THE SOUTHERN OCEAN 25 



was 33 ; thence it rose steadily to 35, at 164 

 fathoms ; below that depth it fell slowly to 

 31.4 at 1504 fathoms, while the bottom tem- 

 perature at 2515 fathoms was 31*2. The 

 layer of warmer water between 70 and 900 

 fathoms remains beneath the colder water 

 owing to the fact that it contains more salt ; the 

 increase in its weight, due to the salt, balances 

 the lightness due to its warmth, and thus it 

 floats sandwiched between the cold water layers. 

 The Valdivia, generally speaking, found water 

 colder than the freezing point of fresh water, 

 extending from the surface to below 60 fathoms ; 

 then there was a layer of warmer water, 7000 

 feet thick,- ranging in temperature from 32 to 

 35 ; and lastly, the bottom zone, 7500 feet 

 thick, with water below 32, but not quite so 

 cold as the surface layer.* 



CHAPTER III. -CURRENTS AND DRIFTS OF 

 THE SOUTHERN OCEAN. 



The currents of the Southern Ocean appear 

 to be simple, so far as our crude knowledge of 

 them goes. Ocean currents are mainly de- 

 pendent on the winds ; and the winds that blow 

 across the Southern Ocean are arranged with 



*The Valdivia and the Challenger both found the coldest water at 

 the depth of about 50 fathoms ; the striking difference between their 

 results was that the Valdivia found a layer of warm water, and the 

 Challenge* a layer of cold water below that depth. 



D 



