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and hence we have the instrument called the thermometer, for measuring the quantities of heat existing in bodies, agreeably to the import of the Greek words composing the name; in the same way as the instrument for measuring the relative weights of the air is called a barometer.
The sensation of heat is produced in our body by particles of heat entering it; and the sensation of cold is excited by such particles passing out of the body. Heat seems to be the chief cause of the fluidity of bodies: wax, lead, silver, &c. become fluid by the application of heat; and vil, water, even mercury itself, are rendered solid by being deprived of heat.
In general it may be observed, that the highest ranges
of mountains on the surface of the earth are situated between the tropics, and that their elevation diminishes as their position approaches to the poles. The loftiest parts of the grand chain or cordillera of the Andes, in South America, lie under the equator, one of the summits, Chimborazo, springing up to no less a height than 20,608 English feet, while the highest mountains in North America do not exceed 4000 feet.
The following Table shows the height of some of the most remarkable mountains in the world, whose elevation has yet been accurately ascertained. The second column gives the elevation as determined by means of the baromefer ; the third column, that discovered by geometrical operations : and when the methods by which the measurements were performed are unknown, the results are entered in the fourth column
highest in Britain}
Arthur's Seat (Edinburgh) In Ireland,
Puy de Sansy Plomb de Cantal Puy de Dome
6,300 6,200 5,000
pathian mountains ;
Peak of Teneriffe
The sea or ocean covers about two thirds of the surface of the globe; but the quantity of water it contains will perhaps never be ascertained, from our ignorance of its various depths. The greatest depth which has ever been measured is 5,346 feet, or a little more than an English mile; and its mean depth has been calculated at about 1,300 feet, or a quarter of a mile. At great distances from the land the depth of the sea increases or diminishes with some regularily, but near the shore it varies very considerably; bearing, however such a relation to the land, that along a high steep shore the water deepens very rapidly, while before a low flat beach, it deepens very slowly for a good way out.
If the whole inhabited parts of the earth be supposed to contain 38,990,569 square miles, Europe will contain 4,456,065, Asia 10,768,823, Africa 9,654,807, and America 14,110,874 : and if the whole population be estimated at 700,500,000 persons, Europe will possess about 150,000,000; Asia, including the great country of New Holland and the isles in the Pacific Ocean, 500,500,000; Africa 30,000,000, and America 20,000,000: so that the population on a square mile, at an average, will be in Europe 34, in Asia 46, in Africa 3, and in America lj, or 3 for every 2 square miles.
Before entering on the description of the several quarters of the globe, it will be convenient for the student to possess the following table of the latitude and longitude of some of the most remarkable towns, capes, &c. collected from the latest and most accurate observations.
In this table the longitude is reckoned not from the meridian of London, but from that of the observatory erected on the summit of the hill in Greenwich Park, which being the station of the Astronomer Royal, (at present the eminent Dr. Nevil Maskelyne) where a regular system of celestial observation is carried on, and to which all calcula. tions relating to geography, navigation, and astronomy are referred, it has for a considerable time been determined, that the first nieridian should be that which passes over this observatory.
The difference of longitude between the observations of Greenwich and Paris having been carefully ascertained to be 2°, 19', 51", the student will have no difficulty in reducing longitudes calculated for the meridian of Paris, as in the French maps and sea-charts, to the meridian of Greenwich, and vice versa; for Paris being situated 2°, 19', 51'to the eastward of Greenwich, if the longitude be given east from Paris, the above difference must be added to obtain the longitude from Greenwich; but if the given longitude be west from Paris, this difference must be subtracted : thus, if Rome be situated in longitude east from Paris 30', 7', 40", by adding the difference we have 32°, 27', 31" for the longitude of Rome east from Greenwich ; again, if the Royal Marine Observatory in Cadiz be situated in longitude west from Paris 8°,37', 33", by wbtracting the above difference we have 6°, 17', 44" for the longitude of Cadiz west from Greenwich. By means of this difference of longitude between Greenwich and Cadiz, all longitudes reckoned from this last place, as is done in the modern Spanish maps and charts, may, in a similar way, be reduced to the meridian of Greenwich.