not only visible, but conspicuous, to the naked eye, circling about the
earth, and appearing at times to recede from it to a distance of about
half a degree--equal to the diameter of the full moon as we see it. The
disk of the earth is not quite four times greater in diameter than that
of the moon, and nowhere else in the solar system is there an instance
in which two bodies, no more widely different in size than are the moon
and the earth, are closely linked together. The moons of the other
planets that possess satellites are relatively so small that they
appear in the telescope as mere specks beside their primaries, but the
moon is so large as compared with the earth that the two must appear, as
viewed from Venus, like a double planet. To the naked eye they may look
like a very wide and brilliant double star, probably of contrasted
colors, the moon being silvery white and the earth, perhaps, now of a
golden or reddish tinge and now green or blue, according to the part of
its surface turned toward Venus, and according, also, to the season that
chances to be reigning over that part.

Such a spectacle could not fail to be of absorbing interest, and we can
not admit the possibility of intelligent inhabitants on Venus without
supposing them to watch the motions of the moon and the earth with the
utmost intentness. The passage of the moon behind and in front of the
earth, and its eclipses when it goes into the earth's shadow, could be
seen without the aid of telescopes, while, with such instruments, these
phenomena would possess the highest scientific interest and importance.

Because the earth has a satellite so easily observable, the astronomers
of Venus could not remain ignorant of the exact mass of our planet, and
in that respect they would outstrip us in the race for knowledge, since,
on account of the lack of a satellite attending Venus, we have been able
to do no more than make an approximate estimate of her mass.