The celebrated forty-foot telescope, first described to the Royal Society by Herschel, June 2, 1795, was the result of a long series of experiments on the construction of mirrors, begun at Bath, on telescopes from two to twenty feet in length. And we may here remark, that “the bulk of his fortune arose from the sale of telescopes of his own construction, many of which were purchased for the chief observatories of Europe,” and not from the salary of £400 a year which he received as private astronomer to George III. See ‘Statement of Circumstances,’ &c., a pamphlet printed on the occasion of the last election of a President by the Royal Society. In 1785, George III. furnished Herschel with the means of undertaking an instrument larger than any he had yet made. The greatest difficulty (independent of the stand) was the obtaining a mirror of sufficient size, which should not crack in cooling, and should be strong enough not to bend under its own weight. This instrument has been so frequently described that we shall say no more of it, except that Herschel dates the completion of it from August 28, 1789, when he discovered the sixth satellite of Saturn, and obtained his best view of the spots on that planet. A month later, the seventh satellite was discovered by Herschel. This telescope is now never used. Sir J. Herschel prefers a twenty-foot reflector for his own observations. The first discovery of the satellites of Uranus was also in a minor degree the work of thought. Such bodies were repeatedly looked for by Herschel, but none were seen. A small change in the instrument, by which the light was increased, suggested one more trial; and the result was the establishment of the existence of the two first satellites, in January, 1787. Two more were discovered by Herschel, in 1790, and two more in 1794. These satellites cannot be seen but with an instrument of first-rate power, and in a favourable position of the planet. No one has observed the four last satellites except Herschel himself, or the two first, except himself and Sir J. Herschel, who has confirmed his father’s determination of their periods. See _Mem. Royal Astron. Soc._ vol. viii. He found that their orbits were nearly perpendicular to the plane of the ecliptic, and ascertained their retrograde motion, and some remarkable relations between their mean distances. It has a brilliant sound, but it is literally true as to the number of _known_ bodies composing the solar system, that Herschel left it exactly half as large again as he found it. To the Sun, Mercury, Venus, the Earth and Moon, Mars, Jupiter and four satellites, Saturn and five satellites, and Halley’s Comet, eighteen in all, he added nine, namely, two satellites to Saturn, Uranus and six satellites.