1878.] Analysis in connexion with the Spectrum of the Sun, 173 



which, the relative intensity is reversed or the two intensities are- 

 assimilated. What might happen does happen ; the relative intensity 

 of the two triplets in the spark photograph is grandly reversed in 

 the spectrum of the sun. The lines barely visible in the spark photo- 

 graph are among the most prominent in the solar spectrum, while the 

 triplet which is strong in that photograph is represented by Fraunhofer 

 lines not half so thick. Indeed, while the hypothesis that the iron 

 lines in the region I have indicated are produced by the vibration of 

 one molecule does not include all the facts, the hypothesis that the 

 vibrations are produced by at least three distinct molecules includes 

 all the phenomena in a most satisfactory manner. 



Lithium. 



Before the maps of the long and short lines of some of the chemical 

 elements compared with the solar spectra, which were published in 

 the " Philosophical Transactions " for 1873, Plate 9, were communi- 

 cated to the Society, I very carefully tested the work of prior observers 

 on the non-coincidence of the red and orange lines of that metal with 

 the Fraunhofer lines, and found that neither of them were strongly, if" 

 at all, represented in the sun, and this remark also applies to a line in 

 the blue at wave-length 4603. 



The photographic lithium line, however, in the violet, has a strong 

 representative among the Fraunhofer lines. 



Applying, therefore, the previous method of stating the facts, the 

 presence of this line in the sun differentiates it from all the others. 

 For the differentiation of the red and yellow lines I need only refer to 

 Bunsen's spectral analytical researches, which were translated in the 

 " Philosophical Magazine," December, 1875. 



In Plate 4 two spectra of the chloride of lithium are given, one of 

 them showing the red line strong and the yellow one feeble, the other 

 showing merely a trace of the red line, while the intensity of the 

 yellow one is much increased, and a line in the blue is indicated^ 

 Another notice of the blue line of lithium occurs in a discourse by 

 Professor Tyndall, reprinted in the " Chemical News," and in a letter of 

 Dr. Frankland's to Professor Tyndall, dated November 7, 1861. This 

 letter is so important for my argument that I reprint it entire from 

 the " Philosophical Magazine," vol. xxii, p. 472 : — 



" On throwing the spectrum of lithium on the screen yesterday, I 

 was surprised to see a magnificent blue band. At first I thought the 

 lithic chloride must be adulterated with strontium, but on testing it 

 with Steinheil's apparatus it yielded normal results without any trace 

 of a blue band. I am just now reading the report of your discourse 

 in the ' Chemical News,' and I find that you have noticed the same 

 thing. Whence does this blue line arise ? Does it really belong to 

 the lithium, or are the carbon points or ignited air guilty of its pro- 



