From the putrefying contents of stagnant water, nutriment is afforded to various living plants and insects which there supply the place of those that perish. Its taste is vapid, unpleasant, and wholly destitute of that agreeable freshness which is found in spring water. It is, however, generally soft, and, by filtration, it may be freed from many of its impurities. The air which issues from marshes and stagnant pools is extremely noxious, and is the cause of agues and other distressing complaints, to such persons as reside in the neighbourhood of them or are much exposed to them; and the injurious effects of such air have also been considered to extend to the internal use of these waters. ──────────────────────────────────────────────────────────────────────── ORDER II.—SEA WATER. 279. _SEA WATER is a very heterogeneous compound, not only containing a considerable portion of saline substances, but holding also suspended in it an infinite number of minute animal and vegetable particles, to the gradual putrefaction of which its peculiarly nauseous and bitter taste, at the surface, is in some measure to be attributed._ _The average quantity of salt in sea water is estimated to amount to about one─thirtieth part of its weight. It likewise contains a certain portion of muriat of magnesia, sulphat of magnesia or Epsom salts (199), and a small quantity of sulphat of lime (192). Sea water, taken from a great depth, has not the bitterness which the water of the surface has: it is only saline._ No natural waters, if we except certain brine springs and salt lakes, are so saline as those of the ocean; and the latter differ, in this respect, in different parts of the world. At the tropic, the sea is in general more salt than it is at the poles, a wise ordination to preserve it, in those climates, from the great tendency to putrefaction: and, at a considerable depth, it is always found more salt than at the surface. The water of the Baltic is much less salt than that of the Atlantic; and it is a remarkable circumstance, that its saline contents are increased by a west wind, but still more so by a gale from the north west. Some philosophers have endeavoured, but to little purpose, to account, from second causes, for the saltiness of the ocean. Dr. Halley persuaded himself that it might have been gradually acquired, in very minute portions, by a deposit of salt washed down from the land by rivers, and that, as it could not be carried off by evaporation, instead of being diminished, it must be constantly increasing. But this idea of salting the sea with fresh water, is, to say the least of it, somewhat absurd, more particularly as it presumes that the sea was originally unimpregnated with salt. Had this been the case, the putrefaction of the immense mass of animal and vegetable substances which it gradually contained, would, in a short time, have proved fatal to the whole inhabitants of the earth.