NATURAL PHILOSOPHY. 217 



li.S, and producing a mean range of the extreme of temperature on the 

 western side of almost thrice the amount of the extremes on the eastern 

 side, or, more strictly, in the proportion of 29. 7 to 11. 3. The author 

 drew attention to a diagram in which he had laid down along the entire 

 belt curves showing the whole range of the lowest depressions of tempera- 

 ture and highest elevation, with the means at each longitude distinguished 

 by different shading, and pointed out how the inspection of this, as well as 

 of the tabulated results, affords striking indications of the two great cur- 

 rents, one descending from the Polar, the other ascending from the Tropi- 

 cal regions, with their characteristic changes of cold and heat. The 

 author then proceeded to draw conclusions, showing that sometimes the 

 cold current from the north plunged beneath the warmer current from the 

 south. Sometimes they divided, the colder keeping in shore along the 

 American coast, the other keeping out, and forming the main Gulf-stream. 

 Sometimes where they met they interlaced in alternating stripes of hot 

 and cold water ; sometimes their meeting caused a deflection, as where 

 one branch of the Gulf- stream was sent down to the south-east of Europe 

 and north of Africa, and another brarch sent up past the British Islands 

 to Norway and Scandinavia, by the Polar current setting down to the east 

 of Newfoundland. The author next proceeded to consider the uses in the 

 economy of Nature of these great oceanic currents. The first that he 

 noticed was the equalizing and ameliorating influence which they exercised 

 on the temperature of many countries. Of this he gave several examples. 

 Thus, our own country, though usually spoken of as a very variable cli- 

 mate, was subject to far less variations of range of temperature than many 

 others in similar latitudes, which was chiefly from the general influence 

 of the northern branch of the Gulf-stream setting up past these islands. 

 He had himself, on one occasion, in the month of November, known the 

 temperature to rise no less than 52 in forty-eight hours, having previ- 

 ously descended in a very few days through a still greater range ; while in 

 these countries the extensive range between mean summer and winter 

 temperature scarcely in any instance exceeds 27, and in many places does 

 not amount to nearly as much. Another advantage derived from these 

 currents, was a reciprocation of the waters of high and low latitudes, 

 thus tending to preserve a useful equalizing of the saltness of the waters, 

 which otherwise, by evaporation in low latitudes, would soon become too 

 salt to perform its intended functions. Next he pointed out their use in 

 forming sand-banks, which became highly beneficial as extensive fields 

 for the maintenance of various species of the finny tribes, as in the great 

 banks of Newfoundland. Next, this commingling of the waters of several 

 regions tended to change and renew, from time to time, the soil of these 

 banks, which, like manuring and working our fields, was found to be 

 necessary for preserving these extensive pastures for the fish. Lastly, by 

 bringing down from Polar regions the enormous masses of ice which, 

 under the name of icebergs, were at times found to be setting down 

 towards tropical regions, they tend at the same time to ameliorate the 

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