NATURAL HlSTOllY. 4 



but a continuation of it, and the source of the Gatn- 

 barou, which falls into the Niger, is about 1125 

 leagues; the Nile, which rises in upper Ethiopia, runs 

 about 970 leagues. There are others, the courses of 

 which are but little known, as the Zaira, the Coanza, 

 the Couama, and the Quilmanci, but each of which 

 \ve are acquainted with to the extent of 400 leagues. 



In America, the river of the Amazons runs above 

 1200 leagues. The course of the river St Lawrence 

 in Canada is more than 900 leagues. The river Mis* 

 sisippi runs above 700 leagues. The Plata extends 

 more than 800 leagues, from its mouth to the source 

 of the Parana, which it receives. The Oronoko runs 

 above 575 leagues, if we reckon from the source of 

 the river Caketa, near Pas to, a part of which falls 

 into the Oronoko, and a part runs towards the river of 

 the Amazons. The Madera which falls into the 

 Amazons extends above 660 leagues. 



In order to ascertain the quantity of water discharged 

 into the sea by all the rivers, we shall suppose the one 

 half of the surface of the earth to be sea, and the other 

 half to be dry land. We shall also suppose that the 

 mean depth of the sea is 230 fathoms. The total 

 surface of the earth is 170.981,012 square miles, and 

 that of the sea is 85,4-90,506 square miles, which, 

 when multiplied by one fourth, the depth of the sea, 

 gives 21 3 372,62() cubic miles for the quantity of water 

 contained in the whole ocean. Now that we may pretty 

 nearly ascertain the quantity ef water discharged 

 into the sea from the rivers, let us take the river- Po, 

 for example, which runs through Lombardy, and wa- 

 ters a country 380 miles long. According to Riccioli, 

 the breadth of the Po is 100 feet, and its depth is 10 

 feet, and it runs at the rate of 4 miles an hour. Con-* 



Vol. I. F 



