1881.] Identity of the Spectral Lines of Different Elements. 227 



the supposed coincidences lines of iron are involved. We have, there- 

 fore, chiefly directed our attention to iron lines. 



Taking iron and titanium, we find that we can resolve the lines at 

 the wave-lengths following : — 



6064*7* is a wide double, the iron line less refrangible than the 

 titanium by something like a division on Angstrom's scale. Young 

 did not resolve this line, probably because he was looking for a much 

 closer double line. 



5714*09. A very close double, the iron the less refrangible, but not 

 in Thalen's list. 



5661' 65. A double titanium line, but there appears to be a single 

 iron line between the titanium lines. 



5489*05. A titanium line, but we could not see any iron line in the 

 arc at this place, and no such iron line is in Thalen's list. 



5486*94. The iron line is more refrangible than the titanium. 



5446*07. Rather a close double, the iron line the less refrangible. 



5428*96. A wider double, the iron line the less refrangible. 



5403*28. The iron line in this is the more refrangible. 



5396*19. The iron line is the less refrangible. 



5006*72. We have not resolved this line ; but it is not given as an 

 iron line in Thalen's list. 



4990*48. We have not resolved this line ; but it is a very strong 

 titanium line, and the titanium may have overpowered the iron line if 

 they are not coincident. 



4690*69. The iron line is given by Thalen as slightly less refrangi- 

 ble than the titanium line, but we did not resolve this line (see 

 Appendix to this paper). 



4426*9. Not given as an iron line in Thalen's list. 



4307*25. The iron line is given by Thalen as slightly more refran- 

 gible that the titanium line. We have not resolved this line, the 

 titanium line being weak. 



4293*96. The iron is given by Thalen as slightly less refrangible 

 than the titanium, but we did not resolve this line, or make out that 

 there is any titanium line at this place. 



4287*47. This is not given as an iron line in Thalen's list. 



4171*77. We have repeatedly looked for this titanium line but have 

 not seen it in the arc. 



In the case of calcium it was more difficult to resolve close doubles, 

 because the introduction of a very small quantity of a calcium com- 

 pound into the arc for the purpose of identification caused such an 

 expansion of the calcium lines as to overpower in many cases their 

 weaker neighbours. 



* The numbers by which the lines are here designated are the ware-lengths of the 

 corresponding Fraunhofer lines taken from the catalogue of oscillation frequencies in 

 the Keport of the British Association, 1878, p. 37. 



