Teaching

In 1882 Thevenin was asked to take on the job of teaching the young inspectors of the engineering department at the Ecole Superieure. This was the start of his teaching career and his introduction to the work that led to his famous theorem.

He developed an interest in electrical measurement and, with his former teacher Jules Raynaud, he translated a British work on units and physical constants into French. Translation of such foreign publications was part of the routine work of the School. In conjunction with this work, Thevenin made a very careful study of Kirchoff’s Laws and discovered the rule which he then expressed in his theorem, having proved it by a clever application of the already established Superposition Principle.

Thevenin's Theorem was published in three separate scientific journals in 1883 in a paper entitled "Extension of Ohm's Law to complex electrical circuits". It was introduced as a "new theorem of dynamic electricity" and gave a simple method of calculating the current that would flow in a new conductor when it was added to an existing network. Nowadays it is expressed rather differently (in terms of an equivalent circuit consisting of a voltage source and a series resistor) but it is the same theorem. It was Thevenin's first article and appeared in the same year as the publication of the joint translation with Raynaud.

Three further articles followed in that year. The first gave a method of using a galvanometer to measure potential, and made use of the new theorem. The second described a method for measuring resistance, and the third was on the use of the Wheatstone Bridge.

A Good Launch

Publication of the theorem in three journals gave it a good launch, but Thevenin also taught it himself in his courses to telegraph engineers in France. By 1889, a century ago, others were already writing of it as the "theorem de Thevenin". It is an early example of practical engineering theory, in this case telegraph theory, being originated by an engineer and taught by an engineering school quite outside the scientific tradition of mathematical physics.

All was not, however, without problems. Thevenin reported his discovery to the French Academy of Sciences but first he disclosed it to another French telegraph engineer whom he deeply admired, A. Vaschy. Vaschy found the concept attractive but thought the theorem was wrong. Others were consulted and controversy grew as to whether it was right or wrong.

Though Thevenin produced a rush of publications³ in 1883, he seems to have published nothing thereafter. Yet his career continued to advance and his teaching skills were sought outside the PTT. In 1885 he was asked to teach a course in industrial tools, and later one on industrial electrical engineering, at a school of commerce. The Institut National Agronomique employed him from 1891 to teach mechanics, and later to lead seminars in applied mathematics. He continued all of these teaching appointments until his death in 1926.

He had already proved himself as head of the Bureau des Lignes (where he improved and unified the construction of lines and personally supervised the implementation of his policies) when in 1896 he was appointed director of the telegraph engineering school. It was a job which brought him immense satisfaction.

Having no ambition to rise further he had almost to be prised out of that position in 1901 to take over as engineer-in-chief ⁴ of the workshops, a position he held with distinction until his retirement in January 1914.