At these depths, then, we find the warmest water within the region investigated by the Fram.  If we now compare the distribution of temperature at 400 metres with the chart of currents in the South Atlantic, we see that the warm region lies in the centre of the great circulation of which mention was made above.  We see that there are high temperatures on the left-hand side of the currents, and low on the right-hand side.  This, again, is an effect of the earth’s rotation, for the high temperatures mean as a rule that the water is comparatively light, and the low that it is comparatively heavy.  Now, the effect of the earth’s rotation in the southern hemisphere is that the light (warm) water from above is forced somewhat down on the left-hand side of the current, and that the heavy (cold) water from below is raised somewhat.  In the northern hemisphere the contrary is the case.  This explains the cold water at a depth of 400 metres on the Equator; it also explains the fact that the water immediately off the coasts of Africa and South America is considerably colder than farther out in the ocean.  We now have data for studying the relation between the currents and the distribution of warmth in the volumes of water in a way which affords valuable information as to the movements themselves.  The material collected by the Fram will doubtless be of considerable importance in this way when it has been finally worked out.

Below 400 metres (218 fathoms) the temperature further decreases everywhere in the South Atlantic, at first rapidly to a depth between 500 and 1,000 metres (272.5 and 545 fathoms), afterwards very slowly.  It is possible, however, that at the greatest depths it rises a little again, but this will only be a question of hundredths, or, in any case, very few tenths of a degree.

It is known from previous investigations in the South Atlantic, that the waters at the greatest depths, several thousand metres below the surface, have a temperature of between 0deg. and 3deg.  C. Along the whole Atlantic, from the extreme north (near Iceland) to the extreme south, there runs a ridge about half-way between Europe and Africa on the one side, and the two American continents on the other.  A little to the north of the Equator there is a slight elevation across the ocean floor between South America and Africa.  Farther south (between lats. 25deg. and 35deg.  S.) another irregular ridge runs across between these continents.  We therefore have four deep regions in the South Atlantic, two on the west (the Brazilian Deep and the Argentine Deep) and two on the east (the West African Deep and the South African Deep).  Now it has been found that the “bottom water” in these great deeps —­ the bottom lies more than 5,000 metres (2,725 fathoms) below the surface —­ is not always the same.  In the two western deeps, off South America, the temperature is only a little above 0deg.  C. We find about the same temperatures in the South African Deep, and