THE 



EDINBURGH NEW 



PHILOSOPHICAL JOURNAL 



On an Isothermal Oceanic Chart, illustrating the Geogra- 

 phical Distribution of Marine Animals. With an illus- 

 trative Map. By James D. Dana, Esq. 



The temperature of the waters is well known to be one of 

 the most influential causes limiting the distribution of ma- 

 rine species of life. Before, therefore, we can make any intel- 

 ligent comparison of the species of different regions, it is 

 necessary to have some clear idea of the distribution of tem- 

 perature in the surface waters of the several oceans ; and, 

 if we could add also the results of observations at various 

 depths beneath the surface, it would enable us still more 

 perfectly to comprehend this subject. The surface tempe- 

 rature has of late years been quite extensively ascertained, 

 and the lines of equal temperature may be drawn with con- 

 siderable accuracy. But in the latter branch of thermome- 

 tric investigation almost everything yet remains to be done : 

 there are scattering observations, but none of a systematic 

 character, followed through each season of the year. 



The map (Plate I.) which we present in illustration of this 

 subject, presents a series of lines of equal surface temperature 

 of the oceans. The lines are isocheimal lines, or, more pro- 

 perly, isocrymal lines ; and where they pass, each exhibits the 

 mean temperature of the waters along its course for the 

 coldest thirty consecutive days of the year. The line for 68° 

 F., for example, passes through the ocean where 68° F. is 

 the mean temperature for extreme cold weather. January 

 is not always the coldest winter month in this climate, nei- 



VOL. LVI. NO. CXII. — APRIL 1854. 



