rROPERTIES AND CONSTITUTION OF SEA-WATER. siS 



mixing with either the colder or the ■wanner parts, and also hecause 

 water conducts heat very badly. 



The phenomena are different in the case of sea- water, and also com- 

 plicated in other ways. The point of maximum density descends as 

 the weiffht of the salt-water and its richness in dissolved matter in- 

 crease. The Swedish chemist and hydrographer, Ekman, after long 

 series of experiments relative to this question, has found that this crit- 

 ical temperature may fall to —4° C. (25° Fahr.) in Atlantic water. The 

 properties of a brackish fluid, such as would be drawn from a fiord, 

 would naturally be intermediate between those of a pure and those of 

 a very salt water. Hence the depths of the ocean can not be at 39° 

 Fahr,, as some authors still maintain. A slight excess of salt in solution 

 will weight a stratum of water of mean temperature, whereby a cold 

 zone may be superposed upon another zone which is warmer but more 

 saline. The interior of the ocean, as well as its surface, is plowed 

 by numerous currents, some warm, some cold, which meet, mix, and 

 separate again, so that it is very hard to find out by reasoning what 

 experiment alone can teach. A similar variety is shown in the den- 

 sity of water brought up by soundings. The complication is magni- 

 fied when we reflect that water is not absolutely incompressible, that 

 each thickness of ten metres exercises a vertical pressure nearly equal 

 to an atmosphere, the action of which added to that of the superior 

 parts weighs upon the inferior liquid, so that at about 4,000 metres the 

 pressure is 400 atmospheres. Water must be extremely dense when 

 it it compressed with so much force, and the influence of salinity and 

 temperature must become very small in these unfathomable abysses. 

 The question of submarine temperatures has given rise to many con- 

 troversies. Some, with Perron, suppose that the great depths are 

 always cold, like the tops of the highest mountains. On the other 

 extreme, the author of " Epochs of Nature " attributed to the oceanic 

 depths a high temperature on account of their nearness to the central 

 fire. Denis de Montfort and Humboldt are of the opinion that below 

 the superficial parts there prevails a constant temperature, peculiar to 

 each station, and corresponding with the mean annual temperature of 

 the place. This view is correct for regions where the depth is not 

 very great, and in certain bodies of water. 



The sea, on account of its great specific heat and its feeble conduct- 

 ing power, plays the part of a moderator of temperature something 

 like that of the fly-wheel of an engine as a moderator of force. In 

 winter it is warmer, in summer it is cooler, than the ambient air, and 

 the difference is emphasized the farther we get away from the shore. 



In "The Clouds" of Aristophanes, Strepsiades refuses to pay his 

 creditors who hold that the level of the sea is fixed, believing that, as 

 it receives all the water, it must continue to rise indefinitely. The 

 phenomena of evaporation were not very well understood at that time. 

 Even in the seventeenth century. Father Fournier talked of subterra- 



