By the beginning of the nineteenth century, Herschel's extraordinary activity began somewhat to abate. Not that his mind had become less acute, or his interest in astronomy less marked. But it was physically impossible for any man to maintain the standard of activity which had been his for thirty years. He had now completed his comprehensive surveys of the heavens, and accordingly his studies became more and more specialised. The Sun and Saturn, the newly-discovered asteroids, and several comets, and last but not least, his experiments on light, occupied more and more of his time. But he now allowed himself intervals of rest between his investigations; he found more time for music, always one of his chief delights, and in addition he gave himself more opportunities for holidays. In July, 1801, accompanied by his wife and his son John, then a lad of nine, he visited Paris. Here he made the acquaintance of Laplace, with whom he had many important conversations, and was introduced to Napoleon, then First Consul. At 7 o'clock on 8th August the Minister of the Interior conducted Herschel, along with Laplace and Count Rumford, to Napoleon's palace at Malmaison. Herschel records in his journal that the First Consul, who met the party in the garden, politely put some questions on astronomical subjects. It was reported at the time that Napoleon's astronomical knowledge had astonished Herschel. Such was apparently not the case. Twelve years later, in conversation with the poet Campbell, Herschel contradicted this report. "No," he said, "the First Consul did surprise me by his quickness and versatility on all subjects, but in science he seemed to know little more than any well-educated gentleman, and of astronomy much less, for instance, than our own King. His general air was something like affecting to know more than he did know. I remarked his hypocrisy in concluding the conversation on astronomy by observing how all these glorious views gave proofs of an Almighty wisdom." With his keen, quick intuition, Herschel perceived the incongruity of the man of overweening pride and vainglory taking the Divine name upon his lips and simulating a mock piety. The chief result of Herschel's visit to Paris was his election in 1802 as one of the eight foreign associates of the French Institute.
Summer holidays were usually spent at Dawlish, with his lifelong friend, Sir William Watson, and at Tunbridge Wells, Brighton, and Ramsgate. Nevertheless, his health began to fail by gradual stages. His duties as King's Astronomer, nominal so far as scientific work was concerned, were somewhat exacting, and as he grew older he was less able to spend several hours in an evening explaining the heavenly bodies to groups of royal and aristocratic visitors. In October, 1806, the appearance of a bright comet attracted a large number of visitors to Slough. On the evening of the 4th, Caroline Herschel narrates, "two parties from the Castle came to see the comet, and during the whole month my brother had not an evening to himself. As he was then in the midst of polishing the 40-foot mirror, rest became absolutely necessary after a day spent in that most laborious work; and it has ever been my opinion that on the 14th of October his nerves received a shock from which he never got the better afterwards; for on that day (in particular) he had hardly dismissed his troop of men, when visitors assembled, and from the time it was dark till past midnight, he was on the grass-plot surrounded by between fifty and sixty persons without having time for putting on proper clothing or for the least nourishment passing his lips. Among the company, I remember, were the Duke of Sussex, Prince Galitzin, Lord Darnley, a number of officers, Admiral Boston, and some ladies." This tremendous strain told on Herschel, and the result was that in the spring he became dangerously ill. Caroline tells us that on 26th February, 1807, he was so ill that even she was not allowed to see him, and until 8th March his recovery was despaired of. However, he rallied and recovered, but his health was permanently impaired. But his mind was as clear as ever, and some of his most remarkable papers were written after his illness—that of 1811, in which he developed the nebular hypothesis, and those of 1814, 1817, and 1818, on the construction of the heavens. Physically, however, he was unequal to the task of attending to his great telescopes. On 30th September, 1815, his sister recorded that "his strength is now, and has for the last two or three years, not been equal to the labour required for polishing 40-foot mirrors. And it was only by little excursions and absences from his workrooms he for some time recovered from the effects of over-exertion". During these last years, Caroline's diaries make sad reading, for they record little more than the gradual decay of health and vigour in the "best and dearest of brothers". His inability to repolish his great mirror was a bitter disappointment to him, and he became depressed and sorrowful. She afterwards recorded that "when all hopes for the return of vigour and strength necessary for resuming the unfinished task was gone, all cheerfulness and spirits had also forsaken him. . . . Every nerve of the dear man had been unstrung by over-exertion," so that "a further attempt at leaving the work complete became impossible". In 1819, before his departure for a holiday at Bath, "the last moments before he stepped into the carriage were spent in walking through his library and workrooms, pointing with anxious looks to every shelf and drawer, desiring me to examine all and to make memorandums of them as well as I could. He was hardly able to support himself, and his spirits were so low that I found difficulty in commanding my voice so far as to give him the assurance he should find on his return that my time had not been misspent."
