July 12, 1900] 



NA TURE 



247 



The main objects of the investigations undertaken 

 were a photographic and visual study of the structure of 

 the lower corona, and a determination by the bolometer 

 of the heat radiated from it, and lastly an examination of 

 the form of its spectrum energy curve. 



Prof. Langley, who was in charge of this expedition, 

 observed the eclipse of 1878 from Pike's Peak (14,000 



-Portion of Smithsonian Astrophysical Observatory 

 135-foot telescope (under canvas), the 38-foot coron 



feet), and he was then particularly struck by the remark- 

 able definiteness of filamentary structure close to the 

 sun's limb, a structure which, he remarks,'has never been 

 found in any photographs, not even in those beautiful 

 pictures taken by Prof. Campbell at the Indian eclipse of 

 1898. The eclipse this year afforded him an opportunity 

 of examining this inner corona region with a much more 

 powerful instrument. This 

 instrument was a 12-inch 

 achromatic lens of 135 feet 

 focal length, obtained for 

 the Harvard College Ob- 

 servatory, and lent by Prof. 

 E. C. Pickering. The tube 

 was mounted horizontally 

 in conjunction with a coelo- 

 stat of 1 8-inch aperture, and 

 30-inch square plates were 

 used, the diameter of the 

 solar image being i jinches. 

 To supplement this instru- 

 ment, a 5-inch lens of 

 38 feet focal length, loaned 

 by Prof. Young, was 

 pointed directly at the 

 suQ, and photographs were 

 secured on plates 11 by 

 14 inches, moved in the 

 focus of the lens by a water clock. For the study of 

 the outer corona and possible intramercurial planets, 

 specially equatorially mounted lenses of 6-, 4- and 3-inch 

 apertures, driven by clock-work, were used. 



The accompanying illustration (Fig. i) shows a small 

 part of the 135-foot telescope. The photographic hut is 

 seen at the end of it, and beyond that the tube contain- 



ing the lens of 38 feet focal length pointed at the sun. 

 Prof. Langley is seen observing at the 5-inch equatorial. 

 For the bolometric work a massive siderostat with a 

 mirror of 7 inches was used in conjunction with a large 

 part of the delicate adjuncts employed at the Smith- 

 sonian Institution in recent years. 



Further work that was attempted, and for which 

 other apparatus had been 

 taken out, was an auto- 

 matic method of obtaining 

 photographs of the lower 

 chromosphere at about 

 second contact by means 

 of an objective prism work- 

 ing in connection with the 

 135-foot lens ; visual and 

 photographic observations 

 of times of contact ; and 

 sketches of the corona, 

 both from telescopic and 

 naked eye observations. 



The observers, under 

 the general charge of Prof. 

 Langley, were distributed 

 as follows : — Prof. Langley 

 used the same 5-inch as he 

 observed with in 1878 ; 

 Messrs. Abbot and Men- 

 denhall were in charge of 

 the bolometer ; Mr. T. W. 

 Smillie made exposures at 

 the 135-foot telescope, and 

 Mr. F. E. Fowle, jun., at 

 the38-foottelescope. Father 

 Searle, assisted by Mr. P. A. 

 Draper and Mr. C. W. B. 

 Smith, employed four tele- 

 scopes, mounted on a single 

 polar axis and driven by 

 clock-work, for obtaining photographs of the outer corona 

 and the intramercurial planets. Latitude, longitude, 

 time and contact observations were made by Mr. G. R. 

 Putnam, assisted by Mr. Hoxie. Sketches of the 

 inner corona and contacts were made by Mr. R. C. 

 Child with a 6-inch, and by Father Woodman with 

 a 3|-inch. 



p. showing a part of the large 

 the 5-inch equatorial. 



Fig. 2. — Showing prominences 

 Exposure eight seconds. At ei 



at the south-west limb. Taken with a 12-inch lens of 135 feet focal length, 

 d of totality. (Natural size of original photc^raph. Moon, 15 inches diam.). 



Among the more general observations made at the 

 time of the eclipse may be mentioned the following : — 



Before totality a fall of temperature and a rising breeze 

 were distinctly noticeable. Shadow bands were seen, 

 but their velocity was too rapid and flickering for accurate 

 determination ; their size and distance apart (about 5 

 inches) were also estimated. __ 



NO. t602. vol. 62] 



