78 



Spectroscopic Observations of the Sun. [Recess, 



With regard to the second assertion, I would remark that if such a 

 continuous-spectrum-giving envelope existed, I entirely fail to see how it 

 could be regarded as a region of selective absorption. Secondly, my obser- 

 vations have indicated no such stratum, although injections of sodium, 

 magnesium, &c. into the chromosphere not exceeding the limit of the 

 sun's limb by 2" have been regularly observed for several months past. 

 To-day I have even detected a low level of barium in the chromosphere not 

 1" high. This indicates, I think, that my instrument is not lacking in 

 delicacy ; and as I have never seen anything approaching to a continuous 

 spectrum when my instrument has been in perfect adjustment, I am in- 

 clined to attribute the observation to some instrumental error. Such a 

 phenomenon might arise from a local injection of solid or liquid particles 

 into the chromosphere,, if such injection were possible. But I have never 

 seen such an injection. If such an occurrence could be observed, it would 

 at once settle that part of Dr. Frankland's and my own theory, which re- 

 gards the chromosphere as the last layer of the solar atmosphere ; and if 

 it were possible to accept Father Secchi's observation, the point would be 

 settled in our favour. 



The sodium experiments to which I have referred, however, and the 

 widening out of the lines in the spot-spectra, clearly indicate, I think, that 

 the base of the atmosphere is below the spot, and not above it. I there- 

 fore cannot accept Father Secchi's statement as being final against another 

 part of the theory to which I have referred — a conclusion which Father 

 Secchi himself seems to accept in other communications. 



Father Secchi remarks also that the F line is produced by the absorption 

 of other bodies besides hydrogen, because it never disappears. This conclu- 

 sion is also negatived by my observations ; for it has very often been ob- 

 served to disappear altogether and to be replaced by a bright line. At 

 times, as I pointed out to the Royal Society some months ago, when 

 a violent storm is going on accompanied by rapid elevations and depressions 

 of the prominences, there is a black line on the less-refrangible side of the 

 bright one ; but this is a phenomenon due to a change of wave-length 

 caused by the rapid motion of the hydrogen. 



With regard to the observation of spot-spectra, I find that every increase 

 of dispersive power renders the phenomenon much more clear, and at the 

 same time more simple. The selective absorption I discovered in 1866 

 comes out in its most intense form, but without any of the more complicated 

 accompaniments described by Father Secchi. I find, however, that by using 

 three prisms this complexity vanishes to a great extent. We get portions of 

 the spectrum here and there abnormally bright, which have given rise doubt- 

 less to some of the statements of the distinguished Roman observer ; but the 

 bright Hues, properly so-called, are as variable as they are in any other 

 part of the disk, but not much more so. I quite agree that the " interpre- 

 tation " of sun-spot phenomena to which Father Secchi has referred *, 

 * Comptes Rendus, 1869, l r sem. p. 764. 



