150 SOLAE ECLIPSE OF MAY 28, 1900. 



Professor Hale, of the Yerkes Observatory, was a member of the 

 party, while still in general charge of the Yerkes expedition, and his 

 counsel and aid were of the greatest service. Mr. Clayton, of Blue 

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

 Smithsonian party. 



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

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

 (second) a determination bj' the bolometer Avhether 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 Pikes Peak, b}- the remarkable definiteness 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 

 14,000 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, b}^ 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-inch diameter, was mounted so as to give a horizontal 

 beam from a coelostat clock-driven mirror by Brashear, of 18-inch 

 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 

 by 11 inch plates moved in the focus of the lens by a water clock. 

 Specially equatorially mounted lenses of 6, 4, and 3 inch aperture, 

 driven by clockwork, were provided for the study of the outer corona, 

 and the search for possible intramercurial planets. 



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

 mirroi', with a large part of the delicate adjuncts employed at the 

 Smithsonian Institution in recent j^ears to investigate the sun's spec- 

 trum, was transported to Wadesboro. The excessively sensitive gal- 

 vanometer reached camp without injury even to its suspending fiber, 

 a thread of quartz crystal one fifteen-thousandth of an inch in diameter. 



Besides these two chief aims (the photography and bolometr}^ of the 

 inner corona), several other pieces of work were undertaken, including 

 the automatic reproduction of the "flash spectrum" by means of an 

 objective prism with the 135-foot focus; the photographic stud}^ of 

 the outer coronal region, including provision for recognizing possible 

 intramercurial planets, already alluded to, visual and photographic 

 observations of times of contact, and sketches of the corona, both 

 from telescopic and naked-eye observations. 



