Читать книгу The Herschels and Modern Astronomy онлайн

18 страница из 49

Herschel began in 1780 his second review of the heavens, using a seven-foot Newtonian, of 6¼ inches aperture, with a magnifying power of 227. “For distinctness of vision,” he said, “this instrument is, perhaps, equal to any that was ever made.” His praise was amply justified. As he worked his way with it through the constellation Gemini, on the night of March 13th, 1781, an unprecedented event occurred. “A new planet swam into his ken.” He did not recognise it as such. He could only be certain that it was not a fixed star. His keen eye, armed with a perfect telescope, discerned at once that the object had a disc; and the application of higher powers showed the disc to be a substantial reality. The stellar “patines of bright gold” will not stand this test. Being of purely optical production, they gain nothing by magnification.

At that epoch new planets had not yet begun to be found by the dozen. Five, besides the earth, had been known from the remotest antiquity. Five, and no more, seemed to have a prescriptive right to exist. The boundaries of the solar system were of immemorial establishment. It was scarcely conceivable that they should need to be enlarged. The notion did not occur to Herschel. His discovery was modestly imparted to the Royal Society as “An Account of a Comet.” He had, indeed, noticed that the supposed comet moved in planetary fashion from west to east, and very near the ecliptic; and, after a few months, its true nature was virtually proved by Lexell of St. Petersburg. On November 28th, Herschel measured, with his freshly-invented “lamp-micrometer,” the diameter of this “singular star;” and it was not until a year later, November 7th, 1782, that he felt sufficiently sure of its planetary status to exercise his right of giving it a name. Yet this, in the long run, he failed to accomplish. The appellation “Georgium Sidus,” bestowed in honour of his patron, George III., never crossed the Channel, and has long since gone out of fashion amongst ourselves. Lalande tried to get the new planet called “Herschel;” but the title “Uranus,” proposed by Bode, of Berlin, was the “fittest,” and survived.