Being settled at Bath Miss Herschel entered with ardour into her brother's career as musician and his studies as astronomer. He toiled hard in his profession for the purpose of gaining a livelihood, at the same time reading and working for the object nearest his heart. In both his pursuits his sister became his ready and laborious helper—his constant and sympathising companion. For this purpose she acquired a considerable proficiency in music, and for many years assisted her brother, not only by copying musical scores for large orchestras, but also in taking part in lessons and rehearsals, and herself singing in oratorios conducted by him.
The industry of both brother and sister at this period of their joint labours seems, indeed, to have been almost without parallel. While, their days were given to musical work to such an extent as would have sufficed for an ordinary occupation—and that a busy one—their nights were devoted to the heavens, and to the manufacture of telescopes and telescopic appliances on a scale hitherto unknown.
William Herschel's fame as an astronomer, inventor, and discoverer having become established, in 1782 he gave up his attention to music, in order to devote himself entirely to astronomical research, and was appointed Royal Astronomer. In this year he removed to Datchet, and, a few years after, to Slough. Absorbing as was their pursuit, it was carried on at an enormous self-sacrifice and hardship, and was not by any means free from danger. Miss Herschel writes in her diary: "That my fears of danger and accidents were not wholly imaginary I had an unlucky proof on the night of the 31st December. The evening had been cloudy, but about ten o'clock a few stars became visible, and in the greatest hurry all was got ready for observing. My brother, at the front of the telescope, directed me to make some alteration in the lateral motion, which was done by machinery, on which the point of support of the tube and mirror rested. At each end of the machine or trough was an iron hook, such as butchers use for hanging their joints upon, and having to run in the dark on ground covered a foot deep with melting snow, I fell on one of these hooks, which entered my right leg above the knee. My brother's call, 'Make haste!' I could only answer by a pitiful cry, 'I am hooked!' He and the workman were instantly with me, but they could not lift me without leaving nearly two ounces of my flesh behind. The workman's wife was called, but I was afraid to do anything, and I was obliged to be my own surgeon by applying aquabusade and tying a kerchief about it for some days, till Dr. Lind, hearing of my accident, brought me ointment and lint, and told me how to use them. At the end of six weeks I began to have some fears about my poor limb, and asked again for Dr. Lind's opinion. He said if a soldier had met with such a hurt, he would have been entitled to six weeks' nursing in a hospital. I had, however, the comfort to know that my brother was no loser through the accident, for the remainder of the night was cloudy, and several nights afterwards afforded only a few short intervals favourable for sweeping, and until the 16th of January there was no necessity for my exposing myself for a whole night to the severity of the season."
"It would be impossible for me," she also writes, "if it were required, to give a regular account of all that passed around me in the lapse of the two following years, for they were spent in a perfect chaos of business. The garden and workrooms were swarming with labourers and workmen, smiths and carpenters going to and fro between the forge and the forty-foot machinery, and I ought not to forget that there is not one screw-bolt about the whole apparatus but what was fixed under the immediate eye of my brother. I have seen him lie stretched many an hour, in a burning sun, across the top beam whilst the iron-work for the various motions was being fixed. At one time no less than twenty-four men (twelve and twelve relieving each other) kept polishing day and night; my brother, of course, never leaving them all the while, taking his food without allowing himself time to sit down to table."
Miss Herschel's services to her brother, as well as to science as an independent discoverer, were recognised, when, in 1787, she was appointed assistant to her brother at a salary of £50 per annum.
In the following year, after she had enjoyed the closest companionship and identity with her brother for sixteen years, Mr. Herschel's marriage brought a considerable change in the life of the sister. Her devotion to his interests and pursuits became no less, but the supreme place by his side was gone.
