42 Temperature of the Ocean. 



represents the intermediate stratum will form a steep incline. 

 On the contrary, when two masses of water flow in the same 

 or nearly the same direction, the intermediate stratum will 

 appear in the curve as a gradual incline representing the slow 

 increase or decrease of temperature from one stratum to the 

 other. Hence the gradient of any part of the curve is not only 

 the measure of the rate of increase or decrease of temperature, 

 but also an indication of the relative motion or relative rest of 

 the strata in contact. A low gradient expresses the presence 

 of strata of equal or nearly equal temperature moving in the 

 same direction, i.e.^ at relative rest towards each other ; a steep 

 gradient indicates the existence of strata of different tempera- 

 tures, and moving in different directions. 



Thus, in Fig. 1, we have a warm surface-stratum of con- 

 siderable thickness, the decrease of temperature in the first 

 200 fathoms amounting to only 2°.4 C. The steep gradient 

 between 200 and 500 fathoms shows that this surface-stratum 

 moves in a direction different from that of the bottom-stratum, 

 which, at this station, is found to rise up to within 600 fathoms 

 from the surface. The temperature at the bottom, at a depth 

 of 2550 fathoms, is o°.7 C. ; at 1500 fathoms, 2° C. ; at 600 

 fathoms, 2°.9 C, or a difference of only o°.9 C. in 900 fathoms. 



In Fig. 2, Curve A, belonging to Station 41, near the eastern 

 limit of the Gulf Stream, the hump extending down to 300 

 fathoms represents a stratum of nearly uniform temperature. 

 The latter is, at the surface, i8°.3 C. ; at 125 fathoms, i8°.o C. ; 

 at 300 fathoms, i7°.o C. In Curve B, at Station 43, in the 

 Gulf Stream itself, all this warm water below 100 fathoms 

 has disappeared; but a surface -stratum has been added, 

 of a temperature rising to 24° C. Still further on, at Station 

 44 (Curve C), a short distance beyond the western limits of 

 the Gulf Stream, we find ourselves in the midst of an Arctic 

 current rising up to within 300 fathoms from the surface, with a 



