358 



Spectroscopic Observations of the Sun. 



[May 19, 



determining the depth from which the vapours are torn, and varying 

 almost directly with the amount of motion indicated. 



Here, then, we have, I think, the chain that connects the prominences 

 with the brighter points of the faculse. 



These lozenge-shaped appearances, which were observed close to the 

 spot on the 1 6th, were accompanied by the " throbs " of the eruption, to 

 which I have before referred ; while Mr. Holiday was with me — a space 

 of two hours — there were two outbursts, separated by a state of almost 

 rest, and each outburst consisting of a series of discharges, as I have 

 shown. I subsequently witnessed a third outburst. The phenomena 

 observed on all three were the same in kind. 



On this day I was so anxious to watch the various motion-forms of the 

 hydrogen-lines, that I did not use the tangential slit. This I did the next 

 day (the 1 7th of April) in the same region, when similar eruptions were 

 visible, though the spot was no longer visible. 



Judge of my surprise and delight, when upon sweeping along the spec- 

 trum, I found hundreds of the Fraunhofer lines beautifully bright at 

 the base of the prominence ! ! ! 



The complication of the chromosphere spectrum was greatest in the 

 regions more refrangible than C, from E to long past b and near F, and 

 high-pressure iron vapour was one of the chief causes of the phenomenon. 



I have before stated to the Royal Society that I have seen the chromo- 

 sphere full of lines ; but the fullness then was as emptiness compared with 

 the observation to which I now refer. 



A more convincing proof of the theory of the solar constitution, put 

 forward by Dr. Frankland and myself, could scarcely have been furnished. 

 This observation not only endorses all my former work in this direction, 

 but it tends to show the shallowness of the region on which many of the 

 more important solar phenomena take place, as well as its exact locality. 



The appearance of the F line, with a tangential slit at the base of the 

 prominence, included two of the lozenge-shaped brilliant spots to which I 

 have before referred ; they were more elongated than usual — an effect of 

 pressure, I hold — greater pressure and therefore greater complication of the 

 chromosphere spectrum. This complication is almost impossible of obser- 

 vation on the disk. 



It is noteworthy that in another prominence, on the same side of the 

 sun, although the action was great, the erupted materials were simple, i. e. 

 only sodium and magnesium, and that a moderate alteration of wave-length 

 in these vapours was obvious. 



Besides these observations on the l/th, I also availed myself of the 

 pureness of the air to telescopically examine the two spots on the disk, 

 which the spectroscope reported tranquil as to up and down rushes. I 

 saw every cloud-dome in their neighbourhood perfectly, and I saw these 

 domes drawn out, by horizontal currents doubtless, in the penumbrae, 



