356 



Mr. J. N. Lockyer on Spectroscopic [May 19, 



April 12. The prominence was persistent. 



April 15. Spot nearing the limb, prominence still persistent over spot. 

 At eleven I saw no prominence of importance on the limb, but about an 

 hour afterwards I was absolutely startled by a prominence not, 1 think, 

 depending upon the spot I have referred to, but certainly near it, more 

 than 2' high, showing a tremendous motion towards the eve. There were 

 light clouds, which reflected to me tbe solar spectrum, and I therefore saw 

 the black C line at the same time. The prominence C line (on which 

 changes of wave-length are not so well visible as in the F line) was only 

 coincident with the absorption-line for a few seconds of arc ! 



Ten minutes afterwards the thickness of the line towards the right was 

 all the indication of motion I got. In another ten minutes the bright and 

 dark lines were coincident. 



And shortly afterwards what motion there was was towards the red ! 



I pointed out to the Royal Society, now more than a year ago *, that 

 the largest prominences, as seen at any one time, are not necessarily those 

 in which either the intensest action or the most rapid change is going on. 

 From the observations made on this and the following day, I think that 

 we may divide prominences into two classes : — 



1 . Those in which great action is going on, lower vapours being injected ; 

 in the majority of cases these are not high, they last only a short time — 

 are throbs, and are oft renewed, and are not seen so frequently near the 

 sun's poles as near the equator. They often accompany spots, but are not 

 limited to them. These are the intensely bright prominences of the Ame- 

 rican photographs. 



2. Those which are perfectly tranquil, so far as wave-length evidence 

 goes. They are often high, are persistent, and not very bright. These 

 do not, as a rule, accompany spots. These are the " radiance " and dull 

 prominences shown in the American photographs. 



I now return to my observations of the spot. On the 16th the last of 

 the many umbrae was close to the limb, and the most violent action was 

 indicated occasionally. I was working with the C line, and certainlv 

 never saw such rapid changes of wave-length before. The motion was 

 chiefly horizontal, or nearly so, and this was probably the reason why, in 

 spite of the great action, the prominences, three or four of which were 

 shut out, never rose very high. 



I append some drawings made, at my request, by an artist, Mr. Holi- 

 day, who happened to be with me, and who had never seen my instrument 

 or the solar spectrum widely dispersed before. I attach great importance 

 to them, as they are the untrained observations of a keen judge of form. 



The appearances were at times extraordinary and new to me. The hy- 

 drogen shot out rapidly, scintillating as it went, and suddenly here and 

 there the bright line, broad and badly defined, would be pierced, as it 

 were, by a line of intensely brilliant light parallel to the length of the 

 * Proc. Eov. Soc. 1869, p. 354, Mar. 17. 



