Zone, in astronomical geography, is applied to a division of the earth's surface by certain parallels of latitude. The Zones are 5 in number, viz. 1. The torrid zone, lying between the two tropics. It comprehends the West India Islands, the greater parts of South America and of Africa, the southern parts of Asia, and the East India Islands. 2. The north frigid zone, lying round the north pole, and bounded by the north polar circle. It comprehends part of Greenland, of the northern regions of North America, and a little of the northern parts of Europe and Asia. 3. The south frigid zone, lying round the south pole, and bounded by the south polar circle. It contains no dry land, so far as yet discovered. 4. The north temperate zone, lying between the torrid and north frigid. It comprehends almost the whole of North America, Europe, and Asia, with the northern part of Africa. 5. The south temperate zone, lying between the torrid and south frigid. It comprehends the southern part of South America, of Africa, and of the great island of NewHolland. In the torrid zone, the sun is vertical twice a year to every part of it, and there is very little diversity in the length of the day throughout the year, the longest day varying only from 12 to about 13 hours. In the temperate zones the sun is never vertical, and the length of the longest day varies from about 131 to 24 hours. In the frigid zones, the length of the longest day (or time between the sun's rising and setting) varies from 24 hours to 6 months. REMARKS. 1. There is a small variation in the inclination of planets' orbits, the longitude of nodes, the longitude of perihelion, and excentricity of orbits, the amount of which in 100 years is usually inserted in astronomical tables, and termed secular variations. 2. The diameter of the earth being 1. that of the sun will be 111.45 and that of the moon .2731. The density of the sun, (water being 1.) will be 1.1468, and that of moon, 3.339. 3. The inclination of the sun's axis is about 8°, and the time of his rotation about 25 days 6h. 4. The inclination of the moon's orbit to the ecliptic is about 5° 8', that of her axis about 2°. 18′, and the time of her rotation that of her revolution round the earth. 5. The periodical revolutions in the tables are those termed sidereal, and the distances of the 6. The orbits of the 1st, 2d, and 3d, satellites of Jupiter are very nearly circular, and coincident 7. The elements of the above Tables are taken chiefly from Laplace and Lalande, the places 102 VI. The Ptolemean System refuted. The Motions and Phases of Mercury and Venus explained, VII. The physical Causes of the Motions of the Planets. The Excentricities of their Orbits. The Times in which the Action of Gravity would bring them to the Sun. ARCHIMEDES' ideal Problem for moving the Earth. The World not eternal, 109 VIII. Of Light. Its proportional Quantities on the dif- ferent Planets. Its Refractions in Water and Air. The Atmosphere; its Weight and Proper- X. The Circles of the Globe described. The different Lengths of Days and Nights, and the Vicissi- tudes of Seasons, explained. The Explanation of the Phenomena of Saturn's Ring, concluded, XI. The Method of finding the Longitude by the 134 142 XIV.. Of the Precession of the Equinoxes, XV. The Moon's Surface mountainous: Her Phases described: Her Path, and the Paths of Jupi- ter's Moons delineated: The Proportions of the Diameters of their Orbits, and those of Saturn's |