on Rivers and Canals . 651 
Scheld and the Lys, above Ghent, have about one foot 
declivity in each four thoufand feet of length. 
According to this, the furface of the Scheld in Ghent 
is about forty feet higher that it is at Antwerp; and at 
Tournay it is fixty-fix feet higher than at Ghent, and 
one hundred and fix feet higher than at Antwerp. So 
alfo the furface of the Lys at Commines is fixty-one feet 
higher than at its junction with the Scheld in Qhent, and 
one hundred and one feet higher than the fame at 
Antwerp. From hence it may be deduced, that the 
Scheld at Tournay is about five feet higher than the Lys 
at Commines, through twenty-five miles of interjacent 
country. 
84. Suppofe it be required to find the difference of 
height between the furface of the Lys at Commines and 
the furface of the canal at Ipres which falls into the fea 
at Nieuport on the Coaft of Flanders. The diftance be- 
tween Ipres and Commines is nearly feven meailired 
miles, through which there is no communication by 
water; but there is one a great way round, which there- - 
fore, for the purpofe required, muff be followed through 
all the differences of elevation comprized therein, viz. 
Dejcenl 
