354 



Mr. J. N. Lockyer on Spectroscopic [Mar. 18 ; 



minences and of the chromosphere itself are rendered perfectly visible and 

 easy of observation. 



Addendum. — Received March J7, 1869. 



Since the foregoing paper was written, I have had, thanks to the some- 

 what better weather, some favourable opportunities for continuing two of 

 the lines of research more especially alluded to in it ; I refer to the method 

 I had adopted for viewing the prominences, and to the injection of sodium, 

 magnesium, &c. into the chromosphere. 



With regard to seeing the prominences, I find that, when the sky is free 

 from haze, the views I obtain of them are so perfect that I have not thought 

 it worth while to remount the oscillating slit. I am, however, collecting 

 red and green and violet glass, of the required absorptions, to construct a 

 rapidly revolving wheel, in which the percentages of light of each colour 

 may be regulated. In this way I think it possible that we may in time be 

 able to see the prominences as they really are seen in an eclipse, with the 

 additional advantage that we shall be able to see the sun at the same time, 

 and test the connexion or otherwise between the prominences and the 

 surface-phenomena. 



Although I find it generally best for sketching-purposes to have the 

 open slit in a radial direction, I have lately placed it at a tangent to the 

 limb, in order to study the general outline of the chromosphere, which 

 in a previous communication I stated to be pretty uniform, while M. 

 Janssen has characterized it as " a niveau fort inegal et tourmente" My 

 opinion is now that perhaps the mean of these two descriptions is, as 

 usual, nearer the truth, unless the surface changes its character to a large 

 extent from time to time. I find, too, that in different parts the outline 

 varies : here it is undulating and billowy ; there it is ragged to a degree, 

 flames, as it were, darting out of the general surface, and forming a ragged, 

 fleecy, interwoven outline, which in places is nearly even for some distance, 

 and, like the billowy surface, becomes excessively uneven in the neighbour- 

 hood of a prominence. 



According to my present limited experience of these exquisitely beautiful 

 solar appendages, it is generally possible to see the whole of their structure ; 

 but sometimes they are of such dimensions along the line of sight that 

 they appear to be much denser than usual ; and as there is no longer under 

 these circumstances any background to the central portion, only the 

 details of the margins can be observed, in addition to the varying bright- 

 nesses. 



Moreover it does not at all follow that the largest prominences are 

 those in which the intensest action, or the most rapid change, is going on, 

 — the action as visible to us being generally confined to the regions just in, 

 or above, the chromosphere, the changes arising from violent uprush or 

 rapid dissipation, the uprush and dissipation representing the birth and 

 death of a prominence. As a rule, the attachment to the chromosphere 



