368 



Profs. Liveing and Dewar 



[Feb. 27, 



wliile the aluminium lines remain with dark middles for a long time. 

 When a mixture of lime and potassium carbonate (to produce a 

 stronger current of vapour in the tube) was introduced into a carbon 

 crucible the calcium (?) line with wave-length 4,095 was seen strongly 

 reversed, and the group 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 the longest, while the most 

 refrangible was least strongly reversed and for the shortest time. 



Besides these reversals, which were regularly observed, the following 

 were noticed by us as occurring in lime crucibles but with less 

 certainty, perhaps only at the highest temperatures. Dark bands 

 appearing for a short time and dwindling into sharp dark lines with 

 wave-lengths about 6,040 and 6,068 (perhaps due to the oxide); a 

 dark line replacing the most refrangible of a well-niarked group of 

 several bright lines with wave-length 5,581 (or possibly the - brighter 

 line 5,588) ; and the lines with wave-lengths 6,121 and 6,161 reversed 

 simultaneously for an instant and reappearing bright immediately ; 

 and the line with wave-length 5,188 reversed. When aluminium was 

 put into the crucible only the two lines of that metal between H and K 

 were seen reversed. The lines at the red end remained steadily bright. 



When some magnesium was put into a lime crucible, the b group 

 expanded a little without appearing reversed, but when some alu- 

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

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

 put on the same appearance ; 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 

 the inverse of that of refrangibility. Of the other magnesium lines, 

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

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

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

 expanded each time that magnesium was added. These last two lines 

 expanded much more on their less refrangible than on their more 

 refrangible sides, and were not seen reversed. The bright blue line 

 (wave-length 4,481) seen when the spark is used, was not visible either 

 bright or reversed ; and this seems to be in agreement with Capron's 

 photographs, which show this line very strong with the spark but not 

 with the arc. 



The following experiments were made in carbon crucibles : — 

 When strontia was put in 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. After adding 

 some aluminium and some potassium carbonate to increase the current 

 of vapour, no reversal of any strontium red line could be detected, 

 though momentary cloudy dark bands were seen in the red when 



