EARTH. 589 EARTH LODGE. sun dep.irts from the eqinitor lowaril the north, till, about .Tune 21st, he has reached a northern declination of 23.5°. when he aj;ain approaclies ihe equator, which he reaches about September 23d. He then advances southward, and about December 21st has reached a southern decdina- tion of 23.5°. when he turns once more toward tile equator, at which he arrives March 21st. The 21st of .June is the Innscst ilay in the North- ern Hemisphere, and the sliortcsl in the South- ern: with the 21st of December it is the reverse. The linear velocity of axial rotation at the earth's surface evidently increases gradually from the poles to the equator, where it is about 24.840 miles a day. or about 1440 feet in a sec- ond. A direct proof of the rotation of the earth is furnislied by experiments with the pendulum, which, as we have already pointed out. show a decrease of the force of fjravity from the poles toward the equator: and thoujih a part of this decrease is owing to the want of perfect s|)heric- ity. a part also arises from the centrifugal fon-e caused by the motion of rotation. Another di- rect proof of rotation may be drawn from the observation that bodies dropped from a consider- able height deviate toward the east from the vertical line. The analogy of our earth to the other planets may be also adduced as an argu- ment, since their rotation, with the exception of the smallest and the most distant, is distinctly discernible. Finally, an additional proof of the earth's rotation was given in 1851 by Foucaulfs experiment with the pendulum. The principle of the experiment is this — that a i)endulum once set in motion, and swinging freely, continues to swing in the same plane, while at any place on the earth the plane of the meridian continues to change its position relative to this fixed plane. This experiment, being tried, verified the expect- ed rotation most satisfactorily. If the turning of the earth on its axis is once admitted to be the cause of the apparent daily motion of the heavens, it is an easy step to con- sider the annual motion of the sun through the constellations of the zodiac as also apparent, and arising from that revolution of the earth about the stin which we have already mentioned. If we consider that the mass of the sun is about 332,000 times greater than that of the earth, and that by the laws of mechanics two bodies that revolve round each other must revolve about their common centre of gravity, the idea of the sun revolving about the earth is seen to be simply impossible. The common centre of grav- ity of the two bodies, being distant from the centre of each inversely as their respective masses, is calculated to be far within the body of the sun, which has a diameter of S(i(i,400 miles. But it is easy to see how the apparent motion of the sun on the ecliptic naturally arises from a motion of the earth about the Bun. The motions of the jilanets. also, that ap- pear so complicated and irregular as seen by us, can only be satisfactorily explained by assuming that they. too. revolve rotind tlic sun in (he same direction as the earth. Sec the articles PRF.rES.siON and XtTATTON for an account of a small periodic motion of the earth's axis and its elTects. The Earth's Tempfkattrk. The phenomena of heat on the earth's surface are described tinder Climate; Meteorolooy: and other heads. .Xs we go below the surface, we reach a depth be- yond which the interior of the earth seems to have no sympathy with the external causes of heat or cold, and its heat appears to be its own, and to increase according to a fixed law the deeper we descend. The average rate of observed increase is 1° 1*". -for a descent of between 40 and 50 feet. The distribution of the land and water surfaces, with their area, is discussed in the article Geography (q.v.). For the physical features of the earth, see (iEOLOGY. niiiLio(iKAPiiv. liurmcister, (leschkhtc der t^cliopf till (/ (7th ed., Leipzig, 1872); Suess. Das Antlit:: dcr Erde (I^ipzig, 1883 et seq.); Kireh- liofT, i'liser Wissen con der Erde (ib., 188G et seq.); Hann. Hochstetter. and Pokornv. Allge- meine Urdkidide (ib.. 1896-99); Ratzel. OiV Erde iiiid das Leben (ib., 1901 et seq.): Shaler. As- pects of the Earth (Xew York, 1889); Hum- boldt, Cosmos (new ed. London, 18S9); Rechis, The Earth and Its Inhabitants (trans, ed. by Keane and Ravcnstcin, London. 1890 95): the .tlases of Physical Geography of .Vlcxander Keith .Tohnston, Bartliohmiew. and Heighaus; Habcnicht. (Inindriss einerejcaklen ftehij/jftiiifisge- srhiehlc (Leipzig, 1896); Ncwconib, "Tables of the Motion of the Earth on Its Axis .Around the Sun." in Asfronomiefil Papers, vol. vi. (Wash- ington. 1805) : and Xeuinayr. Erdiiesehichte (Leipzig. 1895). EARTH-CHESTNXJT. See Eartiinit. EARTH-EATING. The practice of eating <lav. II' ( iKOIMIAl.Y. EARTHENWARE. See Pottery. EARTH-HOG, or Pig. A name for the Aabd- VaKK I q.v. ) . EARTH LODGE. A domicile of earth, or within the eartii. The middle-latittide Amerind tri'oes made typical earth lodges for winter use. The Caddoan, Siouan, and Athapa.scan domicile for the winter was constructed by making an excavation from two to four feet deep, within which a framework of poles was erected. This was covered with grass or shrubbery and the ex- cavated earth was heaped over all. The entrance was a long covered way. Among the California tribes there was a corresponding type, thougVi placed deeper in the earth and with a projior- tionately longer covered entrance. This building was used as a "medicine' lodge, i.e. a temple, or place for sacred ceremonies. In southern Cali- fornia and throughout the arid region generally a single domicile usually served both for winter and summer use. This was commonly built of grass or cones or wattled shrubbery supported by a framework of poles, but a trace of the more j)rimitivc form survived in a roof-eovering of earth and sometimes in a plastering of mud with imbedded pebbles. This latter type is of much interest as a precursor of the pise type in which .merican aboriginal architecture may be said to have culminated. The pebble-set plaster- ing was thickened, then the pebbly mud was rammed between two wattled walls. As a further development the wattling was reduced to mov;ibIe screens between which successive ledges of rammed earth were built up and permitted to set by drying: while the earthen roof gradu- ally became a resting-place, then a refuge as the walls developed into parapets, and eventually an upper floor when the parapet had become a full story. This perfect typ<' of eartli lodge co- exists with the essentially primitive neighbor-
