23G rnveiCAL geogkafhy of the sea, and its meteorology. 



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

 rays of heat to penetrate its bosom ;* but for these, the solar ray, 

 instead of heating large masses of water like the Gulf Stream, 

 would play only at or near the surface, raising the temperature 

 of the waters there, like the sand in desert places, to an inordi- 

 nate degree. The salts of the sea invest it with adaptations 

 which it could not possess were its waters fresh. Were they 

 fresh, they would attain their maximum 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 of fresh water. — Were the sea fresh and not 

 salt, Ireland would never have presented those ever-green shores 

 which have won for her the name of the " Emerald Isle ;" and 

 the climate of England would have vied with Labrador for 

 inhospitality. 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 certain parts of the earth would have been deluged 

 with rain. Had the seas been of fresh M^ater, the amount of 

 evaporation, the quantity of rain, the volume and size of our 

 rivers, would all 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 contrivances, flashing 

 only with such sparks as the vegetable kingdom might, when 

 the juices of its plants were converted into vapour, lend to the 

 clouds. It might seem strange, this idea that the thunderbolt of 

 the sky, the sheet-lightning of the clouds, and the forked flashes 

 of the storm, 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 little zinc can evolve electricity 

 enough for a thunder-clap ; therefore, were there no salts in the 



* INIelloni has shown that tlie power of salt water to transmit heat is very 

 much greater than that of fresh. 



