ON THE TOTAL SOLAR ECLIPSE OP MAY 17, 1882. 
263 
the violet and ultra-violet in which the strongest impressions occur could not 
be in proper focus. The solar line F, and everything which is below, are well defined. 
It is clear that with this instrument we obtain a series of rings corresponding to the 
different rays sent out by the prominences. We are at once struck by the intensity 
of two of these rings lying close together near the boundary between the violet and 
ultra-violet. A comparison with the photographs obtained in the spectroscopic 
camera leaves no doubt that these rings are due to calcium, and are in fact coinci¬ 
dent with the solar lines H and K. They may serve therefore as a starting-point for 
the determination of other wave-lengths. Measurements of the distances between the 
different prominence rings, and comparison with a photograph of the solar spectrum, 
taken with -the same prism, renders it easy to identify the hydrogen lines, Ha (C), 
H/3 (F), Hy (near G), and HS (h), and these may again stand as reference lines for 
the other images. 
Three prominences especially are noticeable by their great intensity. We 
shall designate them by the numbers I., II., and III. I. and II. were close to the 
east point of the sun, III. was a little more towards the north. Next in intensity came 
a prominence (V.) near the west point of the sun. I., II., and III. show all the 
hydrogen lines in the visible part of the spectrum, Y. shows all but C. A series 
of prominences towards the southern edge of the sun show F strong and Hy very 
distinctly; a prominence on the northern edge (IV.) shows Hy faintly, and only a trace 
of F. The prominence III. shows a number of lines in the ultra-violet. Want of focus 
readers them difficult to measure on this plate, but as the slit of the spectroscopic 
camera happened fortunately to cut the same prominence, the want is fully supplied. 
It is found that these lines are in part due to the same hydrogen lines which Dr. 
Httggins has photographed in several star-spectra. The prominences I. and II. show 
these lines also, but not so markedly. It ought to be mentioned that the prominence 
which we have called III. is by far the strongest in the direct photographs of 
the corona, and is that which we have already stated to be centrally reversed in one 
of the plates. The results of the prismatic camera show that the intensity of III. 
as compared with I. and II. was most marked in the most refrangible part of the 
spectrum. The same relation of relative intensity holds in the line coincident 
with C, but is reversed with F, I. and II. being here the strongest. This points to 
the conclusion that I. and II. -were cooler than III., for we know that on cooling 
H/3 (F) becomes the strongest hydrogen line, while other lines gain in relative 
intensity on heating. The prominence IY. gives an anomalous result, showing H/3 
(F) and Hy (near G) but the latter with greater intensity. It was perhaps a hot, but 
thin and therefore black prominence. 
We may turn now to the lines due to other substances. The wave-lengths were 
determined by measuring the distance of the image of any prominence to the 
corresponding image of one of the hydrogen lines. A first approximate result is 
obtained by employing the ordinary interpolation formula which is based on the 
