166 On an Isothermal Oceanic Chart, etc. 
30th of March, 1827, just south of the equator, in 100° west. 
But in October, Fitzroy, going westward and southward from the 
Gallapagos, found a sea-temperature of 66° EF. at the same place; 
and ina nearly straight course from this point to 10° south, 120° 
west, found the sea-temperatures successively, 68°, 70°, 703° 
724°, 734°, 74°; and beyond this, 754°, 763°, 774° F., the last on 
November 8, in 14° 24’ south, 136° 51’ west. These observations 
give a wide sweep to the cold waters of the colder seasons, and 
throw the isocrymes of 74° and 68° F., far west of the Gallapagos. 
Captain Wilkes, in passing directly west from Callao, found a tem- 
perature of 68° F’., in longitude 85° west F’., in 95° west; 
and 74° F’., in 102° to 108° west. These and other observations 
lead to the positions of the isocrymes of 74°, 68°, and 62°, given 
on the Chart. The line of 74° passes close by Tahiti and Tong- 
atabu, and crossing New Caledonia, reaches Australia in latitude 
25° 8 
In mid-ocean there is a bend in all the southern isocrymes.* — 
Isocrymes of 56° and 50° F.—The temperature at Callao, in 
July, averages 584° or 59° F. At Tquique, near.20° south, Fitz- 
roy had 58° to 6U° F., on Jnly 14, 1835 ; and off Copiapo, in the 
same month, 564° F. At Valparaiso, Captain Wilkes found a 
sea-temperature of 524° F., in May; and Fitzroy, in September, 
occasionally obtained 48° F'., but generally 52° to 53°. off 
Chiloe, Fitzroy found the temperature 48° to 514° in July. 
Inpran Ocean.—Isocrymes of 74° and 68° F,—Off the south 
extremity of Madagascar, in 27° 33’ south, 47° 17’ east, on 
August 4th, Vaillant found the temperature 69:26° F.; and 
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 tem 
perature 63-5° F’.; on August 14, in 35° 41’ sonth, 22° 34’ east, 
a temperature of 63-3° F.; while off Cape Town, two hundre 
miles to the west, the temperature was 50° to 54° F 
In the above review, we have mentioned only a few of the ob- 
servations which have been used in laying down the lines, hav- 
ing selected those which bear directly on some positions of spec! 
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 4 
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 gi¥ 
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 increase, 
* See Observations by W. C. Cunningham, Am, J. Seu, [2] xv, 66. 
