on Rivers and Canals. 635 
city of Ipres and falls into the fea at Nieuport, having a 
very moderate current when the flukes upon it are open, 
I found its mean declivity to be nearly three fathoms four 
feet and eight inches in 20,000 fathoms of extent of its 
courfe,or very nearly one foot in a meafuredEnglifh mile. 
I fay its mean declivity , becaufe from what has been faid 
above (N° 13. 27. 28. 29.) it is plain, that a greater or 
lefs quantity than ordinary of water in it wilt add to, or 
take from, fomething thereof ; but the declivity in each 
part of its bed is nearly uniform. 
As the fources of this river, and thofe of the Ifere 
which joins it at Fort Knock, four leagues from Nieu- 
port, are in the higher grounds of Flanders towards 
Houthem, Mount Kemele, Swaertfberg, Catfberg, and 
the other hills as far as Mount Caflel ; and as the reft of 
their courfe is in a flat country with a very fmall defcent 
towards the fea, the declivity thereof may be taken as a 
tnean between that of the other rivers and canals of 
Flanders : the artificial canals will have lefs, not above 
a fix or feven thoufandth part of their extent, or one 
twelfth of an inch in each eight fathoms : the rivers Lys 
and Efcaut, before they fall into the flat country, fome- 
thing more, after which they may have about the fame* 
or even fomething lefs between Ghent and Antwerp. 
