Boyle, Robert New experiments physico-mechanicall, touching the spring of the air and its effects 1660
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106
none of the Air been drawn away from a­
bout the Needle, which when the Load­
stone was removed, after some tremu­
lous Vibrations to and fro, rested in a po­
sition wherein it look'd North and
South.

Experi­
ment 16

PRoceed we now to the mention of

that Experiment, whereof the satis­
factory tryal was the principal Fruit I
promis'd my self from our Engine. It
being then sufficiently known, that, in
the Experiment De Vacuo, the Quick­
silver in the Tube is wont to remain ele­
vated, above the surface of that whereon
it leans, about 27 digits: I considered,
that, if the true and onely reason why the
Quick-silver falls no lower, be, that at
that Altitude, the Mercurial Cylinder in
the Tube, is an Æquilibrium with the
Cylinder of Air, suppos'd to reach from
the adjacent Mercury to the top of the
Atmosphere: If this Experiment could
be try'd out of the Atmosphere, the
Quick-silver in the Tube would fall
down to a levell with that in the Vessel,
since then there would be no pressure up­
on the Subjacent, to resist the weight of