1870.] 



as observed in the United States. 



181 



continuous in the American photographs ; but in the case of some of the 

 larger prominences, notably those at + 146 (Young) and —130 (Young), 

 there are strong apparent indents on the moon's limb. 



I next come to the obliterating effect of the illumination of our atmo- 

 sphere on the spectrum of the chromosphere. 



This is considerable ; in fact the evidences of it are very much stronger 

 than one could have wished, but hardly more decided than I had anticipated. 

 Professor Winlock's evidence on this point, in a letter to myself, is as 

 follows : — " I examined the principal protuberance before, during, and after 

 totality. I saw three lines (C, near D and F) before and after totality 

 and eleven during totality ; eight were instantly extinguished on the first 

 appearance of sunlight ." 



This effect was observed with two flint prisms and 7 inches aperture. 

 Professor Young, with five prisms of 45° and 4 inches aperture, found the 

 same result in the part of the spectrum he was examining at the end of 

 the totality. 



He writes : " I had just completed the measurements of 2602, when the 

 totality ended. This line disappeared instantly, but 2796 [the hydrogen 

 line near Gr] was nearly a minute in resuming its usual faintness." These 

 observations I consider among the most important ones made during the 

 eclipse ; for they show most unmistakably that, as I have already reported 

 to the Secretary of the Government-Grant Committee, the new method to 

 be employed under the best conditions must be used with large apertures 

 and large dispersion. 



On the fourth point the evidence is but negative only, and therefore in 

 favour of the view I have some time ago communicated to the Royal 

 Society. 



We next come to the question of the corona, — a question which has 

 been made more difficult than ever (in appearance only I think) by the 

 American observations. 



I propose to discuss only the spectroscopic observations of Professors 

 Young and Pickering in connexion with Dr. Gould's before quoted re- 

 marks. 



Professor Pickering, with an ordinary chemical spectroscope merely 

 directed to the sun's place during totality, obtained the combined spectrum 

 of the protuberances and corona. He saw a continuous spectrum with 

 two or three bright lines, one " near E," and a second "near C." 



Professor Young, who used a spectroscope specially adapted for the 

 work, in which only one part of the prominence at +146° was being exa- 

 mined, saw 0, near D, a line at 1250 + 20, and another at 1350 + 20 of 

 Kirchhoff's scale. The rest of the observations I give in his own words. 



" Then came the 1474 K line, which was very bright, though by no means 

 equal to C and D 3 ; but attention was immediately arrested by the fact 

 that, unlike them, it extended clean across the spectrum ; and on moving 

 the slit away from the protuberances, it persisted, while D 3 , visibly in the 



p 2 



