on Rivers and Canals. 639 
been found, by a long feries of barometrical obfervations, 
to be about feventy-five fathom '% which gives the pro- 
portion of the declivity to the extent as one to 262,0, or 
about one third of a line to each fathom. This is double 
the mean declivity of the rivers in Flanders; but the 
velocity of the current in the Rhone is at leaf!: triple 
that in the others (N° 29.)* 
78. From the above data , got from obfervations and 
actual menfuration, and from many others of the fame 
nature too long to mention here, we may deduce the fol- 
lowing table of comparative proportions between the de- 
clivities and velocities in different kinds of rivers. 
(0 ) See Cours de Pbyfique de Para, tom. II. N® 740. 
4 O 2 
Rates 
