1873.] Mr. J. N. Lockyer on Spectrum- Analysis. 511 



two metallic spectra, being made to occupy the position between the 

 two. 



III. On the Lines coincident in different Spectra. 



The bearing of the former papers on the lengths of the lines of the 

 elements is briefly recapitulated. 



The examination of the various spectra of metals and alloys indicated 

 the great impurity of most of the metals used, and suggested the possi- 

 bility of the coincidences observed by Thalen and others being explained 

 in the light of former work. 



It is observed that coincidences are particularly numerous in the 

 spectra of iron, titanium, and calcium, and that nearly every other solar 

 metallic spectrum has one or more lines coincident with lines of the last 

 element. These coincident lines are, as a rule, very variable in length and 

 intensity in various specimens of the metals in which they occur, and are 

 sometimes altogether absent. 



One of the longest calcium lines, that at wave-length 4226*3, is also seen 

 in the strontium spectrum as a line of medium length; and 4607'5, a very 

 long line in strontium, appears in calcium as a short line. Another very 

 long strontium line, 4215*3, is asserted by Thalen to be seen in calcium ; 

 but the author has never seen it till lately, and then only in a specimen of 

 calcium Jcnoiun to contain strontium. 



We have here, then, a case of coincident lines, in which the one that 

 is long and bright in one spectrum is short and faint in the other, and a 

 case of a line said to be coincident in two spectra being, though always 

 visible in one, sometimes absent in the other of them, and only appear- 

 ing in it when the two substances were mixed. The hypothesis of im- 

 purity at once explains the whole case, even without the third line, which 

 renders the fact of mixture certain. 



The longest lines of calcium occur in iron, cobalt, nickel, barium, stron- 

 tium, &c; and the longest lines of iron occur in calcium, strontium, ba- 

 rium, and other metals. 



Other cases are adduced ; and the following general statements are 

 hazarded, with a premise that further inquiry may modify them. 



1. If the coincident lines of the metals be considered, those cases are 

 rare in which the lines are of the first order of length in all the spectra 

 to which they are common : those cases are much more frequent in which 

 they are long in one spectrum and shorter in the others. 



2. As a rule, in the instances of those lines of iron, cobalt, nickel, 

 chromium, and manganese which are coincident with lines of calcium, 

 the calcium lines are long, while the lines as they appear in the spectra 

 of the other metals are shorter than the longest lines of those metals. 

 Hence we are justified in assuming that short lines of iron, cobalt, nickel, 

 chromium, and manganese, coincident with long and strong lines of cal- 

 cium, are really due to traces of the latter metal occurring in the former 

 as an impurity. 



vol. xxi. 2 s 



