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 mathematical instruction he there received exercised a material influence on the whole complexion of his scientific career. In due time the young student won the highest academical distinction of his year, graduating as senior wrangler in 1813. It was during his undergraduateship that 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 cognate 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 the 24th of January 1814, and placed himself under the guidance of an eminent special pleader. Probably this temporary choice of a profession was inspired by the extraordinary success in legal pursuits which had attended the efforts of some noted Cambridge mathematicians. Be that as it may, an early acquaintance with Dr Wollaston in London soon changed the direction of his studies. He experimented in physical optics; took up astronomy in 1816; and in 1820, 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 1821–1823 we find him associated with Sir James South in the re-examination of his father’s double stars, by the aid of two excellent refractors, of 7 and 5 ft. focal length respectively. 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 held the responsible post of 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 presidential 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.” The award significantly commemorated his completion of his father’s discovery of gravitational stellar systems by the invention of a graphical method whereby the eye could as it were see the two component stars of the binary system revolving under the prescription of the Newtonian law.

Before the end of the year 1833, being then about forty years of age, 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 provided with those valuable automatic contrivances which at present materially abridge the labour and increase the accuracy of their determinations. Equatorially mounted instruments actuated by clockwork, electrical chronographs for recording the times of the phenomena observed, were not available to Sir John Herschel; and he had no assistant.

His scientific life now entered upon another and very characteristic phase. The bias of his mind, as he subsequently was wont to declare, was towards chemistry and the phenomena of light, rather than towards astronomy. Indeed, very shortly after taking his degree at Cambridge, he proposed himself as a candidate for the vacant chair of chemistry in that university; but, as he said with some humour, the result of the election was to leave him in a glorious minority of one. In fact Herschel had become an astronomer from a sense of duty, and it was by filial loyalty to his father’s memory that he was now impelled to undertake the completion of the work nobly begun at Slough. William Herschel had searched the northern heavens; John Herschel 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 employed in this, so as to give a unity to the results of both portions of the survey, and to render them comparable with each other.” In accordance with this resolution, he and his family embarked for the Cape on the 13th November 1833; they arrived in Table Bay on the 15th January 1834; and proceedings, he says, “were pushed forward with such effect that on the 22nd of February I was enabled to gratify my curiosity by a view of Crucis, the nebula about  Argûs, and some other remarkable objects in the 20-ft. reflector, and on the night of the 4th of March to commence a regular course of sweeping.”

Herschel returned to his English home in the spring of 1838. As was natural and right, he was welcomed with an enthusiastic greeting. By the queen at her coronation he was created a baronet; and, what to him was better than all such rewards, other men caught the contagion of his example, and laboured in fields similar to his own, with an adequate portion of his success.

Herschel was a highly accomplished chemist. His discovery in 1819 of the solvent power of hyposulphite of soda on the otherwise 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,