But Herschel was not always, even in extreme old age, depressed and gloomy. A German visitor to Slough, in, thus described the great astronomer: "While we were standing by the great telescope, which we more admired than comprehended, its master appeared, a cheerful old man aged eighty-one. How unassumingly did he make his communications! How lightly did he ascend the steps to the gallery! With what calm pleasure did he seem to enjoy the success of his efforts in life. All accounts from his native country seemed to please him, although the German language had become somewhat less familiar to his ear. After a short comversation, we took our leave, charged with friendly greetings to all beyond the sea who might still remember him."
On 5th April, 1816, he received the first mark of recognition from the British Government the third class of the Hanoverian Guelphic Order. In the following month he was created a Knight of the same Order. In 1920, when the Astronomical Society of London—now the Royal Astronomical Society—was founded, Herschel was elected as the first President. His health did not permit him to attend the meetings, but he communicated his last paper—on double stars—to its "Memoirs" in 1821.
Caroline Herschel's Memoirs record the agony of soul through which she passed as her brother became weaker and weaker. In 1819 he sent a note across to her lodgings, notifying her of the appearance of a "great comet". She preserved this, with the comment, "I keep this as a relic! Every line now traced by the hand of my dear brother becomes a treasure to me." Her own health was seriously impaired, and she sometimes expected to pass away before him. But a different fate was in store for her. The hot summer of 1822 told heavily upon Herschel, but apparently no imminent danger was anticipated, for his son John, then a graduate of Cambridge, started on the 8th of August for a tour on the continent. On the 15th, "after half-an-hour's vain attempt to support himself," the faithful chronicler relates, "my brother was obliged to consent to be put to bed, leaving no hope ever to see him rise again". Ten days later, 25th August, 1822, he passed away, within three months of completing his eighty-fourth year. He was buried in the church of St. Lawrence at Upton, near Slough. The long Latin inscription claims for him that "coelorum perrupit claustra"—"He broke through the barriers of the skies".
The end was not unexpected, but to his devoted sister—the companion and co-worker of a lifetime—the loss was irreparable. After his death, she tells us, there was but one comfort left her, "that of retiring to the chamber of death, there to ruminate without interruption on my isolated situation. Of this last solace I was robbed on the 7th September, when the dear remains were consigned to the grave." Her own life, she felt, was finished; she had no further interests. And so she decided to leave England and return to Hanover and the scenes of her girlhood, there to spend the evening of her days. There was another reason for her decision. Only one of her brothers now survived; Alexander had died a year before William, and sentimental reasons impelled her to make her home with Dieterich. In the midst of her deep sorrow she had made over to Dieterich—shiftless and impecunious as ever—her little capital sum of £500; in her own words, "I gave myself, with all I was worth, up to my brother Dieterich and his family". No sooner had she arrived in Hanover, in October, 1822, than she realised her great mistake. She found herself among uncongenial company. "In the last hope of finding in Dieterich a brother to whom I might communicate all my thoughts of past, present and future," she wrote to her nephew in 1827, "I saw myself disappointed the very first day of our travelling on land. For let me touch on what topic I would, he maintained the contrary, which I soon saw was done merely because he would allow no one else to know anything but himself." The old lady could find no congeniality in the company of a soured, fractious old man, and among people who could not enter in the slightest into her scientific interests. "From the moment I set foot on German ground," she said, "I found I was alone." She described herself as leading a "solitary and useless" life "not finding Hanover or anyone in it like what I left when the best of brothers took me with him to England in August, 1772".
Solitary her life was, so far as congeniality went, but by no means useless. Soon after her settlement in Hanover, she formed a catalogue of all her brother's nebulæ and clusters, arranged in zones. In April, 1825, she forwarded this to her nephew, John Herschel, then engaged in his review of these objects. This catalogue was described by Sir David Brewster, as "an extraordinary monument of the unextinguished ardour of a lady of seventy-five in the cause of abstract science". It was rewarded by the presentation to her of the Gold Medal of the Royal Astronomical Society, in 1828 an honour by which, with characteristic modesty, she said she was "more shocked than gratified ". In 1835 she was elected an honorary member of the Royal Astronomical Society, membership of which was not then open to women; and in 1838 the Royal Irish Academy enrolled her name among its members. These honours sat very lightly on her. "Saying too much of what I have done," she said in 1826, "is saying too little of him, for he did all. I was a mere tool which he had the trouble of sharpening and adapting for the purpose he wanted it, for lack of a better."
