58 a Mr. mann’s ft eat if e 
neceffary to the motion of their waters, can only be at- 
tributed, fays Signor guglielmini to the infinite wif- 
dom of the fupreme Author of Nature. 
29. The velocity of flowing waters is very far from 
being in proportion to the quantity of declivity in their 
bed : if it was, a river whofe declivity is uniform and 
double to that of another, ought only to run with dou- 
ble the fwiftnefs when compared to it; but in effect it is 
found to have a much greater, and its rapidity, inftead of 
being only double, will be triple, quadruple, and fome- 
times even more : for its velocity depends much more on 
the quantity and depth of the water, and on the com- 
preffion of the upper waters on the lower, than on 
the declivity of the bed. Confequently, whenever the 
bed of a river or canal is to be dug, the declivity mull 
not be diftributed equally throughout the whole length ; 
but, to give a fwifter current to the water, the declivity 
muft be made much greater in the beginning of its 
courfe than towards the end where it difembogues itfelf, 
and where the declivity muft be almoft infenfible, as we 
fee is the cafe in all natural rivers ; for when they ap- 
proach near the fea their declivity is little or nothing, 
yet they flow with a rapidity which is fo much greater, 
as they contain a greater volume of water ; fo that in 
(dj Della Natura de Fiumi. 
great 
