THE SOLAR ECLIPSE. 303 



Hill Meteorological Station, occupied a part of the grounds of the 

 Smithsonian party. 



The main object of investigation was, of course, the corona, and of 

 this, (first) a photographic and visual study of its structure; with, 

 (second) a determination by the bolometer whether appreciable heat 

 reaches us from it, and, if possible, an examination of the form of its 

 spectrum energy curve. 



The writer had been particularly struck, when observing the eclipse 

 of 1878 on Pike's Peak, by the remarkable defmiteness of filamentary 

 structure close to the sun's limb, and had never found in any photo- 

 graphs, not even in the excellent ones of Campbell taken at the Indian 

 eclipse of 1898, anything approaching what he saw in the few seconds 

 which he was able to devote to visual observations at^the height of 

 fourteen thousand feet. His wish to examine this inner coronal region 

 with a more powerful photographic telescope than any heretofore used 

 upon it, was gratified by the most valued loan by Prof. E. C. Pickering 

 of the new 12-inch achromatic lens of 135 feet focus, just obtained for 

 the Harvard College Observatory. This lens, furnishing a focal image 

 of more than 15 inches diameter, was mounted so as to give a horizontal 

 beam from a ccelostat clock-driven mirror by Brashear, of 18 inches 

 aperture, and used with 30-inch square plates. To supplement this 

 great instrument, a 5-inch lens of 38-feet focus, loaned by Professor 

 Young, was pointed directly at the sun. This formed images upon 

 11 x 14 plates moved in the focus of the lens by a water clock. Spe- 

 cially equatorially mounted lenses of 6, 4 and 3-inch aperture, driven 

 by clock work, .were provided for the study of the outer corona, and the 

 search for possible intra-mercurial planets. 



For the bolometric work, the massive siderostat with its 17-inch 

 mirror, and a large part of the delicate adjuncts employed at the Smith- 

 sonian Institution in recent years, to investigate the sun's spectrum, 

 was transported to Wadesboro. The excessively sensitive galvanometer 

 reached camp without injury even to its suspending fibre, a thread of 

 quartz crystal 1-15,000 inch in diameter. 



Besides these two chief aims (the photography and bolometry of 

 the inner corona), several other pieces of work were undertaken, in- 

 cluding the automatic reproduction of the 'flash spectrum' by means 

 of an objective prism with the 135-foot lens, the photographic study 

 of the outer coronal region, including provision for recognizing possible 

 intra-mercurial planets, already alluded to, visual and photographic ob- 

 servations of times of contact, and sketches of the corona, both from 

 telescopic and naked-eye observations. 



The assignment of the observers was as follows: Mr. Langley, in 

 general charge of the expedition, observed with the same 5-inch tele- 

 scope used by him on Pike's Peak in 1878, which was most kindly lent 



