614 



Dr. AY. B. Carpenter on the 



[June 13, 



warmer Stream carries it northwards as a loop, which, however, stops 

 in February at Cape Fear (N. Lat. 34°), and in March at Cape Hat- 

 teras (N. Lat. 35J°) ; and thus we see that instead of carrying far into 

 the North Atlantic the temperature of the Equatorial current, the Gulf- 

 stream has lost thus early more than ten degrees of the heat which its 

 water possessed when it crossed the Equator, and is only Jive degrees 

 warmer than the sea through which it flows. 



125. Very little change takes place during March and April in the 

 general position of the Isotherm of 80°; but the temperature of the Carib- 

 bean Sea and of the Gulf of Mexico rises considerably, so that the Gulf- 

 stream in May issues from the Florida Channel at the temperature of 

 nearly 80°. The Isotherm of 70° moves northwards with the approach 

 of the Sun to the Tropic of Cancer ; but the looped bend in its 

 western portion occasioned by the Gulf-stream still stops at about 37° 

 N. Lat. From June to September, however, the northward range of 

 the Isotherm of 80° extends on its western side over the Caribbean Sea 

 and Gulf of Mexico ; whilst it also includes a considerable part of the 

 Sargasso Sea, ranging to the north of the Bermuda group and approach- 

 ing the American coast off Cape Hatteras. The Gulf-stream during 

 these months issues from the Florida Channel at an average surface- 

 temperature of about 83°, which is higher than that of the Equatorial 

 current at its entrance into the Caribbean Sea ; and for this there is 

 no difficulty in accounting, when we bear in mind the fact that the Sun 

 shines vertically on the Tropic of Cancer at the Summer solstice. There 

 is nothing special, however, in the surface-temperature of the Caribbean 

 Sea and Gulf of Mexico at this season ; for that of the outside Atlantic 

 between the same parallels, though in no way influenced either by the Equa- 

 torial current or by the Gulf-stream, is just as high. In the eastern 

 portion of the Atlantic, however, the Isotherm of 80° is greatly de- 

 flected towards the Equator, not merely by the colder North- African 

 current, but also, it would appear, by the southward flow of that portion 

 of the Gulf-stream which passes round the Azores to return into the 

 Equatorial current (§ 147). — Thus the surplus heat which the Gulf- 

 stream carries northwards during the summer months is not that of the 

 Equatorial region, but that of the northern Tropical region ; and we 

 shall presently see (§ 142) that the slow dissipation of its surplus Heat 

 in this part of its course is due to its near equality in Temperature with 

 the Sea and Air through which it passes for a considerable distance. 



126. From October to January, on the other hand, there is a progres- 

 sive return towards the conditions indicated by the course of the Isothermal 

 lines for February and March ; with this difference, however, that while 

 the January Isotherm of 70° for the most part lies south of 30° N. Lat., 

 and does not range further north than Cape Hatteras, the Isotherm of 80° 

 extends, in the course of the Equatorial current, into the southern part of 

 the Caribbean Sea. Thus as the temperature of the Gulf-stream at its 



