212 Principal Line in the Spectrum of the Nebula in Orion, 



fineness of the nebular lines under the very considerable dispersion 

 used. There is not the least doubt in my mind that they are all of 

 gaseous origin not ' remnants of flutings.' " 



[The observations with large dispersion by Professor Young, and 

 especially those of Mr. Keeler, after observing with one prism, and 

 then with a compound prism, that the line remained sharp even when 

 examined in the 4th spectrum of a grating 14,000 + to the inch, 

 are of great value in regard to Mr. Maunder's observations. It was 

 on one occasion only when he made use of the very great disper- 

 sion of 80 from A to H, equal to about sixteen prisms of 60, that 

 he observed the nebular line to be otherwise than sharp and de- 

 fined. On this unique occasion he says: "The three lines were 

 seen as narrow bright lines, but none of them were perfectly sharp ; 

 each showed a slight raggedness at both edges, but in the case of 

 the line near A, 5005 it was clear that this fringe or raggedness was 

 more developed towards the blue." Mr. Maunder significantly adds: 

 " In the case of the other two lines they were not bright enough for 

 it to be possible to ascertain whether the fringes were symmetrical 

 or not/' * The new observations at Princeton and at the Lick Ob- 

 servatory would seem to leave little doubt that if the other lines had 

 been as bright as the principal line, the raggedness about them would 

 have been found to be equally unsymmefcrical, and that the want of 

 symmetry affected all three lines, and was probably instrumental. 

 July 4.] 



Second Addendum. Received July 4. 



On the Position of the Line. 



On account of the unusual weather at the Lick Observatory during 

 the early part of this year, Dr. Holden informs me that " The ob- 

 serving chances have been amazingly small." For this reason, 

 although, in addition to the observations on the character of the chief 

 line in the nebula of Orion, measurements of its position were 

 attempted on two nights, the interruption from clouds was so constant 

 that they could not be satisfactorily completed. 



Under these circumstances, I asked Dr. Holden to have the kind- 

 ness to telegraph to me if Mr, Keeler should be able to confirm the 

 position of the line as not coincident with the magnesium-flame fluting 

 in the nebula S. 5. 



On June 15th, I received a telegram with the words : " Confirmed 

 Struve. 5. Keeler." 



I have received since a letter from Mr. Keeler, dated June 14th, 

 1890, in which he says : " Last night I compared the brightest lint 



* ' Monthly Notices, K. A. S.,' vol. 49, 1889, p. 308. 



f 



