18G5.] 



Carter on a Plurality of Worlds. 



235 



lessens, and his rays consequently traverse greater lengths of atmo- 

 sphere, an element has been obtained which serves as a standard 

 whereby to judge of the existence of atmospheres around other 

 planets. Many observers have decisively settled this point with 

 regard to Jupiter, Saturn, and other members of the solar system. 

 For, by comparing the spectra of the Moon and Jupiter when at the 

 same altitude, and when therefore the light reflected from them was 

 under precisely similar atmospheric conditions, bands were present in 

 the former which were not found in the latter, and which were due 

 therefore to some modification before reaching our atmosphere. 





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The drawing which, through the kindness of Mr. Huggins, we are 

 able to give, demonstrates this even more satisfactorily, for, in the ob- 

 servation of which it is the result, the spectrum of Jupiter was seen in 

 direct contact with that of the sky, and the lines in both were seen to 

 be exactly coincident. The comparison in this case was rendered pos- 

 sible by the slit in the spectroscope being greater than the telescopic 

 image of the planet, and by there being just enough light left after 

 the sun had gone down to form a visible spectrum of the sky, which 

 therefore was directly superposed on that of Jupiter. Though co-inci- 

 dent in position the lines will be seen to vary somewhat in intensity, 

 those at 882 and 833 being less intense in Jupiter's spectrum, while 

 those at 914 are stronger. The coincidence probably shows, as Mr. 

 Huggins and Dr. Miller remark, that the planet's atmosphere, with 

 respect to some of its elements at least, is similar to ours. Other 

 lines were present, but were too faint to be represented. Many more, 

 however, have been given by Father Secchi, some of which have no 

 representatives among lines due to our atmosphere, while one of those 

 most closely coincident is always found to prevail during foggy 

 weather. 



But the vapours which produce these atmospheric lines in the solar 

 spectrum are principally found in the lower and denser parts of the 

 terrestrial atmosphere, while the parts corresponding to these on 

 Jupiter are not traversed by the light, forming his spectrum, which, 

 as before observed, is reflected from cloud-like masses above the sur- 

 face. Therefore if there is an atmosphere dense enough to give such 

 well-marked lines above these clouds (as we shall show them to be), 



VOL. II. s 



