Make as strong a Solution of Salt as you are able, then filling a Glass of
some depth half full with it, fill the other half with fresh Water, and
poyse a little Glass-bubble, so as that it may sink pretty quick in fresh
Water, which take and put into the aforesaid Glass, and you shall find it
to sink till it comes towards the middle, where it will remain fixt,
without moving either upwards or downwards. And by a second Experiment, of
poising such a bubble in water, whose upper part is warmer, and
consequently lighter, then the under, which is colder and heavier; the
manner of which follows in this next Quaery, which 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.
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