322 On an Isothermal Oceanic Chart, illustrating 
and 74° F., where they cross the meridian of 15° west, as the mean 
position for this ocean, we find that the former is eight degrees in 
latitude farther north than 68° F. in the South Pacific ; and the 
mean for the latter isin 7° south, while for the same in the Pa- 
cific it is 20° south, making a difference of thirteen degrees. The 
effect of the cold southern waters is consequently not along the 
African coast alone, but pervades the whole ocean. It is hence 
obvious, how utterly untenable the common notion, that the tropi- 
cal current from the Indian Ocean is the same which flows up the 
west African coast. With a temperature of 56° south of Ca 
Town, it would be wholly incapable of causing the great deflec- 
tions for the whole South Atlantic which have been pointed out. 
It combines with the cold current, but does not constitute it. 
The facts thus sustain the opinions long since brought forward by 
the distinguished meteorologist Mr. : edfield, that the 
currents flowing north along the African and South American 
coasts are alike antarctic or cold temperate currents. 
e may now turn to the North Atlantic. In this part of the 
ocean, the mean positions of the isocrymes of 74° and 68° F., 
are near the normal positions deduced from the Pacific. The 
line of 62° F., is in a somewhat higher latitude, the mean position, 
excluding the eastern and western deflections, being near the 
parallel of 36°. The line of 56° F. has the parallel of 424° north 
for its mean position over the middle of the ocean, which is five 
and a half degrees above the normal in the Pacific. The line 
of 50° has in the same manner for its mean position over mid- 
ocean, the parallel of 474°, or again five and a half degrees above 
the normal position in the Pacific. The line of 44° F. may be 
considered as having for its mean position the parallel of 52° 
north, while it rises to 60° north. The lines in the North Atlan- 
tic above that of 68°, average about five degrees higher in latitude 
than the mean normal positions, while 68° and 74° have nearly 
the same places asin the Pacific. There is hence a great contrast 
between the Pacific, South Atlantic, and North Atlantic Oceans. 
is is seen in the following table containing these results : 
Normal, deduced Mean position in Mean position in 
from Pacific. South Atlantic. North Atlantic. 
Isocryme of 74° F., 202 4° south, 
_ 68° ba 19° 
4 62° 32° 29° 26° 
56° 37° 86° 424° 
: 50° 42° 89° 474° 
“ 44° 47° 44° 52° (max. 60° north.) 
85° 56° 59° 61° 
The influence of the warm tropical waters in the North Atlan- 
tic lifts the isocrymes of 74° and 68° as they approach the coast 
of America, while the same lines are depressed on the east by the 
colder northern currents. Moreover, north of 68° the whole 1- 
* American Journal of Science, xly, 299, 1843. 
