1Sucker move eaſily enough up and down
in the Cylinder by the help of the Manu
brium; yet if the Manubrium be taken off,
it will require & conſiderable ſtrength to
move it either way. Nor will it ſeem
ſtrange, that if, when the Valve and
Stop-cock are well ſhut, you draw down
the Sucker, and then let go the Manubri
um; the Sucker will, as it were of it ſelf,
re-aſcend to the top of the Cylinder, ſince
the ſpring of the external Air findes no
thing to reſiſt its preſſing up the Sucker.
And for the ſame reaſon, when the Re
ceiver is almoſt evacuated, though, ha
ving drawn down the Sucker, you open
the way from the Receiver to the Cylin
der, and then intercept that way again by
returning the Key; the Sucker will, up
on the letting go the Manubrium, be
forcibly carried up almoſt to the top of
the Cylinder: Becauſe the Air within the
Cylinder, being equally dilated and weak
ned with that of the Glaſs, is unable to
withſtand the preſſure of the external Air,
till it be driven into ſo little ſpace, that
there is an Æquilibrium betwixt its force
and that of the Air without. And con
gruouſly hereunto we finde, that in this
caſe, the Sucker is drawn down with little
in the Cylinder by the help of the Manu
brium; yet if the Manubrium be taken off,
it will require & conſiderable ſtrength to
move it either way. Nor will it ſeem
ſtrange, that if, when the Valve and
Stop-cock are well ſhut, you draw down
the Sucker, and then let go the Manubri
um; the Sucker will, as it were of it ſelf,
re-aſcend to the top of the Cylinder, ſince
the ſpring of the external Air findes no
thing to reſiſt its preſſing up the Sucker.
And for the ſame reaſon, when the Re
ceiver is almoſt evacuated, though, ha
ving drawn down the Sucker, you open
the way from the Receiver to the Cylin
der, and then intercept that way again by
returning the Key; the Sucker will, up
on the letting go the Manubrium, be
forcibly carried up almoſt to the top of
the Cylinder: Becauſe the Air within the
Cylinder, being equally dilated and weak
ned with that of the Glaſs, is unable to
withſtand the preſſure of the external Air,
till it be driven into ſo little ſpace, that
there is an Æquilibrium betwixt its force
and that of the Air without. And con
gruouſly hereunto we finde, that in this
caſe, the Sucker is drawn down with little