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Hugh Christopher Longuet-Higgins

Professor Christopher Longuet-Higgins died at the end of March at the age of 81.

Hugh Christopher Longuet-Higgins, always known as Christopher, was an exceptional scholar who made important scientific advances in two quite different disciplines, chemistry and artificial intelligence; many people think he was unlucky not to receive a Nobel Prize for his work in the former. He was one of the last great polymaths.

Christopher was born at the Vicarage in Lenham in Kent in 1923. While a school-boy at Winchester, he solved a problem concerning four-dimensional solids, which unbeknownst to Christopher had just been solved a few months earlier. While still an undergraduate at Oxford, where he simultaneously studied both Chemistry and Music degrees, he published a landmark paper in the Journal of the Chemical Society on the molecular structure of an unusual molecule called diborane. Christopher
continued at Oxford for a DPhil under the supervision of Charles Coulson. Together they derived many important theorems concerning the electronic states of aromatic molecules.

After Oxford Christopher had a short spell at Chicago and Manchester Universities, before moving to a chair in Theoretical Physics at King's College London in 1952. Two years later Christopher became John Humphrey Plummer Professor of Theoretical Chemistry at Cambridge. The Cambridge department that Christopher joined was eminent when he arrived and he built it further to become arguably the outstanding theoretical chemistry department in the world. In theoretical chemistry he made outstanding contributions in quantum chemistry and statistical mechanics. It was a surprise therefore to most chemists when in 1967 he decided to move into the field of artificial intelligence, giving up his Cambridge position for a Science Research Council senior research fellowship, and one year later a Royal Society Research Professorship, at Edinburgh University. Christopher showed a formidable talent in his new field. He also had already started publishing important papers in music from 1962 onwards.

Together with Richard Gregory and Donald Michie, Christopher founded the Department of Machine Intelligence and Perception in Edinburgh, and he took a leading role in starting the School of Epistemics, an interdisciplinary group, which brought together people with an interest in the mind. Together with postgraduate and postdoctoral workers  he made important early contributions in informatics, neural networks and language generation by computer. Christopher, unsure what to call the sort of research he conducted, coined the term “cognitive science” in a paper in 1973.

In 1974 Christopher transferred his Royal Society Fellowship to Sussex University where he joined the Experimental Psychology Group in the School of Biological sciences. He continued his work on artificial intelligence, making an important contribution to understanding how the brain analyses information about depth and distance in sequences of visual images. From 1984 to 1986 he was director of the Institute of Cognitive and Information Sciences at Sussex whose aim was to bring together widely dispersed groups in computer engineering, computer science, linguistics, and experimental psychology. Christopher's musical talents were combined with his academic skills in an influential paper on classical harmony, and he developed a computer program to determine key-signatures, accidentals, and bar lines from the keyboard strokes of performances of classical music. In his late active years he worked on the difficult problem of turning a musical score into a performance, with musically satisfying phrasing. This work was never published, and awaits reconstruction from his meticulously-kept notebooks. Christopher's postgraduate students and postdoctoral associates hold many important posts in the academic world. He was a tough supervisor, and an aggressive contributor to colloquia and scientific meetings; many an invited speaker wilted under his comments. Christopher's penultimate scientific paper, which was published in 1995, has the title '150 words on Consciousness'; he never wasted words in his writings.

Christopher's full list of awards and prizes is too long to be addressed here. He was elected a Fellow of the Royal Society in 1958, and a Foreign Associate of the US Academy of Sciences in 1968. He became a Fellow of the Royal Society of Arts in 1970 From 1979 to 1984 he was a governor of the BBC. He had honorary doctorates from the universities of York, Essex, Bristol, Sussex and Sheffield, the last being in music. In his time at Oxford he explored the possibility of being a professional
musician but science was lucky that he kept to being an inspired amateur in that field.