THE EARTH. 179 



instead of rubbing against four shores, now only 

 rubs against two. And, besides, the current be- 

 ing deeper, becomes, of consequence, more fit- 

 ted 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 supply the 

 greatest and most extensive rivers. It may also 

 be remarked, in 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 j however, they are liable 

 to many exceptions, 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 scarcely 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 unhappily disappointed, in the year 1741. 

 The next in order is the Danube. The course of 

 this is about four hundred and fifty leagues, from 



DrHalley. 



