SMITHSONIAN EXPLORATIONS, I929 3 



little hindrance, a station was established near Calama in the nitrate 

 desert of Chile. Here the work (now conducted nearljy on Mount 

 Montezuma at 9,000 feet elevation) has been continued through nearly 

 80 per cent of the days ever since its establishment. This long Chilean 

 series of solar-radiation observations has no counterpart in the world 

 for length and continuity of observation. It confirms beyond question 

 the variation of the sun. As the accuracy of the work has grown, the 

 range of variation formerly supposed solar has indeed diminished, 

 but still periodic changes of 1 1 years. 2 years, 14 and 1 1 months are 

 clearly shown, and irregular, short-interval changes also appear. 

 ■ Mr. H. H. Clayton, formerly chief forecaster of Argentina, has 

 made a very extensive study of the changes in weather which may be 

 associated w^ith these solar changes. He believes himself to have es- 

 tablished certain relations between weather and solar variation which 

 are capable of being used for forecasting purposes, and he now con- 

 ducts a private forecasting bureau. 



In 1920 another station for all the year was occupied on Mount 

 Harqua Hala in Arizona. In 1925 this station was removed to Table 

 Mountain in California, where the sun has been observed on 80 per 

 cent of days until now. The National Geographic Society, appreciat- 

 ing the world-wide interest and importance of measuring the life- 

 supporting solar rays, financed in 1925 the selection, equipment, and 

 continued occupation of a new station on Mount Brukkaros in South 

 West Africa. This station is still cooperating with the Smithsonian 

 stations in North and South America for the study of the variability 

 of the sun. 



It has become possible, as a result of the long study and experience 

 with this problem, to measure the sun's radiation as it is outside cur 

 atmosphere in free space with an accuracy better than half of one 

 per cent. Thus we are able to detect variations of one per cent and less 

 in the amount of solar energy available to warm the earth. The values 

 recently obtained range from 1.910 to 1.960 calories per square centi- 

 meter per minute. 



During the past year the three stations have cooperated as before. 

 Messrs. Hoover and Cireeley, having been three years in South 

 West Africa, have been relieved by Messrs. Sordahl and Froiland. 

 Mr. Butler has relieved Mr. Baughman in Chile, and Mr. Greeley is 

 returning to Table Alountain in California. By the generous assis- 

 tance of Mr. Roebling the continuance of the station in South West 

 Africa has been assured for the years 1930 and 1931, after which it 



