He went up to Edinburgh University from Thurso High School in 1914 and graduated M.A. (with first class honours in mathematics and natural philosophy) and B.Sc. (with special distinction in natural philosophy) in 1920. He was absent from the university on military service for two of these six years.
Immediately after graduation he was appointed Assistant in Natural Philosophy at Edinburgh University, and started research under Dr George Carse on X-ray corpuscular emission from iron in a magnetised or unmagnetised state. He left Edinburgh in 1924 and went to the Carnegie Institute of Technology as Associate Professor of Mathematics, but after one year in America he accepted an invitation from Professor Stanley Allen to go to St Andrews as Carnegie Teaching Fellow, a post which, in theory, only involved half-time teaching.
In those days St Andrews was a small university, and the staff was correspondingly small. The staff of the Natural Philosophy Department consisted of a professor, two lecturers and half an assistant (the teaching fellow). As they had to teach three classes in Arts and Science and one in Medicine, the teaching load was heavy. In 1925 an extension of the Natural Philosophy Laboratory had just been opened, and David was given a small research room there. In 1928 he gained his Ph.D. for a thesis on the band spectra of water vapour. This work was published in Proc. Roy. Soc. Lond. (A) 115 (1927), p. 373, 118 (1928), p. 647; 120 (1928), p. 222.
A fire in the new laboratory in 1931 proved a serious set-back. He lost much of his research apparatus; and part of the teaching of practical physics had to be done in improvised accommodation. People do not realise nowadays the difficult conditions under which their predecessors had to work.
During the last war he had charge in St Andrews of the courses under the Hankey Scheme for the training of radar officers and also of the physics course for the R.A.F. Initial Training Wing. This work was not confined to the three academic terms and additionally he had a responsible post in A.R.P.
He was appointed lecturer in 1930, reader in 1948, and retired in 1963. Elected to the Fellowship of the Society in 1930, he served on the Council from 1953 to 1956.
Dr Jack played an important part in university affairs. He served on the Business Committee of the General Council, was the first St Andrews lecturer to be a member of the University Court, and the first non-professorial Dean of the Faculty of Science. In all these offices he won the affection and respect of his colleagues.
His activities were not confined to the University. For many years he was a trustee of the St Andrews Preservation Trust, whose magnificent collection of photographs and colour slides of St Andrews owes a very great deal to his artistic sense and his outstanding skill as a photographer.
In 1927, he married his former pupil and namesake Isabel Grace Jack. Theirs was a happy home where they entertained generously students and colleagues, who will always remember the unfailing courtesy and hospitality of their kindly host. Our sincere sympathy goes to his widow and their two sons.