With telescopes, too, in the case of a solar eclipse occurring at the
time of the earth's opposition, they could see the black spot formed by
the shadow of the moon, where the end of its cone moved across the earth
like the point of an invisible pencil, and could watch it traversing
continents and oceans, or thrown out in bold contrast upon the white
background of a great area of clouds. Indeed, the phenomena which our
globe and its satellite present to Venus must be so varied and wonderful
that one might well wish to visit that planet merely for the sake of
beholding them.

Thus far we have found so much of brilliant promise in the earth's twin
sister that I almost hesitate to approach another phase of the subject
which may tend to weaken the faith of some readers in the habitability
of Venus. It may have been observed that heretofore nothing has been
said as to the planet's rotation period, but, without specifically
mentioning it, I have tacitly assumed the correctness of the generally
accepted period of about twenty-four hours, determined by De Vico and
other observers. This period, closely accordant with the earth's, is, as
far as it goes, another argument for the habitability of Venus.

But now it must be stated that no less eminent an authority than
Schiaparelli holds that Venus, as well as Mercury, makes but a single
turn on its axis in the course of a revolution about the sun, and,
consequently, is a two-faced world, one side staring eternally at the
sun and the other side wearing the black mask of endless night.

Schiaparelli made this announcement concerning Venus but a few weeks
after publishing his discovery of Mercury's peculiar rotation. He
himself appears to be equally confident in both cases of the