1865.] Carter on a Plurality of Worlds. 237 



The quantity of solar light at the outside of the Jovian atmosphere, 

 though but in the proportion of 1 to 27 of that immediately outside 

 of ours, would yet, even after allowing for great diminution before 

 reaching the surface, be much more than is required by many terres- 

 trial animals and plants. The reflection from his four moons, too, 

 must at least make some small compensation, if any deficiency of 

 direct solar light exist. Of this, however, there is no certainty, 

 because the amount which reaches the planet itself depends on the 

 absorptive and other qualities of the media through which the rays 

 pass to it — qualities which differ entirely in their effects on rays of 

 different periods of vibration. Both of these truths are well shown in 

 the Earth's case, as by far the larger portion of solar rays is absorbed 

 before its surface is reached, but in different proportion, according to 

 their refrangibility and to the prevalence of certain atmospheric con- 

 stituents ; aqueous vapour and carbonic acid gas, for instance, being 

 almost completely diactinic, i.e. penetrable by the more refrangible 

 rays, while they hinder the passage of thermic ones.* And very 

 recently it has been even proved that, under special circumstances, 

 substances may absorb non-visual rays and give them out again trans- 

 muted into visual ones.f Still, as no modification of any of the kinds 

 indicated can be proved .to exist ; that the planet's atmosphere does 

 differ in absorptive capacity in some way, is all that can at present be 

 said, this difference being clearly indicated by the spectroscope. Of 

 the planets beyond Saturn very little is known ; but if we can see 

 indications of a specific adaptation up to the extreme point cognizable, 

 it is fair to presume that it extends further and involves the entire 

 series. These indications are not wanting with respect to Saturn. 

 He has belts which are sometimes almost as distinct as those on 

 Jupiter, and obviously arise from a similar cause, namely, the combi- 

 nation of some external influence with the planet's rotation. There 

 are, moreover, independent proofs of an atmosphere by the spectro- 

 scope. The most wonderful feature connected with him, however, is 

 his system of rings, which, says Sir J. Herschel, " must present a 

 magnificent spectacle, as vast arches spanning the sky from horizon to 

 horizon," to the inhabitants, if there be any. How far they, with the 

 eight satellites, make up by their reflection for any diminution of 

 direct solar bight cannot be said ; but that they possess great, though 

 not uniform reflective power, observations prove. A striking analogy 

 has been remarked to Mars in the presence of a space around each 

 pole, which varies in extent and brilliancy according to the seasons of 

 Saturn's long year. Whether this results from the formation and 

 melting of snow, or the accumulation of clouds, it would seem equally 

 to indicate a variable atmospheric influence. 



In many respects all the exterior planets resemble each other. 

 They are all large, of low specific gravity, accompanied by more than 

 one satellite, and have a nearly equal revolution, and but small incli- 

 nation and orbital excentricity ; so that, except as they are differently 



* Dr. Miller in ' Journ. Chom. Soc' 



t ' Phil. Mag.' No. 192. ' Phil. Proc.' No. 71. 



s2 



