MADE USE OF IN ASTRONOMY. 42.7

magnitude; the next in brightness to these stars of thesecond magnitude; and so on.

Mars, a primary planet belonging to the solar system,which is the fourth in order from the fun, and whosemagnitude is about four times less than that of theearth.

Mean motion of a planet, is that which would talesplace if it moved in a perfect circle, and equally everyday.

Medium Coeli, the mid-heaven, that degree of theecliptic which is upon the meridian at any time of theday or night.

Mercury, a primary planet, the first in order from thefun, and whose magnitude is about fifteen times lessthan that of the earth.

Meridian, a great circle of the sphere, which passesthrough the zenith and poles, and is perpendicular tothe horizon; it is so called, because when the sun isupon this circle it is always mid-day or noon.

Me tonic Year, the fame with the cycle of the moon ja period invented by Meton, a Greek philosopher, wholived in the eighty-lixth olympiad, or about 430 yearsbefore Christ.

Micrometer, an instrument by which the apparentmagnitudes of objects, viewed through telescopes ormicroscopes, are measured with great exactness.

Microscope, an optical instrument, by means of whichvery minute objects are represented much larger, andviewed distinctly at small distances.

Minute, the both part of an hour in time, or of a de-gree in motion. *

Monoceros, a southern constellation, consisting of thirty-two stars.

Mons