426 Mr. J. N. Lockyer. On some Spectral Phenomena [Mar. 20, 



We may say, roughly, that the carbons employed give a spectrum 

 containing the flutings of carbon and the lines of calcium, some of 

 them reversed, as I have shown many years ago, both in the case of 

 this and other substances. 



In the photographs of the arc taken under the conditions I ha^e 

 stated, the calcium lines cling to one pole and the carbon flutings to 

 the other ; the lines which reverse themselves in the case of calcium 

 being those which have their intensity most pronounced close to the 

 pole. That this is a phenomenon not dependent upon the chemical 

 constitution of the two poles, but rather on some electrical separation, 

 is rendered evident by the fact that on changing the direction of the 

 current the calcium and carbon spectra change positions. 



Although these phenomena are very marked in the photographic 

 region, as is evidenced by the photographs which I submit to the 

 Society, they yet appear more strongly developed in the less refran- 

 gible regions. The exquisite carbon flutings in the yellow-green, 

 for instance, cling more closely to the pole than those in the violet. 



So much for the spectrum of the poles themselves. 



If now we introduce a metal and observe its vapour, we find a per- 

 fectly new set of phenomena. We get long and short lines, but the 

 law which they obey is no longer the one in operation when the parts 

 of the arc examined are symmetrical with reference to the positive 

 and negative poles as when a horizontal arc is employed. 



Some lines stretch across the spectrum with their intensities 

 greatest close to one pole, while other lines invisible at this pole are 

 most intense at the other. In one photograph, for instance, the blue 

 line of calcium is visible alone at one pole, the H and K lines without the 

 blue lines at the other. 



More than this, there is a progression of lines, so to speak, from 

 pole to pole. They lie en echelon along the spectrum. 



In the case of other lines, only the central region is occupied, the line 

 being enormously distended either like a spindle or a half -spindle, with 

 the bulging portion in some cases on the more, in others on the less, 

 refrangible side. 



It is very difficult to understand what process is here at work if we 

 are not in presence of separations brought about by temperature and 

 electricity. 



However this may be, a most convenient method is afforded of 

 separating basic from non-basic lines. I have already, in previous 

 communications, referred to the repetition of doublets in some spectra, 

 and of triplets in others ; and it often happens that one member of a 

 doublet or triple group is basic. The wide iron triplet near G, to 

 which I referred in my communication read on the 12th December, 

 has its central member basic with calcium; and this is most beautifully 

 shown by the extension of the iron triplet right across the arc, while 



