Castelli, Benedetto, Of the mensuration of running waters, 1661

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1not give me a certain and ſtable meaſure and quantity of Water,
began deſervedly to be ſuſpected by me, as difficult and defective,
being alwayes various, and the meaſure, on the contrary, being
to be alwayes determinate, and the ſame; it is therefore written,
that Pondus & Pondus, Menſura & Menſura, utrumque abomi­
nabile eſt apud Deum, Exod.
I conſidered that in the Terri­
tory of Breſcia, my native Countrey, and in other places, where
Waters are divided to overflow the Grounds, by the like way of
meaſuring them, there were committed grievous and moſt impor­
tant errours, to the great prejudice of the Publique and of Pri­
vate perſons, neither they that ſell, nor they that buy under­
ſtanding the true quantity of that which is ſold and bought: In
regard that the ſame ſquare meaſure, as is accuſtomed in thoſe
parts, aſſigned one particular perſon, carried to ſometimes above
twice or thrice as much water, as did the ſame ſquare meaſure aſ­
ſigned to another.
Which thing proveth to be the ſame incon­
venience, as if the meaſure wherewith Wine and Oil is bought
and ſold, ſhould hold twice or thrice as much Wine or Oil at one
time as at another.
Now this Conſideration invited my minde
and curioſity to the finding out of the true meaſure of Running
Waters.
And in the end, by occaſion of a moſt important bu­
ſineſſe that I was imployed in ſome years ſince, with great in­
tenſeneſſe of minde, and with the ſure direction of Geometry, I
have diſcovered the miſtake, which was, that we being upon the
buſineſſe of taking the meaſure of the Waters that move, do make
uſe of two dimenſions onely, namely, breadth and depth, keep­
ing no account of the length.
And yet the Water being, though
running, a Body, it is neceſſary in forming a conceit of its quan­
tity, in relation to another, to keep account of all the three Di­
menſions, that is of length, breadth, and depth.
Here an objection hath been put to me, in behalf of the ordi­
nary way of meaſuring Running Waters, in oppoſition to what
I have above conſidered and propoſed: and I was told, Its true,
that in meaſuring a Body that ſtands ſtill, one ought to take all
the three Dimenſions; but in meaſuring a Body that continually
moveth, as the Water, the caſe is not the ſame: For the length
is not to be had, the length of the water that moveth being infi­
nite, as never finiſhing its running; and conſequently is incom­
prehenſible by humane underſtanding, and therefore with reaſon,
nay upon neceſſity it cometh to be omitted.
In anſwer to this, I ſay, that in the aboveſaid Diſcourſe, two
things are to be conſidered diſtinctly; Firſt, whether it be poſſible
to frame any conceit of the quantity of the Body of the Water
with two Dimenſions onely.
And ſecondly, whether this length
be to be found.
As to the firſt, I am very certain that no man, let

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