227of the Air may be suppos'd indefinite;
228to what degree the Air is rarifi'd at
any distance above the Surface of the
Earth: how, from this, Inflection is
229inferr'd; and several Phænomena
230explain'd. That the Air near the
Earth is compos'd of parts of differing
231density; made probable by several
232Experiments and Observations; how
this propriety produces the effects of
the waving and dancing of Bodies;
and of the twinkling of the Stars.
233Several Phænomena explicated.
Some Quæries added.
1. Whether this Principle may not
be made use of, for perfecting Optick
234Glasses? What might be hoped from
it if it were to be done?
2. Whether from this Principle
the apparition of some new Stars may
not be explicated?
3. Whether the height of the Air
may be defin'd by it?
4. Whether there may not sometimes
be so great a disparity of density
between the upper and under parts
of the Air, as to make a reflecting
Surface?
2355. Whether, if so, this will not
explicate the Phænomena of the
Clouds. An Experiment to this purpose?
2367. Whether the Rayes from the
top of Mountains are not bended into
Curve-lines by inflection? An Argument
for it, taken from an Experiment
made on St. Paul's Steeple.
8. Whether the distance of the
Planets will not be more difficult to
237be found? What wayes are most likely
to rectifie the distance of the Moon:
the way of fitting Telescopes for
such Observations. How to make the
238Observations, and how from them to
find the true distance of the Moon at
any time. How the distance of the Sun
239may be found by two Observators. The
way by the Dicotomy of the Moon uncertain.
That the distance of the
Moon may be less then it has
been hitherto suppos'd. Kepler's Supposition
240not so probable: the explication of
the Phænomena by another Hypothesis.
241Observ. 59.Of the fixt Stars.
Of the multitudes of Stars discoverable
by the Telescope, and the
variety of their magnitudes: 78. Stars
distinguisht in the Pleiades: that there
are degrees of bigness even in the Stars
accounted of the same magnitude: the
longer the Glasses are, and the bigger
apertures they will indure, the more
fit they are for these discoveries: that
'tis probable, longer Glasses would yet
242make greater discoveries. 5. Stars
discover'd in the Galaxie of Orion's Sword.
Observ. 60.Of the Moon.
A description of a Vale in the
Moon; what call'd by Hevelius and
Ricciolus, and how describ'd by them:
243with what substances the hills of the
Moon may be cover'd. A description
of the pits of the Moon, and a conjecture
at their cause: two Experiments
that make it probable, that of the surface
244of boyl'd Alabaster dust seeming
the most likely to be resembled by eruptions
of vapours out of the body of the
Moon: that Earthquakes seem to be
generated much the same way, and
their effects seem very similar. An Argument
that there may be such variations
in the Moon, because greater
have been observ'd in the Sun: because
245the substance of the Moon and Earth
seem much alike: and because 'tis probable
the Moon has a gravitating
principle: this is argued from several
246particulars. The reason why several
pits are one within another. The use
that may be made of this Instance of
a gravity in the Moon.
