1879.] on the Reversal of the Lines fo Metallic Vapours. 369 



fresh strontia was thrown in. Two dark lines were seen in the 

 extreme red, which proved to be the potassium lines reversed (wave- 

 lengths 7,670 and 7,700). 



With a mixture of barium and potassium carbonates the line with 

 wave-length 5,535 was strongly reversed, and that with wave-length 

 4,933 distinctly so. When barium chlorate was dropped into a cruci- 

 ble, the four lines with wave-lengths 4,553, 4,933, 5,535, and 5,518, 

 were reversed, and as they remained so for some time, it is probable 

 that the action of the oxygen of the chlorate had nothing to do with the 

 result. The last-named line (5,518) was the least strongly reversed. 



To observe particularly the effects of potassium a mixture of lime 

 and potassium carbonate previously ignited was thrown in. The violet 

 lines of potassium, wave-length 4,044, came out immediately as a broad 

 black band, which soon resolved into two narrower dark bands having 

 wave-lengths nearly 4,042 and 4,045. On turning to the red end the 

 two extreme red lines were both seen reversed. No lines of potassium 

 between the two extremes could be seen reversed, but the group of 

 three yellow lines were all expanded though not nebulous, and other 

 lines in the green were seen much expanded. These observations on 

 potassium were more than once repeated with the same results. 



Using sodium carbonate only the D lines were seen reversed though 

 the other lines were expanded, and the pairs in the green had each 

 become a very broad nebulous band, and D almost as broad a black 

 band. When sodium chlorate was dropped into a crucible, the pair of 

 lines with wave-lengths 5,681, 5,687, were both momentarily reversed, 

 the latter much more strongly than the former. 



When a very little charred rubidium tartrate was put in, the two 

 violet lines were sharply reversed, appearing only as black lines on a 

 continuous light background. Turning to the red end, the more refran- 

 gible of the two lines in the extreme red (wave-length 7,800) was seen 

 to have a decided dark line in the middle, and it continued so for some 

 time. The addition of more rubidium failed to cause any reversal of 

 the extreme red line, or of any but the three lines already mentioned. 



On putting some lithium carbonate into the crucible, the violet line 

 of lithium appeared as a nebulous band, and on adding some aluminium 

 this violet band became enormously expanded, but showed no reversal. 

 The blue lithium line (wave-length 4,604) was well reversed, as was 

 also the red line, while a fine dark line passed through the middle of 

 the orange line. On adding now a mixture of aluminium filings, and 

 carbonates of lithium and potassium, the red line became a broad 

 black band, and the orange line was well reversed. The green line 

 was exceedingly bright, but not nebulous or reversed, and the violet 

 line still remained much expanded, but unreversed. With regard to 

 the green lithium line, we may remark that we have no doubt what- 

 ever that it belongs to lithium, and that there must have been some 



