on Rivers and Canals. 641 
I fliould think it quite fuperfluous to give any expla- 
nation of a table fo clear and intelligible as the -above; and 
fli all only remark upon it that the comparative degrees of 
the mean velocities of the refpeclive currents in the fecond 
column are the refult of obfervations and experiments, 
the method of making which has been given above 
(N° 26.) : but as the velocity of rivers is very different in 
different feafons of the year, which augment or diminifli 
greatly the mafs of waters in their beds,*? mean has been 
kept to, as much as poffible, in the above table. 
By taking the degree of velocity of the current in any 
river, a thing fo eafy to be done ; and obferving its other 
charatferiftics as laid down above under the title of dif- 
tinclive attributes , it will be eafy to judge very nearly of 
the quantity of declivity in that part of the river. 
79. After carefully comparing what has been faid in 
the relations of travellers, and in the belt treatifes of 
geography, upon the principal rivers in the known 
world, I fliould be inclined to clafs them in the following 
manner, particularly entreating at the fame time that 
my opinion about it may be regarded as fimple conjec- 
ture, which I leave to be rectified by thole better ac- 
quainted with the matter than it is poffible for me to be. 
Under the firft rate or clafs in the above table I fhould 
put that part of the channel of moil great rivers which 
is 
