HERSCHEL, SIR JOHN FREDERICK WILLIAM, BART. (1792-1871), English astronomer, the only son of Sir William Herschel, was born at Slough, Bucks, on March 7, 1792. He was educated for a short while at Eton, then by a private tutor and then at St. John's, Cambridge, where he graduated as senior wrangler in 1813. During his undergraduateship he and two of his fellow-students who subsequently attained to very high eminence, Dean Peacock and Charles Babbage, entered into a compact that they would "do their best to leave the world wiser than they found it"--a compact loyally and successfully carried out by all three to the end. As a commencement of this laudable attempt we find Herschel associated with these two friends in the production of a work on the differential calculus, and on cog nate branches of mathematical science, which changed the style and aspect of mathematical learning in England, and brought it up to the level of the Continental methods. Two or three memoirs communicated to the Royal Society on new applications of mathematical analysis at once placed him in the front rank of the cultivators of this branch of knowledge. Of these his father had the gratification of introducing the first, but the others were presented in his own right as a fellow.
With the intention of being called to the bar, he entered his name at Lincoln's Inn on January 24, 1814 and placed himself under the guidance of an eminent special pleader. Probably this temporary choice of a profession was inspired by the extraor dinary success in legal pursuits which had attended the efforts of some noted Cambridge mathematicians. Be that as it may, an early acquaintance with D. Wollaston in London soon changed the direction of his studies.
He took up astronomy in 1816; and in 182o, assisted by his father, he completed for a reflecting telescope a mirror of 18 in. diameter and 20 ft. focal length. This, subsequently improved by his own hands, became the instrument which enabled him to effect the astronomical observations forming the chief basis of his fame. In 1821-23 we find him associated with Sir James South in the re-examination of his father's double stars. For this work he was presented in 1826 with the Astronomical Society's gold medal ; and with the Lalande medal of the French Institute in 1825; while the Royal Society had in 1821 bestowed upon him the Copley medal for his mathematical contributions to their Transactions. From 1824 to 1827 he was secretary to that society; and was in 1827 elected to the chair of the Astronomical Society, which office he also filled on two subsequent occasions. In the discharge of his duties to the last named society he delivered presi dential addresses and wrote obituary notices of deceased fellows, memorable for their combination of eloquence and wisdom. In 1831 the honour of knighthood was conferred on him by William IV., and two years later he again received the recognition of the Royal Society by the award of one of their medals for his memoir "On the Investigation of the Orbits of Revolving Double Stars." Before the end of the year 1833, Sir John Herschel had re examined all his father's double stars and nebulae, and had added many similar bodies to his own lists; thus accomplishing, under the conditions then prevailing, the full work of a lifetime. For it should be remembered that astronomers were not as yet pro vided with those valuable automatic contrivances which at pres ent materially abridge the labour and increase the accuracy of their determinations. John Herschel then determined to explore the southern, besides re-exploring northern skies. "I resolved," he said, "to attempt the completion of a survey of the whole surface of the heavens; and for this purpose to transport into the other hemisphere the same instrument which had been em ployed in this, so as to give a unity to the results of both por tions of the survey, and to render them comparable with each other." So, he and his family embarked for the Cape on Nov. 13, 1833; they arrived in Table bay on Jan. 15, 1834; and he began regular observations on March 4.
To give an adequate description of the vast mass of labour completed during the next four busy years of his life at Feld hausen would require the transcription of a considerable portion of the Cape Observations, published in 1847, nine years after the author's return to England, for the cogent reason, that as he said, "The whole of the observations, as well as the entire work of reducing, arranging and preparing them for the press, have been executed by myself." It contains catalogues and charts of southern nebulae and star-clusters, a catalogue of the relative positions and magnitudes of southern double stars and his obser vations on the varying and relative brightness of the stars. Herschel returned to his English home in 1838, and was welcomed with an enthusiastic greeting.
He was created a baronet by Queen Victoria at her coronation and, what to him was better than such reward, other men caught this contagion of his example and laboured in fields similar to his own, with an adequate portion of his success. He also paved the way for Sir George Stokes's discovery of fluorescence by his addition of the lavender rays to the spectrum and, by his an nouncement in 1845 of `epipolic dispersion' as exhibited by sul phate of quinine.
Herschel was a highly accomplished chemist. His discovery in 1819 of the solvent power of hyposulphite of soda on the other wise insoluble salts of silver was the prelude to its use as a fixing agent in photography; and he invented in 1839, independently of Fox Talbot, the process of photography on sensitized paper. He was the first person to apply the now well-known terms positive and negative to photographic images, and to imprint them upon glass prepared by the deposit of a sensitive film. Perhaps no man can become a truly great mathematician or philosopher if devoid of imaginative power. John Herschel possessed this endow ment to a large extent ; and he solaced his declining years with the translation of the Iliad into verse. But the main work of his later life was the collection of all his father's catalogues of nebulae and double stars combined with his own observations and those of other astronomers into a single volume. A com plete list of his contributions to learned societies will be found in the Royal Society's great catalogue, and from them may be gathered most of the records of his busy scientific life. Sir John Herschel met with an amount of public recognition which was unusual in the time of his illustrious father. He was a member of almost every important learned society in both hemispheres. For five years he held the same office of master of the mint, which a century before had belonged to Sir Isaac Newton.
In private life Sir John Herschel was a firm and most active friend; he had no jealousies; he avoided all scientific feuds; he gladly lent a helping hand to those who consulted him in scien tific difficulties; he was pleased by appreciation of his work with out being solicitous for applause. It was truthfully said of him that his life was `full of the serenity of a sage and the docile innocence of the child.' He died on May 11, 1871, and his remains are interred in Westminster abbey close to the grave of Sir Isaac Newton.
Besides the laborious Cape Observations, Sir John Herschel was the author of several books, one of which at least, On the Study of Natural Philosophy (183o), possesses an interest which no future advances of the subjects on which he wrote can obliter ate. In 1849 came the Outlines of Astronomy, a volume still replete with charm and instruction. His articles, "Meteorology," "Physical Geography," and "Telescope," contributed to the 8th edition of the Encyclopedia Britannica, were afterwards published separately. Less known are his volumes, Familiar Lectures on Scientific Subjects (1866) and Collected Addresses (1857), in which he is seen in his happiest and most instructive mood.
See also R. Grant, History of Physical Astronomy (1852) ; Lord Kelvin in the Report of the British Association (1871) ; T. Romney Robinson in the Proceedings of the Royal Society (vol. xx., 1872) ; M. C. Herschel, Memoir of Caroline Herschel (5876) ; J. H. Madler, Geschichte der Himmelskunde (vol. ii., 1873) ; E. Dunkin, Obituary Notices of Astronomers (1879) ; A. M. Clerke, The Herschels and Modern Astronomy (1895) and Popular History of Astronomy (4th ed., 1902) ; Sir I. Herschel: Papers (Collected and edited under direction of Royal Society and Royal Astronomical Society, 2 vol., 1912) ; H. Macpherson, Herschel (1919) .
Reductions, based on standard magnitudes of 919 southern stars, observed by Herschel in sequences of relative brightness, were pub lished by W. Doberck in the Astrophysical Journal (vol. xi., 1900) and Annals of the Astronomical Observatory of Harvard College (vol. xli., 1902) .