100 THE OCEAN RIVER 



constant difference in temperature will maintain marked cli- 

 matic differences. These differences are being traced even 

 today in the Arctic, as we shall later discuss. 



The River of the Ocean is not alone. Satellite rivers and 

 countercurrents, clinging to the skirts of the great circular 

 stream, are thrown off from the outer border of the flowing 

 water, while eddies swirl along the inner boundary, small pat- 

 terns of the Great Gyre itself. Most important of the satellite 

 rivers is a cold mass of arctic water that flows down from the 

 north as the Labrador Current, between the River and the 

 eastern shores of the United States, until it finally disappears 

 beneath the warmer and lighter waters of the Gulf Stream. 



Today's charts of the great Atlantic River and its currents 

 were not easily plotted. More than 400 years elapsed after the 

 first recorded Atlantic crossing before even the general out- 

 lines appeared in print. Before Columbus' first voyage a few 

 serious speculations had appeared regarding the Atlantic 

 Ocean; but mostly myth had grown up around it, and only 

 an adventurous man would dare advance away from its east- 

 ern shores into the sea of mystery. And yet, as we have seen, 

 the conception of the Atlantic as a river is a very ancient one. 

 The Chaldeans imagined that the earth floated on eternal 

 waters, and that a river perpetually flowed in a ditch around it. 

 The Egyptians added their own embellishment to this by 

 picturing a boat that supported the sun, floating in the 

 encircling stream. 



The Phoenicians ventured as far afield as the British Isles, 

 but like so many others who followed them in the slow chart- 

 ing of the Atlantic River they guarded their knowledge of 

 navigation as a trade secret and left no maps behind them. 

 With few preconceptions to hamper them, the Greeks who 

 followed were able to speculate without restraint on the 

 nature of the world. Homer considered the earth to be flat 

 and to consist only of the Mediterranean countries he knew. 



