1 58 SPECTRA OF PLANETARY NEBULA. PART i. 



of vapours similar to those existing in our atmosphere, 

 another band has no counterpart among the lines of 

 absorption of the earth's atmosphere, and tells of some 

 gas which it does not contain. 



In the feeble spectrum of Saturn there are lines 

 similar to those in the spectrum of Jupiter. These lines 

 are less strongly marked in the ansse of the rings, and 

 show that the absorptive power of the atmosphere 

 about the rings is less than that of the atmosphere 

 which surrounds the ball. 



M. Jansen has found lines denoting aqueous vapour 

 in the atmospheres of both Jupiter and Saturn. Some 

 very remarkable lines have been seen in the more re- 

 frangible part of the spectrum of Mars supposed to be 

 connected with his red colour. Though the spectrum 

 of Yeiius is brilliant, and the dark lines distinct, 

 no additional lines indicate the existence of an atmo- 

 sphere differing from our own. 



The phenomena resulting from an examination of 

 the nebulae are most wonderful ; their light is very 

 feeble, even that of the brightest. ' The total light of 

 the whole nebula in Orion, the largest and brightest 

 of them, makes so small an impression on the naked 

 eye, that you may look twenty times at its place and 

 not perceive any nebulous light at all.' 5 Besides, 

 the brightness of a surface cannot be increased by a 

 telescope, however good. Notwithstanding difficulties 

 which seem to be almost insurmountable, Mr. Huggins 

 in England, and Padre Secchi at Eome, have been, 

 and still are, engaged in these researches. 



The planetary nebulae are beautiful objects; they 

 are like planets with a round or oval disc, equable, 

 slightly mottled and of enormous magnitude ; one near 

 7 Aquarii is twenty seconds, and another is twelve 



5 Sir John Herschel, who is of the highest authority with regard to the 

 nebulae in both hemispheres. 



