1889.] On the Spectrum of the Great Nebula in Orion. 55 



side, but as a similar appearance is presented by G, and the stronger 

 of the lines of the group, it may arise from some optical or photo- 

 graphic cause. The line at 3724 impresses me strongly as a single line, 

 and there s certainly no trace of the first line of the triplet at 3730. 

 The line appears to me stronger where it is upon the star- spectra. 



As therefore there seems to be little doubt that the "remnant of 

 the fluting at 500 " is not coincident with the brightest nebular line, 

 and the next most characteristic group of this spectrum, the triplet 

 at 3720, 3724, and 3730, according to Liveing and • Dewar, does not 

 appear to be present in the photographs, we may conclude that the 

 remarkable spectrum of the gaseous nebulae has not been produced by 

 burning 1 magnesium.* 



I should mention that Mr. Lockyer attributes one other line occa- 

 sionally seen in the gaseous nebulae to the flame spectrum of 

 magnesium, namely, a very faint line at about X 4700. Now, accord- 

 ing to my experience, it is only in the spark and arc that a line of 

 magnesium appears at this place, a condition of the spectrum when 

 the lines at b are very conspicuous, and the band at A 5006*5 is 

 usually absent. When, however, the spark is taken in magnesium 

 chloride, the band is present under some conditions, but the triplet at 

 6 is always bright. I therefore consulted Professor Liveing, who 



* On the narrower basis of the magnesium spectrum only, Professors Liveing 

 and Dewar point out that : " the appearance of a line in the position of the first 

 band without any trace of the second band, which is nearly as bright as the first, 

 and without any trace of the b group, is qiiite sufficient to create a suspicion of 

 mistaken identity when Mr. Lockyer ascribes the sharp green line in the spectrum 

 of nebulae to this band of magnesia. This suspicion will be strengthened when it is 

 noticed that the line in question is usually in nebula? associated with the F line of 

 hydrogen, if it be borne in mind that the spark of magnesium in hydrogen does not 

 give the bands, and that the oxyhydrogen flame hardly produces them from 

 magnesia when the hydrogen is in excess." (' Roy. Soc. Proc.,' vol. 44, p. 245.) 

 Mr. Taylor records a brightening of the continuous spectrum of the nebula at 

 X 5200, which he suggests may be magnesium. But this position is twenty -five 

 units from that of the middle of the magnesium triplet at " (' Monthly Notices 

 Pv.A.S.,' vol. 49, p. 125.) 



