REPORT OF THE SECRETARY 107 



confirmatory of real solar changes. The work went on in summer 

 months at Mount Wilson, with gradual improvements up to 1920. 



In the meantime Mr. H. H. Clayton, forecaster of the meteoro- 

 logical service of Argentina, had communicated evidence, at first by 

 letter and later in two Smithsonian publications (Effect of Short 

 Period Variations of Solar Radiation on the Earth's Atmosphere, 

 Smithsonian Miscellaneous Collections, Vol. 68, No. 3, 1917; and 

 Variation in Solar Radiation and the Weather, Smithsonian Mis- 

 cellaneous Collections, Vol. 71, No. 3, 1920), showing dependence of 

 the weather of various parts of the world on fluctuations • of solar 

 radiation. These indications he has now amplified and recently 

 elaborately published (H. H. Clayton, "World Weather," Macmillan 

 Co., New York, 1923). But even at the beginning, to one trained 

 by the late Secretary S. P. Langley to hope that some time some con- 

 nection would appear between solar and terrestrial changes, Mr. 

 Clayton's work was very interesting. 



At the writer's suggestion, Secretary Walcott approved the ex- 

 penditure of accrued interest from the Hodgkins Fund to undertake 

 all-year-round observations of solar variation in a cloudless climate. 

 The Great War hindered the expedition, but it went forward in 1918 

 to Calama, Chile, a station chosen on the advice and extensive manu- 

 script data furnished by Dr. Walter Knoche, formerly in charge of 

 the weather service of Chile. 



By that time Mr. Clayton's researches had led him to believe that 

 actual forecasts might advantageously be based on solar radiation 

 work. Accordingly, soon after the establishment of the Chile sta- 

 tion, arrangements were made to telegraph its results to Buenos 

 Aires, and a system of forecasting based thereon has actually been in 

 use in Argentina for several years. Some of its results are quoted in 

 the book of Mr. Clayton, just cited. 



The work almost immediately attracted the favorable attention 

 of Mr. John A. Roebling. By his advice and financial assistance, 

 the Mount Wilson work was transferred to a more cloudless locality 

 for all-year-round observing at Mount Harqua Hala, Ariz., and also 

 the Calama work was transferred to a higher station, Montezuma, 

 outside the dust and smoke of Calama and Chuquicamata, which 

 had been serious inconveniences. 



During these many years we had plodded on in hope of a satis- 

 fying fruition of our labors. Many signs there were that the solar 

 radiation varies sufficiently to be of importance in terrestrial con- 

 cerns. But they were of the nature of incompletely verified evi- 

 dences of various sorts, all pointing the same way, but none in itself 

 conclusive. With the continuous all-year-round occupation of the 

 two first-rate stations, made possible by Mr. Roebling's generosity, 



