192 Mr. J. N. Lockyer. 



seen, occupying in the spectrum apparently the same position as the 

 brightest of the lines of nitrogen. When the slit was made as narrow 

 as the intensity of light would permit, this bright line was not so well- 

 defined as the corresponding line in some of the other nebulce under 

 similar conditions of slit, but remained nebulous at the edges." An ob- 

 servation of the spectrum of General Catalogue No. 4572,* also 

 made in 1864, led the observer to record : " The spectrum of this 

 nebula consisted of one bright nebulous line of the same refrangibility 

 as the brightest of the lines of nitrogen," and in the same paper we 

 read : " One bright line only was distinctly seen, of apparently the 

 same refrangibility as the brightest of the nitrogen lines. This bright 

 line appeared by glimpses to be double. Possibly this appearance was 

 due to the presence near it of a second line." 



These observations show conclusively that the chief nebula line 

 has not always been described as " sharply and perfectly defined at 

 both edges," to use Dr. Huggins's language of 1889, and to no one 

 should this fact be more manifest than to Dr. Huggins, since the 

 above observations were made by him. 



Secchi, one of the first observers of nebular and stellar spectra, in 

 observations of some planetary nebulae made in 1866,f saw the three 

 principal lines, and noted that " the planetary nebula in Andromeda 

 has the lines above named, but the principal one is a little diffused." 



The observation relating to the presence of a second bright line 

 very near to the chief nebula line might have been of considerable 

 importance, and have afforded an almost crucial test of the validity 

 of my identification of the line. This second line might well have 

 been the second maximum of the magnesium fluting, but Dr. 

 Huggins's statement as to its position is so loose as to make it 

 impossible for me to say whether such is the case or not. 



I should, however, have been unjustified in relying upon Dr. 

 Huggins alone ; and it will be seen from what follows that nearly 

 all observers of nebula spectra have noted at some time or other that 

 the chief nebula line appeared undefined at one edge, as if it were 

 part of a fluting. 



In 1871 Vogel made some observations of the spectra of nebulae.J 

 I have noted that in 1864 'Dr. Huggins observed only one bright line 

 in the spectrum of the Dumb-bell nebula, and recorded this line as 

 nebulous at the edges. Vogel's observations of the spectrum of the 

 same nebula in 1871 agree, as regards the character of the line, in 

 every respect with that of Dr. Huggins. 



The following is Vogel's description : " Sehr heller grosser Nebel 

 der unter dem N"amen Dumb-bell bekannt ist. Das Spectrum desselben 



* ' Phil. Trans.,' 1866, p. 386. 



t ' Bullettino Meteorologico,' 31st Oct., 1866. 



I ' Bothk. Beob.,' Leipzig, Heft 1, 1872, p. 56. 



