James Challis

James Challis FRS (12 December 1803 – 3 December 1882) was an English clergyman, physicist and astronomer. Plumian Professor of Astronomy and Experimental Philosophy and the director of the Cambridge Observatory, he investigated a wide range of physical phenomena though made few lasting contributions outside astronomy. He is best remembered for his missed opportunity to discover the planet Neptune in 1846.

Early life Challis was born in Braintree, Essex where his father, John Challis, was a stonemason. After attending various local schools, he graduated from Trinity College, Cambridge in 1825 as Senior Wrangler and first Smith's prizeman. He was elected a fellow of Trinity in 1826 and was ordained in 1830. He held the benefice of Papworth Everard, Cambridgeshire from the college until 1852. In 1831 Challis married Sarah Copsey, née Chandler, a widow, and consequently resigned his Trinity fellowship. The couple had a son and a daughter.

Plumian professor In 1836, he became director of the Cambridge Observatory and Plumian Professor, holding the latter post until his death. He lectured in all areas of physics. As examiner for the Smith's prize, he appraised the early work of G. G. Stokes, Arthur Cayley, John Couch Adams, William Thomson (later Lord Kelvin), Peter Guthrie Tait and James Clerk Maxwell. For over a decade, in correspondence and publications, Challis repeatedly disagreed with Stokes's conclusions from his research.

Challis was referee for Thomson and for Stokes in their respective applications for chairs at the University of Glasgow, and for Maxwell at Aberdeen. He and Thomson together set and examined the Adams prize topic on Saturn's rings, won by Maxwell in 1857.

Cambridge Observatory Challis succeeded George Biddell Airy at the observatory and gradually improved the instrumentation and accuracy of observations. He made some early observations of the fracture of comet 3D/Biela into two pieces on 15 January 1846 and re-observed both fragments in 1852. He published over 60 scientific papers recording other observations of comets and asteroids. He invented the meteoroscope (1848) and the transit-reducer (1849). Challis published twelve volumes of Astronomical Observations Made at the Observatory of Cambridge.

Physicist Challis also worked in hydrodynamics and in optics where he supported the wave theory of light and advanced the theory of a luminiferous ether as a medium for its propagation. However, he rejected the idea that the ether was an elastic solid, insisting that it was a fluid, bringing him into conflict with Airy and Stokes. Driven by Sir Isaac Newton's somewhat obscure assertion of "a certain most subtle spirit which pervades and lies hid in all gross bodies", Challis was driven to attempt to derive all physical phenomena from a model of inert spherical atoms embedded in an elastic fluid ether, an enterprise described as an attempt at a "Victorian unified field theory". His ideas won few supporters. He went on to interpret the word "law", as used in a spiritual sense by Saint Paul, in the sense of scientific law.

Assessment Challis published 225 papers in mathematics, physics and astronomy. He was re-elected fellow of Trinity in 1870. He died in Cambridge and was buried beside his wife in Mill Road Cemetery, Cambridge. His wealth when he died was £781 . Olin J. Eggen claimed that "At a later time, or under less amiable circumstances, he would have been branded a charlatan. He would now be as forgotten as his peculiar ideas had not the events surrounding the discovery of Neptune in 1845 given him a genuine opportunity for scientific immortality. But he fumbled it."

Honours and memorials Fellow of the Royal Astronomical Society, (1836);