"August 4, 1773, north latitude 80° 30'. The heat of the air was 32, of the water at the surface 36, of water fetched up from the depth of 60 fathoms under the ice, 39.
" September 4. 1773, north latitude 65°. The heat of the air was 661, of the water at the surface 55, of water from the depth of 683 fathoms, 40.
"It appears from all these experiments, that, when the atmosphere was hotter than the surface of the sea, the superfi cial water was hotter than that at a great depth ; and when the atmosphere was colder than the surface of the sea, it is evident that the superficial water was somewhat colder than at a considerable distance below it" Sea-water may be rendered fresh by freezing, which excludes or precipitates the saline particles ; or by distillation, which leaves the salt in a mass at the bottom of the vessel. Upon tliese prin ciples, a mode of obtaining a supply of fresh water at sea was recommended some years ago to the Admiralty, by Dr. Irving. It consisted in only adapting a tin tube of suitable dimensions to the lid of the common ship's kettle, and con densing the steam in a hogshead which served as a receiver. By this mode a supply of twenty five gallons of fresh water per hour might be obtained from the kettle of one of our ships of war.
The saline taste of sea-water, is chiefly derived from common salt which it holds in solution. Sea-water is also distinguish ed by a nauseous bitter taste, which is ascribed to the animal and vegetable mat ters which are floating in it. This taste has been considered as in some measure foreign to it, for it is only found in the water on the surface of the ocean, or near the shores. Sea-water, taken up at considerable depths, contains only saline matters. The specific gravity of sea water varies from 1.027 to 1.028. Its greater density is owing to the salts which are dissolved in it ; and to this impreg nation also it is owing, that it is not fro zen till the temperature is reduced nearly to 28°. The salts which are chiefly found in sea-water are, muriate of soda, or com mon salt, muriate of magnesia, sulphate of magnesia, sulphate of lime and soda. The quantity of saline ingredients in the waters of the ocean varies from to part. Mr. Kirwan makes the average quantity about of its whole weight.
The quantity of saline contents of water, taken up by Lord Mulgrave at the back of Yarmouth Sands, in latitude 53°, amounted nearly to ; while Bergman found the water taken up in the latitude of the Canaries, to contain about 3, of its weight of saline matter. These quan tities, however, vary, even in the same latitude, during rain and dry seasons, near the land, or the mouths of great rivers. The difference of latitude does not seem to make any considerable dif ference in the proportion of saline mater. In latitude 8U° north, sixty fathoms un der ice, sea-water, taken up by Lord Mid grave, yielded about in latitude 74°, nearly the same ; and in latitude Pages obtained four per cent. from water taken up in latitude 81°, and the same quantity of saline matter from water ta ken up in latitudes 45° and 39° north. In southern latitudes the proportion was still greater ; he found it to contain the following proportions : In the Mediterra nean, the proportion is said to be still greater ; but the Euxine and Caspian seas are found to be less salt than the ocean. This is also the case with the Baltic. If the saline matters of the waters of the ocean did not consist of different kinds, the proportion of salts which it contains might be ascertained by the specific gra vity. The experiments of Mr. Wilcke show that the proportion of saline matter in the Baltic is less than that of the ocean : and that it is salter during the prevalence of a westerly wind, by which the water is driven from the ocean, than during any easterly wind. The proportions of the different salts in an analysis, by Bergman, are the following : Muriate of soda . 30911 Muriate of magnesia 6.222 Sulphate of lime . 1.000 38.133 In 1,000 parts of water taken up near Dieppe, Lavuisier found the following salts : Muriate of soda 1375 Muriate of lime and magnesia 256 Muriate of magnesia . 156 Lime 87 Sulphate of soda and magnesia 84 1958 The luminousness of the sea is a phe nomenon that has been noticed by many nautical and philosophical writers. Mr. Boyle ascribes it to some cosmical law or oustom of the terrestrial globe, or at least of the planetary vortex.