Thus, you see, the telescope itself may be made to furnish us with many valuable illustrations. We may also turn to good account the lessons to be learned by the study of the stars for the purpose of navigation. The mariner, crossing the trackless sea, by taking astronomical observations, can steer himself with accuracy to his desired haven. Captain Basil Hall tells us, in the book I have previously mentioned, that "he once sailed from San Blas, on the West Coast of Mexico; and, after a voyage of eight thousand miles, occupying eighty-nine days, he arrived off Rio de Janeiro, having in this interval passed through the Pacific Ocean, rounded Cape Horn, and crossed the South Atlantic, without making land, or seeing a single sail except an American whaler. When within a week's sail of Rio, he set seriously about determining, by lunar observations, the position of his ship, and then steered his course by those common principles of navigation which may be safely employed for short distances between one known station and another. Having arrived within what he considered, from his computations, fifteen or twenty miles of the coast, he hove to, at four o'clock in the morning, to await the break of day, and then bore up, proceeding cautiously on account of a thick fog. As this cleared away, the crew had the satisfaction of seeing the great Sugar-Loaf Rock, which stands on one side of the harbor's mouth, so nearly right ahead that they had not to alter their course above a point in order to hit the entrance of the port. This was the first land they had seen for nearly three months, after crossing so many seas, and being set backward and forward by innumerable currents and foul winds. The effect upon all on board was electric; and, giving way to their admiration, the sailors greeted the commander with a hearty cheer." In a similar manner, we also sail by guidance from the heavenly bodies, and we have for a long season no sight of land, and sometimes do not even see a passing sail; and yet, if we take our observations correctly, and follow the track which they point out, we shall have the great blessing, when we are about to finish our voyage, of seeing, not the great Sugar-Loaf Rock, but the Fair Haven of Glory right straight before us. We shall not have to alter our course even a single point; and, as we sail into the heavenly harbor, what songs of joy will we raise, not in glorification of our own skill, but in praise of the wondrous Captain and Pilot who has guided us over life's stormy sea, and enabled us to sail in safety even where we could not see our way!