85. The quantity of light, afforded by the Sun of Jupiter, being but
1/28th part, and to Saturn only 1/90th part, of what we enjoy; may at
first thought induce us to believe that these two Planets are entirely
unfit for rational beings to dwell upon. But, that their light is not so
weak as we imagine, is evident from their brightness in the night-time;
and also, that when the Sun is so much eclipsed to us as to have only
the 40th part of his Disc left uncovered by the Moon, the decrease of
light is not very sensible: and just at the end of darkness in Total
Eclipses, when his western limb begins to be visible, and seems no
bigger than a bit of fine silver wire, every one is surprised at the
brightness wherewith that small part of him shines. The Moon when Full
affords travellers light enough to keep them from mistaking their way;
and yet, according to Dr. SMITH[16], it is equal to no more than a 90
thousandth part of the light of the Sun: that is, the Sun’s light is 90
thousand times as strong as the light of the Moon when Full.
Consequently, the Sun gives a thousand times as much light to Saturn as
the Full Moon does to us; and above three thousand times as much to
Jupiter. So that these two Planets, even without any Moons, would be
much more enlightened than we at first imagine; and by having so many,
they may be very comfortable places of residence. Their heat, so far as
it depends on the force of the Sun’s rays, is certainly much less than
ours; to which no doubt the bodies of their inhabitants are as well
adapted as ours are to the seasons we enjoy. And if we consider, that
Jupiter never has any winter, even at his Poles; which probably is also
the case with Saturn, the cold cannot be so intense on these two Planets
as is generally imagined. Besides, there may be something in their
nature or soil much warmer than in that of our Earth: and we find that
all our heat depends not on the rays of the Sun; for if it did, we
should always have the same months equally hot or cold at their annual
returns. But it is far otherwise, for _February_ is sometimes warmer
than _May_, which must be owing to vapours and exhalations from the
Earth.
[Sidenote: It is highly probable that all the Planets are inhabited.