Mean distance of a planet, half the sum of the aphelion and perihelion distances.
Measurements, celestial, [57].
Mercury, [138].
Meridian, terrestrial, of a place, a great circle of the heavens passing through the poles, the zenith, and the north and south points of the horizon; celestial, any great circle passing from one pole to the other.
Meteors, [119]; swarm of, meeting the earth, [118]; explosion of, [120]; systems of, [123]; relation of, to comets, [124].
Micrometer, any instrument for the accurate measurement of very small distances or angles.
Mind, origin of force, [252]; continuous relation of, to the universe, [252].
Mira, the Wonderful, [221].
Moon, the, [151]; greatest and least distance from the earth, [10]; telescopic appearance of, [155].