Aerolite (air-stone), [122].
Air, refraction of the, [40].
Algol, the variable star, [222].
Almanac, Nautical, [71]; explanation of signs used, [275].
Alphabet, Greek, [275].
Altitude, angular elevation of a body above the horizon.
Angle, difference in directions of two straight lines that meet.
Annular (ring-shaped) eclipses, [158]; nebulæ, [218], [220].
Aphelion, the point in an orbit farthest from the sun.
Apogee, the point of an orbit which is farthest from the earth.