Perhaps we may thereby also judge (as other
Creatures seem to do) what is wholsome, what poyson; and in a word, what
are the specifick properties of Bodies.
There may be also some other mechanical wayes found out, of sensibly
perceiving the _effluvia_ of Bodies; several Instances of which, were it
here proper, I could give of Mineral steams and exhalations; and it seems
not impossible, but that by some such wayes improved, may be discovered,
what Minerals lye buried under the Earth, without the trouble to dig for
them; some things to confirm this Conjecture may be found in _Agricola_,
and other Writers of Minerals, speaking of the Vegetables that are apt to
thrive, or pine, in those steams.
Whether also those steams, which seem to issue out of the Earth, and mix
with the Air (and so to precipitate some _aqueous_ Exhalations, wherewith
'tis impregnated) may not be by some way detected before they produce the
effect, seems hard to determine; yet something of this kind I am able to
discover, by an Instrument I contriv'd to shew all the minute variations in
the pressure of the Air; by which I constantly find, that before, and
during the time of rainy weather, the pressure of the Air is less, and in
_dry weather_, but especially when an _Eastern Wind_ (which having past
over vast tracts of Land is heavy with Earthy Particles) blows, it is much
more, though these changes are varied according to very odd Laws.
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