hich is,

6. Whether the rarifaction and condensation of Water be not made after the
same manner, as those effects are produc'd in the Air by heat; for I once
pois'd a seal'd up Glass-bubble so exactly, that never so small an addition
would make it sink, and as small a detraction make it swim, which suffering
to rest in that Vessel of Water for some time, I alwayes found it about
noon to be at the bottom of the Water, and at night, and in the morning, at
the top: Imagining this to proceed from the Rarifaction of the Water,
caus'd by the heat, I made tryal, and found most true; for I was able at
any time, either to depress, or raise it, by heat and cold; for if I let
the Pipe stand for some time in cold water, I could easily raise the Bubble
from the bottom, whither I had a little afore detruded it, by putting the
same Pipe into warm Water. And this way I have been able, for a very
considerable time, to keep a Bubble so poys'd in the Water, as that it
should remain in the middle, and neither sink, nor swim: For gently heating
the upper part of the Pipe with a Candle, Coal, or hot Iron, till I
perceived the Bubble begin to descend, then forbearing, I have observed it
to descend to such or such a station, and there to remain suspended for
some hours, till the heat by degrees were quite vanished, when it would
again ascend to its former place. This I have also often observed naturally
performed by the heat of the Air, which being able to rarifie the upper
parts of the Water sooner then the lower, by reason of its immediate
contact, the heat of the Air has sometimes so slowly increased, that I have
observed the Bubble to be some hours in passing between the top and bottom.

7. Whether the appearance of the _Pike_ of _Tenerif_, and several other
high Mountains, at so much greater a distance then seems to agree with
their respective heights, be not to be attributed to the _Curvature_ of the
visual Ray, that is made by its passing obliquely through so differingly
_Dense_ a Medium from the top to the eye very far distant in the Horizon:
For since we have already, I hope, made it very probable, that there is
such an _inflection_ of the Rays by the differing density of the parts of
the Air; and since I have found, by several Experiments made on places
comparatively not very high, and have yet found the pressure sustain'd by
those parts of the Air at the top and bottom, and also their differing
Expansions very considerable: Insomuch