Page:Hector Macpherson - Herschel (1919).djvu/50

44 As was to be expected, the planet Uranus was an object of special interest to its discoverer. In 1783 he communicated the results of his preliminary study of the new planet to the Royal Society. He then estimated that "the real diameter of the planet must be between four and five times that of the Earth". In a later paper, in 1788, he announced the diameter as 34,217 miles—a remarkably accurate measure. He commenced soon after the discovery to search for Uranian satellites. At first he was continually disappointed and gave over the attempt. Resuming his observations, however, with the front-view method, he detected on 11th January, 1787, two very faint stars. After careful search of these objects in motion he tells us that he deferred a final judgment as to their nature till 10th February. "And in order to put my theory of these two satellites to a trial, I made a sketch on paper to point out beforehand their situation with respect to the planet and its parallel of declination. The long-expected evening came on, and notwithstanding the most unfavourable appearance of dark weather, it cleared up at last, and the heavens now displayed the original of my drawing by showing in the situation I had delineated them, the Georgian planet attended by two satellites."

He determined the times of revolution of these moons; estimated their size as probably not less than that of the satellites of Jupiter; and noted the great inclination of their orbits. In 1797 Herschel announced the discovery of four additional satellites, but this was never confirmed, and there can be little doubt that what he actually observed were small faint stars; although it is just possible that he may have glimpsed the very faint inner pair detected in 1847. A suspicion that Uranus was encircled by a ring similar to Saturn was finally negatived by his investigations in 1792, which he described as "very decisive against the existence of a ring".

Herschel never discovered a comet. This branch of