NO. 30 SMITHSONIAN EXPLORATIONS, IQI2 7 
establish this point. Hence, it was thought best to return to Algeria 
in 1912 for further data. 
In this expedition Mr. Abbot was assisted in Algeria by Mr. Anders 
Knutson Angstrom, of Upsala, Sweden. 
The observations made by the Smithsonian party in Algeria in 
1912 were on the whole very satisfactory. They occupied 64 days, 
and on more than 50 of these days Mr. F. E. Fowle made similar 
Fic. 15.—River scene at M’Sila, Algeria, an oasis of the Sahara. 
Photograph by Abbot. 
observations on Mt. Wilson, in California. Much volcanic dust from 
the eruption of Mt. Katmai in Alaska, June 6 and 7, I912, was 
diffused in the upper atmosphere, and greatly reduced the intensity 
of solar radiation observed at both stations. Many otherwise ex- 
cellent days were spoiled by it. However, it did not prove fatal to the 
success of the expedition. 
The results of the work of 1911 and 1912 thoroughly establish the 
supposed variability of the sun. 
