Deductions from the Curve. 37 



perature, and the direction in which we must seek for a solution 

 of the problem of oceanic circulation. 



In looking over the temperature curves and sections which 

 accompany these pages, we find that, as a general rule, the 

 temperature of the ocean decreases from the surface to tlie bottom. 

 One of the first surprises in store for the early observers of 

 deep-sea temperature was the discovery that the temperature 

 of the deeper strata, and at the bottom of the ocean, is only a 

 few degrees removed from freezing-point. Subsequent observa- 

 tions have shown that, with certain exceptions, this is the case in 

 every part of the ocean, in tropical latitudes as well as in the 

 temperate and frigid zones, and that over some areas the tem- 

 perature of the lowest strata falls even below zero. The first 

 well-ascertained example of the presence of cold water in low 

 latitudes is due to the soundings of H.M.SS. "Lightning" and 

 " Porcupine" in 1868-69, m tne channel between the Faeroe 

 Islands and Scotland. Over an area situated between lat. 6o° 

 and 6i° N., long. 4 and 9 W., the temperature of o° C. is 

 reached at a depth of only 300 fathoms, descending to -i°4 C. 

 at a depth of 640 fathoms. This mass of cold water — about 

 120 miles long, 60 miles broad, and a quarter-mile in depth — 

 must have come from the Arctic region, and the soundings of 

 the Norwegian ship " Voringen," in the course of last year, show 

 that it is a southern extension of the mass of cold water which 

 fills up the basin between Iceland and Norway to a depth of 

 1 800 fathoms. A still more remarkable instance of the existence 

 of a cold area with a temperature below zero was discovered off 

 the mouth of the Rio de la Plata by H.M.S. "Challenger" on 

 her return voyage in 1876. Between lat. 36 and 42 S., long. 

 33 and 55 W., the bottom-temperature at seven different 

 stations was found below o° C, varying from — o°.3 to — o°.6 

 C. The maximum depth found in this area was 2900 fathoms, 

 and the zero-point was reached in 1900 fathoms (Station 323). 



