1879.] on Spectroscopic Investigation. 213 



gradually tho dark line disappears from IT, and afterwards from K, 

 while the alnminiura lines remain with dark middles for a long time. 

 When a mixture of lime and jiotassium carbonate was introduced 

 into a carb(m crucible, the groui) of three lines with wave-lengths 

 4,425, 4,434, and 4,454 were all reversed, the least refrangible being 

 the most strongly reversed, and remaining so longest, while the most 

 refrangible was least strongly reversed, and for the shortest time. 



When aluminium was put into the crucible, only the two lines of 

 that metal between H and K were seen reversed. The lines at tho 

 red end remained steadily bright. 



When magnesium was put into a lime crucible, the h group 

 expanded a little wdthout appearing reversed, but when some alumi- 

 nium was added, the least refrangible of the three lines appeared 

 with a dark middle, and on adding more magnesium the second lino 

 put on the same ajipearance; and lastly, the most refrangible was 

 reversed in like manner. The least refrangible of the three remained 

 reversed for some time ; and the order of reversibility of the group is 

 that of refrangibility. Of the other magnesium lines, that in tho 

 yellowish-green (wave-length 5,527) was much expanded, while the 

 blue line (wave-length 4,703), and a line still more refrangible than 

 the hitherto recorded lines, with wave-length 4,354, were still more 

 expanded each time that magnesium was added. 



The following experiments were made in carbon crucibles : — 



With strontia the lines with wave-lengths 4,607, 4,215 and 4,079 

 were all seen with dark lines in the middle, but no reversal of any 

 strontium line less refrangible could be seen. 



A mixture of barium and potassium carbonates produced the 

 reversal of the lines with wave-lengths 5,535 and 4,933. When 

 barium chlorate was dropped into a crucible, the four lines with 

 wave-lengths 4,553, 4,933, 5,545, and 5,518 were 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. 



Sodium carbonate gave only the D lines 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 



