IN CONNEXION WITH THE SPECTRUM OF THE SUN. 
649 
found to be the case, it became necessary to determine whether the ordinary spectra are 
due to the metals or their oxides, since according to my experiments all compounds 
which contain the metal in the form of oxide give the same spectra.” 
As a result of his experiments on sodium, he states that in the flames which give the 
line of sodium the spectrum is due to the metals and not to the oxide. Hence he 
concludes that in the case of oxides the spectrum is the spectrum of the metals*. 
He then states that the new lines which had then lately been discovered without 
corresponding elemental lines were probably due to binary compounds. 
The main view in Mitscherlich’s paper, that each binary compound has a spectrum 
of its own, is borne out by the conclusion arrived at by Clifton and Roscoe, who remark 
in their paper above referred to : — 
“ Kirchhoff, in his interesting memoir on the Solar Spectrum and the Spectra of the 
Chemical Elements, noticed in the case of the calcium-spectrum that bright lines which 
were invisible at the temperature of the coal-gas flame became visible when the tempe- 
rature of the incandescent vapour reached that of the intense electric spark. We have 
confirmed this observation of Kirchhoff’s, and have extended it, inasmuch as we, in the 
first place, have noticed that a similar change occurs in the spectra of strontium and 
barium ; and, in the second place, that not only new lines appear at the high temperature 
of the intense spark, but that the broad bands characteristic of the metal or metallic 
compound at the low temperature of the flame or weak spark totally disappear at the 
higher temperature. The new bright lines which supply the part of the broad bands 
are generally not coincident with any part of the band, sometimes being less and some- 
times more refrangible. Thus the broad band in the flame-spectrum of calcium named 
Ca ,6 is replaced in the spectrum of the intense calcium-spark by five fine green lines, all 
of which are less refrangible than any part of the band Ca /3 ; whilst in the place of the 
red or orange Ca a, three more refrangible red or orange lines are seen. The total dis- 
appearance in the spark of a well-defined yellow band seen in the calcium-spectrum at 
the lower temperature was strikingly evident. We have assured ourselves, by repeated 
observations, that in like manner the broad bands produced in the flame-spectra of 
strontium and barium compounds, and especially Sr a, Sr/3, Sry, Baa, Ba/3, Bay, Bat), 
Ba s, Ba q, disappear entirely in the spectra of the intense spark, and that new bright 
non-coincident lines appear. The blue Sr § line does not alter either in intensity or in 
position with alterations of temperature thus effected ; but, as has already been stated, 
four new violet lines appear in the spectrum of strontium at the higher temperature. 
“ If, in the present incomplete condition of this most interesting branch of inquiry, 
we may be allowed to express an opinion as to the possible cause of the phenomenon of 
the disappearance of the broad bands and the production of the bright lines, we would 
suggest that, at the lower temperature of the flame or weak spark, the spectrum observed 
is produced by the glowing vapour of some compound, probably the oxide, of the diffi- 
cultly reducible metals; whereas at the enormously high temperature of the intense 
* This opinion he corrects in his next communication, to which reference will be made hereafter. 
4 S 2 
