78 4 



ZONES AND REGIONS 



[Pt. Ill, Sect. V 



The following analyses give an idea of the salinity of the ocean. In I, the sample 

 of water was obtained in the harbour of Callao ; II, in the Atlantic at 41 18' N. and 

 36 28' W. 



Percentage of salts 



Sodium chloride 

 Magnesium chloride 

 Potassium chloride 

 Sodium bromide . 

 Calcium sulphate . 

 Magnesium sulphate 



One liter of water from Lake Geneva, according to Forel, contains : — 



Milligram. 

 Sodium and potassium chlorides . . . i-8 



Sodium sulphate . 

 Ammonium sulphate 



Calcium sulphate 



Calcium nitrate . 



Calcium carbonate 



Silica 



Alumina and ferric oxide 



Organic matter and loss 



150 

 traces 



47-9 

 i-o 



73-9 

 37 

 1-9 



u-9 



1 74. 1 



Temperature. Even the temperature at the surface of expanses of water 

 exhibits much less variation than the superincumbent air. and the differ- 

 ence becomes much greater if the inland air be brought into comparison, 

 for expanses of water exercise an equalizing influence on the temperature 

 of the adjacent portion of the atmosphere. The highest temperature on the 

 surface of the sea hitherto observed is 31° C. near Celebes: the lowest 

 corresponds to the freezing-point of sea-water, —3-6° C. 



The fall in temperature as the depth increases is naturally less in polar than in 

 temperate and tropical waters. On the coast of Greenland in August, 1877, on the 

 surface of the sea a temperature of 3 C. was measured, at a depth of 37 meters o° C, 

 at a depth of 3,000 meters on the bottom of the sea - 1-5° C. In the equatorial part of the 

 Pacific, the ' Gazelle ' observed 29 at the surface, and i-6° C. at a depth of 3,oco meters. 



The depth-isotherms for differences of i° C. at first succeed one another, from 

 the surface downwards, very rapidly, then gradually more slowly. Thus, the tem- 

 perature in the equatorial Pacific at a depth of from o to 200 fathoms diminishes by 

 l° C. every 10 fathoms. Then the intervals become rapidly greater. The isotherm of 

 3 C. extends from 1,000 to 1,400 fathoms in depth, then down to the bottom (3,4co 

 fathoms) a fairly uniform temperature of 2 C. prevails '. The last-mentioned great 

 depths are merely of very subordinate import to plant-life. 



In the Mediterranean daily variations of temperature cease at a depth of 18 

 meters, annual variations at 400 meters ; in the China Sea, the effects of the seasons 



1 All these figures are taken from Walther, Allgemeine Meereskunde. 



