THE DISCOVERY OF URANUS.
It was in the year 1774 that Herschel first had a view of the heavens through the telescope he had himself constructed. During the early part of his career he does not seem to have made any important discoveries. He was gradually preparing himself for the great achievement by which his name became famous.
It was on the 13th of March, 1781, that the organist of the Octagon Chapel at Bath turned his telescope on the constellation of the Twins, and began to look at one star after another. You must know that a star merely looks like a little point in a telescope; even the greatest instrument will only make a star look brighter, and will never show it with a perceptible disk. In looking over the stars that night, Herschel’s attention was arrested by one object that did look larger when magnified, and therefore was not a star. The only other objects which would behave in this way were the planets, or possibly a comet. Indeed, at first Herschel imagined that what he saw must be a comet. It could hardly have occurred to him that he was to have such good fortune as to discover a new planet. The five great planets had been known from all antiquity. Was it reasonable to suppose that there could be yet another that had never been perceived? Fortunately, there was a test available. A star remains in the same place from night to night and from year to year; while a planet, as we have already had occasion to mention, is a body which is wandering about. The movements of a planet are, however, not at all like those of a comet. To decide on the nature of Herschel’s newly discovered body, it was sufficient to observe the character of its motion. A few nights sufficed to do this. The position of the body was carefully marked relatively to the neighboring stars, and it was soon shown that it was a planet.
Here, then, a great discovery was made. A new planet, now called Uranus, was added to our system. It would be nothing to discover a new star. You might as well talk of discovering a new grain of sand on the seashore. The stars are in untold myriads. They are so far off that they have no relation whatever to our system, which is presided over by the sun. But by the detection of a new planet, revolving far outside Saturn, Herschel showed that a new and most interesting member had to be added to the five old planets which have been known from the earliest records of history.
It may well be imagined that a discovery so startling as this excited astonishment throughout the scientific world. “Who is this Bath organist?” everybody asked. Accounts of him and his discoveries appeared in the papers. His fellow-citizens were not so familiar with the name as we are, happily, now; and the spelling of the unusual name showed many varieties. When George III. heard of Herschel’s great achievement, he directed the astronomer to be summoned to Windsor, that the King might receive an account of the wonderful discovery from the lips of the discoverer himself. Herschel of course obeyed, and he brought with him his famous telescope, and also a map of the whole solar system, to show to the King. No doubt he thought that his Majesty had probably not paid much attention to astronomy. Herschel was, therefore, prepared to explain to the King what it would be necessary for him to know before he could fully appreciate the magnitude of the discovery.
You will remember that Herschel while still a boy had deserted from the army, many years previously. It appears that the King had learned this fact in some way, so that when Herschel was ushered into his presence his Majesty said that before the great astronomer could discuss science there was a little matter of business that must be disposed of. The King accordingly handed Herschel a paper, in which he was, I dare say, greatly surprised to find a pardon to the deserter written out by the King himself.
Then Herschel unfolded his wonderful discovery, which the King thoroughly appreciated, and in the evening the telescope was set up in the gardens, and the glories of the heavens were displayed. Herschel made a most favorable impression on his Majesty, and when the King told the ladies of the Castle next day of all that Herschel had shown him, their astronomical ardor was also aroused, and they asked to see through the marvellous tube. Of course Herschel was ready to comply, and the telescope was accordingly carried to the windows of the Queen’s apartments at Windsor, which would have commanded a fine view if the clouds had not been in the way, which they unfortunately were. Even for royalty the clouds would not disperse, so what was to be done? Herschel was equal to the occasion. He specially wanted to exhibit Saturn, for it is one of the most beautiful objects in the sky, and will fascinate any intelligent beholder. No astronomers would have been able to see Saturn through the clouds, but Herschel did not disappoint his visitors; he directed the instrument, not to the sky (nothing was there to be seen); he turned it towards a distant garden wall. Now what would you expect to see by looking through a telescope at a garden wall—bricks, perhaps, or ivy? What these ladies saw was a beautiful image of Saturn, his globe in the centre and his rings all complete, forming so true a resemblance to the planet that even an experienced astronomer might have been deceived. In the afternoon Herschel had seen that the clouds were thick, and that there would be little probability of using the telescope properly. Accordingly he cut out a little image of Saturn, illuminated it by lamps, and set it up at a suitable distance on a garden wall.
