Sir Alan Cook

Physicist and former Master of Selwyn College, Cambridge

Alan Cook was a physicist with an unusually wide range of interests, centred on the structure of the Earth and other planets, as well as phenomena arising from the vast clouds of attenuated gas that abound in more distant regions of our galaxy. In pursuit of these interests he became involved in exact measurement and the establishment of standards in metrology.

Alan Hugh Cook, physicist: born Selstead, Kent 2 December 1922; Superintendent, Standards (later Quantum Metrology) Division, National Physical Loboratory 1966-69; FRS 1969; Professor of Geophysics, Edinburgh University 1969-72; FRSE 1970; Jacksonian Professor of Natuural Philosophy, Cambridge University 1972-90, Head of Department of Physics 1979-84; Fellow, King's College, Cambridge 1972-83; President, Royal Astronomical Society 1977-79; Master, Selwyn College, Cambridge 1983-93; Kt 1988; Chairman, Press Syndicate, Cambridge University Press 1988-93; married 1948 Isabell Adamson (one son, one daughter); died Cambridge 23 July 2004.

Alan Cook was a physicist with an unusually wide range of interests, centred on the structure of the Earth and other planets, as well as phenomena arising from the vast clouds of attenuated gas that abound in more distant regions of our galaxy. In pursuit of these interests he became involved in exact measurement and the establishment of standards in metrology.

From Westcliff High School he went to Corpus Christi College, Cambridge in 1940 and on graduating in 1943 joined the Admiralty Signals Establishment. He returned to Cambridge at the end of the Second World War to begin research for his PhD in the Department of Geodesy and Geophysics.

It was here that he became interested in the precise determination of the gravitational acceleration (g) of a falling body. Small variations in g over the Earth's surface give valuable hints on the density and depth of deep-lying rocks; at the time he went to the National Physical Laboratory (NPL) in Teddington - he was there from 1952 to 1969 - expeditions were setting out with very precise pendulums to map them. The results played a major role in overthrowing apparently secure views on the Earth's crust and initiating the concept of slowly wandering plates; their collisions and separations generate mountain ranges and the deep-sea trenches from which spring the most powerful earthquakes and devastating volcanoes.

It may seem tame in this context to devote time and technical skill to throwing up perfect spheres of glass in a vacuum and timing their passage up and down past two pairs of slits. This is what Cook worked on to the point of determining g with a reliable standard against which all the pendulums could be checked, so that as they roamed around the globe any tiny differences in g that were noted could be seen as real and requiring explanation. Good though Cook's device was, it was soon improved on by others; but he was the pioneer.

He soon rose to be superintendent of the division at the NPL that covered metrology in general. It developed into quantum metrology using atomic vibrations and lasers to achieve ever higher degress of exactness in measurement of length and time that are essential in advanced technology and in such academic pursuits as radio astronomy. His personal input and the organisation of the enterprise are not the stuff of heroic legend, but without such things there would be no heroes. His success was signalled by election to the Royal Society in 1969.

In the same year, he left NPL on appointment to the Chair of Geophysics at Edinburgh. The department apparently needed enlivening, and he spent three years getting it into shape before he was called back to Cambridge as Jacksonian Professor of Natural Philosophy at the Cavendish Laboratory. He was now 50 and perhaps a little weary of experiment, even perhaps discouraged at the prospect of building a new research effort in a department where competition to attract the brightest graduates was so fierce. At all events he did not manage to put together a team of his own, though he gave encouragement to a small new enterprise devoted to laser physics which has continued to thrive.

For his own part he was drawn more into administration. Among other tasks were two years as President of the Royal Astronomical Society, five years as head of the Cavendish and five years as Chairman of the Syndics of the Cambridge University Press.

On arrival as Jacksonian Professor he was elected a Fellow of King's College and only left in 1988 to become Master of Selwyn College, a position he held until he reached the retiring age of 70 in 1993. It was an uneventful time for the college, which had recently added to the buildings and was not quite ready for the next phase of expansion. He is remembered for his courteous hospitality and kindly management at a time when what had been an exclusively Anglican male foundation was successfully coming to terms with a broader outlook. Tidy in dress, seriously learned, to outsiders he must have seemed the epitome of a don.

In his latter days he was a rare visitor to the Cavendish, being fully occupied, when not at meetings, with theoretical investigations and the books that resulted. He had been among the first to appreciate, in 1965, that intense (astronomically speaking) microwave radiation was the outcome of maser action in interstellar gas, particularly the hydroxyl radicals it harboured. This was covered in his Celestial Masers of 1977, and he had already published a rather severe treatment of microwaves and their interference in 1971 ( Interference of Electromagnetic Waves). Several technical books followed, but his last, in 1997, was a biography of Edmund Halley ( Edmund Halley: charting the heavens and the seas) whose comet is but one episode in a brilliant life of discovery. The book was very well received.

It reveals another side of Alan Cook, his devotion to the history of science. For some years he edited Notes and Records of the Royal Society, which helps keep alive the memory of otherwise forgotten scientists and the research which later work has overshadowed. It was appropriate work for a somewhat reclusive but quietly humorous man whose own achievements will remain valuable as they are absorbed, and because they are absorbed, into the fabric of science.

Brian Pippard