Although Miss Herschel seems to have felt keenly the separation from her brother in domestic life, her zeal in the objects to which he had devoted himself never waned. Having entered upon them from a sense of grateful love, she became passionately attached to the work. Although living apart from him, she continued to the end of his life to be his indefatigable assistant, as well as an independent observer of the heavens. In this character she came into contact from time to time not only with members of the Royal families of England and Germany, but with the leading astronomers of the age, who acknowledged in her an honoured comrade. A celebrated astronomer, referring to one of the many comets she was the first to discover, says in a letter to her: "I am more pleased than you can well conceive that you have made this discovery. You have immortalised your name, and you deserve such a reward from the Being who has ordered all these things to move as we find them, for your assiduity in the business of an astronomer, and for your love for so celebrated and deserving a brother."
As all the world knows, Mr. Herschel (then Sir William) was long recognised as the most celebrated astronomer of the time. And while none rejoiced more in his proud position than his sister, he was ever ready to acknowledge his indebtedness to her, as his companion in his herculean toils. The marvel is that the constant and exhausting strain of many long years did not prematurely wear out the strength and brain of both. They, however, grew old together, and alike lived to a remarkable old age. Sir William, who was twelve years the senior, was the first whose splendid constitution gave way. He died in the year 1822.
After her brother's death Miss Herschel, then in her 72nd year, seems to have felt unsettled in England and unable to face the scenes and life she had for so many years shared with her brother. Notwithstanding her attachment to her sister-in-law and her favourite nephew (who in some measure took the place in her affections of her beloved brother), she decided to return to Hanover. An absence of half a century from any place makes a wonderful difference in its associations, and Miss Herschel lived to regret her return to her native city, where, however, she resided for the remainder of her life. If her work by her brother's side was done, her long evening of life was, nevertheless, one of grateful recollection and laborious industry. Among other tasks, she undertook and completed a "Reduction and Arrangement, in the form of a catalogue in zones, of all the Star Clusters and Nebulæ observed by Sir W. Herschel in his Sweeps." For this she was, at a meeting of the Royal Astronomical Society in 1828, awarded the gold medal of the Society. The remarks made by Mr. South, the Vice-President, on that occasion, perhaps best summarise her great achievements. He said: "The labours of Miss Herschel are so intimately connected with, and are generally so dependent upon, those of her illustrious brother, that an investigation of the latter is absolutely necessary ere we can form the most remote idea of the extent of the former. But when it is considered that Sir W. Herschel's contributions to astronomical science occupy sixty-seven memoirs, communicated from time to time to the Royal Society, and embrace a period of forty years, it will not be expected that I should enter into their discussion. To the Philosophical Transactions I must refer you, and shall content myself with the hasty mention of some of her more immediate claims to the distinction now conferred. To deliver an eulogy, however deserved, upon his memory is not the purpose for which I am placed here…. But when we have thus enumerated the results obtained in the course of sweeps with this instrument, and taken into consideration the extent and variety of the other observations which were at the same time in progress, a most important part yet remains untold. Who participated in his toils? Who braved with him the inclemency of the weather? Who shared his privations? A female. Who was she? His sister. Miss Herschel it was who by night acted as his amanuensis; she it was whose pen conveyed to paper his observations as they issued from his lips; she it was who noted the night ascensions and polar distances of the objects observed; she it was who, having passed the night near the instrument, took the rough manuscripts to her cottage at the dawn of day, and produced a fair copy of the night's work on the following morning; she it was who planned the labour of each succeeding night; she it was who reduced every observation, made every calculation; she it was who arranged everything in systematic order; and she it was who helped him to obtain his imperishable name.
"But her claims to our gratitude do not end here. As an original observer she demands, and I am sure she has, our unfeigned thanks. Occasionally, her immediate attendance during the observations could be dispensed with. Did she pass the night in repose? No such thing. Wherever her brother was, there you were sure to find her. A sweeper planted on the lawn became her object of amusement; but her amusements were of the higher order, and to them we stand indebted for the discovery of the comet of 1786, of the comet of 1788, of the comet of 1791, of the comet of 1793, of the comet of 1795, since rendered familiar to us by the remarkable discovery of Encke. Many also of the nebulæ contained in Sir W. Herschel's catalogues were detected by her during these hours of enjoyment. Indeed, in looking at the joint labours of these extraordinary personages, we scarcely know whether most to admire the intellectual power of the brother, or the unconquerable industry of the sister."