He moved to Datchet in 1782, and set up his twenty-foot telescope. In 1783 he had made three reviews of the heavens. In 1784 he made a fourth review with his twenty-foot telescope. Caroline says: "My brother began his sweeps when the instrument was yet in a very unfinished state, and my feelings were not very comfortable when every moment I was alarmed by a crash or a fall, knowing him to be elevated fifteen feet or more on a temporary crossbeam, instead of a safe gallery. The ladders had not even their braces at the bottom; and one night, in a very high wind, he had hardly touched the ground before the whole apparatus came down.... I could give a pretty long list of accidents which were near proving fatal to my brother as well as myself."
A gentleman who visited him at Datchet wrote: "The thermometer in the garden stood at 13° Fahrenheit; but in spite of this, Herschel observes the whole night through, except that he stops every three or four hours and goes in the room for a few moments. For some years Herschel has observed the heavens every hour when the weather is clear, and this always in the open air, because he says that the telescope only performs well when it is at the same temperature as the air. He protects himself against the weather by putting on more clothing. He has an excellent constitution, and thinks about nothing else in the world but the celestial bodies."
But, occupied as Herschel was about "celestial bodies," he yet found time to think about earthly things, for we find him at forty-five, May 8, 1783, marrying Mary, the wealthy widow of John Pitt, Esq., a lady of much intelligence and amiability.
The sad feature of the new relationship was the misery it brought to Caroline. Her whole life had centred in William. For eleven years she had devoted every moment, every wish, every thought to him. She had watched all night among the stars with him, month after month, and year after year, in cold and in heat, and superintended his home by day. His every desire was her law. She loved no other, and he was her all. Perhaps she ought to have known that another might come into his life, but she trusted blindly, and did not question the future.
When the wife came into the home, Caroline went out of it forever. For more than twenty years she lived in lodgings, always "cheerless and solitary," her only happiness found in coming day by day to help her brother in his great work. Sometimes, when the wife was absent, Caroline came back for a few days and lived over the old unalloyed life, and then went back to her lonely lodgings.
For ten years following this marriage, she probably told her heart-aches in her journal; but before her death she destroyed the record of these years, that the feelings of those who were alive might not be pained. In later days she became more reconciled to Lady Herschel, as "a dear sister, for as such I now know you," and idolized their only son, the renowned Sir John Herschel, born nine years after their marriage.
In 1785, Herschel began to construct his great forty-foot telescope, and the next year removed to Slough, not far from Windsor. "In the whole of the apparatus," he said, "none but common workmen were employed, for I made drawings of every part of it, by which it was easy to execute the work, as I constantly inspected and directed every person's labor; though sometimes there were not less than forty different workmen employed at the same time. While the stand of the telescope was preparing, I also began the construction of the great mirror, of which I inspected the casting, grinding, and polishing; and the work was in this manner carried on with no other interruption than that occasioned by the removal of all the apparatus and materials from where I then lived, to my present situation at Slough." He had his first view through the telescope February 19, 1787. George III. gave twenty thousand dollars for the building of this instrument, and one thousand dollars yearly for its maintenance.
A half-century afterwards, the woodwork having become decayed, it was taken down, the great tube laid horizontally, and, after Sir John Herschel and his family had passed through it, a poem written by Sir John having been read, it was sealed January 1, 1840, and placed on piers.
With this great telescope, Herschel discovered two satellites of Saturn, Mimas and Enceladus; one on August 27, 1789, and the other on September 17 of the same year. Two years before this, January 11, 1787, he discovered two satellites of Uranus, Oberon and Titania. Sixty years afterwards, Mr. Lassell, of England, discovered the remaining two satellites of Uranus, called Ariel and Umbriel.
From this time his work went forward grandly. He had already completed more than two hundred seven-foot, one hundred and fifty ten-foot, and eighty twenty-foot mirrors. For many of the telescopes sent abroad he made no stands, but provided the drawings. He wrote much about Saturn and its rings, and showed that its most distant satellite, Japetus, turns once on its axis in each revolution about its primary, as our moon does about the earth.