In March 1821, the younger Herschel, in conjunction with Sir James South, undertook a series of observations on the distances and positions of three hundred and eighty double and triple stars, by means of two splendid achromatic telescopes of five and seven focal length. These were continued during 1822 and 1823, and have proved of great service to astronomers.
Having pursued with much zeal the study of optics, and experimented largely and carefully on the double refraction and polarization of light, he compiled a treatise on the subject for the "Encyclopaedia Metropolitana" It has been translated into French by M. Quetelet; and both foreign and English men of science have been accustomed to regard it as indicating a new point of departure in the important branch of science to which it is devoted.
Astronomy, however, became for him, as for his father, the great pursuit of his laborious life; and having constructed telescopes of singular magnitude and power, he entered upon a study of the Sidereal World. In 1825 he commenced a careful re-examination of the numerous nebulae and starry clusters which had been discovered by his father, and described in the "Philosophical Transactions," fixing their positions and investigating their aspects. He devoted eight years to this _magnum opus_, completing it in 1832. The catalogue which he then contributed to the "Philosophical Transactions" includes 2306 nebulae and star-clusters, of which 525 were discovered by himself. While engaged in this difficult task, Herschel discovered between three and four thousand double stars, which he described in the Memoirs of the Astronomical Society. His observations were made with an excellent Newtonian telescope, twenty feet in focal length, and eighteen and a half inches in aperture; and having obtained, to use his own expression, "a sufficient mastery over the instrument," the idea occurred to him of making it available for a survey of the southern heavens. Accordingly, he left England on the 13th of November 1833, and arrived at Cape Town on the 16th of January 1834. Five days later he wrote to his aunt as follows:--
"Here we are safely lauded and comfortably housed at the far end of Africa; and having secured the landing and final storage of all the telescopes and other matters, as far as I can see, without the slightest injury, I lose no time in reporting to you our good success _so far_. M----[1] and the children are, thank God, quite well; though, for fear you should think her too good a sailor, I ought to add that she continued sea-sick, at intervals, during the whole passage. We were nine weeks and two days at sea, during which period we experienced only one day of contrary wind. We had a brisk breeze 'right aft' all the way from the Bay of Biscay (which we never entered) to the 'calm latitudes;' that is to say, to the space about five or six degrees broad near the equator, where the trade-winds cease, and where it is no unusual thing for a ship to lie becalmed for a month or six weeks, frying under a vertical sun. Such, however, was not our fate. We were detained only three or four days by the calms usual in that zone, but never _quite_ still, or driven out of our course; and immediately on crossing 'the line' got a good breeze (the south-east trade-wind), which carried us round Trinidad; then exchanged it for a north-west wind, which, with the exception of one day's squall from the south-east, carried us straight into Table Bay. On the night of the 14th we were told to prepare to see the Table Mountain. Next morning (_N.B._, we had not seen land before since leaving England), at dawn, the welcome word land' was heard; and there stood this magnificent hill, with all its attendant mountain-range down to the farthest point of South Africa, full in view, with a clear blue ghost-like outline; and that night we cast anchor within the Bay. Next morning early we landed, under escort of Dr. Stewart, M----'s brother, and you may imagine the meeting. We took up our quarters at a most comfortable lodging-house (Miss Robe's), and I proceeded, without loss of time, to unship the instruments. This was no trifling operation, as they filled (with the rest of our luggage) fifteen large boats; and, owing to the difficulty of getting them up from the hold of the ship, required several days to complete the landing. During the whole time (and indeed up to this moment) not a single south-east gale, the summer torment of this harbour, has occurred. This is a thing almost unheard of here, and has indeed been most fortunate, since otherwise it is not at all unlikely that some of the boats, laden as they were to the water's edge, might have been lost, and the whole business crippled.