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POPULAR SCIENCE REVIEW. 
strative evidence. The few instances of anything like reasoning 
which I have been able to find scattered here and there in books 
of astronomy amount to what follows : — First, because Jupiter 
and Saturn are planets, and the earth is a planet, therefore those 
planets are like the earth. (This argument is open to the 
objection that it begs the question, which is, Whether other 
planets resemble the earth.) Jupiter and Saturn are globes 
like the earth (also like the sun and moon). They rotate on 
their axes, and therefore if they are inhabited worlds like the 
earth, they have day and night, and in that respect are like the 
earth. They circle around the sun, and thus if they are worlds 
like the earth, they are like the earth in having a year ; also in 
having seasons, since their axes are not perpendicular to the 
planes in which they travel. It would be absurd to suppose 
that globes so magnificent were made for no special purpose, 
but we can conceive no special purpose they can subserve except 
to be the abodes of life ; therefore they are worlds like our earth 
(though the sun, constructed on a still more magnificent scale, 
is certainly not such a world, or the abode of life). Their moons 
are manifestly intended to make up to them for their remote- 
ness from the sun (only, when we calculate how much light 
these moons reflect to their primaries we find that they supply 
but a small fraction of the amount we receive from our moon). 
The rings of Saturn were manifestly intended for the benefit of 
Saturn’s inhabitants (though they only reflect light to the summer 
hemisphere of the planet, and besides turning their darkened 
side to the other hemisphere, cut off the whole of the sun’s light 
for many months, in some cases for several of our years, in suc- 
cession). The belts on Jupiter and Saturn may be likened 
again to our trade wind zones, to which, however, they bear not 
the remotest resemblance, whether we consider their condition 
at any given time, or the rapid changes they undergo from time 
to time. In fine the arguments used by the few writers who 
have condescended to present even a show of reasoning in favour 
of the theory that Jupiter and Saturn resemble our earth in 
condition, amount practically to this — that, assuming all planets 
to be generally similar, Jupiter and Saturn are like our earth in 
general respects, in which case they also resemble her in several 
details. 
I do not consider it necessary to discuss Whewell’s theory that 
Jupiter and Saturn are intensely cold planets, because it is pro- 
fessedly based on the theory that they are formed of such ter- 
restrial elements as would, if in the same condition as upon 
the earth, have the observed density of Jupiter and Saturn, and 
that these substances, being further removed from the sun, are 
correspondingly refrigerated. There is not a line of direct 
reasoning, either a priori or a posteriori , in Whewell’s 
