NO. 3 RADIATION OF THE ATMOSPHERE ANGSTROM O, 



lower station the sky was cloudy almost the entire time, which con- 

 dition, however, furnished an opportunity to demonstrate the effect 

 of dense homogeneous cloud banks upon the nocturnal radiation. 



The first simultaneous observations at different altitudes, favored 

 by a clear sky at both stations, were obtained during a subsequent 

 expedition, also of a preliminary nature, when the author and 

 Mr. Brewster, proceeded to Indio in the Salton Sea Desert, and 

 Prof. Brackett, Prof. Williams, and Dr. Kennard succeeded in climb- 

 ing Mount San Gorgonio (3,500 m.), the highest peak of the San 

 Bernardino range. Indio was chosen because of its low altitude 

 (o m.) and because of its meteorological conditions, the sky being 

 almost always clear in this part of the desert. The horizon was 

 almost perfectly free, the San Bernardino and San Jacinto moun- 

 tains rising only to about io° above the horizon. The temperature 

 at the lower station, which is situated in one of the hottest regions of 

 America, reached, in the middle of the day, a point between 40 and 

 46 ° C. ; in the night-time it fell slowly from about 30 in the evening 

 to about 20 in the morning. Here some interesting observations 

 were obtained, showing the influence of temperature upon radiation 

 to the sky. At the same time, the other party made observations on 

 the top of Mount San Gorgonio (3,500 m.) situated about 40 miles 

 farther north. The party climbed to the top in a heavy snow- 

 storm, and during the two following, perfectly clear, nights, observa- 

 tions were taken, the temperature at the top being about o° C. Thus 

 simultaneous observations were obtained on two " places differing 

 in altitude by 3,500 meters. 



The expedition to Mount Whitney, for which preparations were 

 made immediately after the return of the parties to Claremont, was 

 regarded as the most important part of the field work. On the pro- 

 posal of Director Abbot, the U. S. Weather Bureau had resolved to 

 cooperate with my expedition in this part of the undertaking. Under 

 the direction of Mr. Gregg and Mr. Hathaway of that Bureau, the 

 upper air was to be explored by means of captive balloons, carrying 

 self-recording meteorological instruments. In this way the tempera- 

 ture and the humidity would be ascertained up to about 1,500 meters 

 above the point from which the balloons were sent up. The ascents 

 were to be made from Lone Pine (by Mr. Hathaway) and from 

 the summit of Mount Whitney (by Mr. Gregg). The latter ascents 

 are probably the first that have been carried on by means of captive 

 balloons at altitudes exceeding 4,000 meters. 



