hey
revolved round him in periods which were soon determined.

The reason why they were not all visible at first, and why their
visibility so rapidly changes, is because they revolve round him
almost in the plane of our vision, so that sometimes they are in
front and sometimes behind him, while again at other times they
plunge into his shadow and are thus eclipsed from the light of the
sun which enables us to see them. A large modern telescope will
show the moons when in front of Jupiter, but small telescopes will
only show them when clear of the disk and shadow. Often all four
can be thus seen, but three or two is a very common amount of
visibility. Quite a small telescope, such as a ship's telescope, if
held steadily, suffices to show the satellites of Jupiter, and very
interesting objects they are. They are of habitable size, and may
be important worlds for all we know to the contrary.

The news of the discovery soon spread and excited the greatest interest
and astonishment. Many of course refused to believe it. Some there were
who having been shown them refused to believe their eyes, and asserted
that although the telescope acted well enough for terrestrial objects,
it was altogether false and illusory when applied to the heavens. Others
took the safer ground of refusing to look through the glass. One of
these who would not look at the satellites happened to die soon
afterwards. "I hope," says Galileo, "that he saw them on his way to
heaven."

The way in which Kepler received the news is characteristic, though by
adding four to the supposed number of planets it might have seemed to
upset his notions about the five regular solids.

He says,[9] "I was sitting idle at home thinking of you, most
excellent Galileo, and your letters, when the news was brought me
of the discovery of four planets by the help of the double
eye-glass. Wachenfels stopped his carriage at my door to tell me,
when such a fit of wonder seized me at a report which seemed so
very absurd, and I was thrown into such agitation at seeing an old
dispute between us decided in this way, that between his joy, my
colouring, and the laughter of us both, confounded as we were by
such a novelty, we were hardly capable, he of speaking, or I of
listening....

"On our separating, I immediately fell to thinking how there could
be any ad