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the force of any thruft, or a boat’s running againft them, may 
do’no prejudice to them: for if they are any thing ftrained, 
they are apt to prove leaky; and in fo great an height as is 
needful for deep waters, a fmall matter will do it, satel they 
are extraordinarily well abutted. 
The timber-work muft be heart of oak, efpecially the top, 
and that all of one piece, how long foever it be; and the vent 
hole muft be guarded with large boxes perforated fo as the 
water, but no fifth, may pafs. And all this well framed, and 
what is under ground extraordinarily rammed with clay, elfe 
it will be apt to leak. 
The ufe of thefe is very great: for if a great water muft 
be emptied, you muft either apply engines, cut the bank, 
or draw a fluice. As for engines, they are too chargeable, 
and puzzling to ix; however, I may propofe to them that 
are lovers of art, fome facile ways of lifting great quantities of 
water. Then, if you cut the bank, the paffage is interrupted 
and made troublefome by the earth, and you fhall fearce ram 
it up fo well again, but it will perpetually leak about the place 
where the fiffure was; but fluices vent the water certainly, 
though flowly, without any labour, charge, or inconvenience. 
Of 
