On the Chief Line in the Spectrum of the Nebulce. 193 



wnrde am 21 Mai, 1871, untersucht, es besteht aus zwei Linien, von 

 denen die erste mit der Stickstofflinie (Wellenlange 500'4 Milliontel 

 Millimeter) coincidirt ; diese Linie erscheint aber hier breiter als in 

 den Spectren der planetarischen Nebel und ist besonders nach dem 

 violetten Ende des Spectrums SEHR VERWASCHEN." 



Here, then, it is again explicitly stated that the nebula line was 

 considerably ill-defined on the violet edge. 



Bredichin made a series of observations of the three nebula lines 

 in 1877, and he noted also that the chief line was less defined on 

 the blue edge. In the words of this observer, "se presentait 

 comme nne bande, une peu plus claire vers le rouge."* 



The following is the description of the chief nebula line, as seen in 

 the Orion nebula, given by Mr. Maunder in 1884 : f 



" The line X 5005 was examined with this latter dispersion (two- 

 prism train), the slit being very narrow, and was seen to be a single 

 line. None of the lines in the spectrum of the nebula are, however, 

 very sharp. \ 5005 showed a faint fringe mainly on the side nearer the 

 blue.' 1 



It must be borne in mind that as these observations of the unde- 

 fined condition of the blue edge of the nebular line were made before 

 special attention had been directed to it by my paper of November, 

 1887, they were absolutely unbiassed. Prior to 1887, no one had 

 suggested that the line might be the remnant of a fluting. Indeed, 

 Dr. Huggins contended for a line of an unknown form of nitrogen. 



I have already quoted Dr. Huggins's present declaration, that since 

 his discovery of the nebula line in 1864 he had always observed it as 

 sharply and perfectly defined at both edges, by which assertion he 

 practically repudiates his own published observations. But Dr. Hug- 

 gins has done more than this ; he has put himself to the trouble of 

 communicating with other observers of nebula spectra with a view of 

 obtaining their opinions as to the character of the chief line. I need 

 only refer to Dr. Huggins's correspondence with Professor Vogel, 

 who wrote, J in answer to a letter from him and in support of his 

 view : " Beeile ich mich Ihnen mitzutheilen, dass meine langjahrigen 

 Beobachtungen tiber die Spectra der Gas-Nebel vollkommen mit den 

 Ihrigen darin iibereinstimmen, dass die Nebellinie X 5004 schmal, 

 scharf und NICHT VERWASCHEN IST." With reference to the observa- 

 tion of Dr. Vogel as to the undefined character of one edge of the 

 nebula line, previously referred to in this reply, Dr. Huggins remarks 

 as follows : " In an early observation of the Dumb-bell nebula, 

 Prof essor Vogel, indeed (' Beobachtungen zu Bothkamp,' p. 59, 1872), 

 describes this line as less defined towards the violet side. In a letter 



* ' Annales de 1'Obs. de Moscou,' vol. 3, 1877, p. 120. 

 t ' Greenwich Spectroscopic .Results,' 1884, p. 5. 

 I 'Boy. Soc. Proc.,' vol. 46, p. 53. 



