4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



for I cm. ozone as obtained in the lalioratory by Colange.' The 

 agreement is remarkable. The layer of ozone used by Colange was 

 1 8 cm. ntp., and from this the above curve was computed for 

 I cm. ntp., by Bouguer's formula. 



The same authors," using a somewhat similar process, later utilized 

 published observations, made by Smithsonian observers at their various 

 stations, for further determinations of the ozone above these stations. 

 These data had not been corrected for water vapor; also the values 

 were taken from somewhat smoothed curves drawn through the 

 plotted observed points. Further, because of gradually progressive 

 changes in the transparency of the sky, comparatively few days furnish 

 observations which are good enough for the above treatment. On 

 these several accounts the investigation just cited is not fully satis- 

 factory. In the following discussion only the original observations 

 are used and they are treated by a method probably nearly independent 

 of sky changes. 



The results presently to be considered are to a considerable extent 

 a by-product of spectro-bolometric observations originally made for 

 the determination of the radiation emitted from the sun. X'alues 

 from about i,ooo days have been utilized. In the ordinary reductions 

 of this work, the ordinates of the solar energy curves (generally 

 6 curves per day) obtained with a 6o° u. v. glass prism had already 

 been read for about half of the days used. It has been the custom 

 to read them on our plates at abscissae, among others, of i8, 20, 22, 

 24, 26, 28, and 30 cm. towards the violet from the infra-red band, wi, 

 at 2/t. These places correspond to wave-lengths of 0.764, 0.686, 0.624, 

 0.574, 0.535, 0.503, and 0.475/i., respectively- This spectrum region 

 includes the yellow Chappuis band due to ozone. 



A preliminary futile attempt was made to use these ordinates to 

 determine directly the depth of the ozone band. The liand is masked 

 by the numerous solar lines in that part of the spectrum. Indeed 

 Fabry says : " The Chappuis bands have never been observed directly 

 in the solar spectrum. I have often looked for them in the spectrum 

 of the setting sun, but have never found them." 



However, if the several observations of any day, made at each 

 place in the spectrum at different zenith distances, are used to deter- 

 mine atmospheric transmission coefficients, and the resulting values are 

 plotted against the corresponding deviations, the band is strongly 



' Journ. de Phys. et le Rad. 8, 257, 1927. 



' Journ. de Phys. et le Rad. 7, 257, 1926; 8, 353, 1927. 



