76 THE ATLANTIC. [chap. ii. 



temperature ; it is doubtless joined, and considerably aug- 

 mented, by a cooler current passing down the coast of Africa, 

 past the Canary and Cape Verde Islands, a portion of the 

 southern branch of the Gulf-stream ; and tliis tributary stream, 

 whose direction so nearly coincides with tliat of the Guinea 

 Current, formerly tended to prevent the full recognition of the 

 principal source of the latter in the equatorial counter-current. 



After leaving San lago, on the 9th of August, we began al- 

 most at once to feel the influence of the Guinea Current, or 

 rather, perhaps, of its northern tributary ; and from that date 

 to the ITtli our course lay in a south-easterly direction, parallel 

 with the coast of Africa, and nearly in the path of the current. 

 The temperature of the sea-surface during this time was nearly 

 constant at 26° C, and the temperature of the air slightly lower. 

 Serial soundings were taken at several stations, and these gave 

 a singularly rapid fall in temperature of from l-i° to 15° C. for 

 the flrst 100 fathoms ; showing that the warm current, as in all 

 other cases which we have observed, is very superficial. Where 

 the rate of the current is highest, we have as usual the iso- 

 therms crowding upward ; the cooler water rising to supjily the 

 place of the hot surface-water, which is being rapidly drifted 

 and evaporated away. 



"We sounded on the 10th in 2300 fathoms, with a bottom of 

 globigerina ooze, and took a series of temperatures at intervals 

 of 100 fathoms, down to 1500. The surface-temperature was 

 high, and from the surface the temperature fell with unusual 

 rapidity, losing nearly 15° C. in the flrst hundred fathoms. 



Surface 2G°-1 C. 



5 fathoms 25 '-t 



10 " 24-4 



15 fathoms 20°-5C. 



20 " 18-4 



100 " 11-3 



There was a marked tendency at this station to the gathering 

 together upward of all the higher lines (Plate XIX.), the iso- 

 therm of 6° C. occurring at a depth of 400 fathoms, nearly 400 

 fathoms higher than the position of the same line at Madeira. 



