Page:A Physical and Topographical Sketch of the Mississippi Territory, Lower Louisiana, and a Part of West Florida.djvu/29

 from what might be estimated its main standard, are those on the banks of the Mississippi, where I am authorized to say I have generally seen it much lower than in interiour situations, the most elevated not excepted. Where the sea-breeze prevails, we find little difficulty in accounting for this difference: but in situations remote from its influence, as on the banks of the Mississippi, four or five hundred miles from the sea, the solution of the phenomenon becomes more difficult—I would attempt its explanation in this way.—The Mississippi originating in such northern latitudes, and rolling down such a depth of water, requires so great a length of time to become equalized to the temperature of the countries through which it passes, that it must absorb a great deal of the circumambient caloric. Thus, at Natchez, even as late as the autumnal equinox, we find many portions of the Mississippi water much lower in temperature than that taken from small rivers in the neighbourhood of this place; a circumstance of which the boat-men on this river often avail themselves in the hottest weather, when they are in the habit of letting down some heavy vessel to the bottom of the river, to procure water of a low temperature for the purpose of mixing with their taffia. We are not surprised at this being the case, when we take into view the great opacity of the Mississippi water, owing to the immense quantities of sand suspended in it, which, by obstructing the solar rays in their passage through that fluid, and thus making the evaporatory process commence near