Between Cape May and Madeira. 59 



The isotherms of 5° C. and 2°. 5 C retain an ahnost uniform 

 level, the former at 600 fathoms, the latter at 1 500 fathoms, as 

 far as Station 52, where they both commence to rise rapidly and 

 • come to the surface off Halifax, as seen in the above table. 

 The isotherm of 2°. 5 C. rises with the sea-bottom around 

 Bermudas. The bottom-temperature of i°.5 C. is found at 

 Station 51 at 2920 fathoms, at Station 52 at 2800 fathoms, and 

 at Station 27 at 2960 fathoms. 



Section between Cape May and Madeira (Plate 8, Table 

 III.). — This section crosses the North Atlantic from west to east 

 between the latitudes of 32° and ^Z" N. It presents at Station 

 45, distant 140 miles from Sandy Hook, a section of the 

 Labrador current, and at Station 43 a section of the Gulf 

 Stream current. The latter formed, at the time of the " Chal- 

 lenger's" visit, the ist of May, 1873, a surface-current about 60 

 miles broad and 100 fathoms deep, flowing in an east-north- 

 easterly direction at the rate of three miles an hour. Later in 

 the season the volume and velocity of this great oceanic river 

 are much greater. As seen in the diagram, the Gulf Stream 

 constitutes the extreme western border of the enormous mass of 

 water which composes the North Atlantic Equatorial Current, and 

 virtually flows over the Labrador Current found immediately 

 below it. The temperature of the current was 2 3°. 9 C. at the sur- 

 face, 20° C. at 80 fathoms, and 18°. 3 C. at 100 fathoms. But at 

 125 fathoms it had fallen already to i3°.8 C, and at 350 fathoms 

 to 7°. I C. At Station 44, just beyond the edge of the Gulf 

 Stream, the temperature at the surface was 11°. i C, at 125 

 fathoms 8°. 3 C, and at 350 fathoms 3°.9 C. The distance 

 between Station 43 and Station 44 is little over 60 miles. 



The table on page 71 shows the remarkable changes of 

 temperature observed by the " Challenger " in crossing the Gulf 

 Stream. 



