Castelli, Benedetto
,
Of the mensuration of running waters
,
1661
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ſelves, as have the mouths, which are the numbers 32 and 8
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in our example: Then this
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being done, let the velocity
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of the Water by the paſſa
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ges A and B, be examined
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(which may be done keeping
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account what ſpace a piece
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of Wood, or other body that
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ſwimmeth, is carried by the ſtream in one determinate time; as
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for inſtance in 50 pulſes) and then work by the golden Rule, as
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the velocity by A, is to the velocity by B, ſo is the number 8, to
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another number, which is 4. It is clear by what is demonſtra
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ted in the ſaid ſecond Propoſition, that the quantity of water,
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which paſſeth by the mouth A, ſhall have the ſame proportion of
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that which paſſeth by the mouth B, that 8 hath to 1. Such pro
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portion being compoſed of the proportions of 32 to 8, and of 8 to
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4; namely, tothe greatneſs of the mouth A, to the greatneſs of the
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mouth B, and of the velocity in A, to the velocity in B. </
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<
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>This being
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done, we muſt then contract the mouth which diſchargeth more
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then its juſt quantity of water, or enlarge the other which diſchar
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geth leſs, as ſhal be moſt commodious in practice, which to him that
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hath underſtood this little that hath been delivered, will be very
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afie.</
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>APPENDIX XII.</
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>Theſe opperations about Water, as I have hitherto on ſun
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dry occaſions obſerved, are involved in ſo many difficul
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ties, and ſuch a multiplicity of moſt extravagant accidents,
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that it is no marvel if continually many, and very important er
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rours be therein committed by many, and even by Ingeneers
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themſelves, and Learned-men; and becauſe many times they
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concern not onely the publique, but private intereſts: Hence it
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is, that it not onely belongeth to Artiſts to treat thereof, but very
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oft even the vulgar themſelves pretend to give their judgement
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therein: And I have been troubled many times with a neceſſity
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of treating, not onely with thoſe, which either by practice, or
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particular ſtudy, underſtood ſomewhat in theſe matters; but alſo
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with people wholly void of thoſe notions, which are neceſſary for
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one that would on good grounds diſcourſe about this particular;
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and thus many times have met with more difficulty in the thick
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skulls of men, than in precipitous Torrents, and vaſt Fennes.
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>And in particular, I had occafion ſome years paſt to go ſee the
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Gave or Emiſſary of the Lake of
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Perugia,
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made many years agon
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by
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Braccio Fortobraccio,
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but for that it was with great ruines by
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Time decayed, and rendred unuſeful, it was repaired with in</
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