IN CONNEXION WITH THE SPECTEUM OF THE SUN. 
265 
In the case of the chromosphere, the observation of the order of lengths of the 
bright lines is invested with a new importance, as also the observation of lines which 
are not reversed in the ordinary solar spectrum. As an instance of this, I may state 
that the fact that the re-reversal into brightness in the chromosphere of the line 1474 K 
is not due to iron vapour, is settled by the other fact, which this new method has 
enabled me to determine, that the coincident line in the iron spectrum is one of the 
shortest lines in the whole spectrum. 
In the case of the photosphere, not only may we hope to account for such cyclical 
changes as I have long had reason to suspect and have referred to in prior communica- 
tions to the Society, but it is essential that spot-spectra shall be photographed with 
special reference to the consideration that in such spectra the new lines may now be 
found in all probability, to be those which are only slightly shorter than those 
ordinarily reversed. This research I am making arrangements to carry on. 
It will be observed that in the maps the elements are arranged in the order of their 
atomic weights. This was done before all the comparisons were made, because, as I 
have before announced to the Royal Society in the case of several of the elements, the 
length of the lines in the spectra of the vapours observed in the chromosphere are 
also most frequently arranged in this order, as predicted by Mr. Stoney*. The 
comparison rendered possible by the maps also bears out this view with regard 
to the outer layers ; for in the case of Ii and Na all the lines are reversed ; 
o 
in the case of Mg, about which there was a doubt in Angstrom’s observations, only 
one line is possibly dropped, and this is not certain. When we come, however, to 
the elements with higher atomic weights the number of lines reversed is less. But 
the maps also show that when once the higher layers of the chromosphere, where less 
constant action goes on, are passed, atomic weight ceases to be a guide, and we are 
therefore driven to other considerations, which promise to largely increase our knowledge 
of the kind of action at work in the solar atmosphere and the cyclical variation of that 
action. 
The Maps which accompany this communication have been made by my assistant, Mr. 
R. J. Feiswell. They have only been revised by myself. I am anxious to take this oppor- 
tunity of testifying to the zeal and ability he has displayed in a research necessarily 
very tedious from its character, and requiring great patience and care. 
* This arrangement has since been broken np for the convenience of the engraver. Some of the spectra 
having both sun and chloride lines had to be displaced by others without these, in order to get the whole of 
the maps on to the three Plates. 
