NO. 8 SAMUKL PIERPONT LANGLEY ABBOT I? 



ress at the Allegheny Observatory, at the base and at the summit of 

 a lofty mountain, would justify the labor and expense of such an 

 undertaking. There would have been little probability, however, of 

 such a plan being carried out by the Observatory, were it not for the 

 generosity of a citizen of Pittsburgh [William Thaw], who placed 

 at its disposal the considerable means demanded for the outfit of an 

 expedition for this purpose. 



" Upon the objects of the expedition and their bearings upon 

 meteorology becoming known to the Chief Signal Officer of the 

 United States Army, he consented to give it the advantage of his 

 official direction and the aid of Signal Service Observers, and upon 

 the reasons which made the choice of its objective point in a remote 

 part of the United States territory being approved by him, he con- 

 tributed further material aid in transportation Finally, upon 



the advice of Mr. Clarence King, and with the concurrently fav- 

 orable opinion of officers of the Coast Survey and others familiar 

 with that region, Mount Whitney, in the Sierra Nevada Range of 

 Southern California — approximate longitude, ii8°3o'(7h.54m.) ; lati- 

 tude, 36°35' — was found to be, on the whole, most desirable. Its 

 height was known to be between 14,000 and 15,000 feet. Its eastern 

 slopes are so precipitous that two stations can be found within 12 

 miles, visible from each other, and whose difiference of elevation is 

 11,000 feet, and it rises from and overlooks one of the most desert 

 regions of the continent, while its summit is almost perpetually clear 

 during June, July, August, and September." 



On account of limitations of space, it is impossible to give by quota- 

 tions a fair idea of this extraordinary expedition. Space even for- 

 bids that we should quote from the inspiring description Langley gives 

 of the expedition, its guard of soldiers, the desert journey, the insuf- 

 ferable heat under which observations were nevertheless made at Lone 

 Pine, the ascent of the mountain, its grandeur, the dark blue of its 

 cloudless sky, the long delays waiting for the mule train and instru- 

 ments, and the observations at Mountain Camp. 



Many kinds of observations were carried through. Measurements 

 of total radiation of the solar beam by the globe and the Violle 

 actinometers ; measurements of homogeneous solar rays by the linear 

 spectrobolometer ; measurements of the brightness of the sky by day 

 and by night ; measurements of the temperature and humidity of the 

 air at frequent intervals ; barometric measurements for determining 

 the then only approximately known elevation of Mount Whitney; 



