twenty-six hours at a stretch. One mirror was never removed from the tube for repolishing until another was ready to take its place, and Miss Herschel relates that ‘the last night at Clay Hall was spent in sweeping till daylight, and by the next evening the telescope stood ready for observation at Slough.’ Many evenings were occupied in transporting telescopes to and from the Queen's Lodge for the purpose of gratifying royal curiosity with views of the heavenly bodies; meetings of the Royal Society were attended when the moon was in the way; funds were supplied by the sale of telescopes. Herschel's polishing machine was perfected in 1788. Before 1795 he had made 200 seven-foot, 150 ten-foot, and 80 twenty-foot, besides a multitude of smaller mirrors. The king paid him six hundred guineas apiece for four ten-foot telescopes, one of them a present for the university of Göttingen, which Herschel delivered personally in July 1786, when he was elected a fellow of the Royal Society of Göttingen, and spent three weeks with his family at Hanover. For a twenty-five-foot telescope, ordered in 1796 for the Madrid observatory, he eventually received 3,150l.; from the Prince of Canino in 1814 2,310l. for a ten-foot and a seven-foot. Innumerable minor commissions were executed. (For the prices of his telescopes see Bode, Jahrbuch, 1788, p. 254; Von Zach, Monatliche Correspondenz, 1802, p. 56; and manuscript Letter Book, pp. 135, 167.)
Herschel pursued meantime with incredible ardour his great object of enlarging telescopic powers. Untoward accidents marred in 1781 his attempts to obtain a thirty-foot mirror; one of forty feet was, however, with the aid of a royal grant of 2,000l., begun at Clay Hall in 1785. His felicity was now complete. He seemed to Miss Burney ‘a man without a wish that has its object in the terrestrial globe.’ She describes him as ‘perfectly unassuming’ yet ‘openly happy’ in his success (Madame d'Arblay, Diary, August 1786).
The discovery, on 11 Jan. 1787, of two Uranian satellites (‘Oberon’ and ‘Titania’), consequent upon the economy of light effected by discarding the small mirror of his twenty-foot (Phil. Trans. lxxvii. 125), determined Herschel to construct his new instrument on the Herschelian or front-view plan. The first great speculum was put into the tube at Slough on 19 Feb. 1787, but proved too thin. A second, cast on 26 Jan. 1788, cracked in cooling. A third was figured by 24 Oct., but not to the satisfaction of its maker, who continued working at it for ten months longer. At the first instant of turning it upon Saturn, on 28 Aug. 1789, a sixth satellite (‘Enceladus’) was detected, and a seventh (‘Mimas’) on 17 Sept. following (ib. lxxx. 10).
A second sum of 2,000l. was in August 1787 granted by George III for the completion of the giant reflector, besides an allowance of 200l. a year for repairs. The tube was 39 feet 4 inches long; the mirror, of 49½ inches diameter, weighed 2,118 pounds. An inclination of about three degrees caused it to throw the image slightly to one side of the tube, where the eye-piece was fixed, the observer standing with his back to the sky. Ladders fifty feet high led to a platform, whence he communicated by means of speaking-tubes with his assistants. Before the optical parts were finished, Miss Herschel narrates, many visitors walked through the tube. Among them was George III, who helped on the Archbishop of Canterbury, saying, ‘Come, my lord bishop, I will show you the way to heaven.’ The definition of this instrument, at first superb, probably fell off later. Since, with a magnifying power of 1,000, it could be made available in England only during about one hundred hours in the year, Herschel estimated that eight hundred years would be needed for a review with it of the whole heavens. The last object upon which it was turned, on 19 Jan. 1811, was the Orion nebula. For thirty-nine years longer it stood with its scaffolding, as represented on the seal of the Royal Astronomical Society, and continued to be designated as a landmark on the Ordnance Survey map of England. But on New-year's eve 1839 a ‘Requiem’ composed by Sir John Herschel was sung by his assembled family within the tube, which was then rivetted up, and laid horizontally on three piers in the garden at Slough, where it still remains, the great speculum adorning the hall of ‘The Herschels.’
Before the completion of the great reflector Slough had become a place of scientific pilgrimage. Piazzi, Lalande, Cassini, Méchain, Legendre, besides princes and grand dukes without number, paid their personal respects to the great astronomer. Von Magellan wrote an interesting account of his methods of observation (Berliner Astr. Jahrbuch, 1788, p. 162); the king of Poland sent him his portrait; the empress of Russia desired specifications of his telescopes; academic distinctions came from all quarters. The university of Edinburgh in 1786, and that of Glasgow many years later, conferred upon him honorary degrees of LL.D.; the American Philosophical Society, the Société Hollandaise, the Academies of Paris, Dijon, Berlin, St. Petersburg, and Stockholm opened
