waters of the ocean, the sound of thunder would scarce be heard in the sky[1]—there would be no Gulf Stream, and no open sea in the Arctic Ocean.
463. Uniform character of sea water.—As a general rule, the constituents of sea water are as constant in their proportions as are the components of the atmosphere. It is true that we sometimes come across arms of the sea, or places in the ocean, where we find the water more salt or less salt than sea water is generally; but this circumstance is due to local causes of easy explanation. For instance: when we come to an arm of the sea, as the Red Sea (§ 376), upon which it never rains, and from which the atmosphere is continually abstracting, by evaporation, fresh water from the salt, we may naturally expect to find a greater proportion of salt in the sea water that remains than we do near the mouth of some great river, as the Amazon, or in the regions of constant precipitation, or in other parts, as on the polar side of 40° in the North Atlantic, where it rains more than it evaporates. Yet in the case of the Red Sea, and all such natural salt-pans, as that and other rainless portions of the sea may be called, there is, on account of currents which are continually bearing away the water that has given off its vapours and bringing forward that which is less concentrated as to brine, a moderate degree of saltness which its waters cannot exceed. We moreover find that, though the constituents of sea water, like those of the atmosphere, are not for every place invariably the same as to their proportions, yet they are the same, or nearly the same, as to their character. When, therefore, we take into consideration the fact that, as a general rule, sea water is, with the exception above stated, everywhere and always the same, and that it can only be made so by being well shaken together, we find grounds on which to base the conjecture that the ocean has its system of circulation, which is well calculated to excite our admiration, for it is as wonderful as the circulation of the blood.
- ↑ The great American lakes afford, it may be supposed, a considerable portion of the vapour which goes to make rain for the hydrographic basin in which they are. Visiting the Lake country in 1858, I was struck with the fact that so few trees bore the marks of lightning. The rule appeared to be, the nearer the lakes, the more rare was it for one of these ornaments of the forest to have been defaced by lightning; and, on inquiry from the Lake Board of Underwriters, I was informed that among the records of lake disasters there was not a single instance of a vessel having been struck by lightning on the North American lakes!
