One night, March 13, 1781, when William Herschel was busily exploring the heavens with a powerful telescope, he noticed something which he took for a comet without a tail. He saw it was no mere point of light like the stars, but had a tiny round disk or face, which could be magnified. So he watched it carefully, and found in the course of a few nights that it moved--very slowly, certainly; but still it did move. Further watching and calculation made it clear that, though the newly-found heavenly body was at a very great distance from the sun, yet it was moving slowly in an orbit _round_ the sun. Then it was known to be a planet, and another member of the Solar System. From that day the reputation of Herschel rapidly increased. King George III, who loved the sciences and patronized them, had the astronomer presented to him; charmed with the simple and modest account of his efforts and his labors, he secured him a life pension and a residence at Slough, in the neighborhood of Windsor Castle. His sister Caroline assisted him as secretary, copied all his observations, and made all his calculations; the king gave him the title and salary of assistant astronomer. Before long the observatory at Slough surpassed in celebrity the principal observatories of Europe; we may say that, in the whole world, this is the place where the most discoveries have been made. Astronomers soon applied themselves to the observation of the new body. They supposed that this “comet” would describe, as usually happens, a very elongated ellipse, and that it would approach considerably to the sun at its perihelion. But all the calculations made on this supposition had to be constantly recommenced. They could never succeed in representing all its positions, although the star moved very slowly: the observations of one month would utterly upset the calculations of the preceding month. Several months elapsed without a suspicion that a veritable planet was under observation, and it was not till after recognizing that all the imaginary orbits for the supposed comet were contradicted by the observations, and that it had probably a circular orbit much farther from the sun than Saturn, till then the frontier of the system, that astronomers came to consider it as a planet. Still, this was at first but a provisional consent. [Illustration: PROMINENT ASTRONOMERS OF FORMER TIMES. Tycho Brahe, Hipparchos, Galilei, Newton, Kepler, Kant, Kopernikus, Laplace.] It was, in fact, more difficult than we may think to increase without scruple the family of the sun. Indeed, for reasons of expediency this idea was opposed. Ancient ideas are tyrannical. Men had so long been accustomed to consider old Saturn as the guardian of the frontiers, that it required a rare boldness of spirit to decide on extending these frontiers and marking them by a new world.