NO. 3 RADIATION OF THE ATMOSPHERE ANGSTROM J 



A further investigation of the problem seemed, however, neces- 

 sary. My special attention was directed to the influence of altitude 

 and the influence of the temperature conditions of the instrument 

 and of the atmosphere upon the radiation to the sky. For this 

 purpose the climatic and geographic conditions of California were 

 recommended as being suitable by Dr. Abbot. 



There is probably no country in the world where such great dif- 

 ferences in altitude are found so near one another as in Cali- 

 fornia. Not far from Yosemite Valley, in the mountain range of 

 Sierra Nevada, the highest peak in the United States, Mount Whit- 

 ney, raises its ragged top to 4,420 meters, and from there one can 

 look down into the lowest country in the world, the so-called 

 Death Valley — 200 meters below sea level. And further south, near 

 the Mexican frontier, there is the desert of the Salton Sea, of which 

 the lowest parts are below sea level; a desert guarded by mountain 

 ranges whose highest peaks attain about 3,500 meters in altitude. 

 In the summer the sky is almost always clear ; a month and more may 

 pass without a cloud being visible. It was evident that the geographi- 

 cal as well as the meteorological conditions of the country were very 

 favorable for the investigations I contemplated. 



On the advice of Dr. Abbot, I therefore drew up a detailed plan 

 for an expedition to California, which was submitted to the Smith- 

 sonian Institution, together with an application for a grant from 

 the Hodgkins Fund. The application was granted by the Institution, 

 to whose distinguished secretary, Dr. Charles D. Walcott, I am much 

 indebted for his great interest in the undertaking. The program for 

 the expedition was as follows: 



1. Preliminary observations at the top of Mount San Antonio 

 (3,000 m.) and at Claremont (125 m.) simultaneously (3 nights). 



2. Simultaneous observations at the top of Mount San Gorgonio 

 (3,500 m.) and at Indio in the Salton Sea Desert (o m.), (3 nights). 



3. Expedition to Mount Whitney. Here the observations were to 

 be extended to three stations at different altitudes, where simultane- 

 ous measurements should be made every clear night during a period 

 of about two weeks. The stations proposed were: Lone Pine, at 

 the foot of the mountain, at 1,200 m. altitude ; the summit of Mount 

 Whitney (4,420 m.) ; and an intermediate station on one of the 

 lower ridges that project on the eastern side of the mountain. Dur- 

 ing this part of the expedition, as well as during the preliminary 

 ones, the observations were to be made once an hour during the 

 entire night, from 8 o'clock in the evening to 4 o'clock in the morn- 



