EXPLANATION OF SCIENTIFIC TERMS. YEAR. The period of time in which the earth performs her revolution round the sun, or that in which the sun apparently moves from a point in the ecliptic until he returns to the same point, is the Solar Year. It is also termed the Tropical Year, and consists of 365 days, 5 hours, and nearly 49 minutes. The Silereal Year, that between the departure of the sun from any fixed star to his return to the same star, is about 17 minutes longer. The Anomalistical Year is the time that elapses from the sun's leaving his apogee till he returns to it, and is 365 days, 6 hours, and about 14 minutes. See Calendar. ZENITH.-See Nadir. ZODIAC. The ecliptic (as is stated under lately, that Juno, Pallas, Ceres, and Vesta ZONE (Latin Zona, a girdle), in Geography, ZOOLOGY (Greek_zöon, an animal, and logos, a discourse), is that division of Natural History which treats of animals, and ZOOPHYTES (Greek phyton, a plant) are such natural productions as are supposed to participate of the qualities both of plants and animals. GENERAL INDEX. The references are given to the treatise or treatises in which the article is found. Of the Action of gravity explained Afternoon of the day, why warmest Albinoes, description of that variety of man Alexandria, the ground of its site did not exist in the time of Alexandrian school, astronomers of America and Europe, comparative temperature of ASTRONOMY HIST. OF ASTRO. ASTRONOMY 153,170-174 elements of Aratus, his astronomical poem . 23,24 Arctic regions, red coloured snow of, accounted for Arcturus, proper motion of that star his heliacal rising in the age of Hesiod Aristarchus, his method of ascertaining the distance of the sun and moon from the earth another account of his method of ascertaining the sun's distance Aristotelian philosophy overthrown by Galileo Aristotle supposed that the earth was shaped like a drum Aryabhatta, an ancient Indian astronomer, taught the diurnal Asteroids proposed designation for the planets Juno, Ceres, Astrolabium of Ptolemy, construction of Astrology originated in Chaldæa not known in Greece before the time of Alexander infected some of the greatest astronomers of modern Astronomers of Chaldæa, their method of calculating eclipses only one of eminence during the Roman republic Regiomontanus, an account of his works Copernicus, account of his system and discoveries Tycho Brahé, account of his discoveries Galileo, account of his discoveries accused of impiety by the church . 43-47 54-59 57 Hevelius, account of his observations (early) description of their quadrants 63,64 67 Römer, account of his inventions and discoveries 70,75 Descartes, account of his system Newton, account of his system Bradley, account of his discoveries La Caille, account of his astronomical labours Mayer, account of his labours Astronomical day distinguished from the civil twilight distinguished from the popular observations, correct the variation of the magnetic Tables of the Chinese, account of of the Hindoos, account of theories of Hipparchus, account of poem by Aratus, account of of Manilius, account of discoveries of Hipparchus, account of doctrines of Ptolemy, account of observatories, when first established system of Newton, account of clocks regulated by sidereal time Astronomy the immediate results of observation contrary to its 82,83 needle 255 253-255 HIST. OF ASTRO. 1-7 7-11 observations on telescopes of immense length, account of ASTRONOMY HIST. OF ASTRO. Astronomy, progress of Eratosthenes in of the Persians, history of patronised by Alphonso, King of Castile by Charles the Second physical, origin and history of principal periods in its history of the Hindoos, tabular view of its elements Atmosphere, shooting stars are meteors engendered in of the moon different from that of the earth has no clouds of the sun, its density of Venus, similar to that of the earth of Jupiter, on the clouds in currents in, account of appearances of, in South America Attraction of the planets disturbs the elliptical figure of the earth's NAVIGATION 26-32 18 86 86 125 126 126 PHYS. GEOG. 30 41 . 194 105 • 36 30 10 27 why there are no tides in Barlow's method of finding the deviation of the compass Beccaria and others measure a degree of the meridian in Italy Betelgeuse, the brightest star in Orion. Birds, each species confined to one quarter of the globe account of their migrations Black Sea, its surface higher than that of the Caspian law of the distances of the planets from the sun, confir- Boiling Fountain, description of Bones of known and unknown quadrupeds found buried in the Books on mathematical geography, referred HIST. OF ASTRO. Canada, its climate compared with that of England Cape of Good Hope, measure of a degree of the meridian at, by |