 measures of the altitude of the ozone layer by light reflected from 

 the zenith at the time of the setting sun. They foimd an altitude of 

 40 to 50 km. above the earth's surface. 



The Chappuis band (3) is used in the present research. The band 

 in the infra-red (4) is of importance because of its location at a 

 wave-length where otherwise the atmosphere would be nearly trans- 



^Journ. de Phys. 2, 197, 1921. 



' Proc. Roy. Soc. iioA, 660, 1926; 120A, 251. 1928. 



"Jonrn. de Phys. ct le Rad. 8, 125. 1927. 



