WEATHER GOVERNED BY CHANGES IN THE 

 SUN'S RADIATION 



By C. G. Abbot 

 Secretary, Smithsonian Institution 



[With 1 plate] 



It is now nearly 20 years since the Smithsonian Institution began 

 to observe daily, whenever possible, the intensity of the rays of the 

 sun. The.se studies have been continued first at the city of Calama, 

 in northern Chile, and since 1920 by the generous aid of John A. 

 Roebling, at Montezuma, a mountain 9,000 feet high about 12 miles 

 south of Calama. Plate 1 shows the barren location at Montezuma. 

 Neither bird nor beast, shrub nor tree, grass nor desert plant, in- 

 sect nor creeping thing (except the ubiquitous house fly) can exist 

 in this waterless desert. The great naturalist Darwin, in his journal 

 entitled " The Voyage of the Beagle ", relates that he rode all day in 

 that Desert of Atacama seeing no live thing except some flies feast- 

 ing on the body of a dead mule. In such a place our observers de- 

 votedly measure and compute about 9 hours each day for a 3-year 

 period before being relieved. Water and provisions they must haul 

 by auto from Calama, 12 miles distant. 



Two other Smithsonian solar stations are in occupation. One is in 

 a still more desolate and remote location. Mount St. Katherine, 8,500 

 feet in elevation, 10 miles from the ancient monastery of St. Kath- 

 erine on Mount Sinai in Egypt. The other, at 7,500 feet elevation, 

 overlooks the Mojave Desert in California. But here trees, water 

 and easy accessibility relieve the lonely plight of the observers. 



At these desert mountain stations, where rain seldom falls, it is 

 possible to observe the sun through cloudless sky on upward of 

 75 percent of all days. The great majority of dwellers on low ground 

 and in the cities have never in their lives seen such blue, cloudless, 

 and limpid sky as these stations afford. They have been chosen after 

 much research, travel, and actual testing. For to measure the rays 

 of the sun in such a way as to be able to eliminate the losses its beam 

 suffers in passing through our atmosphere, so as to determine the real 

 emissive power of the sun, is a task of extreme difficulty, even under 

 ideal sky conditions, and is impossible otherwise. 



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