It was on the 13th of March, 1781, that Herschel made the discovery to which he owes, perhaps, most of his reputation. He had been engaged for nearly a year and a half in making a survey of the heavens, when, on the evening of the day that has been mentioned, having turned his reflector (an excellent seven feet reflector of his own constructing) to a particular part of the sky, he observed among the other stars one which seemed to shine with a more steady radiance than those around it; and on account of that and other peculiarities in its appearance, which excited his suspicions, he determined to observe it more narrowly. On reverting to it after some hours, he was a good deal surprised to find that it had perceptibly changed its place--a fact which the next day became more indisputable. At first he was somewhat in doubt whether or not it was the same star which he had seen on these different occasions; but, after continuing his observations for a few days longer, all uncertainty upon that head vanished. He now communicated what he had observed to the astronomer royal, who concluded the luminary could be nothing else than a new comet. Continued observation of it, however, for a few months, dissipated this error; and it became evident that it was in reality a hitherto undiscovered planet. This new world so unexpectedly found to form a part of the system to which our own belongs, received from Herschel, the name of the _Georgium Sidus_, or Georgian Star, in honour of the King of England; but by continental astronomers it has been more generally called either _Herschel_, after its discoverer, or _Uranus_. Subsequent observations, made chiefly by Herschel himself, have ascertained many particulars regarding it, some of which are well calculated to fill us with astonishment at the powers of the sublime science which can wing its way so far into the immensity of space, and bring us back information so precise and various. In the first place, the diameter of this new globe has been found to be nearly four and a half times larger than that of our own. Its size altogether is about eighty times that of our earth. Its year is as long as eighty-three of ours. Its distance from the sun is nearly eighteen hundred millions of miles, or more than nineteen times that of the earth. Its density, as compared with that of the earth, is nearly as twenty-two to one hundred; so that its entire weight is more than eighteen times that of our planet. Finally the force of gravitation near its surface is such, that falling bodies descend only through fourteen feet during the first second, instead of thirty-two feet as with us. Herschel afterwards discovered no fewer than six satellites, or moons, belonging to his new planet.