The greatest rivers of America, and which are also the greatest in the world, are the river Amazons, whose course is 1200 leagues, if we go up as far as the Lake near Guanuco, 30 leagues from Lima, where the Maragnon takes its source; and even reckoning from the source of the river Napo, some distance from Quito, the course of the river Amazons is more than a thousand leagues. It might be said that the course of the river St. Lawrence, in Canada, is more than 900 leagues from its mouth to the lake Ontaro, from thence to lake Huron, afterwards to the lake Alemipigo, and to the lake Assiniboils; the waters of these lakes falling one into another, and at last into St. Lawrence. The river Mississippi more than 700 leagues long from its mouth to any of its sources, which are not remote from the lake of the Assiniboils. The river de la Plata is more than 800 leagues long, from the source of the river Parana, which it receives. The river Oroonoko runs more than 575 leagues, reckoning from the source of the river Caketa, near Pasto, part of which falls into the Oroonoko, and part flows also towards the river Amazons. The river Madera, which falls into the Amazons, is more than 660 leagues. To know nearly the quantity of water the sea receives by all the rivers which fall into it, let us suppose that one half of the globe is covered by the sea, and that the other half is land, which is nearly the fact; let us suppose also, that the mediate depth of the sea is 230 fathom. The surface of all the earth being 170,981,012 square miles; and that of the sea 85,490,506 square miles, which being multiplied by 1/4, the depth of the sea gives 21,372,626, cubical miles for the quantity of water contained in the ocean. Now, to calculate the quantity of water which the ocean receives from the rivers, let us take some great river, whose rapidity and quantity of waters are known; for example, the Po, which runs through Lombardy, and waters a tract of land 380 miles long; according to Riccioli, its breadth, before it divides into many trenches, is 100 perches of Boulogne, or 1000 feet, its depth 10 feet, and it runs four miles an hour; therefore the Po supplies the sea with 200,000 cubical perches of water in an hour, or 4 millions 800 thousand in a day; but a cubical mile contains 125 millions cubical perches; therefore 26 days is required to convey a cubical mile of water to the sea: it remains therefore only to determine the proportion between the river Po and all the rivers of the earth taken together, which is impossible to do precisely. But to know it pretty exactly, let us suppose that the quantity of water which the sea receives by the large rivers in all countries is proportional to the extent and surface of these countries, and that consequently the country watered by the Po, and other rivers which fall therein, is in the same proportion on the surface of the whole earth, as the Po is to all the rivers of the earth.