on Rivers and Canals. 637 
ranean Tea. Again, according to the above Abbe chappe, 
the faid floor of the Obfervatory is elevated twenty-four 
fathoms one foot and ten inches above the level of the 
river Seine at Paris ; therefore the level of the Seine un- 
der the Pont Royal at Paris is twenty-one fathoms one 
foot and leven inches above the level of the Ocean ; and 
fuch alfo is the quantity which Meff. cassini have given, 
from their own obfervations and experiments, for the 
mean height of the Seine at Paris above the level of the 
fea. 
Now the courfe of the Seine from Paris to its mouth 
at Havre de Grace, by following all its turns and wind- 
ings, is about 90,000 fathoms in length; therefore 
= 42322 fathoms of extent for one fathom of de- 
clivity in the river Seine, or one line in 42 fathoms, and 
confequently the proportion of its declivity to its length 
is as one to 42322. It is to be obferved, that the bed of 
the Seine is deep, and its current confiderably ftrong. 
76. By flmilar obfervations and actual levellings made 
upon the river Loire by M. M. picarb and pitot (n \ the 
declivity thereof in proportion to its length is found to 
be as one to 3174, which is one line in 32 fathoms * 
Notwithftanding this great declivity of the bed of the 
Loire it is obferved, that the velocity of the water therein, 
(n) See Memoires de PAcad. Royale des Sciences de Paris, pour 1730. 
Vol. LXflX. 4 O compared 
