(as is represented by the
Fig. O; like that of the first Face of _Mars_.) whereas, on the contrary,
{244} He (_Cassini_) pretends to evidence by his Observations, made at the
same time at _Bononia_, that, the same day and hour, those Spots were very
large, neer one another, in the midst of the Disk, the Oriental bigger than
the Occidental (as appears by _Fig._ P, which is that of the second Face of
_Mars_.)

12. Besides, he declares, that those _Astronomers_ were too hasty, in
determining, after 5 or 6 Observations only, in how much time _Mars_
finish's his Revolution; and denies it to be perform'd in 13 hours: adding,
that, though Himself had observ'd for a much longer time, than they; yet he
durst not for a great while define, Whether _Mars_ made but _one_ Turn in
24 hours 40 minuts or _two_; and that all, that he could, for a long time
affirm, was onely this, that after 24 h. 40 m. this Planet appear'd in the
same manner he did before.

13. But since those first Observations, He affirms to have found cause to
determine, that the Period of this Conversion is made in the said space of
24 h. 40 m; and not oftner than once within that time; Alledging for proof;

1. That, whereas _Febr._ 6. (st.n.) he saw the Spots of the first Face of
_Mars_, moving from eleven of the Clock in the night, until break of day,
they appear'd not afterwards in the Evening after the rising of that Planet
(witness several intelligent persons, which he names, that were present at
the Observations) Whence he infers, that after 12 hours and 20 minuts, the
same Spots did not come about; since that the same, which in the morning
were seen in the middle, upon the rising of _Mars_; after 13 or 14 hours,
might have appear'd neer the Occidental Limb. But, because he might be
imposed upon by Vapors, whilst _Mars_ was yet so neer the _Horizon_, he
gives this other determination, _vid._

2. Whereas he saw the first Face of _Mars_ the 6 of _February_ at 11 of the
clock of the night following; he did not see the same after 18 daies at the
same hour; as he ought to have done, if the Period were absolved in the
space of 12 h. 20 m.

[Illustration]

3. Again, whereas he saw _Febr._ 24. in the Evening, the other Face of
_Mars_, he could not see the same, the 13. and 15. day of _March_, to wit
after 17 and 19 days; as he should have done, if the Revolution were made
in the newly mention'd time.

4. Again, whereas the 27. of _March_ in the Evening he saw {2