110 THE CHEMISTRY OF THE SUN. [CHAP. 



touching the chemical nature of the exterior envelope of the sun 

 had reference to the red line of hydrogen. When therefore 

 we had such an observation as this, showing one of the lines 

 produced by this vaporous sea, coincident with the c line of 

 the solar spectrum, we knew at once, on the assumption made 

 by Kirchhoff, that that line was produced by hydrogen. It was 

 necessary, of course, that the other lines of hydrogen should 

 be investigated. The next obvious line of hydrogen is F in 

 the blue-green, and when the question was put to this line, in 

 that case also it was found that the prominences gave out no 

 uncertain sound that the prominences were really and truly 

 composed to a large extent of what we call hydrogen; that is 

 to say, the spectral lines observed when we render hydrogen 

 incandescent are identical with three of the spectral lines 

 observed when we throw one of the solar prominences on 

 the slit. Here then we see that as in the case of the spots we 

 are in full presence of localised chemical phenomena. 



All the prominences have not this simple constitution. Some 

 of them exhibit, besides the lines of hydrogen, those of magnesium,, 

 sodium, iron, and other metals ; indeed they may be divided 

 according to their chemical composition into prominences in 

 which among known lines those of only hydrogen are seen, and 

 others in which the lines visible in the spectra of a great number 

 of metals are very brilliant. 



Extended spectroscopic observation outside the sun's limb on 

 this new method not only revealed the chemical nature of 

 the prominences, but proved that they were merely local heapings 

 up of an envelope chiefly characterised ly the hydrogen lines which 

 entirely surrounded the sun. It was found that outside the 

 photosphere the prominence spectrum was never absent. To the 

 continuous envelope thus revealed I gave the name Chromosphere 

 a term suggested by my late friend, Dr. Sharpey, who was 

 then one of the secretaries of the Royal Society, and who took 

 the keenest interest in the new revelations to distinguish it 



