hence collected, not onely
for that time, but at all other times, by any single Observator's viewing
her with a _Telescope_, and measuring exactly her _Apparent_ Diameter. It
were likewise desirable, that as often as there happens any considerable
_Eclipse_ of the _Sun_, that this also might be observed by them, noting
therein the exact measure of the greatest Obscuration compared with the
then _Apparent_ Diameter of his Disk. For by this means, after the distance
of the _Moon_ hath been exactly found, the distance of the _Sun_ will
easily be deduced.

As for the time, fittest for making Observations of the _Moon_, that will
be, when she is about a Quarter or somewhat less illuminated, because then
her light is not so bright, but that with a good _Telescope_ she may be
observ'd to pass close by, and sometimes over several _Fixt Stars_; which
is about four or five days before or after her Change: Or else at any other
time, when the _Moon_ passes near or over some of the bigger sort of _Fixt
Stars_, such as of the first or second _Magnitude_; which may be easily
calculated and foreseen: Or best of all, when there is any _Totall Eclipse_
of the _Moon_; for then the smallest _Telescopical Stars_ may be seen close
adjoyning to the very body of the _Moon_. Of all which particulars the two
Correspondents are to agree, as soon as he, that is to joyn abroad, shall
be found out; whereupon they are mutually to communicate to each other,
what they shall have thus observed in each place.

* * * * *

_Of an Observation, not long since made in _England_, of _Saturn_._

[Illustration]

This Observation was made by Mr. _William Ball_, {153} accompanied by his
brother, Dr. _Ball_, _October_ 13. 1665. at six of the Clock, at _Mainhead_
near _Exeter_ in _Devonshire_, with a very good _Telescope_ near 38 foot
long, and a double Eye-glass, as the observer himself takes notice, adding,
that he never saw that _Planet_ more distinct. The observation is
represented by _Figure_ 3. concerning which, the Author saith in his letter
to a friend, as follows; This appear'd to me the present figure of
_Saturn_, somewhat otherwise, than I expected, thinking it would have been
decreasing, but I found it full as ever, and a little hollow above and
below. Whereupon the Person, to whom notice was sent hereof, examining this
shape, hath by Letters desired the worthy Author of the _Systeme of this
Planet_, that he would now a