e place, as if the Earth were at T. But then, after the Full, the
Moon at D, the Earth at d; _Mars_ will be seen, not at [gamma], but at
[delta], too forward: and yet more, when the Moon (at the last Quarter) is
at E, the Earth at e, and _Mars_ seen at [epsilon]. If therefore _Mars_
(when in opposition to the Sun) be found (all other allowances being made)
somewhat too backward before the Full moon, and somewhat too forward after
the Full-moon, (and most of all, at the Quadratures:) it will be the best
confirmation of the Hypothesis. (The like may be fitted to _Mars_ in other
positions, _mutatis mutandis_; and so for the other Planets.)

But this proof, is of like nature as that of the Parallaxis of the Earths
Annual Orb to prove the Copernican Hypothesis. If it can be observed, it
proves the Affirmative; but if it cannot be observed, it doth not convince
the Negative, but only proves that the Semidiameter of the Earths Epicycle
is so small as not to make any discernable Parallax. And indeed, I doubt,
that will be the issue. For the Semidiameter of this Epicycle, being little
more than the Semidiameter of the Earth it self, or about 1-1/3 thereof (as
is conjectured, in the _Hypothesis_, from the Magnitudes and Distances of
the Earth and Moon compared;) and there having not as yet been observed any
discernable _Parallax_ of _Mars_, even in his neerest position to the
Earth; it is very suspicious, that here it may prove so too. And whether
any of the other Planets will be more favourable in this point, I cannot
say.

* * * * *

_ANIMADVERSIONS of Dr. _Wallis_, upon Mr. _Hobs_'s late Book, _De
Principiis & Ratiocinatione Geometrarum_._

These were communicated by way of Letter, written in _Oxford_, July 24.
1666. to an Acquaintance of the _Author_, as follows:

Since I saw you last, I have read over Mr. _Hobs_'s Book _Contra Geometras_
(or _De Principiis & Ratiocinatione Geometrarum_) which you then shewed me.
A New Book of _Old_ matter: Containing but a _Repetition_ of what he had
before told us, more than once; and which hath been Answered long agoe.

In which, though there be Faults enough to offer ample {290} matter for a
large Confutation; yet I am scarce inclined to believe, that any will
bestow so much pains upon it. For, if that be true, which (in his
_Preface_) he saith of himself, _Aut solus insanio Ego, aut solus non
insanio_: it would either be _Needless_, or _to no Purpose_.