162 On an Isothermal Oceanic Chart, iliustrating 
the La Plata, is to some extent, a limit between the warmer 
waters of the north, and the colder waters from the south; not 
an impassible limit, but one which is marked often by a more 
abrupt transition than occurs elsewhere along this part of the 
coast. The water was generally three or four degrees colder at 
Montevideo, than at Maldonado, the latter port being hardly shel- 
tered from the influence of the tropical waters, while Montevideo 
is wholly so. The exact point where the line of 44° F. reaches 
the coast is somewhat uncertain; yet the fact of its being south 
of Rio Negro is obvious. After leaving the coast, it passes north 
of 474° south, in longitude 53° west, where Beechey, in July, 
1828, found the sea-temperature 40°70° F. 
The line of 35° F. through the middle of the South Atlantic, 
follows nearly the parallel of 50°; but towards South America it 
bends southward and passes south of the Falklands and Fnegia. 
At the Falklands, Captain Ross, in 1842, found the mean tem- 
perature of the sea for July, 38:73°, and for August, 38°10°; 
while in the middle of the Atlantic, on March 24, latitude 52° 
31/ south, and longitude 8° 8 east, the temperature was down to 
34-3° F., and in 50° 18’ south, 7° 15/ east, it was 37° F.; March — 
20, in 54° 7’ south on the meridian of Greenwich, it was 33°4° 
F. The month of March would not give the coldest temperature. 
The temperature of the sea along the south coast of Fuegia 
sinks almost to 35°, if not quite, and the line of 35° therfore runs 
very near Cape Horn, if not actually touching upon Fuegia. 
Nortu Paciric Ocran.—Jsocryme of 80° F.—The waters of 
the Atlantic in the warmest regions, sink below 80° F. in the 
colder season, and there is therefore no proper Supertorrid Region 
in that ocean. In the Gulf of Mexico, where the heat rises at 
times to 85° F.., it sinks in other seasons to 74° and in some parts, 
even to 72° F.; and along the Thermal equator across the ocean, 
the temperature is in some portions of the year 78°, and in many 
places 74°. 
But in the Pacific, where the temperature of the waters rises iN 
some places to 88° F’., there is a small region in which through 
all seasons, the heat is never below 80°. It is a narrow area, eX- 
tending from 165° east to 148° west, and from 74° north to 11° 
south. In going from the Feejees in August, and crossing be- 
tween the meridians of 170° west and 18U°, the temperature of 
the waters, according to Captain Wilkes, increased from 79° to 
84° F., the last temperature being met with in latitude 5° south, 
longitude 175° west and from this, going northward, there was 4 
slow decrease of temperature. The Ship Relief, of the Expedi- 
tion, in October, found nearly the same temperature (833°) in the 
same latitude and longitude 177° west.* But the Peacock, im 
* See, for these facts, Captain Wilkes’s Report on the Meteorology of the Ex- 
