ON THE TOTAL SOLAR ECLIPSE OF MAY 17, 1882. 
267 
The prominence spectrum. 
Close to the solar limb, on both sides of the photograph, bright lines are seen which 
evidently belong to the prominences. On the northern limb these are most numerous 
and brightest. It seems certain, in fact, from a comparison with the photograph 
obtained in the prismatic camera, that the slit must have crossed the prominence 3, 
which, as has already been mentioned, was rich in ultra-violet light. On the same 
plate above and below, the solar spectrum had been photographed after the eclipse, 
and we had, therefore, no difficulty in identifying the principal lines. We see in the 
first place the calcium lines H and K. These two lines are, indeed, the great feature 
of the photograph. Being of great intensity they do not confine themselves to the 
prominence regions, but appear as bright lines through the corona and over the body 
of the moon. The light which is due to them must, in fact, have been so strong that 
the scattered light was sufficiently intense in our atmosphere to give the appearance 
and to be conspicuous everywhere in the neighbourhood of the moon, or else that the 
lens forming the image on the slit was so illuminated as to give this result. It can, 
indeed, be traced to a distance of quite three solar radii. In addition to these lines 
the hydrogen lines must, of course, be expected to be present; and, indeed, their identifi¬ 
cation presents no difficulties. The full series is present, including those photographed 
by Dr. Huggins in the ultra-violet spectra of stars. Once these lines had been 
traced, and their characteristic distribution identified, the work of mapping was 
rendered comparatively easy, as they could be used as reference lines, and thus the 
wave-lengths of the remaining lines determined. The result is given in the following 
Table. The first column gives the intensity of the lines as they appear in the promi¬ 
nence, 1 denoting the greatest and 6 the smallest intensity. The second column 
gives the wave-lengths as determined by means of the hydrogen lines. In the third 
column the origin of the lines is identified as far as possible. In the last column we 
have added the numbers given by Dr. Huggins for the lines seen in a. Aquike ; and it 
will be noticed how, in the ultra-violet especially, many of the lines which we have not 
been able to identify are common to our photograph and to the spectrum of a Aquilse. 
This correspondence was so striking that we felt justified in bringing it forward. The 
relative intensities of the less refrangible lines cannot be given, as their own light is 
so much overpowered by the continuous spectrum that even a strong line can only be 
traced with difficulty. 
2 m 2 
