Line in the Spectrum of the Nebula in Orion. 205 



the nebular line to fall within the termination of the magnesium 

 band " (loc. cit., p. 49). 



This year the position of the nebular line within the termination 

 of the magnesia band has been confirmed by both of us independently 

 on several nights. 



The more refrangible position of the nebular line relatively to the 

 termination line of the MgO band has been ascertained not only by 

 repeated comparisons of the two spectra by means of a suitably 

 illuminated pointer, bat also this year, as last year, by occasional 

 moments of direct vision of the nebular line upon and within the 

 magnesia band. It is only occasionally that the necessary relative 

 brightness of the band can be secured, but such moments of direct 

 vision of the two spectra are very trustworthy. 



On February Oth, Professor Liveing made some observations on 

 the spectrum of the nebula, and I have his permission to quote from 

 the notes which he entered at the time in my observatory book. 

 During the afternoon he examined the adjustments of the little 

 mirror. His words are: "Observed in Dr. Huggins' spectroscope 

 attached to his telescope the Fraunhofer lines 6, as given by the 

 clouds, and the bright lines of burning magnesium thrown in by 

 reflexion. The solar spectrum was but faint, so that it was necessary 

 to use rather a wide slit. I observed a close coincidence between the 

 dark lines of the sky light and the bright lines of the burning mag- 

 nesium ; the two overlapped, but the dark lines extended a very little 

 on the less refrangible side, the brightest line a very little on the more 

 refrangible side beyond the dark line." 



In the evening he observed the nebula, and recorded his observations 

 in the following words : "Observed the spectrum of the nebula in 

 Orion, and compared the position of the least refrangible line with 

 the magnesia fluting. The latter was thrown in by reflection from 

 burning magnesium. I put the nebular line on the pointer first, and 

 then from time to time the magnesium was burnt. I made quite sure 

 that the edge of the magnesia fluting was less refrangible than the 

 nebular line ; repeated the observations several times. Tried to see 

 both the nebular line and the fluting at the same time, but found it 

 hard to see both at once, but I still came to the same conclusion, 

 namely, that the edge of the fluting was less refrangible than the 

 nebular line." 



Afterwards, Professor Liveing observed the third line of the 

 nebula, together with H/3 from a vacuum-tube. He says : " Com- 

 pared the position of the most refrangible of the nebular lines with 

 the F line of hydrogen thrown in by reflexion from a vacuum-tube, 

 the coincidence seemed perfect, the one line falling upon the other."* 



* [On April 29, Professor Liveing was kind enougli to go over again with us the 

 arrangements for the comparison spectrum, and, in particular, to see if any error 



