H 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 8l 



where A' = /? + 8 + ax 



[i is the absorption coefficient (kie to small particles, 

 8 is the absorption coefficient dne to large particles, 

 a is the absorption coefficient due to i cm. ozone ntp., 

 X is the thickness of ozone atmospheric in cm. ntp. 



Now it seems to the writer that the very variations with atmos- 

 pheric pressure which Dr. Dol)Son throws into x, belong fully as 



Fig. 10. 



legitimately, and very probably, to both ^ and 8. All this relates to 

 what Dr. Dobson calls his " long method," dependent upon several 

 observations during the day. In his second or " short method " he 

 uses the expression 



(log Jo-log I'o) - (log /-log r) - (13- ft') sec ^ 

 (a — a) sec ^ 



In the determinations by this " short method " he assumes that 8 

 does not vary with A and uses a value for ft obtained from the formula 



X- 



