50 NATURAL HISTORY. 



sequenily, the Po discharges into the sea 200,000 cu- 

 bical perches of water in an hour ; and as a cuhic mile 

 contains 125,000,000 cuhic perches, the Po will re- 

 quire 26 days to discharge into the sea a cuhic mile 

 of water. It now only remains to determine the pro- 

 portion that the Po bears to all the other rivers of the 

 earth taken together, which cannot be done exactly. 

 But, to come as near to the truth as possible, let us 

 suppose the quantity of water, which the sea receives 

 from the great rivers in every country, to he propor- 

 tioned to the extent of the surfaces of those countries; 

 and, consequently, that the country watered by the 

 ** and by the rivers that fall into it, is to the total 

 su rface of the dry land, as the Po is to all the rivers 

 f the earth. Now, from the most accurate charts, it 

 appears, that the Po waters a country 380 miles long 

 and 120 broad, which makes 45,6'00 square miles. 

 But the surface of the dry land is 85,4-90,506 square 

 miles ; consequently, the quantity of water conveyed 

 to the sea by all the rivers, will be 1874 times greater 

 than the quantity discharged by the Po. But, as 26 

 rivers, equal to the Po, furnish a cubic mile of water 

 every day, it follows, that, in the space of a year, 1874 

 rivers equal to the Po, will convey to the sea 26,308 

 cubic miles of water ; and that in 8 1 2 years, all these 

 rivers would discharge 21,372,626 cubic miles, which 

 is a quantity equal to what is contained in the ocean ; 

 of course, if the ocean were empty, 812 years would 

 be necessary to fill it from the rivers. 



There results from this calculation, that the quantity 

 of water evaporated from the sea, and which the winds 

 convey on the earth, producing rivulets, streams, and 

 rivers, is from 20 to 21 inches in- a year, or about two 

 thirds of a line each day ; this is a very trifling eva- 



