John Carruthers Beattie was born in the north of England, but grew up in Dumfries and Galloway (formerly Dumfriesshire) in the south of Scotland. In 1884 he entered Moray House training college for teachers in Edinburgh for a two year course. Continuing his studies at the University of Edinburgh he graduated as a Bachelor of Science (BSc) in 1891. With the support of several scholarships he pursued post-graduate studies and research at the universities of Edinburgh, Munich, Vienna and Berlin during 1892-1896 and was awarded the Doctor of Science (DSc) degree by the University of Edinburgh in the latter year. He then continued his research at the University of Glasgow under Lord Kelvin, leading to several papers on the effect of X-rays, ultra-violat light and the radiation emitted by uranium on the electrical conductivity of gases.
In August 1897 Beattie was appointed temporarily to the chair of applied mathematics and physics at the South African College in Cape Town, in the place of professor James Holm*, who was ill. When Holm died later that year Beattie was appointed permanently and when the post was divided in 1904 he became professor of physics for the next thirteen years.
His early research in South Africa related to the effect of temperature and surface coatings on the leakage of electricity from charged bodies in air. It led to two papers in the Philosophical Magazine in 1899 and 1901, and another in the Report of the South African Association for the Advancement of Science in 1903 (pp. 144-153). With W.H. Logeman* and J. Lyle* as observers he also studied atmospheric electricity - especially the conductivity of air - in Cape Town and Bloemfontein, publishing a preliminary note on the work in the same Report (pp. 102-105).
However, Beattie's most important work was an extensive geomagnetic survey of southern Africa, carried out in collaboration with Professor John T. Morrison* of Victoria College, Stellenbosch. From 1898 to 1906 they spent their vacations and a year's leave during 1903 in the field, measuring the magnetic declination, inclination and field intensity at more than 400 stations all over southern Africa. At about 20 stations the observations were repeated to determine the secular variations of the magnetic elements. In a joint paper before the South African Philosophical Society in 1901 (published in its Transactions, Vol. 14, pp.1-27) they reviewed and interpreted earlier observations of the magnetic elements at the Cape from 1605 to 1900. The results of their own survey were published in London in 1909 under Beattie's name in a book entitled Report of a magnetic survey of South Africa. Beattie also read several papers on parts of the survey before the meetings of the South African Association for the Advancement of Science during 1906 to 1908 and contributed a chapter on "Earth magnetism in South Africa" to the volume Science in South Africa (Cape Town, 1905) edited by W. Flint* and J.D.F. Gilchrist*.
From November 1908 to March 1909 he extended the survey northwards to Windhoek. In May 1909 he and Morrison, both again on leave for the year, made observations from Kabwe (formerly Broken Hill) in Zambia, through north-western Zambia, the Democratic Republic of the Congo and north-eastern Zambia to Mbala. From there Morrison travelled to the east coast while Beattie continued northwards to the upper Nile and, suffering many hardships, eventually to Al-Khartüm in the Sudan. Their results were published in Land magnetic observations, 1905-1910 by L.A. Bauer of the Carnegie Institution in Washington (Publication No. 175, 1912). During 1910 to 1913 Beattie made observations at 64 additional stations in the Northern Cape, North-West and Botswana, and reported the results in two papers before the Royal Society of South Africa (Transactions, Vol. 4, 1914-5, pp. 9-56 and pp. 57-64). He followed these up with a paper on the secular variations of the magnetic elements in South Africa during 1900-1913 (Transactions, Vol. 4, pp. 181-204). These variations were of particular interest because they were abnormally large. His observations at an additional 25 stations during 1913-1915 were published in the latter year (Transactions, Vol. 5, pp. 669-670), together with a paper on the geographic variation of the magnetic elements over southern Africa (pp. 671-684).
Beattie joined the South African Philosophical Society on his arrival in 1897, served frequently on its council, and was its president in 1905-1906. He was one of the first Fellows of the Royal Society of South Africa in 1908, served as its secretary from 1912 to 1914, and as a member of council during most years between 1910 and 1922. He was a founding member of the South African Association for the Advancement of Science, served on its council for many years, was joint vice-president during 1907-1908, served on its committee to standardise South African weights and measures in 1908, was president of Section A in 1909-1910, received the associations's South Africa Medal and Grant in 1910, served as a trustee of the association for many years, and eventually was elected president for 1927-1928. His presidential address dealt with "Some possible extensions of the activities of the association" (South African Journal of Science, 1928, Vol. 25, pp. 1-9). He was furthermore a Fellow of the Royal Society of Edinburgh and of the Physical Society of London. He joined the British Association for the Advancement of Science in 1905 and read two papers on his geomagnetic research at its meeting in South Africa that year.
Beattie was a fine lecturer and in addition to his teaching at the South African College gave an evening course of lectures on electricity to railway and post office staff in 1899 and lectured in climatology and meteorology at the newly established South African School of Forestry in 1906. His research career ended in 1917, but thereafter he became an excellent administrator. He served on the council of the University of the Cape of Good Hope from 1902 to 1918, and on that of the South African College from 1903. At various times from 1903 to 1907 and again in 1916 he was an examiner in physics for the BA or MA degrees of the University of the Cape of God Hope. He campaigned vigorously for the development of the South African College into a teaching university and was a member of various committees investigating this possibility from 1904 onwards. Legislation to create the Universities of Cape Town and Stellenbosch was eventually passed in 1916 and Beattie served on the Universities Statutes Commission during 1916-1918. In 1917 he was elected principal of the South African College, and in 1918 the first principal and vice-chancellor of the new University of Cape Town, a post he filled with distinction until his retirement in 1937. A knighthood was bestowed on him in 1920 and he received honorary doctorates from the Universities of Edinburgh, the Witwatersrand, and Cape Town.
Beattie participated actively in the work of other public bodies. He served on the Meteorological Commission of the Cape of Good Hope from 1898 to 1908; on the Scientific and Technical Committee on Industrial Research, created in 1917 and later amalgamated with the Industrial Advisory Board; as chairman of the Survey Commission in 1921; on the Mining Industry Board in 1923; on the Board of Governors of the SABC from 1937 to 1943; and on the Committee of Inquiry into Technical Colleges. He was a kind, generous and unassuming person, with a zest for life and the ability to form lasting friendships.