SUN'S HEAT ABBOT. 157 



scribed, not only in Australia but also in New Zealand. Later on, 

 within the last year or two, further inquiries have come from Austra- 

 lia in regard to the work and it may be possible that even yet this 

 kind of observing may be undertaken there. 



The writer felt that the regular observation of the solar radiation 

 at several first-class cloudless stations remote from one another in 

 different quarters of the world ought to be undertaken, now that the 

 variation of the sun in short irregular periods had been established. 

 This conviction was much strengthened by the painstaking work of 

 Mr. H. Helm Clayton, chief forecaster of the Argentine Weather 

 Service, who about 1914 began to discuss all the measurements made 

 at Mount Wilson with a view to determine if the apparent changes in 

 the sun appeared to be correlated with the climatic conditions of 

 Argentina and other parts of the world. His computations from the 

 first seemed to point to interesting correlations, so that the desirability 

 of making a better groundwork of " solar constant " observations for 

 the use of meteorologists was strongly indicated. 



SOUTH AMERICAN EXPEDITION. 



In 1917, Secretary Walcott, of the Smithsonian Institution, decided 

 to employ a part of the income of the Hodgkins fund, which had been 

 bequeathed to the Smithsonian Institution for the advancement of 

 knowledge of atmospheric air, to promote these "solar constant" 

 studies. The entrance of the United States into the war prevented the 

 sending of an expedition immediately to South America as had been 

 expected, and it was temporarily located at Hump Mountain in North 

 Carolina. Here under the charge of Mr. A. F. Moore, assisted by Mr. 

 L. H. Abbot, the measurements were made from June, 1917, to March, 

 1918. On one occasion observations were carried through successfully 

 with an average air temperature of— 5° F. Mr. Abbot froze fingers 

 and feet in making the pyrheliometric observations on this occasion. 

 The results of this day of work did not, however, differ from those 

 obtained under more comfortable auspices, but still further widened 

 the variety of circumstances which seem to have no influence on the 

 accuracy of the results. 



In March, 1918, the expedition was removed to Calama, Chile, on 

 the farther edge of the Atacama nitrate desert. Here it was hoped to 

 obtain cloudlessness equal to any which could be found in the whole 

 world. The rainfall in that region is almost nil. Calama, a city of 

 several thousand inhabitants, is situated on the bank of the River Loa, 

 about 10 miles from Chuquicamata where the Guggenheim Co. has a 

 great copper mine, and where is collected a colony of several hundred 

 Americans engaged in the mining operations, in addition to the 10,000 

 or more Chileans and Bolivians employed there. The officials of the 



