214 



PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



to 18^ before freezing; but as soon as freezing commenced 

 the thermometer would mount up to 28^. The same water 

 was used for the following series of observations upon the ther- 

 mal changes of the specific gravity of sea water, fresh water being 

 the unit : 



Temperature 27^.1 Spec. grav. 1.0290 



28^.3 

 28^.8 

 29^.0 

 290.5 

 30^.0 

 32^.0 

 34^.0 

 34^.4 

 350.2 



89 

 91 



885 



906 



885 



88 



88 



89 



89 



443. All these experiments unite in showing that sea water at 

 nlTr'morJexpa^' equatorial temperatui-es is many times more ex- 

 sibio than sea water pausible than soa water at polar temperatm-es ; that 



at wmter tempera- 

 ture. 



IS, sea water, according to its rate of dilatation 

 (§ 441), will expand about seventeen times as much for 5°, 

 is raised from 85^, 



when 

 its temperatm-e is raised from 85"^, as it vail when raised from 

 28^ ; and yet, according to Plate X., the cuitos of temperature 

 and specific gravity are symmetrical in polar, non-spumetrical in 

 equatorial seas. These experiments, and the compressibility of 

 sea water (§ 404), show that we have not yet data sufficient to 

 establish the depth, or even the existence of such an isothermal 

 floor all the way from pole to pole. 



444. "The physical consequences of this great law, should. 

 Data for Plate x. it be found Completely verified by farther research, 



are in the last degree important." The observations which fur- 

 nished the data for Fi^. 1 were made in the North Pacific between 

 the months of August, 1855, and April, 1856, and in the South 

 Pacific during April and May; whereas for Fiff. 2 the southern 

 observations v/ere made in May and June, the northern in Jmie and 

 Jdy. 



445. It is well to bear this difference as to season north and 

 Athermaitide; it ebbs south in mind, and to comparo these curves with 

 and flows once ; year, thoso of the thermal, cliarts ; for the two together 

 indicate the existence in the ocean of the thermal tide, which, as 

 before stated, ebbs and flows but once a year. By this figure the 

 South xltlantic appears to be cooler and heavier than the northern. 



* Specific gravity at 2000=: 0-9908. 



