John F.W. Herschel was the only child of the famous astronomer Frederick William Herschel, discoverer of the planet Uranus. After a private education and further schooling at Eton he entered St John's College, Cambridge, where he stood out as a result of his extraordinary intellectual ability and obtained the highest marks in mathematics in his final examination (i.e., became "Senior Wrangler") in 1813. Returning to Slough he continued his studies in mathematics and the natural sciences on his own and started publishing a variety of scientific papers which represent a remarkable range of scientific interests and accomplishments. In recognition of his outstanding talent he was elected a fellow of the Royal Society of London for his mathematical work at the age of 21.
From about 1816 he began to take a serious interest in astronomy and in collaboration with James South re-observed the many double stars discovered during his father's survey of the northern sky from 1783-1803. With his father he cast, ground and polished a new 460 mm speculum mirror with a focal length of some 6 m and by 1820 had used it to construct one of the most powerful telescopes in use at the time. During the years 1825-1833 John used this instrument to repeat his father's survey of the northern hemisphere, confirming and adding to the nebulae and double stars. This work made him as prominent in astronomical circles as his father (who died in 1822) had been. He served as secretary of the Royal Society of London from 1824 to 1827. In 1826 he was awarded the Gold Medal of the Royal Astronomical Society, and the next year was elected its president. He travelled widely in Europe, spoke several languages, and corresponded with numerous scientists. In 1829 he married Margaret B. Stewart and the two produced a large family. In 1831 King William IV honoured him as a Knight of the Hanoverian Order (KH).
In 1833 he decided to extend his comprehensive astronomical survey of double stars and nebulae to the southern hemisphere, using his own telescope. He chose the Cape of Good Hope as a base because of its relative accessibility and the presence there of the Royal Observatory, from which he could expect professional assistance. This was a private venture and he therefore held no official position at the Cape. The family arrived in Cape Town in January 1834 and bought a country estate which Herschell called Feldhausen, in the present suburb of Claremont. Within weeks he had erected his main telescope, as well as an equatorially mounted 127 mm refractor. He spent most of his time systematically searching the sky on every clear night and processing his observations during the day. The search was performed in zones of declination three degrees wide, with a view to recording all the planetary and extragalactic nebulae, star clusters, and double stars.
In addition to his sky survey Hershel made a study of various other astronomical phenomena. His chart of the Argo nebula gave the places of 1200 stars. He catalogued over 1100 objects in the Magellanic Clouds. He studied the structure of the Milky Way on the basis of his star counts in different areas of the sky. He designed an instrument, the astrometer, with which he determined the brightness of nearly 500 stars by comparing them with the brightness of a reduced image of the full moon, thus initiating objective stellar photometry. Late in 1836 he made the first satisfactory measurement of the intensity of direct solar radiation, using an instrument of his own design which he called an actinometer, and even did some experiments with solar cooking. He observed Saturn's satelites, and numerous sunspots. Between October 1835 and May 1836 he observed Halley's comet.
Though working on his own, he soon formed a close friendship with Thomas Maclear*, HM Astronomer at the Royal Observatory, Cape of Good Hope, who had arrived only days befor him. The two communicated frequently by letter and collaborated on many occassions. Herschel supported and advised Maclear in matters such as instrumental problems, initiating tide measurements and measuring a base line for survey work; on the other hand Maclear often supplied him with technical information that he required. After his return to England Herschel used his influence to ensure the expansion of the Cape Observatory over the next ten years.
He found time also for pursuits outside astronomy. From September 1834 he served as president of the South African Literary and Scientific Institution for several years. He was a member also of the institution's meteorological committee and compiled Instructions for making and registering meteorological observations in southern Africa, and other countries in the south seas, and also at sea, a pamphlet published both in Cape Town (1834) and in London (1835). In June 1834 he served on the committee that drew up instructions for the expedition into the interior led by Dr Andrew Smith*. And upon the expedition's return he chaired a general meeting of the Association for Exploring Central Africa in March 1836 to hear Dr Smith's report. He was re-elected as a member of the association's committee of management at that same meeting. Using a camera lucida to project images of Cape scenes on paper, he made more than 100 accurate pencil sketches of landscapes near Cape Town, Paarl and Stellenbosch, which are of historical interest. He also made sketches of local wild flowers, some of which his wife then painted; eighteen of them ended up in the South African Library. This interest led to a friendship with William Harvey*, who arrived at the Cape in September 1835. The orchid genus Herschelia was named in his honour.
Of particular significance was Herschel's interest in education and the key role he believed it could play in the social improvement of people in the lower social classes. With John Bell, secretary to the government, and John Fairbairn, newspaper editor and parliamentarian, he drew up recommendations on educational reform at the request of the Governor. His memorandum to the Governor, dated February 1838, appears to have carried much weight in the subsequent revision of education at the Cape. As a protagonist for a system of state education he recommended an undenominational system of public shools, and conditions of service for teachers that would ensure a more stable and efficient staff. He also advocated the adaptation of the syllabus to the needs of the colony, for example, by giving more attention to practical education and less to the study of classical languages. He supported the appointment of a full-time superintendent-general of education and had the satisfaction of seeing his friend, James Rose Innes* appointed to this new position in 1839. After his return to England he assisted the secretary for the colonies, Lord Glenelg, in selecting suitable teachers for the Cape.
Having accomplished his main objective, Herschel left the Cape for England in March 1838, his bagage including some live ground orchids. Members of the South African Literary and Scientific Institution took leave of him at a ceremony on 10 March, at which he was presented with a gold medal in recognition of his services to the institution. The high regard in which he was held at the Cape was shown soon after his departure by a successful movement to raise funds in order to erect a monument on the site where his main telescope had stood. A stone obelisk was erected on the exact spot in 1841, with an inscription recognising his contributions to science and education at the Cape. In further recognition of his services a new magisterial district in the eastern Cape was named after him in 1873. At present the town Herschel still caries his name.
Much of his time during the next few years was spent in working up his Cape observations. The work was finally published in London in 1847 as Results of astronomical observations made during the years 1834, 5, 6, 7, 8, at the Cape of Good Hope; being the completion of a telescopic survey of the whole surface of the visible heavens commenced in 1825. Its most important feature is a catalogue of 1707 nebulae and star clusters, many of them not seen before, and many observed more than once. A list of over 1000 pairs of double stars was next in importance, as little further work on double stars was done in South Africa until the end of the century. Also included are his surveys of the Magellanic clouds; estimates of the relative magnitudes of the principal southern stars; and more. Because of the high quality of his telescope, even compared to those available to professional astronomers at the time, his work was of major international significance. Thus his discoveries formed the main basis for the southern part of Dreyer's New general catalogue of nebulae and clusters (1888 and supplements), for decades a standard work of reference.
Meanwhile he had made some important chemical discoveries relating to photography and was the first to apply the terms "negative" and "positive" to photographic images. Among the honours he received were a baronetcy at the coronation of Queen Victoria in 1838, and an honorary doctorate from Oxford University in 1839. He served as president of the British Association for the Advancement of Science in 1845 and was a member of numerous scientific societies. From 1850 he held an appointment as master of the mint, but resigned in 1855 because of ill health. As he became older he preferred a quiet life in Kent, where he had settled in 1840. However, he continued to write on a variety of scientific subjects in mathematics, astronomy and solar physics, producing a total of more than 150 publications. For relaxation he started translating poetry, including works of Schiller, Homer's Iliad (1866), and the first part of Dante's Inferno (1868).
In spite of his prodigeous talent Herschel was a modest man, with a ready friendliness and charm, always ready to help younger scientists.