THE SALTS OF THE SEA. 227 



and of thermal dilatation which have been described in a previous 

 chapter (IX.). It is the salts of the sea that assist the rays of 

 :beat-to penetrate its bosom;* but for these, the solar ray, instead 

 of heating large masses of water like the Gulf Stream, w^ould play 

 only at or near the surface, raising the temperature of the. waters 

 there, like the sand in desert places, to an inordinate degree. 

 The salts of the sea invest it w^th adaptations which it could not 

 possess were its waters fresh. Were they fresh, they would attain 

 their maximiun density at 39^.5 instead of 25°. 6, and the sea then 

 would not have dynamical force enough to put the Gulf Stream in 

 motion, nor could it regulate those climates we call marine. 



462. Were the sea fresh and not salt, Ireland would never have 

 Were the sea of presented thoso ever-green shores which have won 

 freshwater- foj, i^^j. ^^q j^^mo of the " Emerald Islc ;" and the 



climate of England would have vied with Labrador for inhospi- 

 tahty. Had not the sea been salt, the torrid zone would have 

 been hotter and the frigid colder for lack of aqueous circulation ; 

 had the sea not been salt, intertropical seas would have been at a 

 constant temperature higher than blood heat, and the polar oceans 

 would have been sealed up in everlasting fetters of ice, while cer- 

 tain parts of the earth would have been deluged with rain. Had 

 the seas been of fresh water, the amount of evaporation, the quan- 

 tity of rain, the volume and size of our rivers, would aU have been 

 different from what they are ; the quantity of electricity in the air 

 would have been permanently changed from what it is, and its 

 tension in the sky would have been exceedingly feeble. In the 

 evaporation of fresh water at normal temperatures, but little of 

 that fluid is evolved; while vapour from salt water carries off 

 vitreous, and leaves behind resinous electricity in abundance. 

 Hence, with seas of fresh water, our thunder-storms would be 

 feeble contrivanjces, flashing only with such sparks as the vegetable 

 kingdom raight, when the juices of its plants were converted into 

 vapour, lend to the clouds. It might seem strange, this idea that 

 the thmiderbolt of the sky, the sheet-lightning of the clouds, and 

 the forked flashes of the «torm, all have their genesis chiefly in the 

 salts of the sea, and so it would be held were it not that Faraday 

 has shown that a single grain of water and a httle zinc can evolve 

 electricity enough for a thmider-clap ; therefore, were there no salts 

 in the waters of the ocean, the somid of thunder would scarce be 



* Melloni lias sLo-svn that the power of salt water to transmit heat is very much 

 greater than that of fresh. ^ o 



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