1874.] The Saturnian System. 13 
of bodies, these planets resemble the sun, and are utterly 
unlike the earth. In mean density Jupiter is almost exactly 
like the sun, and Saturn has even a less mean density than 
the earth. This last is the most important distin¢tion of 
all, as we shall presently see ; in faét, I think I shall be able 
to show that of itself it demonstrates the fact that the major 
planets are utterly unlike the earth and her fellow minor 
planets. Again, in the condition and phenomena of their 
atmospheric envelopes, Jupiter and Saturn to a certain 
degree resemble the sun, as will presently appear; and 
though the resemblance is not altogether complete, yet this 
is counterbalanced by the circumstance that the want of 
resemblance between the major and minor planets in this 
respect is very marked indeed. 
It will be understood that I rely in the main for evidence 
as to the condition of the atmosphere of Jupiter and Saturn 
on the results of telescopic researches. Other evidence 
there is, and in particular the spectroscope has afforded 
information of an interesting nature. But as yet this infor- 
mation is not definite enough to be reliable as a basis of 
reasoning; whereas the evidence given by the telescope is 
sufficient, rightly used, to convey very important information. 
I would note that we may properly combine the information 
given by both Jupiter and Saturn, since these planets 
manifestly resemble each other in those leading features 
which we can alone deal with in our present enquiries. It 
is altogether likely that in minor respeCts Jupiter and 
Saturn are as unlike as the earth and Mars. But precisely 
as we can trace a general resemblance between all the 
members of the minor family of planets, so manifestly 
Saturn and Jupiter (as also probably Uranus and Neptune) 
resemble each other in the broader features of their con- 
dition. It is very important to recognise this, because, in 
point of fact, the information conveyed by one planet 
supplements in an interesting way that given by the other. 
Jupiter being very much larger and far nearer to the earth 
can be more satisfactorily studied; and we can only recognise, 
in the case of Jupiter, the details of those atmospheric belts 
which girdle both planets. But on the other hand Saturn 
affords a test as to the nature of these belts, which is 
wanting in the case of the larger planet. For Jupiter’s 
equator plane is very little inclined to the level in which the 
planet travels, whereas, as has been mentioned in the 
elements given above, the equator plane of Saturn is 
inclined at a very considerable angle, so that what we 
may for convenience term the seasonal changes of Saturn 
