Page:Physical Geography of the Sea and its Meteorology.djvu/262

236 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 inordinate 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 water, 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