In the darkest period of human history, astronomy was the Ararat of human reason; but it became especially the support and rallying point of the scientific world, when intellect at large was astir to investigate the new wonders which rose to view with the effulgent noon of the middle age. Alphonso, king of Castile, in the year 1252, corrected the astronomical tables of Ptolemy; and Copernicus, of Thorn, revived the true solar system, about 1530. Tycho Brahe and Longomontanus brought forward opposing systems, but which were soon rejected. Kepler, soon after, gave the first analysis of planetary motions, and discovered those laws on which rests the theory of universal gravitation. Galileo advocated the Copernican system; and by the aid of one of the first telescopes, discovered the satellites of Jupiter. Hygens discovered Saturn's ring, and fourth satellite; and four others were soon after noticed by Cassini. Thus was the great secret of the sidereal universe read, its movements comprehended, and the glories thereof proclaimed, while emancipated and sublimated thought, from the loftiest throne of observation began forever to soar aloft. As a ray of light became the conductor of mind upward into infinite space, so a bit of gray stone projected the invisible bridge which spans from continent to continent, and makes the path over trackless oceans plain as a broad highway. The properties of this wonderful mineral were not unknown to the ancients, who, Pliny says, gave the name "Magnet" to the rock near Magnesia, in Asia Minor; and the poet Hesiod also makes use of the term "magnet stone." The compass was employed twelve hundred and fifty years before the time of Ptolemy, in the construction of the magnetic carriage of the emperor Tsing-wang; but the Greeks and Romans were completely ignorant of the needle's pointing toward the north, and never used it for the purpose of navigation. Before the third crusade, the knowledge of the use of the compass for land purposes had been obtained from the East, and by the year 1269 it was common in Europe. But as the time approached when God would advance, by mightier strides than before, the work of civilization, he discovered the nations one to another, through the agency of a tiny instrument, then first made to vibrate on the broadest sublunary element, and the throne of grandest power. The discovery of the polarity of the magnet, and the birth of scientific navigation resulting therefrom, was as simple as it was providential. Some curious persons were amusing themselves by making swim in a basin of water a loadstone suspended on a piece of cork. When left at liberty, they observed it point to the north. The discovery of that fact soon changed the aspect of the whole world. This invention, which is claimed by the Neapolitans to have been made by one of their citizens about the year 1302, and by the Venetians as having been introduced by them from the