on Rivers and Canals. 
653 
Jf cent from the fea at Nieuport to the city of Ipres. 
Feet* 
Difference of height which the river from Nieuport 
to Ipres has above the canal from Nieuport to 
Plafchendahl, taken crofs the harbour of Nieu- 
port, by means of the tides which come up againft 
the outer gates of the fluices next the fea on each, 3 
Declivity of the river Iprelee from Nieuport to 
Boefinghe, - - - 1 1 
Difference of level of the water above and below the 
fluice of Boefinghe, - - 22 
Declivity in the canal from Boefinghe to Ipres, 
Total afcent, all one way, from Nieuport to Ipres, 37 
Now 84-37=47 feet for the difference of height 
which the furface of the Lys at Commines has above 
the furface of the canal at Ipres. I have made ufe of the 
above example preferably to any others, as it is very 
complicated, and becaufe the quantities of declivity 
which I have put down are not arbitrary; and, moreover, 
becaufe I had the good fortune to find, fome years after I 
had taken thofe meafures, that I only differed two feet 
Vol. LXIX. 4 Q from 
wj t* 
