1ſign that there is no need of opening it; and if there be any oc
caſion to open it, it is eaſily done. As for the reſt your Lordſhip
may pleaſe to keep account of all the particulars that occur, for
the memory of things paſt is our Tutreſſe in thoſe that are to
come. If occaſion ſhall offer, I intreat you to bow humbly in
my name to His Highneſs the Grand Duke, and the moſt Serene
Prince Leopold; and to attend the ſervice of Their Highneſſes, for
you ſerve I rinces of extraordinary merit; And to whom I my
ſelf am alſo exceedingly obliged. In the controverſies that ariſe
reſpect the pious end of ſpeaking the Truth, for then every
thing will ſucceed happily. I kiſs the hands of Padre Franceſco,
of Sig. Bartolotti, and of your Lordſhip.
caſion to open it, it is eaſily done. As for the reſt your Lordſhip
may pleaſe to keep account of all the particulars that occur, for
the memory of things paſt is our Tutreſſe in thoſe that are to
come. If occaſion ſhall offer, I intreat you to bow humbly in
my name to His Highneſs the Grand Duke, and the moſt Serene
Prince Leopold; and to attend the ſervice of Their Highneſſes, for
you ſerve I rinces of extraordinary merit; And to whom I my
ſelf am alſo exceedingly obliged. In the controverſies that ariſe
reſpect the pious end of ſpeaking the Truth, for then every
thing will ſucceed happily. I kiſs the hands of Padre Franceſco,
of Sig. Bartolotti, and of your Lordſhip.
Rome, 14. March 1642.
Your Honours
most Obliged Servant
D. BENEDETTO CASTELLI.
Vpon this occaſion I will here inſert a Diſcourſe that I made
upon the Draining and improvement of the Pontine Fens,
for that I think that whatſoever may be done well and to pur
poſe in this matter hath abſolute dependance on the perfect know
ledge of that ſo important Propoſition, by me demonſtrated and
explained in my Treatiſe of the Menſuration of Running Wa
ters, namely, That the ſame water of a River doth continually
change Meaſures, according as it altereth and changeth the ve
locity of its courſe; ſo that the meaſure of the thickneſſe of a
River in one Site, to the meaſure of the ſame River in another
Site, hath the ſame proportion reciprocally that the velocity in
this ſite hath to the velocity in the firſt ſite. And this is a Truth
ſo conſtant and unchangeable, that it altereth not in the leaſt
point on any occurrences of the Waters that change: and
being well underſtood, it openeth the way to the knowledge of
ſundry advertiſements in theſe matters, which are all reſolved by
this ſole Principle; and from it are derived very conſiderable be
nefits; and without theſe it is impoſſible to do any thing with
abſolute perfection
upon the Draining and improvement of the Pontine Fens,
for that I think that whatſoever may be done well and to pur
poſe in this matter hath abſolute dependance on the perfect know
ledge of that ſo important Propoſition, by me demonſtrated and
explained in my Treatiſe of the Menſuration of Running Wa
ters, namely, That the ſame water of a River doth continually
change Meaſures, according as it altereth and changeth the ve
locity of its courſe; ſo that the meaſure of the thickneſſe of a
River in one Site, to the meaſure of the ſame River in another
Site, hath the ſame proportion reciprocally that the velocity in
this ſite hath to the velocity in the firſt ſite. And this is a Truth
ſo conſtant and unchangeable, that it altereth not in the leaſt
point on any occurrences of the Waters that change: and
being well underſtood, it openeth the way to the knowledge of
ſundry advertiſements in theſe matters, which are all reſolved by
this ſole Principle; and from it are derived very conſiderable be
nefits; and without theſe it is impoſſible to do any thing with
abſolute perfection