THE EARTH. 8? 



its dormant waters into motion. In this manner the \onetian branch 

 of the Po was pushed on by the Ferarese branch and that of Panaro, 

 without any enlargement of its breadth or depth from these acces- 

 sions. 



A river tending to enter another, ^either perpendicularly, 01 in ai 

 opposite direction, will be diverted by degrees from that direction ; 

 and lie obliged to make itself a more favourable entrance downward, 

 md more conspiring with the stream of the former. 



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

 the same quantity of water, instead of rubbing against four shores, 

 now only rubs against two. And, besides, the current being deeper, 

 becomes, of consequence, more fitted for motion. 



With respect to the places from whence rivers proceed, it may be 

 taken for a general rule, that the largest* and highest mountains sup- 

 ply the greatest and most extensive rivers. It may be also remarked, 

 iu whatever direction the ridge of the mountain runs, the river takes 

 an opposite course. If the mountain, for instance, stretches from 

 north to south, the river runs from east to west ; and so contrariwise. 

 These are some of the most generally received opinions with regard 

 to the course of rivers ; however, they are liable to many excep- 

 tions ; and nothing but an actual knowledge of each particular river 

 can furnish us with an exact theory of its current. 



The largest rivers of Europe are, first, the Wolga, which is about 

 six hundred and fifty leagues in length, extending from Reschow to 

 Astrachan. It is remarkable of this river, that it abounds with water 

 during the summer months of May and June ; but all the rest of the 

 year is so shallow as scarce to cover its bottom, or allow a passage 

 for loaded vessels that trade up its stream. It was up this river that 

 the English attempted to trade into Persia, in which they were so un- 

 happily disappointed, in the year 1741. The next in order is the 

 Danube. The course of this is but about four hundred and fifty 

 leagues, from tlie mountains of Switzerland to the Black Sea. It is 

 so deep between Buda and Belgrade, that the Turks and Christians 

 have fleets of men of war upon it ; which frequently engaged, during 

 the last war between the Ottomans and the Austrians ; however, it is 

 unnavigable further down, by reason of its cataracts, which prevent 

 its commerce into the Black Sea. The Don, or Tanais, which is 

 four hundred leagues from the source of that branch of it called the 

 Softna, to its mouth in the Euxine Sea. In one part of its course, it 

 approaches near the Wolga ; and Peter the Great had actually begun 

 a canal, by which he intended joining those two rivers ; but this he 

 did not live to finish. The Nieper, or Boristhenes, which rises in the 

 middle of Muscovy, and runs a course of three hundred and fifty 

 leagues, to empty itself into the Black Sea. The Old Cossacks inhabit 

 the banks and islands of this river; and frequently cross the Black 

 Sea, to plunder the maritime places on the coasts of Turkey. The 

 Dwina ; which takes its rise in a province of the same name in Rus- 

 ^sia, that runs a course of three hundred leagues, and disembogues in 

 to the White Sea, a little below Archangel. 



* Dr. Hallev. 



