for them.

* * * * *

_Of a permanent Spot in _Jupiter_: by which is manifested the conversion of
_Jupiter_ about his own Axis._

Besides that Transient Shadow last mentioned, there hath been observed, by
Monsieur _Cassini_, a permanent Spot in the Disque of _Jupiter_; by the
help whereof, he hath been able to observe, not onely that _Jupiter_ turns
about upon his own Axis, but also the Time of such conversion; which he
{144} estimates to be, 9 hours and 56 minutes.

For as _Kepler_ did before conjecture, from the motion of the Primitive
Planets about the Sun as their Center, that the Sun moved about its own
Axis, but could not prove it, till by _Galileo_ and _Shiner_ the Spots in
the Sun were discovered; so it hath been thought reasonable, from the
Secundary Planets moving about _Jupiter_, that _Jupiter_ is also moved
about his Axis; yet, till now, it hath not been evinced by Observation,
That it doth so move; much less, in what Period of Time. And the like
reason there is to judge so of _Saturn_, because of the Secundary Planet
discovered by Monsieur _Hugens de Zulichem_ to move about it; (though such
motion be not yet evinced from Observation:) as well as that of the
_Earth_, from its Attendant the _Moon_.

Whether the same may be also concluded of the other Planets, _Mars_,
_Venus_, and _Mercury_, (about whom have not yet been observed any
Secondary Planets to move,) is not so evident. Yet there may be somewhat of
like probability in those. Not onely, because it is possible they may have
Secundary Planets about them, though not yet discovered; (For, we know, it
was long after those of _Jupiter_, before that about _Saturn_ was
discovered; and who knows, what after times may discover about the rest?)
But because the Primary Planets being all in like manner inlightned by the
Sun, and (in all likely hood) moved by it; it is likely that they be moved
by the same Laws and Methods; and therefore, turn'd about their own Axis,
as it is manifest that some of them are.

But, as for the Secundary Planets, as well those about _Jupiter_, as that
about _Saturn_; it is most likely that they have no such Rotation upon
their Axis. Not so much because, by reason of their smalness, no such thing
hath been yet observed, (or, indeed, could be, though it were true;) But
because they being Analogical to our _Moon_, it is most likely that they
are moved in like manner. Now, though it be {145} true, that