Preliminary Note on the Spectrum of the Corona. 



189 



III. " The lonisation of Dilute Solutions at the Freezing Point." By 

 AV. C. D. Whetham. Communicated by E. H. Griffiths, 

 F.RS. 



"Preliminary Note on the Spectrum of the Corona. Part 2." 

 By Sir J^ORMAX Lockyer, K.C.B., F.Pv.S. Pteceived February 

 8,— Bead February 22, 1900. 



One of the chief results which, in my opinion, would be secured by 

 the use of the prismatic camera in eclipse work was the differentiation 

 between chromospheric and coronal phenomena. The photographs 

 taken diu*ing the eclipses of 1893, 1896, and 1898 all enabled this 

 distinction to be made very clearly, and various radiations formerly 

 attributed to the corona have been shown to belong to the chromo- 

 sphere alone. The photographs taken in Africa in 1893 showed eight 

 rings in the spectrum of the corona ; in Novaya Zemlaya, in 1896, with 

 a, less powerful instrument, a smaller number was secured ; but those 

 taken with increased dispersion in India, in 1898, show a much greater 

 number. 



I have already given the results of an inquiry into the wave-lengths 

 of two of the chief coronal rings (5 303*7 and 4231 '3) as determined 

 from photographs taken in 1898 with the 6-inch prismatic camera f 

 and as the results of the continued investigations may be of service to 

 intending observers of the eclipse of next May, I give a short abstract 

 of them in the present note. 



Eight photographs were obtained during the time the spectrum of 

 the corona Avas least admixed with that of chromosphere ; of these, three 

 taken with instantaneous exposures show only two or three of the 

 brighter rings, so that five, showing many coronal rings, are suitable 

 for measurem^ent. The exposures of the photographs used for measure- 

 ment were as follows, the ratio of focal length to aperture being 15 : — 



No. 2a 50 seconds. 



3c 7 „ 



M 8 „ 



During the earlier part of the exposure of plate 2a, the upper 

 regions of the chromosphere were visible in the north-east, and some 

 of the stronger chromospheric arcs appear, together with the coronal 

 rings, in the corresponding parts of the images. In plates 3c and M 

 chromospheric arcs appear in the south-west quadrant, together with 



* * Roy. Soc. Proc.,' vol. 64, p. 168. 



