( 7?o ) 
were built upon a more folid Foundation than a ten- ' 
tative Calculus and that Allowance had been made for 
the Velocity impreft upon the preceding Water in Ri- 
vers, by the imf>etus of that which follows, which is 
omitted by the Author in his Theory, both of mixt 
and fimple Motion. 
In the Second Book, this Learned Writer propofes 
the State of the Laguna of Venict^ as a proper Exam- 
ple, to demonftrate the Ufefulnefs of his new' Theory. 
He confiders very minutely the feveral Caufcs of choak- 
ing up the Laguna, examins the Methods propofcd by 
various Authors for fcouring and keeping it clear, fome 
of which he rejcds as impradficable on account of the 
Expence, others as ufelefs, or prejudicial; and laftly de- 
livers his own Opinion. 
The principal Caufes, which he afTigns, of filling up 
the Laguna, are the Rivers running into it, and the Sea. 
The Rivers, which enter it, arifing out of the Alp, 
and running down with great Rapidity, carry with them, 
efpecially after Rains, great Quantities of Soil, which is 
eafily fufpended in the Water, fodong as that Swnftnefs 
of Motion continues. But w'hen they come into the 
Laguna, the Water, upon extending it felf over that vaft 
Surface, loofes almoft all its Velocity, and confcquenC'. 
ly the SoiLand Filth, which before it carry ‘d with it, 
fubfides in great Qiiantities to the Bottom. 
The Remedy our Author propoles for this Incon- 
venience, is either wholly to divert the Courfe of the 
Rivers and carry them, by another W'ay, diredfly in* 
to the Sea; or at lead, to fecure their Outlets with 
Sluices, (o as to fufTer them to pafs into the Laguna, 
when their Waters are clear ; but after great Rains, when 
they run foul and turbid, to flop* their PalTage that 
way, and let them out by the other Channel into the 
Sea. 
The 
