VOL. LXIX.] 



PHILOSOPHICAL TRANSACTIONS. 



595 



tion and retardation of currents to rivers and canals in general, whence are deduced 

 the various means of preventing or remedying the defects and inconveniences which 

 must necessarily happen to them in a series of years : then follow observations on 

 the confluence of rivers, and on the separation of the same rivers into divers 

 branches and mouths, with their effects on the velocity of currents, inun- 

 dations, &c. 



Section 3 treats on the laws of the meeting of opposite currents, with the ap- 

 plication of them to sluices. And sect. 4 contains experiments to determine the 

 difl^erent velocities, in different depths of water, of the same floating body 

 moved uniformly by an equal force ; which experiments however are on a scale 

 much too small to be of any real practical use. And section 5 treats on the 

 quantity of declivity in rivers. And here, from certain data, obtained from ob- 

 servations and actual mensuration, and from many others of the same nature, 

 he deduces the following table of comparative proportions between the declivities 

 and velocities in different kinds of rivers. 



Distinctive attribntes of the varioLi-> kinds of rivers and flowing waters. 



Channels where the resistance from the bed, and other obstacles, equal the quantity of current acQuired 

 from the declivity ; so that the waters would stagnate, were it not for the compression and i mpulsion of 

 the upper and back waters. 



Artificial canals in the Dutch and Austrian Netherlands. 



Rivers in low and flat countries, full of turns and windings, and of a very slow current, subject to frequent 

 and lasting inundations. 



Rivers in most countries that are a mean between flat and hilly, which have a good current, but are subject 

 to overflow : also, the upper parts of rivers in flat countries. 



Rivers in hilly countries, with a strong current, and seldom subject to inundations : also, all riv-ers near their 

 sources have this declivity and velocity, and often much more. 



Rivers in mountainous countries, having a rapid current and straight course, and very rarely overflowing. 



Rivers in their descent from among mountains down into the plains below, in which places they run tor- 

 rent-wise. 



Absolute torrents among mountains. 



After carefully comparing what has been said in the accounts of travellers, and 

 in the best treatises of geography, on the principal rivers in the known world, 

 Mr. Mann classes them in the following manner : under the 1 st rate or class in 

 the above table, he puts that part of the channel of most great rivers which is 

 in extensive plains next the sea ; with regard to the declivity alone, but not at 



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