8o Temperature Sections Surveyed. 



account of the relative thinness of the aqueous envelope when 

 compared to the diameter of the areas which it occupies. It 

 arises partly also from the nature of a section composed of 

 isotherms. A difference of o°. i C. in temperature, which in the 

 higher strata corresponds to only a few fathoms, and causes 

 no perceptible alteration in the form of the isothermal line, 

 is represented by 50 or 100 fathoms in the lower strata, 

 and causes the isothermal line to assume the shape of a big 

 wave. This defect, which requires only to be known to be 

 guarded against, is obviated by the employment of iso- 

 bathymetrical lines. As the latter represent the fluctuations of 

 temperature at the same depth along the section of an oceanic 

 basin, their undulations will keep pace with the fluctuations of 

 temperature, greater near the surface, smaller as we enter the 

 lower strata. But as in such a diagram the scale of depth must 

 be replaced by a scale of temperature, it ceases to be a 

 representation of an actual section (all but the horizontal dis- 

 tances) of an oceanic basin, and therefore the employment of a 

 diagram of isotherms is, for general purposes, to be preferred. 

 Of course, where space will allow it, both kinds of thermometric 

 sections may be used, as has been done in the published dia- 

 grams of the U.S. Coast Survey. 



Section from Cape Palmas to Cape S. Roque (Plate 10, 

 Table V.). — The principal feature of this equatorial section has 

 already been discussed above. A comparison of the isotherms 

 between Station 106 and Station 102, and of the isotherms 

 between Stations 339 and 342 of the Atlantic section (Plate 9), 

 with the isotherms between Stations 129 and 119 of the 

 southern section (Plate 10), shows that the north-eastern 

 portion of the South Atlantic is warmer than its north-western 

 portion. 



A line drawn from Station 106 to Station 339 and continued 

 down to the latitude of Tristan d'Acunha, which is a line pro- 



