Angle of Incidence, is the space contained between a ray which falls obliquely upon a body, and a line perpendicular to the surface of the body, at the point where the ray falls.
Angle of Reflection. The space contained between a reflected ray, and a line perpendicular to the reflecting point.
Angle of Vision, or visual angle. The space contained between lines drawn from the extreme parts of any object, and meeting in the eye.
Antarctic Circle. A circle extending round the south pole, at the distance of 23 1-2 degrees from it. The same as the south frigid zone.
Aphelion. That part of the orbit of a planet, in which its distance from the sun is the greatest.
Area. The surface enclosed between the lines which form the boundary of any figure, whether regular or irregular.
Aries. See [Sign].
Asteroids. The name given to the four small planets, Ceres, Juno, Pallas, and Vesta.
Astronomy. The science which treats of the motion and other phenomena of the sun, the planets, the stars, and the other heavenly bodies.
Atmosphere. The air which surrounds the earth, extending to an unknown height. Wind is this air in motion.