(592 Professor Deirar [June 10, 



at the temperature of flames to wliicli we alluded in our paper on 

 the spectrum of water * 



JJItra-Violet Spectrum of the Flame of Burning Magnesium. 



"When magnesium wire or ribbon is burnt in air, we see the three 

 lines of the h group, the blue line about wave-length 4570, first 

 noticed by us in the spark spectrum ; f and photographs show, 

 besides, the well-known triplet in the ultra-violet between the solar 

 lines K and L sharply defined, and the line for which Cornu has 

 found the wave-length 2850 very much expanded and strongly 

 reversed. These lines are all common to the flame, arc, and spark 

 spectra ; and the last of them (2850) seems to be by far the strongest 

 line both in the flame and arc, and is one of the strongest in the 

 spark. But, in addition to these lines, the photographs of the flame 

 show a very strong, somewhat diffuse, triplet, generally resembling 

 the other magnesium triplets in the relative position of its com- 

 ponents, close to the solar line M; and a group of bands below it 

 extending beyond the triplet near L. These bands have, for the 

 most part, each one sharply defined edge, but fade away on the other 

 side ; but the diffuse edges are not all turned towards the same side 

 of the spectrum. The positions of the sharp edges of these bands, 

 and of the strong triplet near M, are shown in PL III., Fig. 1. It 

 is remarkable that the triplets near P and S are absent from the 

 flame spectrum, and that the strong triplet near M is not represented 

 at all either in the arc or spark. The hydrogen-magnesium series of 

 lines, beginning at a wave-length about 5210, are also seen some- 

 times, as already described by us, J in the spectrum of the flame ; but 

 we have never observed that the appearance of these lines, or of the 

 strong line with which they begin, is connected with the non-appear- 

 ance of hi. Indeed, we can almost always see all three lines of the 

 h group in the flame, though as h^ is the least strong of the three, it 

 is likely to be most easily overpowered by the continuous spectrum 

 of the flame. 



Burning magnesium in oxygen instead of atmospheric air does not 

 bring out any additional lines ; on the contrary, the continuous spec- 

 trum from the magnesia overpowers the line spectrum, and makes it 

 more difficult of observation. 



Magnesia heated in the oxyhydrogen jet does not appear to give 

 the lines seen in the flame, except that at 2850. 



Spectrum of the Arc. 



The spectrum of magnesium, as seen in the arc, contains several 

 lines besides those heretofore described. These lines come out 

 brightly, generally considerably expanded, when a fragment of mag- 

 nesium is dropped into the crucible through which the arc is passing, 



* 'Proc. Roy. Soc' 1880, No. 201, p. 152. 

 t Ibid. vol. xxvii. p. 350. % Ibid. vol. xxx. p. 96. 