Herschel’s visit to Windsor was productive of important consequences. The King said it was a pity that so great an astronomer should devote himself to music, and that it would be far better for him to give up that profession and come and live at Windsor. His Majesty promised that he would pay him a salary, and he also undertook to provide the cost of erecting great telescopes. His faithful sister Caroline came with him as his assistant, and also received some bounty from the King. From that moment Herschel renounced all his musical business, and devoted himself to his great life-task of observing the heavens.
He built telescopes of proportions far exceeding those that had ever been then thought of. He used to stand at night in the open air from dusk to dawn gazing down the tube of his mighty reflector, watching the stars and other objects in the heavens as they moved past. He would dictate what he saw to Caroline, who sat near him. It was her business to write down his notes and to record the position of the objects which he was describing. Sometimes, she tells us, the cold was so great that the ink used to freeze in her pen when she was at this work. Until he became a very old man, Herschel devoted himself to his astronomical labors. His discoveries are to be counted by thousands, though not one of them was so striking or so important as the detection of the new planet which first brought him fame.
The question of a name for the addition to the sun’s family had, of course, to be settled. Herschel had surely a right to be heard at the christening, and as a compliment to his Majesty he named the stranger the Georgium Sidus. So, indeed, for a brief while, the planet was actually styled. The Continental astronomers, however, would not accept this designation; all the other planets were named after ancient divinities, and it was thought that the King of England would seem oddly associated with Jupiter and Saturn; perhaps also they considered that the British dominions, on which the sun never sets, were already quite large enough, without further extension to the celestial regions. Accordingly a consultation was held, the result of which was that George III. was deprived of his planetary honors, and the body was given the name of Uranus, which, by universal consent, it now bears.
The planet Uranus lies just on the verge of visibility with the unaided eye. It can sometimes be glimpsed like a faint star, and, of course, with a telescope it is readily perceived. Many generations of astronomers before Herschel’s time had been observing the heavens, making maps of the stars, and compiling great catalogues in which the places of the stars were accurately put down. It often happened that Uranus came under their notice, but it never occurred to them that what seemed so like a star was really a planet. I have, no doubt, said that Uranus looked unlike a star when Herschel examined it; but then that was because Herschel was a particularly skilful astronomer. To an observer of a more ordinary type Uranus would not present any very remarkable appearance, and would be passed over merely as a small star. In fact, the planet was thus observed not once or twice, but no fewer than seventeen times, before the acute eye of Herschel perceived its true character. On many previous occasions the planet had been noted as a star by astronomers who are in every way entitled to our respect. It required a Herschel, determined to see everything in the very best manner, to grasp the discovery which eluded so many others.
When Uranus was observed on these former occasions and mistaken for a star, its place had been carefully put down. These records are at present of the utmost use, because they show the past history of the planet; and they appear all the more valuable when we remember that Uranus requires no less than eighty-four years to accomplish a single revolution around the sun. Thus, since the planet was discovered in 1781, it had completed one revolution by 1865, and is now (1899) about one-third of the way around another. The earlier observations extend backwards almost 200 years, so that altogether we have more or less information about the movements of the planet during the completion of two circuits and a half.
Uranus is a great deal bigger than the earth, as you will see in the view of the comparative sizes of the planets ([Fig. 47]). It appears to be of a bluish hue, but we cannot tell whether it turns round on its axis, or rather, I should say, we are not able to see whether it turns round on its axis; for we can hardly doubt that it does so.
Notwithstanding that Uranus is at so great a distance from the earth, we have been able to put this planet, no less than the nearer ones, in the weighing scales, and we assert with confidence that Uranus is fifteen times as heavy as our earth. We are indebted to the satellites for this information.