on Rivers and Canals. 
563 
SECTION II. 
T'he theory of rivers and canals. 
I. DEFINITIONS. 
3. A river is a greater or leffer quantity of water 
which runs conftantly,by its own gravity, from the more 
elevated parts of the earth, towards thofe which are 
more depreffed, in a natural bed or channel open above. 
4. If this bed or channel is artificial,. and has been 
dug by hands, it is called a canal^ of which there are two 
kinds; thofe where the channel is every where open, and 
without fluices, which I call an artificial river ; and thofe 
where the waters are kept up or let off by the means of 
fluices : it is this fecond fort which I fliall call hence- 
forwards by the proper name of a canal . 
5. A river is J, aid to perfevere in the fame Jlate fo long 
as there runs off an equal quantity of water in the fame 
time, without any increafe or diminution, fo that it re- 
mains always at the fame height in the fame place. 
When the circumftances are different from this, it is faid 
refpedlively that a river increafes or diminifhes. 
6. A fedlion of the bed of a river or canal is a plane * 
drawn perpendicular to the bottom of the bed and to the 
a direction s 
