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



close by Tahiti and Tongatabu, and crossing New Caledonia, 

 reaches Australia, in latitude 25° S. 



In mid-ocean there is a bend in all the southern isocrymes.* 



Tsocrymes of 56° and 50° F. — The temperature at Callao, 

 in July, averages 58$° or 59° F. At Iquique, near 20° south, 

 Fitzroy had 58° to 60° F., on July 14, 1835 ; and off Copiapo, 

 in the same month, 56}° F. At Valparaiso, Captain Wilkes 

 found a sea- temperature of 52 £° F., in May ; and Fitzroy, in 

 September, occasionally obtained 48° F. ; but generally 52° 

 to 53°. Off Chiloe, Fitzroy found the temperature 48° to 

 5U° in July. 



Indian Ocean.— Isocrymes of 74° and 68° F. — Off the 

 south extremity of Madagascar, in 27° 33' south, 47° 17' east, 

 on August 4, Vaillant found the temperature 69*26° F. ; 

 and in 29° 34' south, 46° 46' east, the temperature of 67-84° 

 F. ; off South Africa, August 12, in 34° 42' south, 27° 25' 

 east, the temperature 63*5° F. ; on August 14, in 35° 41' 

 south, 22° 34' east, a temperature of 63*3° F. ; while off Cape 

 Town, two hundred miles to the west, the temperature was 

 50° to 54° F. 



In the above review we have mentioned only a few of the 

 observations which have been used in laying down the lines, 

 having selected those which bear directly on some positions 

 of special interest as regards geographical distribution. 



The chart also contains the heat-equator, — a line drawn 

 through the positions of greatest heat over the oceans. It 

 is a shifting line, varying with the seasons, and hence there 

 is some difficulty in fixing upon a course for it. We have 

 followed mainly the chart of Berghaus ; but we have found 

 it necessary to give it a much more northern latitude in the 

 western Pacific, and also a flexure in the western Atlantic, 

 both due to the currents from the south that flow up the 

 southern continents. 



Vaillant, passing from Guayaquil to the Sandwich Islands, 

 found the temperature, after passing the equator, slowly in- 

 crease from 76° F., August 19, in 2° 39' north, 91° 58' west 

 (of Greenwich), to 81'9° F., in August 31, 11° 15' north, 107° 

 3' west, after which it was not above 80° F. The same place 



* See Observations by W. 0. Cunningbam, Amer. Journ. Sci. (2) xv. 66. 



