202 J. D. Dana on an Isothermal Oceanic Chart, 



in 3' south, January 10, it was 83° F. ; on March 26, in 

 5' south, and longitude 175° east, the temperature was 86° 

 F. ; on April 10, in the same longitude, under the equator, 

 at the Kingsmills, the temperature was 83J° F. ; on May 2, 

 at 5° north, longitude 174° east, 83J° F. ; May 5, latitude 

 10°, longitude 169° east, 82° f. The fact that the region of 

 greatest heat in the middle Pacific is south of the equator, 

 as it has been laid down by different authors, is thus evident ; 

 the limits of a circumscribed region of hot waters in this 

 part of the Pacific were first drawn out by Captain Wilkes. 



Another Supertorrid region may exist in the Indian Ocean, 

 about its north-western portion ; but we have not sufficient 

 information for laying down its limits. 



Isocryme of 74° F. — At San Bias, on the coast of Mexico, 

 Beechey found the mean temperature of the sea for December 

 1827, 74-63° F. ; for January, 73-69° F. ; for February, 7240° 

 F. The line of 74° F. commences therefore a degree or two 

 south of San Bias. In the winter of 1827 on January 16 to 

 18, the temperature of 74-3° to 74-6° F. was found by 

 Beechey, in 16° 4' to 16° 15' north, 132° 40' to 135° west; 

 and farther west, in the same latitude, longitude 141° 58' 

 west, the temperature was 74-83° F. West of the Sandwich 

 Islands, near the parallel of 20° north, the temperature rises 

 five degrees in passing from the meridian of 165° west to 

 150° east, and the isocryme of 74° F. consequently trends 

 somewhat to the north, over this part of the ocean. Between 

 the meridians of 130° and 140° east, the temperature of the 

 sea is quite uniform, indicating no northward flexure ; and 

 west of 130° east, nearing China, there is a rapid decrease 

 of temperature, bending the line far south. Vaillant, of the 

 Bonite, found the sea of Cochin China, in latitude 12° 16' 

 north, 109° 28' east, to have the temperature of 74-12° F. ; 

 and even at Singapore, almost under the equator, the tem- 

 perature on February 17 to 21, was 77'54° to 79-34° F. The 

 isocryme of 74° F. terminates therefore upon the south- 

 eastern coast of Cochin China. 



Isocryme o/68° F.— Off the Gulf of California, in 25° north, 

 117° west, Beechey obtained, for the temperature of the sea, 

 on December 13, 65° F. ; on December 15, in 23° 28' north 



