1leſs difficulty, then if the Cylinder, be
ing devoid of Air, the Stop-cock were
exactly ſhut: We might take notice of
ſome other things, that depend upon the
Fabrick of our Engine it ſelf; but to ſhun
prolixity, we will, in this place, content
our ſelves to mention one of them, which
ſeems to be of greater moment then the
reſt, and it is this; that when the Sucker
has been impell'd to the top of the Cylin
der, and the Valve is ſo carefully ſtopp'd,
that there is no Air left in the Cylinder a
bove the Sucker: If then the Sucker be
drawn to the lower part of the Cylinder,
he that manages the Pump findes not any
ſenſibly greater difficulty to depreſs the
Sucker, when it is nearer the bottom of the
Cylinder, then when it is much further off.
Which circumſtance we therefore think fit
to take notice of, becauſe an eminent Mo
dern Naturaliſt hath taught, that, when the
Air is ſucked out of a Body, the violence
wherewith it is wont to ruſh into it again,
as ſoon as it is allow'd to re-enter, pro
ceeds mainly from this; That the preſſure
of the ambient Air is ſtrengthned upon
the acceſſion of the Air ſuck'd out; which,
to make it ſelf room, forces the neighbor
ing Air to a violent-ſubingreſſion oſ its
parts: which, iſ it were true, he that draws
ing devoid of Air, the Stop-cock were
exactly ſhut: We might take notice of
ſome other things, that depend upon the
Fabrick of our Engine it ſelf; but to ſhun
prolixity, we will, in this place, content
our ſelves to mention one of them, which
ſeems to be of greater moment then the
reſt, and it is this; that when the Sucker
has been impell'd to the top of the Cylin
der, and the Valve is ſo carefully ſtopp'd,
that there is no Air left in the Cylinder a
bove the Sucker: If then the Sucker be
drawn to the lower part of the Cylinder,
he that manages the Pump findes not any
ſenſibly greater difficulty to depreſs the
Sucker, when it is nearer the bottom of the
Cylinder, then when it is much further off.
Which circumſtance we therefore think fit
to take notice of, becauſe an eminent Mo
dern Naturaliſt hath taught, that, when the
Air is ſucked out of a Body, the violence
wherewith it is wont to ruſh into it again,
as ſoon as it is allow'd to re-enter, pro
ceeds mainly from this; That the preſſure
of the ambient Air is ſtrengthned upon
the acceſſion of the Air ſuck'd out; which,
to make it ſelf room, forces the neighbor
ing Air to a violent-ſubingreſſion oſ its
parts: which, iſ it were true, he that draws
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