196 CARNEGIE INSTITUTION OF WASHINGTON. 



Light was supplied to all of these photographic instruments except 

 the concave-grating spectrograph by the 30-inch niirror of the Snow 

 telescope. The apparatus was grouped in a very compact form about 

 the ccelostat mounting. A small plane mirror of speculum metal was 

 attached to the upper end of the polar axis to furnish light for the 

 concave grating and a concave mirror of 27 feet focal length was used 

 to form the solar image upon the slit of the 18-foot spectrograph. 

 For the prismatic spectrograph a lens was employed giving a solar 

 image about 2 cm. in diameter. 



In the selection of a site for the expedition, consideration was given 

 both to records of weather conditions and to the facilities for the 

 transportation of the apparatus, a most essential feature in view of 

 the congestion of freight shipments. The elevation of the site was 

 also of importance, particularly for work in the ultra-violet portion of 

 the spectrum. Green River, in western Wyoming, on the main line of 

 the Union Pacific Railroad, at an altitude of about 6,000 feet, was 

 finally selected. Mr. Ellerman, and Mr. Jones, our superintendent of 

 construction, arrived at the site about three weeks before the eclipse 

 and began the erection of the piers and the assemblage of the appara- 

 tus. The remainder of the party, consisting of Messrs. Adams, Ander- 

 son, Babcock, St. John, and Professor Brackett, of Pomona College, 

 reached Green River on May 31. Mr. Hale, Miss Margaret Hale, and 

 Lieutenant Abetti of the Italian army joined the expedition on June 7. 



The sky on the morning of the day of the eclipse was remarkably 

 transparent, but shortly after noon cumulus clouds began to form in 

 the west. The disk of the sun was entirely clear at first contact, but 

 shortly afterward was obscured by a large cloud which moved slowly 

 toward the east. This became much less dense near the end of the 

 total phase and the brilliant prominences surrounding the sun were 

 readily visible. The outer corona, however, could not be seen with 

 certainty, and at no time was more than a small proportion of the 

 coronal light available. Within a few minutes after third contact 

 the cloud passed completely. 



The observations were carried out in full according to plans, and 

 the development of the negatives showed that more results had been 

 obtained than might have been expected under the conditions. All 

 of the direct photographs showed excellent detail in the corona and 

 prominences, the longest exposure taken throughout totality being 

 especially valuable. The short-focus camera, the polarizing apparatus, 

 and the ultra-violet quartz lens all yielded results of considerable 

 interest. 



The spectroscopic observations, which were much more exacting in 

 their requirements for full illumination, were interfered with greatly 

 by the cloudiness at the time of total phase. Valuable results, however, 

 were obtained with the concave grating spectrograph, a large number 



