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XIII. The Bakeeian Lectuee. — Researches in Spectrum- Analysis in connexion with the 
Spectrum of the Sun. — No. III. By J. Noeman Lockyee, F.R.S. 
Received November 20, — Read November 27, 1873. 
Introduction. 
The Researches in Spectrum- Analysis in which I have been engaged are opening out 
into so many lines of work that I think it desirable to communicate to the Royal 
Society the present state of the inquiry on its most general aspect, and also to enter 
somewhat into detail on some of the points to which my attention has specially been 
directed, the more so as the methods employed are such as can be, and I sincerely trust 
will be, taken up by other workers. 
To commence, then, by a general statement, I may remark that I have in the first 
place endeavoured to determine whether the new method of spectroscopic observation, 
which I have before described to the Royal Society, is really as competent as it pro- 
mised to be in the quantitative direction, what are the conditions essential to its successful 
employment, and how far it would take us. 
As the time I could devote to this inquiry was limited, I confined myself to mixtures 
of two metals. The results of the experiments which I have to report in the present 
paper, and in a separate one which will be communicated by Mr. W. C. Robeets, 
Chemist of the Mint, and myself, are in more ways than one satisfactory, the history 
of science having shown that a great increase in theoretical work may be hoped for as 
soon as an instrument such as the spectroscope gets into practical use in the arts. 
It may be said that while the qualitative spectrum-analysis depends upon the posi- 
tions of the lines, the quantitative analysis depends not upon their position but upon 
their length , brightness , thickness, and number, as compared with the number visible in 
the spectrum of a pure vapour. 
The character of a spectrum when observed by the new method is so entirely different 
from that which results from following the integrating method, that maps of the various 
spectra, in which not only the relative lengths of the various lines, but their individuality 
shall be faithfully recorded once for all, are an absolute necessity before much further 
progress can be made in the research ; while, from what has been stated in my former 
paper, it is clear that for this purpose volatilization of the vapours of the metals in the 
electric arc is necessary, as by this means the densest vapour can readily be procured. 
I have therefore rendered the vapours I have investigated incandescent by a current 
from a battery of 30 pint Geove’s cells. 
The difficulties of eye-observations were found to be very great, not only in identifying 
3 s 2 
