46 rnrsiCAL GEOGRArnY or the sea, and its meteoeologt. 



resisting permeability, we are enabled to comprehend liow the 

 waters on either hand, as their si)ecific gi-avity is increased or 

 diminished, will impart to the trough of this stream a vibratory- 

 motion, pressing it now to the right, now to the left, according to 

 the seasons and the consequent changes of temperature in the sea. 

 12G. Limits of the Gulf Stream in Marcli and Scjitemher. — Plate 

 VI. shows the limits of the Gnlf Stream for March and Septem- 

 ber. The reason for this change of position is obvious. The 

 banks of the Gulf Stream (§70) are cold water. In winter the 

 volume of cold water on the American, or left side of the stream, 

 is* greatly increased. It must have room, and gains it by press- 

 ing the warmer waters of the stream farther to the south, or 

 right. In September, the temperature of these cold waters is 

 modified; there is not such an extent of them, and then the 

 warmer waters, in turn, press them back, and so the pendulum- 

 like motion is preseiwed. 



127. Bcludance of layers or patclies to mingle. — In the offings of 

 the Balize, sometimes as far out as a hundred miles or more from 

 the land, puddles or patches of Mississippi water maybe observed 

 on the surface of the sea with little or none of its brine mixed 

 with it. This anti-mixing property in water has already (§ 98) 

 been remarked upon. It msij be observed from the gutters in 

 the street to the rivers in the ocean, and everywhere, wherever 

 two bodies of water that differ in colour are found in juxta- 

 position. The patches of white, black, green, yellow, and 

 reddish waters so often met with at sea are striking and familiar 

 examples. We have seen, also, that a like proclivity exists 

 (§ 99) between bodies or streams of water that differ in tempera- 

 ture or velocity. This peculiarity is often so strikingly developed 

 in the neighbourhood of the Gulf Stream, that persons have been 

 led to suppose that the Gulf Stream has forks in the sea, and that 

 these are they. 



128. Streaks oficarm and cool. — Now, if any vessel will take 

 up her position a little to the northward of Bermuda, and 

 steering thence for the Capes of Virginia, will try the water- 

 thermometer all the way at shoi-t intervals, she will find its 

 readings to be now higher, now lower ; and the observer will 

 discover that he has been crossing streak after streak of wann 

 and cool water in regular alternations. He will then cease to 

 regard them as bifurcations of the Gulf Stream, and view them 

 rather in the light of theimal streaks of water which have, in the 



