1869.] 



Observations of the Sun. 



75 



and prominences without spots ; but I do not say that a spot is not ac- 

 companied by a prominence at some stage of its life, or that it does not re- 

 sult from some action which, in the majority of cases, is accompanied 

 by a prominence. 



III. At times, when a prominence is seen bright on the sun itself, the 

 bright F line varies considerably, both in thickness and brilliancy, within 

 the thickness of the dark line. The appearances presented are exactly as if 

 we were looking at the prominences through a grating. 



IV. Bright prominences, when seen above spots on the disk, if built up 

 of other substances besides hydrogen, are indicated by the bright lines of 

 those substances in addition to the lines of hydrogen. The bright lines are 

 then seen very thin, situated centrally (or nearly so) on the broad absorp- 

 tion-bands caused by the underlying less-luminous vapours of the same 

 substances. 



V. I have at last detected an absorption-line corresponding to the orange 

 line in the chromosphere. Father Secchi states * that there is a line cor- 

 responding to it much brighter than the rest of the spectrum. My ob- 

 servation would seem to indicate that he has observed a bright line less 

 refrangible than the one in question, which bright line is at times excessively 

 brilliant. It requires absolutely perfect atmospheric conditions to see it in 

 the ordinary solar spectrum. It is best seen in a spot-spectrum when the 

 spot is partially covered by a bright prominence. 



VI. In the neighbourhood of spots the F bright line is sometimes ob- 

 served considerably widened out in several places, as if the spectroscope 

 were analyzing injections of hydrogen at great pressure in very limited re- 

 gions into the chromosphere. 



VII. The brilliancy of the bright lines visible in the ordinary solar spec- 

 trum is extremely variable. One of them, at 187 To, and another, at 1529*5 

 of Kirchhoff s scale, I have detected in the chromosphere at the same time 

 that they were brilliant in the ordinary solar spectrum. 



VIII. Alterations of wave-length have been detected in the sodium-, 

 magnesium-, and iron-lines in a spot-spectrum. In the case of the last 

 substance, the lines in which the alteration was detected were not those 

 observed when iron (if we accept them to be due to iron alone) is injected 

 into the chromosphere. 



IX. When the chromosphere is observed with a tangential slit, the F 

 bright line close to the sun's limb shows traces of absorption, which gradu- 

 ally diminish as the higher strata of the chromosphere are brought on to 

 the slit, until the absorption-line finally thins out and entirely disappears. 

 The lines of other substances thus observed do not show this absorption. 



X. During the most recent observations I have been able to detect traces 

 of magnesium and iron in nearly all solar latitudes in the chromosphere. 

 If this be not merely the result of the good definition lately, it would in- 

 dicate an increased general photospheric disturbance as the maximum sun- 



* Comptes Rendus, 1869, 1' sem.p. 358. 



