NATURE OF THE STREAM 123 



ing to sail against it. He conceived that as the sun moved 

 v^estward this great ocean bulge was dragged along beneath it 

 until the obstacle of the South American shores diverted the 

 water coastwise. The sun, of course, does exert a small gravita- 

 tional force that aids in the periodic swell and movement of 

 the tides; but this is far from being a satisfactory explanation 

 of the continuous current system. 



In contrast to this, another theory involved watery valleys 

 instead of mountains, but it too was based on the supposed 

 direct effect of the sun. The French hydrographer Fournier, 

 who started with the perfectly sound principle that the sun 

 evaporates water from the tropical seas, was led into specula- 

 tions that had little further relation to fact. According to him, 

 the loss of water by evaporation in the tropics is sufficient to 

 leave a prodigious hollow in the sea into which the water is 

 irresistibly drawn. This maritime valley moves from east to 

 west with the sun, the currents naturally follow, and in this 

 simple — and to him completely satisfactory — fashion the 

 North Atlantic circulation is kept in motion. 



Thus far, most speculations were focused on a supposed 

 attraction between sun and water. To some this attraction was 

 a complete mystery, while to others it was due to evaporation 

 or to the rotation of the earth; but gradually these explana- 

 tions were supplanted by others with a little more basis of 

 scientific truth. Athanasius Kircher, who published the first 

 crude chart of the Atlantic River, was among the earliest to 

 realize the importance of the trade winds in causing the Equa- 

 torial Current: ''This motion touches many things, whether 

 partly from the general motion of the trade winds against the 

 opposing shores of that region and thence again reflected, 

 which they call the Sailor's Current, or from wind storms. . . .'' 

 So far he was close enough to modem scientific beliefs, but he 

 fell into error when he advanced a further suggestion that the 

 attraction of the moon produced not merely tides but also con- 



