﻿Mr. J. N. Lockyer on the Spectrum of a Solar Prominence. 143 



The next in prominence is situated about D-f 3*58 (F=D-f 2- 73, 

 Kirchhoff's 232*5 = D + 3*50). It is broader and less vivid, and not 

 so well defined at the edges. 



There are several other conspicuous lines, but none comparable 

 to the first. I noticed a sharp line in the red, but did not get a 

 measure. 



I said that at D + 0*34 the continuous spectrum ends abruptly. 

 A faint continuation, however, is frequently seen in bright flashes, 

 very bright ones bringing out a brilliant red end crossed by a bright 

 line. 



The whole of the ordinary spectrum seems green and blue, or 

 rather greenish blue ; but as the usual prismatic order of colours is 

 recognizable in bright flashes, it is to be inferred that the region from 

 E to F is so much brighter as to give the character in question. 

 What strikes one most, however, is the varying relative brightness 

 of the continuous and linear spectra ; sometimes the lines are 

 scarcely seen, and sometimes very little else is seen. This may be 

 nothing more than an illusion ; but in the absence of any certainty 

 that it is so, the impression left on the mind is worth recording. 



The difficulty of discriminating between the many less prominent 

 lines is immensely increased by the momentary character of the 

 phenomenon. Before the mind has selected an individual, the feeble 

 impression on the retina has vanished; and before another flash 

 succeeds, the memory of the half-formed choice has vanished with 

 it, and there is nothing on which to found a selection. Otherwise 

 it would be easy enough to measure many more lines. 



" Notice of an Observation of the Spectrum of a Solar Prominence." 

 By J. N. Lockyer, Esq., in a Letter to the Secretary. 



October 20, 1868. 

 Sir, — I beg to anticipate a more detailed communication by in- 

 forming you that, after a number of failures, which made the attempt 

 seem hopeless, I have this morning perfectly succeeded in obtaining 

 and observing part of the spectrum of a solar prominence. 



As a result I have established the existence of three bright lines in 

 the following positions : — 



I. Absolutely coincident with C. 

 II. Nearly coincident with F. 

 III. Near D. 



The third line (the one near D) is more refrangible than the more 

 refrangible of the two darkest lines, by eight or nine degrees of 

 Kirchhoff's scale. I cannot speak with exactness, as this part of 

 the spectrum requires remapping. 



I have evidence that the prominence was a very fine one. 

 The instrument employed is the solar spectroscope, the funds for 

 the construction of which were supplied by the Government-Grant 

 Committee. It is to be regretted that its construction has been so 

 long delayed. 



I have, &c, 



J. Norman Lockyer. 

 The Secretary of the Royal Society. 



