HJ van der Bijl

Dr Hendrik Johannes van der Bijl FRS (23 November 1887 – 2 December 1948) was a South African electrical engineer and industrialist.

He was the founding chairman of the Electricity Supply Commission (ESCOM, later to become Eskom) in 1923. In 1927, he was the president of the South African Institute of Electrical Engineers (SAIEE). Dr van der Bijl established the Iron and Steel Corporation of South Africa (ISCOR), and was its chairman for many years. The city of Vanderbijlpark, where ISCOR's major steel works was built and still operates, is named after him.

He was chancellor of the University of Pretoria from 1934 until 1948. He was elected a Fellow of the Royal Society in 1944.

He is now perhaps best remembered for the van der Bijl equation which describes the relationship of the three 'constants' of a vacuum tube, the transconductance g_m, the gain μ and the plate resistance r_p or r_a. The van der Bijl equation defines their relationship as follows:

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