in the Atmospheres of certain Fixed Stars. 



205 



b>ut these coincidences are very doubtful, and it is improbable that 

 such very faint lines would be represented, whilst the neighbouring 

 line 4327-3, intensity 3, is wanting on the photograph. 



The oxygen lines of intensity 4 which are wanting, viz. : — Neovius 

 4465-4 and 4467*8 are in a portion of the .spectrum which is some- 

 what over exposed, and this fact probably accounts for the non-appear- 

 ance on the plate. Possibly also the relative intensities of the oxygen 

 lines at the temperature and pressure of the atmosphere of /? Crucis may 

 be different from their relative intensities in the conditions under which 

 Neovius determined the intensities of the air lines (spark spectrum). 



There remains however not the slightest doubt, that all the stronger 

 oxygen lines are present in the spectrum of /3 Crucis, at least between 

 X 4250 and 4575, and this fact requires no further laboratory experi- 

 ments for its establishment. It is almost equally certain that there is 

 no trace of true nitrogen lines in this spectrum. 



The only measured lines of /S Crucis near known nitrogen lines 

 .are : — 



Neovius 4341-8 Intensity 15 ft Crucis 4342-6 

 4523-0 „ lb „ 4522-84 



but it is improbable, although not impossible, that nitrogen lines of 

 intensity (1) should be present whilst the strong nitrogen line 4507*7, 

 of intensity 6, is absent. 



Besides hydrogen, helium and oxygen, the spectrum of j3 Crucis 

 shows the probable presence of carbon (4267*2) and magnesiun 

 (4481-17). These lines were not included in the first measurement, in 

 the former case because the line could not be distinctly seen with the 

 higher power, in the latter because I was doubtful of the existence of . 

 the line on account of a slight defect in the film at that point, but 

 other negatives confirm its existence. A contact positive from the 

 original negative of the spectrum is sent herewith for reproduction. 



The spectra of /S Crucis, p and e Canis Ma j oris, and probably 

 j3 Centauri are all practically identical. They all contain the three 

 unknown strong lines 



4552*79 

 4567*09 

 4574-68 



besides the probable magnesium line 4481*17, the lines of hydrogen, 

 helium, the stronger oxygen lines, and the probable carbon line 4267*2, 

 Farther investigations on this class of stars will be subsequently 

 communicated; in the meanwhile I forward also for reproduction a 

 contact positive from a negative of the spectrum of e Canis Ma j oris 

 taken on March 15 with the single prism, in which the slit has been 

 ^ focussed for rays of about A 4080, and with a comparison spectrum 

 VOL. LXV. E 



