on Rivers and Canals. 557 
rivers: they are liable to many accidents which the 
others are not, and of a different nature. Thefe accidents 
do not become fenfible till many years after their con- 
ftrudtion, and are better prevented in time than remedied 
when they happen. I have long lived in a country fa- 
mous for its navigable canals, and have been much em- 
ployed, under the eyes of the government of it, upon that 
fubjeft. I only mention this to fhew, that I have not un- 
dertaken to treat a fubjedt to which I am an utter ftranger. 
There are, moreover, many coniiderations concerning 
the laws of motion in rivers and canals in general, the 
velocity of their currents in proportion to the quantity of 
their declivity, and the means of afcertaining therefrom 
the refpedtive heights of the interior parts of continents, 
which merit the attention of a natural philofopher. 1 
fhall venture to offer my thoughts and obfervations (fome 
of which, I believe, are new) on all thele fubjects in the 
enfuing Differtation, which I fubmit entirely to the judg- 
ment of the Royal Society, and fhall efteem myfelf 
happy if I fucceed in it, fo as to be of any ufe to my 
country, and to be able to teftify, at the fame time, my 
profound refpedt and veneration to you, dear sir, and to 
the illuftrious body over which you prefide. 
4D 
Vol. LXIX. 
S E C- 
