So far in this programme, Dr Luca Di Mare’s story of the development of computing has taken us from early ‘computers’ of the ancient and medieval world, through to the famous mechanical computers of Pascal and Babbage. This month, the story continues with a look at the remarkable human computers: teams of ‘calculators’ – predominantly women – who lie behind some of the most crucial technological advancements of the twentieth century.

While Pascal, Babbage and countless others tried to come up with mechanical devices to aid calculations, science and engineering had developed an insatiable appetite for numbers. Large amounts of computations were needed to solve the differential problems arising from the theories of hydrodynamics, elasticity and electromagnetism that represented the highest achievements of 19th century classical physics. Even more intensive computational tasks were required later by the new problems of nuclear physics that arose early in the 20^th century as a result of the birth of quantum mechanics and of the war effort to build nuclear weapons. All these calculations were done by hand by larger and larger teams of workers.

The importance of human computers increased significantly and towards the middle of 20th century their work was organized in very sophisticated ways: multiple teams would perform the same calculation to check the correctness of the results, and the calculations were arranged so that all the workers could operate in parallel. Some computers made history, like the ‘Harvard Computers’ who were responsible for analysing astronomical data that led to the discovery of the expansion rate of the universe. Such was the prestige of the Harvard Computers that many women volunteered to work there for free.

Computing groups were composed almost exclusively by women during WWII because the male workforce was depleted by the war effort. After the war some of the largest and most prestigious computing groups were still composed and headed mainly by women, like the Computing Group of the Jet Propulsion Laboratory, which provided the computing power behind most of the early NASA space exploration missions. Most research laboratories and university departments kept their own teams of computers. The University of Oxford was no exception.

By the early 20^th century the power of human computers was sufficient to contemplate the solution of fairly ambitious problems: the first attempt to solve the equations ruling the evolution of the earth atmosphere at low altitude was performed by Lewis Fry Richardson, with a team of 12 computers. He was not very successful: a first shot at predicting the weather over Reading in the 1920s predicted that the atmospheric pressure would rise to 7 bar (that is, seven times the atmospheric pressure!) within a few hours. Richardson also estimated that an army of 64,000 computers (i.e. people) could predict the evolution of the global atmosphere.

The momentum behind scientific computing was building up. Some of the techniques still in use today to solve the large systems of equations used in approximating fluid flow or structural mechanics problem were developed when most of the work in scientific computing was done by human computers. One of the pioneers of such techniques was Richard V. Southwell. A Cambridge graduate, Southwell came to Oxford in 1925 as professor in Engineering Science and Fellow of Brasenose College. Southwell developed techniques still used today to solve large systems of linear equations arising in solid mechanics and fluid dynamics. The building hosting the University of Oxford Thermofluids Institute is named after him.

Dr Luca di Mare is Tutorial Fellow in Engineering Science at St John’s College, Oxford