Page 573 : EARLY — EARTH
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reptile there is no cochlea, only a small projection in place of it; in the bird this projection is longer and curved; and in the ox it has become long and coiled like a snail-shell — the true cochlea. The semicircular canals are present in all three. It is in the cochlea that the most complicated structures are found. The principal branch of the ear-nerve enters here, and becomes connected with certain large cells provided with hairs that vibrate when sound-waves reach them. The whole is inclosed in very hard bone, so that there are a bony part and a membranous part to the internal ear. The membranous part consists of closed sacs full of fluid, and these are also surrounded by a fluid. Thus the arrangement is exactly suited to receive vibrations and transmit them to the ear-nerves. In the cochlea are many little organs, standing side by side on a membrane and forming an arch or tunnel by arching toward each other. These are the organs of Corti. They vary in size, and possibly respond to different sets of sound-vibrations; but, on the other hand, it is possible that they simply act as dampers, somewhat like those in a piano, to prevent the too long vibration of the parts of the membrane upon which they rest. For fuller descriptions of the ear see text-books on anatomy and physiology. See, also, Sound.
Early (ẽr′ lĭ), Jubal Anderson, a Confederate general, was born in Virginia in 1816. He graduated at West Point and served in the Florida and Mexican Wars, and was practicing law when the Civil War broke out. He entered the Confederate service as a colonel, and was in the battles of Bull Run, Fredericksburg and Gettysburg. He was defeated by Sheridan in several battles and also by Custer at Waynesboro, after which he was relieved of his command. He died at Lynchburg, Va., March 2, 1894.
Earth is the name given to the third planet in order from the sun. Like other members of the solar system, it revolves in an elliptical orbit, in one focus of which is the sun. The average distance of the earth from the sun is 92,800,000 miles. The earth has one moon, at a mean distance of 238,800 miles. It was anciently believed that the earth was a flat disk of land surrounded by water. It is now known that it has approximately the form of a sphere. On a wide, smooth surface, such as the sea, the upper part of a distant receding object, as a ship, remains in sight after the lower part has disappeared. This could be true only if the earth were round. The position cf the stars shows the same thing. If one travels south, new stars, which before could not be seen, rise into view. Another very convincing proof is the fact that vessels steering always in the same genera] direction have gone round the earth, coming back to the point from which they started. The earth is not a perfect sphere, but is flattened slightly at the poles. If it were a perfect sphere, the arc of the surface, corresponding to a definite angle at the earth’s center, would be equal in every part of the circumference. But it is found that an angle of one degree has a longer arc toward the north and toward the south than near the equator, thus showing that the polar regions are flattened and the equatorial regions bulge out. Delicate experiments also show that the force of gravity is greater near the poles than at the equator; but this can be true only if the center of the earth is closer to the other attracting body at the poles than at the equator; that is, the polar regions must be flattened so as to lie nearer the earth’s center than is the equator. The shorter diameter of the earth is 7,899.6 miles, while the equatorial diameter is 7,926.6 miles. The character of the earth’s interior can be inferred from certain tidal phenomena which have led Lord Kelvin to the conclusion that the rigidity of the earth is greater than that of glass. Estimates regarding the age of the earth vary enormously. Kelvin places it somewhere between 20 million and 400 million years.
The earth has four principal motions: that of rotation on its own axis; that of revolution around the sun; that of precession; and that of nutation. As it rotates on its axis half is always exposed to the sunlight and half is always in darkness, one rotation being made every 24 hours. The time taken for the revolution of the earth around the sun is 365¼ days, and forms our year. If its axis were exactly perpendicular, the days would always be the same length. But in fact its axis is inclined at
Image: The inner ear of a reptile (above), a bird (to the left), and an ox (to the right)
Image: JUBAL A. EARLY
