1869.] 



Observations of the Sun. 



509 



May 8. — This morning I received, and read with deep interest, your 

 article in the ' Journal of Science/ Had I received it a week ago, my 

 note of the 3rd would have been differently worded. On the other hand, 

 it is clear that some of the facts I have stated above are still legitimate sub- 

 jects for communication, and will probably lead to further discoveries. 

 The new lines may or may not have been since seen by Mr. Lockyer. In the 

 former case the corroboration will be worth something — the more so as his 

 secondary red line, as mentioned in Mr. Crookes's article in the January No. 

 of the 'Journal of Science,' is apparently misplaced. This line, as also 

 those I have called 2 and £, does not appear to coincide with any known 

 solar line. The elementary substances to which these belong remain yet 

 to be declared. As for y, I suppose the strong solar line to which it 

 corresponds belongs to some known element. 



I have not remarked any tendency in F to vary in width. 



It cannot but be considered strange that no traces have been seen of M. 

 Ra} T et's and Major Tennant's green lines. I have watched that part of the 

 spectrum very closely on purpose, but, even where the four principal lines 

 were more than ordinarily bright, I have failed to distinguish even the 

 slightest fading of the strong magnesium lines, or of others in that neigh- 

 bourhood. This fading invariably precedes the substitution of a bright for 

 a dark line : thus, if the slit admits to view the tops of several adjacent 

 prominences, the line F (for instance) is broken into detached bright por- 

 tions, between which there is in each case a more or less complete hiatus, 

 which may or may not amount to the original dark solar line. The dark 

 line, being only a less intense light, is susceptible of all degrees of darkness, 

 just as the bright line, being only a more intense light, may appear of all 

 lower degrees of brightness. This intermediate condition between dark and 

 bright is constantly to be recognized, more or less strongly marked, within 

 the sun's border ; but I cannot say I have seen a continuation of the bright 

 line inwards. I often see this absence of the dark line y when the light 

 is not intense enough to show it as a " bright " line. So far, then, as re- 

 gards the magnesium element I have strong negative evidence, which is 

 strengthened by the consideration of the improbability that such a very 

 marked group should not have been recognized by the above-mentioned 

 observers if it was actually present, on the one hand, and that the element 

 should have been represented by a single member only of this group, on the 

 other. The confident way in which this metal has been accepted as re- 

 cognized, by more than one speculator, seems to challenge question on the 

 evidence. 



And I would take the present opportunity to remark that, after the 

 studied avoidance (on my part) of such hasty conclusions, I have felt it 

 rather hard to be set right where I had not erred, as in the case of the 

 orange line. I never said that a line, apparently identical though it was 

 with D, represented sodium. One writer, if I recollect right, made me 

 responsible, not only for sodium and hydrogen, but for magnesium as well I 



