[ 983 ] 
XVIII. On the Photographic A/-c Spectrum of Electrolytic Iron. 
By J. Norman Lockyer, C.B., F.R.S. 
Received October 27,—Read November 23, 1893. 
[Plates 12, 13.] 
Contents. 
CAGE. 
I.— Reference to Earlier Work . 983 
Method of eliminating impurities. 983 
ThaljSn’s Eye observations. 984 
II.— The Present Work . 985 
Necessity of the research. 985 
Method employed. 987 
Reference to the observations of Messrs. Kayser and Runge . 989 
Reference to McClean’s work on the Spark Spectrum. 989 
Explanation of the tables. 990 
III. -— Discussion of the Results . 990 
List of impurities in electrolytic iron. 990 
Comparison with Thal^n’s Eye observations (with table). 991 
Comparison with Kayser and Runge’s results. 992 
Comparison with McClean’s photographs (with 3 tables). 993 
General conclusions .. 997 
IV. —General Table. 998 
I.—Comparison of lines photographed with those given by Kayser and Runge 998 
I. Reference to Earlier Work. 
Method oj Eliminating Impurities. 
In the Bakerian Lecture for 1873'“ I gave an account of my early researches on the 
spectrum of iron, which bad been commenced in 1870, and suggested a possible 
method of spectroscopically eliminating impurities. I tben hazarded the statement 
that “ in cases of coincidences found between the lines of various spectra, the line 
may be fairly assumed to belong to that one in which it is longest and brighest.” 
The method was illustrated by three plates, one of which showed the long and short 
* ‘ Phil. Trans.,’ vol. 164, p. 479. 
14.1.95 
