24 On 7) Argils and Jupiter's Spectrum. 



The green lines, difficult before, become almost unmanage- 

 able ; considering, therefore, that mere extra dispersion in- 

 stead of diminishing the visibility of real lines should, if 

 anything, make them more conspicuous, the latter observa- 

 tions throw some doubt on the conclusions originally arrived 

 at. In the paper read at the last meeting it was noticed 

 that there were two ways of accounting for the appearance 

 of the spectrum of 77 Argus. 1st. That it is a spectrum of 

 groups of dark lines separated by more or less bright spaces. 

 2nd. That the bright hues are real and not due merely to 

 comparative absence of absorption. 



The former supposition was discarded in favour of the 

 latter, which was supported by strong collateral evidence. 



The behaviour of the red line,* with the larger dispersion, 

 is strongly in favour of the original conclusion that the star is, 

 even at the present low magnitude, enveloped by an atmo- 

 sphere of hydrogen at high temperature, but the diminished 

 visibility of the green hues points to the possibility that the 

 appearance of this part of the spectrum is due merely to 

 comparative absence of dark lines over moderately wide 

 spaces. 



There seems to be no reason for objecting to tliis double 

 nature of the spectrum, all red variables sufficiently bright 

 to bear a fine slit, are found to have a spectrum of groups, 

 and some variables in certain phrases (T coronse at maximum 

 for instance) develop bright hydrogen lines. Spectroscopic 

 observations of small stars is so very difficult that we can 

 hardly hope to obtain more satisfactory evidence until y 

 Argus has increased in brightness. 



The spectrum of the star near maximum may, from phy- 

 sical causes, differ somewhat in character from that seen at 

 present, but evidence will no doubt be then adduced 

 whereby the appearance at the lower stages may be more 

 certainly accounted for. 



Spectrum of Jupiter. 



In the spectrum of Jupiter, the principal Fraunhofer lines 

 are, as might be expected, readily seen ; besides these there 

 are hues of absorption, one of which is decisively proved by 

 Mr. Huggins' observations to have its origin in Jupiter's 

 atmosphere. 



* Of the blue line I cannot speak with as much confidence, the faintness 

 makes it difficult of observation, but I think it is as well seen with the larger 

 dispersion as it was at first. 



