1870.] On the Spectra of Argo and Orion, and of Jupiter. 21-5 



(on the foregoing assumption) be accounted for by supposing that the 

 cloud-bands are very near the surface, so near that the light reflected 

 therefrom has to pass through a thickness and density of atmosphere com- 

 parable in its effects to that above the more uninterrupted parts of the 

 surface. 



Further observations may obviate the necessity for this or any other 

 more feasible explanation, by proving that the band is mainly due to the 

 earth ; but, as before shown, the weight of evidence, Mr. Huggins's obser- 

 vation taken into account, is in favour of the assumption that the line, as 

 seen on Jupiter at considerable altitude, is mainly due to the planet itself. 



The general appearance of the spectroscopic image is one of nearly uni- 

 form brightness, with the marked exception of the brighter band P Q, 

 and the much darker band QR: in this band the principal absorption 

 takes place at the more refrangible end of the spectrum, where it is very 

 considerable, gradually diminishing, but yet conspicuous, up to E; at mo- 

 ments it may be traced very faintly up to D, with no certainty beyond. 



In this band Q, R are not separable ; considering the size of the image 

 this can hardly be due entirely to closeness, but would seem to show that 

 (at the more refrangible end at least) the absorption of the yellow and 

 somewhat dark space enclosed between Q, R is little inferior to that of Q, R 

 themselves. P is not conspicuous, but is unmistakably seen in good 

 moments as a narrow streak at the blue end. 



The experiment was made of placing the slit parallel to the planet's 

 equator; when in this position and moved slowly over the surface, or 

 arrested at particular points/no peculiarity was distinguishable ; so little do 

 the parts differ in brightness, that by this method it could not, from the 

 mere evidence of the spectrum, be told what part was being admitted 

 through the slit ; in this method, however, greater delicacy of adjustment 

 is required, for slight want of parallelism of the slit to the bands brings 

 in disturbing effects. 



The edges of the disk were examined, but without result. 



Observatory, Melbourne, December 5, 18G9. 



III. " On the Nebulae of Argo and Orion, and on the Spectrum 

 of Jupiter." By A. Le Sueur. Communicated by Prof. G. G. 

 Stokes, Sec. U.S. Received February 21, 1870. 



Among the following observations made with the great Melbourne 

 telescope, the most important are those of r/ Argo ; the spectrum of this 

 star is crossed by bright lines. 



The mere fact of a bright-line spectrum is not very difficult to ascertain 

 on a good night ; for although from faintness of the light the phenomenon 

 is necessarily delicate, yet the bright lines occasionally flash out so sharply 

 that the character of the spectrum cannot be mistaken. The most marked 



