On the broad flat plains of Chaldsea, where the entire celestial hemisphere is continually visible to every eye, and the clear transparent atmosphere shows night after night the heavens gemmed with countless stars, each shining with a brilliancy unknown in our moist northern climes, the attention of man was naturally turned earlier than elsewhere to these luminous bodies, and attempts were made to grasp, and reduce to scientific form, the array of facts which nature presented to the eye in a confused and tangled mass. It required no very long course of observation to acquaint men with a truth, which at first sight none would have suspected--namely, that the luminous points whereof the sky was full were of two kinds, some always maintaining the same position relatively to one another, while others were constantly changing their places, and as it were wandering about the sky. It is certain that the Babylonians at a very early date distinguished from the fixed stars those remarkable five, which, from their wandering propensities, the Greeks called the “planets,” and which are the only erratic stars that the naked eye, or that even the telescope, except at a very high power, can discern. With these five they were soon led to class the Moon, which was easily observed to be a wandering luminary, changing her place among the fixed stars with remarkable rapidity. Ultimately, it came to be perceived that the Sun too rose and set at different parts of the year in the neighborhood of different constellations, and that consequently the great luminary was itself also a wanderer, having a path in the sky which it was possible, by means of careful observation, to mark out.