and of the Analysis of the Solar Atmosphere. 253 



more or less of this yellow light, which I have always found the 

 same in its characters. The only principle which these various 

 bodies have in common with the salts of soda is water; yet I 

 think that the formation or presence of water cannot be the 

 origin of this yellow light, because ignited sulphur produces the 

 very same, a substance with which water is supposed to have no 

 analogy." "It may be worth remark," he adds in a note, 

 " though probably accidental, that the specific gravity of sulphur 

 is 1*99, or almost exactly twice that of water." " It is also re- 

 markable," he continues in the text, " that alcohol burnt in an 

 open vessel, or in a lamp with a metallic wick, gives but little of 

 the yellow light ; while if the wick be of cotton it gives a con- 

 siderable quantity, and that for an unlimited time. (I have 

 found other instances of a change of colour in flames, owing to 

 the mere presence of the substance, which suffers no diminution in^ 

 consequence. Thus a particle of muriate of lime on the wick of 

 a spirit-lamp will produce a quantity of red and green rays for 

 a whole evening without being itself sensibly diminished " *.) 



In a later portion of the memoir he attributes the yellow line 

 in one place to the presence of soda-salts, at another to that of 

 sulphur. Thus, in the above-mentioned statement concerning 

 the spectrum of red-fire, he says, l ' The bright line in the yellow 

 is caused, without doubt, by the combustion of the sulphur" f. 

 Hence we must admit that the conclusion that the aforesaid 

 yellow line can be taken as a positive proof of the presence of 

 sodium-compounds in the flame can in no way be deduced from 

 Herschel and Talbot's researches. On the contrary, the nume- 

 rous modes in which the line is produced would rather point to 

 the conclusion that it is dependent upon no chemical constituent 

 of the flame, but arises by a process whose nature is unknown, 

 which may occur, sometimes more easily, sometimes w T ith diffi- 

 culty, with the most different chemical elements. If we accept 

 such an explanation concerning this yellow line, we must form 

 a similar opinion respecting the other lines seen in the spectrum 

 which were far more imperfectly examined ; and in this we should 

 be strengthened by the statement of Talbot, that a piece of 

 chloride of calcium by its mere presence in the wick of a flame, 

 and without suffering any diminution, causes a red and a green 

 line to appear in the spectrum. 



The experiments of WheatstoneJ, Masson, Angstrom, Van 



* Brewster's Journal, v., 1826. 



[t A short statement of Herschel and Talbot's results, as here quoted, 

 was made by me in a lecture at the Royal Institution on April 5, 1862, and 

 reprinted in the ' Chemical News ' for May 10, 1862.— H. E. R.] 



X "Wheatstone not merely experimented with the spark from an electrical 

 machine, but likewise with the voltaic induction-spark. (Report of the 



