REPORT ON OCEANIC CIRCULATION. 
23 
are iu the lines of the drift of the surface currents. The highest isothermal in any 
other ocean is 53°, or 10° lower than that of the North Atlantic, thus emphatically 
distinguishing this ocean as, in this respect, markedly different from all other oceans. 
The ten observed specific gravities in the Atlantic from lat. 13° to 40° N. give a 
mean of 1*0266, only one occurring as low as 1*0262 near Cape Verde Islands. In 
marked contrast with this, the mean of the fifteen specific gravities observed between 
lat. 10° and 40° S. is 1*0258, only one of which exceeded the minimum of the North 
Atlantic. Thus, we have still in the North Atlantic the specific gravities greatly more 
favourable to the descent of the warm water of the higher strata, and the observa- 
tions of temperature amply show that this descent takes place. 
A very different state of things now holds good in the Pacific Ocean, which in its 
western division has temperatures above the mean uninterruptedly through eighty 
degrees of latitude, and in its eastern division through forty degrees. As in the case 
of the Atlantic, the higher temperatures are in the western part of the ocean or in the 
lines of the warm surface currents. A lower temperature still prevails in mid-ocean 
immediately south of the equator, and from the western projection of this low 
temperature area to the south there is a somewhat rapid increase of temperature 
amounting at this depth to 5°. The two regions of highest temperature are 51° about 
ten degrees of latitude south of Japan, and 50° the same distance north of New Zealand. 
The specific gravities, while still a little higher in the South than in the North 
Pacific, now approximate to each other over the whole extent of the ocean from lat. 
30° N. to 40° S., the mean being 1*0256, very much below the specific gravity of the 
North Atlantic. 
Depth of 400 Fathoms (Map 6). — The mean temperature of the ocean at 400 
fathoms is 41°*8, or 2°*9 less than at 300 fathoms. The excess of temperature in the 
North Atlantic is even more pronounced than at the previous depth. In the South 
Atlantic the highest temperature is 42°*5, or only 0°*7 above the mean temperature of 
the whole ocean, but in the North Atlantic nearly the whole extent of it has a higher 
temperature than this, and the maximum temperature rises to 55°, or 12°*5 higher than 
in the South Atlantic. It is also to be noted that the higher temperatures still occupy 
the western division of the ocean. 
The specific gravities of the two oceans are very different. In the North Atlantic 
the mean is 1*0264, but in the South Atlantic it is 1*0258, and in the Gulf of Guinea 
1*0254. The densities thus favour the descent of the warmer water of the upper layers 
to greater depths in the North than in the South Atlantic. 
In the North Pacific the highest isothermal is 43°, but in the South Pacific this 
isothermal covers a much wider extent, and temperature rises within the warm area to 
47°, or 4° higher than in the North. In this part of the ocean the mean specific gravity 
is 1*0259, but elsew*here in the North and South Pacific it is only 1*0255. 
