The Three Secretaries 221 



thousand feet, and observed the extension of the corona to 

 the hitherto unsuspected extent of nearly ten million miles. 



During the winter of 1878, in the course of a visit to Eu- 

 rope, he spent some time upon Mount Etna, making obser- 

 vations upon the character of astronomical vision, in order to 

 enable comparisons to be made with observations taken under 

 similar conditions in the territories of the United States. The 

 station here was at Casa del Bosco, situated at the height of 

 about 4,200 feet on the southeastern slope of the mountain. 

 There he remained from Christmas until January 14. The 

 conclusion reached was that though the ideal station where 

 atmospheric tremor does not exist, and the observer pursues 

 his studies in an ever transparent sky, is not to be found 

 on any part of the earth's surface yet examined, there is in 

 such stations as this and in the upper and elevated tablelands 

 of Colorado and New Mexico every condition which experi- 

 ence has shown to be favorable. 



In 1 88 1 Mr. Langley organized an expedition to the top of 

 Mount Whitney, in California, for the purpose of applying 

 his new methods and instruments under the most favorable 

 conditions. Here he remained with his party from July 25 

 until September 10, making observations at stations nearly 

 fourteen thousand feet above the sea. The expenses of this 

 expedition were borne in part by the United States Signal 

 Service and in part by William Thaw, of Pittsburg, who had 

 for some years taken great interest in the work of the Alle- 

 gheny Observatory and to whose liberality and appreciation 

 of scientific work many of Mr. Langley's greatest opportuni- 

 ties for investigation were due. A report on the results of 

 this expedition was published in 1884, as one of the profes- 

 sional papers of the United States Signal Service. 



The Mount Whitney observations resulted, first, in the 

 discovery of an entirely unsuspected extension of the solar 



15* 