As the years passed, and her vitality ebbed, all her affection became concentrated in the one being whom she felt understood her and with whom she had community of interests—her nephew John. She followed his career with pride, as a worthy sequel to that of his father; his visits to Hanover were to her oases in the desert of her experience; he and his wife were her principal correspondents. She wrote her last letter to her nephew, December 3rd, 1846: she was then ninety-six, and had survived her brother for twenty-four years. During 1847, tenderly nursed by her niece, Mrs. Knipping, the only one of Dieterich's family who really sought to care for her, she slowly sank, and on 9th January, 1848, she passed away—within two months of completing her ninety-eighth year. She was buried beside her parents in the churchyard of the Gartengemeinde at Hanover. Her epitaph, composed by herself, records that "the eyes of her who is glorified were here below turned to the starry heavens. Her own discoveries of comets and her participation in the immortal labours of her brother, William Herschel, bear witness of this to future ages."
Future ages are not likely to forget Caroline Herschel. Her own original work was, it is true, comparatively small; but her self-sacrificing devotion to her brother, her performance of the countless small petty drudgeries of his scientific life, her tender care for his welfare and comfort, give her an honourable place among women of lasting fame. As long as William Herschel is remembered, his sister Caroline will not be forgotten. As has been truly said, " she shines and will continue to shine by the reflected light that she loved".
The career of the younger Herschel was, in many respects, the sequel to, and completion of, that of his father. John Frederick William Herschel, born "within the shadow of the great telescope," on 7th March, 1792, was educated at Hitcham, Eton and Cambridge. At the University he was a distinguished student, particularly in mathematics, and graduated as Senior Wrangler in 1813. He was in no hurry to choose his life-work, nor was there any need. Since his father's marriage, the family had been in easy, if not affluent circumstances. His father had destined him for the Church, but he preferred the study of law. He never practised at the Bar, however, and at last decided for a scientific career. In 1816 he informed a correspondent that he was "going under his father's directions to take up star-gazing". He had at first no definite inclination in that direction, but he decided to complete his father's work. During his father's lifetime, he re-examined many binary stars, in conjunction with Sir James South, and for these observations he received the Lalande Prize of the French Academy and the Gold Medal of the Astronomical Society.
In 1828 he succeeded in rediscovering the genuine satellites of Uranus, and in the same year commenced his review of his father's nebulæ and star-clusters. The completion of this work was signalised by knighthood. Then, in 1833, after his mother's death, he decided to extend his father's surveys to the southern hemisphere. He transported his great telescope to Cape Colony, and at Feldhausen, near Cape Town, from 1834 to 1838, he swept the southern skies, cataloguing double stars, clusters and nebulæ; and after nine years of arduous labour, the monumental volume known as "Results of Astronomical Observations at the Cape of Good Hope" was published. Meanwhile, honours were showered thick and fast upon the astronomer; he was created a baronet after his return from South Africa, many degrees were conferred upon him, and learned societies vied with each other in enrolling his name among their members. On his return to England, he did not re-erect his telescopes; and his career as an observer was closed. During the latter part of his life he was regarded as the greatest English astronomer of his day, and on his death on 5th May, 1871, at his home at Collingwood in Kent, he was interred in Westminister Abbey, close to the grave of Newton.
Sir John Herschel was survived by three sons, of whom only the eldest, Sir William James Herschel (1832-1917), did not inherit the family taste for astronomy. The second son, Alexander Stewart Herschel (1836-1907), Professor at Durham College, devoted considerable attention to meteoric astronomy, while the younger son, Colonel John Herschel, in his earlier days undertook a spectroscopic examination of southern nebulæ. The names of a grand-daughter and of a great grandson of Sir William Herschel—Miss Francesca Herschel and Rev. J. C. W. Herschel—appear on the roll of Fellows of the Royal Astronomical Society, to testify that the family is still distinguished by love of the oldest of the sciences.