Our Salt-JVater World 329 



or trade-wind current, It has no great basin like the 

 Gulf of Mexico to store the waters of another Gulf 

 Stream; no other ocean but the Atlantic contains a 

 current of such energy and volume. And no other cur- 

 rent affects so large a part of the surface of the earth. 

 At first sight It seems Incredible that a current of water 

 should force Itself through the ocean with distinct 

 boundaries and with a different color, temperature, and 

 even Inhabitants (for the creatures which live In its 

 tropical warmth seldom stray into the colder seas), 

 like a mighty river between Its banks, flowing for thou- 

 sands of miles against counter-currents which some- 

 times actually cross its course, passing under by their 

 greater density, until It loses Its momentum on the 

 shores of far-off continents or spreads out In the dis- 

 tant north to temper the frigid seas. But all this, as 

 closer observation will soon convince us, Is in accord- 

 ance with the physical laws of fluids. It Is well know^n 

 that great Inland streams, such as, for Instance, the 

 clear waters of the Mississippi and the turbid currents 

 of the Missouri, do not unite at once at their conflu- 

 ence, but continue side by side for many miles before 

 they mingle. And all great rivers running Into the 

 ocean are rivers still, far out at sea. The Rio de la 

 Plata, which drains the southern part of South America, 

 continues to flow after It leaves the land, and can be 

 perceived in Its course two hundred miles from the 

 shore. The Amazon runs far Into the Atlantic, though 

 it is there gradually bent to the north by the trade- 

 wind currents, and helps, with the waters of the Ori- 

 noco, to swell the Gulf of Mexico. From this It will 

 be seen that the Mississippi, the Rio Grande, the Ori- 



