A SHELTER FOR OBSERVERS ON MOUNT WHITNEY 



By C. G. abbot 



Director of Smithsonian Astrophysical Observatory 



With Two Plates 



There have been few American scientific expeditions which have 

 excited more interest here and abroad than Mr. Langley's expedition 

 to Mount Whitney in 1881. It was undertaken to determine the 

 relative transparency of the air at high and low altitudes, and thereby 

 to fix the value of the "solar constant of radiation." If we measure 

 the intensity of sun rays at the earth's surface by wholly absorbing 

 them during a noted time interval over a measured area and ex- 

 pressing the results in heat units, we do not get a true measure of 

 the intensity of the sun's output of radiation, owing to the losses in 

 the air ; neither can these losses be allowed for by merely measuring 

 the total radiation at different hours of the day, when different 

 thicknesses of air are traversed, for the losses affect the intensity 

 of rays of different colors differently, and some rays are almost 

 wholly cut off in the upper air, so that they cannot be estimated in 

 any easy manner. Langley recognized the necessity of measuring 

 the intensities of rays of all wave-lengths separately, and acted upon 

 his discovery by employing the bolometer (a highly sensitive electri- 

 cal thermometer) to measure in all parts of the solar spectrum. 

 Observations at Allegheny, Pennsylvania, were disappointing, owing 

 to the dusty state of the lower air; hence he formed the plan of 

 going to a high altitude in the then little known West with the com- 

 plete complex outfit which he called the spectro-bolometer. His 

 plans called for observations at a low station and, as nearly as possi- 

 ble simultaneously, at a very high station near by. On the advice of 

 those who knew the region, he chose Mount Whitney, in the Sierra 

 Nevada range, since shown to be the highest peak in the United 

 States (proper), for his high station, and Lone Pine, in the Owens 

 A^alley, only about 15 miles distant, as the lower one. Mount Whit- 

 ney has an elevation of 14,502 feet; Lone Pine, only 3,850 feet. 



Mr. Langley's expedition was not lacking in features of interest 



and picturesqueness, apart from its highly valuable scientific aims. 



It was financed by the late William Thaw, of Pittsburg, a man who 



supported Langley's work on many occasions, but always stipulated 



7 499 



