118 HISTORY OF 



in the current of a river, wnuM refard its velocity. Bntthedit- 

 ference they make is very inconsiderable. The water, by these 

 stoppages, gets an elevation above the object ; which, when it 

 lias surmounted, it gives a velocity that recompenses the former 

 rlehiy. Islands and turnings also retard the course of the stream 

 hut very inconsiderably ; any cause which diminishes the quan- 

 tity of the water, most sensibly diminishes the force and the 

 velocity of the strenm. 



An increase ' of water in the bed of the river always increases 

 its rapidity ; except in cases of inundation. The instant th - 

 river has overflov,-ed its banks, the velocity of its current is al- 

 ways turned tV.at way, and the inundrttion is perceived to con- 

 tinue for some days ; which it would not otherwise do, if, as 

 soon ;;s the cause was discontinutd, it acquired its former ra 

 pidi'y. 



A violent storm, that sets directly up against the course of 

 the stream, will always retard, and sometimes entirely stop its 

 coiu'se. T have seen an instance of this, v,'hen the bed of a large 

 river was left entirely dry for some hours, and fish were caught 

 among the stones at the bottom. 



Inundations are generally greater towards the source of rivers 

 than farther down ; because the current is generally swifter 

 below than above ; and that for the reasons already assigned. 



A little river - may be received into a large one, without aug- 

 menting either its width or depth. This, which at first view 

 seems a paradox, is yet very easily accounted for. The little 

 river, in this case, only goes towards increasing the swiftness ol 

 the larger, and putting its dormant waters into motion. In this 

 manner the Venetian branch of the Po, v.-as pushed on Viy the 

 Ferrarese branch and that of Panaro, without any enlargement 

 of its breadth or depth from these accessions. 



A river tending to enter another, either perpendicularly, or 

 in an opposite direction, will be diverted by degrees from that 

 direction ; and be obliged to make itself a more favourable en- 

 trance downward, and more conspiring with the stream of the 

 former. 



The union of two rivers into one, makes it flow Uie swifter : 

 since the same quantity of water, instead of rubbing agairs! 

 tour shores, now only rubs against two. And, besides, the ciuv 



1 BuflTon, vol. ii. p. Crl 2 Gii|7lio1:Tiiiii. 



