The phases which the earth presents to the moon are similar in appearance to those which the moon presents to the earth, but in a different order. Thus, when it is new moon at the earth, it is full earth at the moon: and the contrary. When the moon is in her first quarter, the earth is in its third quarter, and so on; while half-moon at the earth is accompanied by half-earth at the moon. There is no branch of science better fitted to be made the leading subject of general instruction than that which relates to the planetary and sidereal universe. The truths which it reveals are so startling in their nature, and apparently so far beyond the reach of human intelligence, that men of high literary name have confessed their incapacity to understand them, and their inability to believe them. There are few, indeed, we fear, who really believe that they sojourn on a revolving globe, and that each day and year of life is measured by its revolutions. There are few who believe that the great luminary of the firmament, whose restless activity they daily witness, is an immovable star, controlling, by its solid mass, the primary planets of our system, and forming, as it were, the gnomon of the great dial which measures the thread of life and the tenure of empires. Fewer still believe that each of the million of stars--those atoms of light which the telescope can scarcely descry--are the centres of planetary systems that may equal or surpass our own; and still smaller is the number who believe that the solid pavement of the globe upon which we nightly slumber is an elastic crust, imprisoning fires and forces which have often burst forth in tremendous energy, and are, at this very instant, struggling to escape--now finding an outlet in volcanic fires--now heaving and shaking the earth--now upraising islands and continents, and gathering strength perhaps for some final outburst which may shatter our earth in pieces, or change its form, or scatter its waters over the land. And yet these are truths than which there is nothing truer, and nothing more worthy of our study.