Harold Max Rosenberg, physicist: born London 26 August 1922; Lecturer in Physics, Oxford University, Reader 1978-89; Fellow, St Catherine's College, Oxford 1970-89; married 1952 Annabel Harris (three daughters); died Brazil 21 November 1993.

HARRY ROSENBERG was one of those dynamic people whose presence never went unnoticed. His intense interest in everything around him, his energy, warmth and wit, brought him to the forefront of any conversation. He also possessed the gift, rare among physicists, of empathy with a wide range of men and women. This perception allowed him to render even the most complex physical phenomena intelligible, while at the same time conveying vividly his personal sense of excitement at new scientific discovery. He was a brilliant teacher, the best I have known, an inspiring lecturer, a successful writer of books as well as scientific papers, and a much sought-after speaker and broadcaster on matters scientific.

Harry Rosenberg's parents kept a small gentleman's outfitter's shop. His early life was not auspicious for a future academic career in that he left school at 16 and became a civil servant in a clerical post. After war service in the RAF and some spare- time study, however, he obtained a further education and training grant enabling him to read physics at University College London. It changed the course of his life. He graduated with First Class honours and proceeded to the Clarendon Laboratory, at Oxford, to undertake a DPhil in low temperature physics under the late Kurt Mendelssohn.

The Clarendon, when Rosenberg arrived there in 1950, was one of a tiny number of centres in the world providing the facilities needed for research at very low temperatures. Rosenberg set to work to investigate the conduction of heat through metals in the temperature range near 1K (one degree Kelvin above the absolute zero of temperature), about which very little was known at the time. The first of his numerous scientific papers, written in collaboration with Mendelssohn, appeared in 1951. The thermal conductivity work led on to investigations of the mechanical properties of metals, including the first studies to be made of metal fatigue at low temperature.

A visit to the Clarendon by the theoretical physicist Ray Orbach, from the University of California, Los Angeles, in 1961, initiated one of Rosenberg's long-term collaborations. From their joint discussions at that time, Rosenberg was launched into a substantial new research programme, using thermal conduction and ultrasound in strong magnetic fields at low temperatures as a means of studying so-called spin-phonon interactions in paramagnetic crystals. These again were pioneering measurements that laid a firm basis for much work carried out subsequently in other laboratories.

Rosenberg's final main research topic, the thermal properties of disordered materials (ie plastics) at low temperatures, was one before which most physicists quailed at the apparent difficulty of understanding or interpreting the measurements. None the less, the enterprise paid off handsomely in the end, when Orbach was able to show that many of the results could be interpreted through the theory of fractals, one of the newest and most exciting concepts in mathematics, closely related to chaos.

In addition to his research and undergraduate teaching, Rosenberg played an active role in the affairs of St Catherine's College, which he served as a while as Senior Tutor, and of Oxford University; he also gave sterling service, in numerous capacities, to the Institute of Physics. He embarked on the violin when he was already over 40, and formed a string quartet. After he had retired, aged almost 70, when most people would be scaling down their activities, he took up sailing.

Retirement also brought Rosenberg another completely new challenge when he was invited to catalogue and interpret the contents of the third Lord Rayleigh's historic (largely 19th-century) laboratory in Terling Place, Essex, a task for which he was peculiarly well fitted on account of his understanding of classical physics and his versatile talents as an experimentalist. He found it fascinating, and lectured widely on the subject, but sadly was unable to finish the job.

At the time of his death, of heart failure while bathing in the sea, Rosenberg was in Brazil with his wife Anna, holidaying and lecturing. He was also preparing to address the British Association, the National Bureau of Standards in Washington, and a seminar on Rayleigh in Cambridge.

Perhaps on account of his early, non-academic and non-Oxford background, Rosenberg remained acutely aware of the world outside Oxford and of the opportunities it offered. His constant advice to his graduate students was to seize every opportunity, to take reasonable risks and, above all, to try to accomplish something new and original in both life and research.

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