Australian Dictionary of Biography

John Conrad Jaeger (1907-1979), mathematical physicist, was born on 30 July 1907 at Stanmore, Sydney, only child of Carl Jaeger, a German-born cigar-manufacturer from South Africa, and his English-born wife Christina Louisa, née Sladden. John was closely attached to his mother and her family, especially her brothers who were engineers in England and South Africa. He won a scholarship to Sydney Church of England Grammar School (Shore) where he gained many prizes and was dux (1923). At the University of Sydney (B.Sc., 1928; D.Sc., 1941) he spent two years in the engineering faculty, then changed to science, and was awarded first-class honours and university medals in mathematics and physics. His first published research (1928), on the motion of electrons in pentane, was carried out under Victor Bailey, but he was more influenced by H. S. Carslaw.

In 1928 Jaeger proceeded on a Barker graduate scholarship to Trinity College, Cambridge (B.A., 1930; M.A., 1934); listed as wrangler, he was awarded the Mayhew prize (1930) for proficiency in applied mathematics. He remained in Cambridge until 1935, studying quantum theoretical topics—in part under (Sir) Ralph Fowler—and continuing his interests in pure and applied mathematics. On 23 December 1935 at St John's parish church, Notting Hill, London, Jaeger married Sylvia Percival Rees; they were to be divorced in 1950. In February 1936 he took up the post of lecturer in mathematics at the University of Tasmania; he and Professor E. J. G. Pitman shared the whole of the teaching until World War II. Although Jaeger gave lectures in pure mathematics, he especially enjoyed expounding applied mathematics to engineers and was an excellent teacher.

Jaeger's return to Australia was marked by a remarkable surge in the number of his publications. He renewed his ties with Carslaw and they co-authored two major books, Operational Methods in Applied Mathematics (Oxford, 1941) and Conduction of Heat in Solids (Oxford, 1947). The latter became the definitive work in the subject and is still in print. Their research papers on heat conduction included the results of many computations which Jaeger carried out on a hand calculator. The Council for Scientific and Industrial Research drew upon his skills and conceptual grasp in its initial development of an electronic computer.

During World War II Jaeger had been engaged on projects of a more immediately applied nature, such as charcoal production and the problem of why sandstone rollers cracked in newsprint production. He was eventually seconded to C.S.I.R.'s division of radiophysics in Sydney and carried out theoretical work on antenna patterns and wave propagation. Back in Tasmania, he published An Introduction to the Laplace Transformation (London, 1949), An Introduction to Applied Mathematics (Oxford, 1951) and further research papers on heat conduction. He was promoted associate-professor in 1949 and professor one year later. On 24 October 1950 at the registrar-general's office, Hobart, he married Martha Elizabeth ('Patty') Clarke (d.1978), the university's chief clerk and a member of an old Tasmanian family.

In 1952 Jaeger was appointed to the foundation chair of geophysics in the Research School of Physical Sciences at the Australian National University, Canberra. He immersed himself whole-heartedly in this new field and set about building up research of international standing in the solid-earth sciences. From the beginning, he had the idea of developing a centre for broad geophysical research, which grew to encompass geochemistry. His achievements reflected a breadth of vision, based on deep roots in classical physics, and an extraordinary perspicacity in making appointments.

Overcoming numerous constraints, Jaeger pursued his goal and the Research School of Earth Sciences was established in 1973, shortly after his retirement. The core of this school represented the body of activities he had fostered in geophysics and geochemistry. While research in these areas became internationally orientated, he had also forged links with organizations in Australia: he collaborated with public authorities and mining companies in seismology, rock mechanics, heat flow and geochronology, and was a member of several national committees concerned with earth sciences.

Although Jaeger made excursions into other fields, his personal research at the A.N.U. was mainly in terrestrial heat flow and rock mechanics. The work on heat flow laid the basis for the first comprehensive picture of the regional variations in the geothermal flux in the Australian continent. Rock mechanics dominated the last fifteen years of his scholarship, with particular emphasis on fracture of rocks and friction at sliding rock surfaces. These investigations were complemented by a considerable amount of consulting for mining and civil-engineering bodies, and by the publication, with N. G. W. Cook, of Fundamentals of Rock Mechanics (London, 1969). Earlier, Jaeger had written a successful monograph, Elasticity, Fracture and Flow (London, 1956). Almost all his books went through several editions.

Jaeger was elected to fellowships of the Australian Academy of Science (1954) and the Royal Society, London (1970); he was awarded an honorary doctorate of science (1975) by the University of Tasmania; he and Cook shared the Rock Mechanics award of the American Institute of Mining, Metallurgical and Petroleum Engineers in 1969; and Jaeger gave the Rankine lecture to the British Geotechnical Society in 1971. In 1963-65 he had acted as head of the school of physical sciences. He retired in December 1972.

In physique Jaeger was tall and, in middle years, of substantial bulk; he had receding hair and wore spectacles. Inclined to be shy and retiring in disposition, he could present a gruff exterior, though it mellowed on closer acquaintance. He enjoyed living in semi-rural surroundings at Oaks Estate, was a connoisseur of old houses and antique furniture, had a fondness for cats and nineteenth-century literature, and collected steam-engines and early farm machinery. Raised as an Anglican, he later showed little interest in conventional religious observance. In his final years he retreated to a remote part of the Tasman Peninsula, about 60 miles (97 km) from Hobart. He died on 15 May 1979 in Canberra and was cremated; he had no children. The Research School of Earth Sciences holds his portrait by Frances Philip.