1460 



CRUSTACEA. 



perature increases two to four degrees. In July, Fitzroy carried a 

 temperature above 68° as far south as 33° 16' south, longitude 50° 10' 

 west, the water giving at this time 68 |° to 691° F. Beechey in August 

 obtained 68° F. in 31° south, 46° west. The isocryme of 68° F. thus 

 bends far south, reaching at least the parallel of 30°. It takes a 

 course nearly parallel with the line of 74° F., as different observations 

 show, and passing just south of St. Helena, reaches the African coast, 

 near latitude 7° south. Fitzroy, on July 10 (mid-winter), had a sea- 

 temperature of 68 2° near St. Helena; and Vaillant, in the Bonite, in 

 September found the sea-temperature 68" 7° to 69*26° F. 



Isocrymes of 56° and 50° F. — These two isocrymes leave the American 

 coast rather nearly together. The former commences just north of 

 the entrance of the La Plata. Fitzroy, in July 23 to 31, 1832. found 

 the sea-temperature at Montevideo 56° to 58° F., and in August, 57° 

 to 54 1° F. These observations would lead to 56° F. as nearly the 

 mean of the coldest month. The temperature 56° F. was also ob- 

 served in 35° south, 53° west, and at 36° south, 56° 36' west. But 

 on July 10 and 13, 1833, at Montevideo, the sea-temperature was 

 46i° to 47a°, a degree of cold which, although only occasional, throws 

 the line of 56° F. to the north of this place. The temperature near the 

 land is several degrees of Fahrenheit, lower than at sea three to eight 

 degrees distant. East of the mouth of the La Plata, near longitude 50° 

 west, Beechey, in July, 1828, found the temperature of the sea 61*86° 

 F. So in April 23 to 29, Vaillant obtained the temperature 59*5° to 

 61*25° F. at Montevideo, while in 35° 5' south, 49° 23' west, on April 

 14, it was 66-2° F., and farther south, in 37° 42' south, 53° 28' west, 

 April 30, it was 64*4° F. ; and in 39° 19' south, 54° 32' west, on May 

 1, it was 571° F.; but a little to the westward, on May 2, in 40° 30' 

 south, 56° 54' west, the temperature was 48° F., an abrupt transition 

 to the colder shore waters. Beechey, in 39° 3V south, 45° 13' west, 

 on August 28 (last of winter), found the temperature 57*25° F., and 

 on the 29th, in 40° 27' south, 45° 46' west, it was 54*20°; while on 

 the next day, in 42° 27' south, and 45° 11' west, the temperature fell 

 to 47*83° F. These and other observations serve to fix the position 

 of the isocryme of 56° F. It approaches the African coast, in 32° 

 south, but bends upward, owing to cold waters near the land. On 

 August 20, Vaillant, in 33° 43' south, 15° 51' east, found the tempe- 

 rature 56° F.; while on the 22d, in the same latitude, and 14° 51' 

 east (or one degree farther to the westward), the temperature was 

 57-74° F., being nearly two degrees warmer. At Cape Town, in June 



