1881.] On the Reversal of the Lines of Metallic Vapours. 405 



Considering the enormons complexity of the iron spectrum, which 

 probably reaches to something like a thousand distinct vibrations, we 

 should expect to find a greater variation in the relative strength and 

 reversibility of the lines of this metal, according to the circumstances 

 in which it is placed, than we find in the case of metals giving simpler 

 spectra. So that we may say, on the whole, that the phenomena in the 

 case of iron are of much the same general character as we have 

 observed before in the case of other metals ; but the number of obser- 

 vations to be made on so extensive a subject renders it extremely 

 difficult to come to any general conclusions. 



When the perforation of the lower carbon is filled with titanium 

 cyanide instead of the iron wire, the titanium lines come out very 

 brilliantly and steadily, and many of them, especially in the green and 

 blue parts of the spectrum, are expanded and reversed. We give a 

 list of those we have observed to be reversed. 



6260 



5038 



4535-5 



4617 



l lines of pair. 



5036 



4535 



4305 



5223 



5035 



4533-2 



4299-5 



5209 



5013 



4531-7 



4299 



5192 



5007 



4690-5 



4298 



5129 



4999 



4681 



4295 



5064 



4990 



4666-5 



4290-7 



5039 



4981 



4655-5 





In the case of chromium, introduced into the crucible either as oxide 

 or as bichromate of ammonia, there were no reversals until a gentle 

 current of hydrogen or of coal gas was led in through the perforated 

 carbon. This brought out the triplet in the green, wave-lengths 5207, 

 5205, 5203, sharply and steadily reversed, and likewise the three strong 

 lines in the indigo, wave-lengths 4289, 4274, 4253 ; also a triplet near 

 N at wave-lengths about 3578, 3593, 3606, apparently coincident with 

 strong lines in Cornu's map of that part of the solar spectrum, and a 

 rather strong double line just below O at about wave-length 3446. 

 The reversal of another chromium line at about wave-length 3217 is 

 doubtful. A triplet at wave-lengths 2799*8, 2797, 2794, is more easily 

 reversed than any other of the chromium lines. This triplet is generally 

 strongly developed whenever a compound of chromium is introduced 

 into the crucible, so that we conclude that it is due to that metal, but it 

 is sometimes visible in the photographs when other chromium lines are 

 not seen. A still more refrangible chromium line, wave-length about 

 2779"6, is also frequently reversed by a gentle current of hydrogen. 



The two aluminium lines near S are frequently reversed when a 

 fragment of the metal is dropped into the crucible, the less refrangible 

 line, wave-length 3091*5, being more strongly reversed, and continuing 

 reversed for a longer time than that at wave-length 3080'5. 



