As an optician, Herschel deserves equal notice for the wonderful improvements which he effected in the dimensions and magnifying power of telescopes, and by the skill with which he applied them to celestial observations. The reflecting telescope was the one to the improvement of which he so successfully devoted himself; and the real secret of his success in this, was his astonishing perseverance; his determination being to obtain telescopes of twenty feet focal length or more, and of a perfection equal or superior to the small ones then in use. He himself relates, that whilst at Bath he had constructed 200 specula of seven feet focus, 150 of ten feet, and about 80 of twenty feet; a proof of extraordinary resolution in a man of limited means, and at that time engaged in a laborious profession. Herschel at last succeeded in constructing his enormous telescope of forty feet focal length, which he erected in the grounds of his house at Slough. This instrument was begun in 1785, and finally completed on August 28th, 1789, on which day Herschel discovered with it the sixth satellite of Saturn; the diameter of the tube was 4 feet 10 inches, the speculum having a useful area of 4 feet: the total cost was 4000_l._, which was entirely defrayed by the liberality of George the Third. After the award of the king's pension, Sir William Herschel fixed his residence at Slough, near Windsor, his family consisting at first of one of his brothers, and his sister, Miss Caroline Herschel, who was his coadjutor and assistant in his computations and reductions, and was also actively employed in astronomical observation, being the discoverer of more than one comet. Herschel married a widow lady, Mrs. Mary Pitt, and left one son, the present Sir John, whose name has long been known to the public as one of the most active and successful adherents of science that our day has produced. Dr. J. D. Forbes thus sums up the philosophical character of Sir William Herschel:-- "He united, in a remarkable degree, the resolute industry which distinguishes the Germans, with the ardour and constancy which has been thought characteristic of the Anglo-Saxon. From his native country he brought with him the boldness of speculation which has long distinguished it, and it is probable that he had also a vigorous and even poetical imagination. Yet he was ever impatient until he had brought his conjectures to the test of experiment, and observation of the most uncompromising kind. He delighted to give his data a numerical character, and where this was (by their nature) impossible, he confirmed his descriptions by reiterated observation, in different states of weather, with different telescopes, apertures, and magnifying powers; and with praiseworthy fidelity he enabled his readers to form their own judgment of the character of his results, by copious and literal transcripts from his journals."