1870.] 



Argo and Orion and of Jupiter, 



247 



In the present state of the inquiry there is little doubt left as to the 

 presence of hydrogen in the star ; the other lines may perhaps be accounted 

 for by nitrogen alone, or by nitrogen, magnesium, and sodium. 



On the whole the weight of collateral evidence will probably be consi- 

 dered to be in favour of the latter combination, with the possibility that 

 for sodium may have to be substituted the substance which produces the 

 line in sun-protuberance spectrum. 



For although there is no direct evidence as to identity of the line near 

 D, if the coincidence were with the orange nitrogen line it would be rea- 

 sonable to expect a line in the star corresponding to the yellow line 1 180 + , 

 yet none has been made out in that position ; again, the second green line 

 has probably less claims for visibility than the orange or yellow lines, yet 

 in the star spectrum this line is not less well seen than that coinciding 

 with the chief nitrogen line. These considerations, though perhaps not en- 

 titled to great weight, at least lead in the direction of the above inference. 



Owing to faintness of the general spectrum no dark lines are made out ; 

 one in the red is strongly suspected, and occasionally there is an appearance 

 as if of a multitude over the spectrum generally, but they refuse to be seen 

 separately and certainly. 



It is fortunate that these observations have been possible in the present 

 magnitude of the star ; may not the bright-line character of the spectrum be 

 due to a commencement of increase ? The star has not perceptibly changed 

 since I knew it. 



I extract the following estimation from the Melbourne observations : — 

 Mag. 

 .... 5 

 .... 4-5 



1863. 



Oct. 14 



1864. 



May 6 . 





19. 



1865. 



„ 22. 





June 14 



1868. 



April 21 



j» 



May 27 . 





„ 26. 



1869. 



„ 2 . 



>> 



„ 11. 



»> 



„ 30. 



4-5 

 4-5 



u 2 



6 



The estimations are by Mr. 

 White, who has charge of the 

 Transit Circle. Mr. Ellery es- 

 timated it last year as a 6|+, 

 and now thinks it is somewhat 

 brighter. 



At an earlier stage of the observations with the Melbourne reflector, I 

 was on the whole inclined to think that the difference between the view of 

 the nebula about rj Argo as seen w r ith the 4-feet reflector, and that seen by 

 Sir J. Herschel with his 18-inch, though strongly marked in the neigh- 

 bourhood of 77, was yet, due regard being had to aperture and other dis- 

 turbing causes, capable of being accounted for without going to the length 

 of assuming such enormous changes as would result if the sketches repre- 

 sented the true facts in both cases. It was thought that the presence 

 of the star rj might have a large disturbing effect, increased by aperture, 

 and that therefore an erroneous impression might be formed of the confi- 



VOL. XVIII. T 



