The four inner planets being nearly alike in size (?) and in
length of day, M. Figuier infers, by strictly scientific methods,
that whatever is true of one of them, as our earth, will be true
of the others (p. 34). Hence, they are all inhabited by human
beings. It is true that human beings must find Venus rather warm,
and are not unlikely to be seriously incommoded by the tropical
climate of Mercury. But we must remember that "the men of Venus
and Mercury are made by nature to resist heat, as those of
Jupiter and Saturn are made to endure cold, and those of the
Earth and Mars to live in a mean temperature: OTHERWISE THEY
COULD NOT EXIST" (p. 72). In view of this charming specimen of a
truly scientific inference, it is almost too bad to call
attention to the fact that M. Figuier is quite behind the age in
his statement of facts. So far from Jupiter and Saturn being
cold, observation plainly indicates that they are prodigiously
hot, if not even incandescent and partly self-luminous; the
explanation being that, by reason of their huge bulk, they still
retain much of the primitive heat which smaller planets have more
quickly radiated away. As for M. Figuier's statement, that polar
snows have been witnessed on these planets, it is simply untrue;
no such thing has ever been seen there. Mars, on the other hand,
has been observed to resemble in many important respects its near
neighbour, the Earth; whence our author declares that if an
aeronaut were to shoot clear of terrestrial gravitation and land
upon Mars, he would unquestionably suppose himself to be still
upon the earth. For aerolites, it seems, are somehow fired down
upon our planet both from Mars and from Venus; and aerolites
sometimes contain vegetable matter (?). Therefore, Mars has a
vegetation, and very likely its red colour is caused by its