Huntsman. — Climates of Our Atlantic Waters 327 



tude, the heat coming from the sun. Currents, both horizontal 

 and vertical, are also a potent factor in such differences, often 

 transporting the conditions of one region to another distant 

 one. As the sun's rays penetrate such a comparatively short 

 distance into water, currents that are more or less vertical are 

 concerned in all important differences in temperature at any 

 considerable depth. 



Naturally we cannot speak of moist and dry climates in 

 water, but there are differences that to some extent correspond 

 with the varying moisture content of the air, namely in the 

 amount of inorganic salts in the water or its salinity, much 

 salt tending to abstract water from the animals and, therefore, 

 resembling dryness. The ocean contains a very uniform mix- 

 ture of a series of salts, but the amount of this mixture pres- 

 ent in a given quantity of sea water varies considerably with 

 the place and depth. Such differences are dependent upon the 

 amount of fresh water entering by precipitation from the air, 

 by melting of ice and by inflow from the land, and upon the 

 amount leaving by evaporation. 



Light is a most important element in the ensemble of 

 climatic conditions, and we are familiar with the great differ- 

 ences in the amount and distribution of sunshine, our chief 

 source of light, depending upon latitude and the presence of 

 moisture and other particles in the air. These differences hold 

 for the water, and to them are added others which depend upon 

 the absorption of light waves by the water, the intensity and 

 character of the light changing with depth, and upon their stop- 

 page by particles of various kinds suspended in the water. The 

 light conditions are consequently more variable in water than 

 in air. 



The extent to which certain gases as, for example, the oxy- 

 gen and carbon dioxide of the air, are dissolved in the water, 

 determines the character of the climate in the ocean. So signifi- 

 cant are these gases that they have been invoked to explain the 

 movement of fishes. Much oxygen in the water has been given 

 by Roule as the factor that determines when and where the sal- 



