pure mathematics. Several of the papers which he contributed to the Royal Society dealt with the calculus of finite differences; for these he received the Copley medal in 1821. In astronomy, he revised the catalogue of double stars made by his father; this work he did in conjunction with (Sir James) South and with the help of two refracting telescopes the property of that scientist. The resulting catalogue, printed in the Philosophical Transactions, brought its author the gold medal of the recently instituted Astronomical Society of London; also the Lalande prize for astronomy (of the Paris Academy) for 1825. Herschel along with Babbage took an active part in the foundation of the Royal Astronomical Society; he wrote its inaugural address, and was its first foreign secretary, while his father was its first president. In optics he investigated the absorption of light by colored media and the action of crystals upon polarised light. In chemistry (1819, when philosophical chemistry was perhaps at its lowest ebb in England) he rediscovered the hyposulphite salts, and ascertained their leading properties, the principal of which is dissolving the nitrate of silver—a property applied by Daguerre twenty years later to fixing photographic pictures. In 1821 he traveled in Italy and Switzerland with Babbage.
In 1822 his father died. His mother continued to reside at Slough, and the younger Herschel now succeeded to all the property, astronomical and otherwise, of his father. His mother survived for ten years, and throughout this interval Herschel made his home at Slough, with the exception that for three years, 1824-7, while he was secretary of the Royal Society he had also a house in London. Towards the end of this interval he married, the object of his choice being Margaret Brodie Stewart, the daughter of a clergyman of the north of Scotland; in this as in many other matters Herschel was a fortunate man. In 1830 he was put forward as the scientific candidate for the presidency of the Royal Society, the titled candidate being the royal Duke of Sussex; in which contest rank prevailed, but the principle which Herschel stood for ultimately prevailed. In this interval he accomplished much work in astronomy. In
