21 S J. D. Dana on an Isothermal Oceanic Chart. 



Soutli American coasts are alike antarctic or cold temperate 

 currents.* 



We may now turn to the North Atlantic. In this part of 

 the ocean the mean positions of the isocrymes of 74° and 

 08 F. are near the normal positions deduced from the Pa- 

 cific. The line of 62° F. is in a somewhat higher latitude, 

 the mean position, excluding the eastern and western deflec- 

 tions, being near the parallel of 36°. The line of 56° F. has 

 the parallel of 42^° north for its mean position over the middle 

 of the ocean, which is five and a half degrees above the nor- 

 mal in the Pacific. The line of 50° has in the same manner, 

 for its mean position over mid-ocean, the parallel of 47J°, 

 or again five and a half degrees above the normal position in 

 the Pacific. The line of 44° F. may be considered as having 

 for its mean position the parallel of 52° north, while it rises 

 to 60° north. The lines in the North Atlantic above that 

 of 68° average about five degrees higher in latitude than the 

 mean normal positions, while 68° and 74° have nearly the same 

 places as in the Pacific. There is hence a great contrast 

 between the Pacific, South Atlantic, and North Atlantic 

 Oceans. This is seen in the following table containing these 

 results : — 









Normal, deduced 

 from Pacific. 



Mean position in 

 South Atlantic. 



Mean position in 

 North Atlantic. 



y 11 



ie of 74° 



F., 



20° 



7°S. 





21° N. 



>> 



68 





27 



19 





28 



» 



62 





32 



29 





36 



» 



56 





37 



36 





42£ 



?> 



50 





42 



39 





m 



j> 



44 





47 



44 





52 (max. 60° N.) 



M 



35 





56 



50 





61 



The influence of the warm tropical waters in the North 

 Atlantic lifts the isocrymes of 74° and 68° as they approach 

 the coast of America, while the same lines are depressed on 

 the east by the colder northern currents. Moreover, north 

 of 68° the whole interior of the ocean is raised four to five 

 degrees in temperature above the normal grade, by the same 

 waters spreading eastward ; and between Great Britain and 



* American .Journal of Science, xlv., 299, 1843. 



