Leon Charles Thevenin (1857-1926)

C H A R L E S S U C H E T

L£ON THEVENIN was born in Meaux, France,

on March 30, 1857. He distinguished himself as a brilliant student at the Ecole Polytechnique, where he was one of a 'group graduated in 1876. In 1878 he joined the corps of "telegraph engi-neers," as they were called at that time, and pursued his entire career in this organization, which he did not leave until he retired in 1914, on the eve of World War I. When he died in 1926, the Annales des P.T.T. published an obit-uary notice, which was signed by Mr. Thomas, Inspector General.1 This notice contains a detailed account of The-venin's administrative career. The present article merely gives a concise review of the high points.

Thevenin began as an engineer in the department of long-distance underground cables; later he was connected with the Department of Material and of Construction at the Central Administration (of posts, telegraphs, and tele-phones), where he took care of the technological problems encountered in the construction of lines and supervised the erection of power lines. During this period he standardized the rules covering the construction of overhead lines. These rules were generally accepted in France and remained in force until the appearance of the Lorain system.

In 1896 Thevenin was made Director of the "Ecole Pro-fessionelle Superieur," which had been organized eight years before and which consisted of two divisions—one training clerical students, the other, student engineers. He left this post in 1901, to be succeeded by Edouard Estaunie, and was appointed manager of the Ateliers du Boulevard Brune. He remained in this position until his retirement.

In addition to his administrative duties, Thevenin con-tinued to devote a considerable portion of his time to teach-ing, for which he had a liking. Many of the graduates of this school who later became officials remember him as an excellent teacher.

In 1882 he had been appointed to teach a course for the training of inspectors of the engineering department. When the Division of Student Clerks was organized at the Ecole Superieure, he was asked to teach mathematics. He continued this course, which was a model of precision and clarity, up to 1910. His teaching talents were taken

Essentially full text of an article translated, through the courtesy of the Westinghouse Electric Corporation, from the Reime des P.T.T. de France (Paris, France), volume 4, number l, January-February 1949, pages 1-4.

Charles Suchet is Inspector General, Manager of Educational Department, Administra-tion of Posts, Telegraphs, and Telephones, Paris, France.

Although Thevenin's theorem is used ex-tensively, particularly by communication engi-neers, little is known of the man himself. This article, translated from the journal of the Administration of Posts, Telegraphs, and Tele-phones with which Thevenin was associated, outlines some of the highlights of his career.

advantage of even outside the Administration of Post, Telegraphs, and Telephones. In 1885 he was asked to teach a course in industrial tools at the Ecole des Hautes Etudes Commerciales, to which a course in industrial electrical engineering was ad-

ded in 1914. He taught these two courses until his death. The Institut National Agronomique engaged Thevenin in

1891 as a tutor (repetiteur) of mechanics, and in 1908, as the leader of seminars in applied mathematics. He con-tinued in these positions to the end of his life. Finally, he became teacher of mathematics at the Ecole Nationale du Genie Rural as soon as the latter institution was organized in 1919.

In connection with his teaching, Thevenin made, at the age of 26, an exhaustive study of the laws of Kirchhoif on electric networks and had occasion to observe the phe-nomenon which he expressed in his now famous theorem.

Here is how he himself formulated it, in 1883, in the Annales TolSgraphiques:

Assuming any system of linear conductors connected in such a manner that to the extremities of each one of them there is connected at least

Leon Charles Thevenin

OCTOBER 1949 Suchet—Lion Charles Thivenin 843

one other, a system having some electromotive forces, E\, E% ES)

no matter how distributed, we consider two points A and A' belonging to the system and having actually the potentials V and V. If the points A and A' are connected by a wire ABA', which has a resistance r, with no electromotive forces, the potentials of points A and A' assume different (other?) values of V and V, but the current ι flowing through this wire is given by the equation

V-V

in which R represents the resistance of the original system, this resist-ance being measured between the points A and A\ which are con-sidered to be electrodes.

Thus the theorem of Thevenin provides a very simple method of calculating the current which will flow in a new branch added to a network so as to connect two of its points, A and A'. If there originally is a potential difference V— V between these two points, and if the resistance equivalent to the whole network included between these two points (minus the electromotive forces) is R, then the current which will flow through the added resistance r located between A and A' will be the same as though the total original circuit were replaced by a simple battery having an electromotive force F— V and an internal resistance R.

The principle thus formulated is valid not only if the points A and A' are connected to a simple resistance r, but also if they are connected to some new circuit. This con-clusion is frequently referred to as the "generalized The-venin theorem."

The practical consequences of this theorem are not diffi-cult to grasp, since it is constantly necessary to add some new branch to an existing network, and Thevenin's theorem makes it unnecessary to make new calculations. This advantage is further increased by the fact that, since the theorem is based directly upon the laws of Ohm and Kirch-hoff, it is applicable, as they are, to alternating current if one resorts to the calculus of imaginaries. This is why it is used by communications engineers even more often than by others.

When Thevenin decided, exultant over his discovery, to report it to the Academy of Sciences, he first spoke of it to Vashy, another famous engineer of the Administration, whom he deeply admired. To his great surprise, Vashy returned his paper with the comment that the law formu-lated by Thevenin, attractive though it was, was un-fortunately wrong. Thevenin then consulted several other scholars well known at the time, and this gave rise to a con-troversy as to whether his law was consistent with the facts or not. Finally, the theorem was presented to the Academy by Cabanellas.2

This controversy shows once more that what is common knowledge today was not considered such when it was still a subject of groping. In any case, it does not detract from his merit.

Thevenin was a humble man and did not realize the im-portance of his discovery. Shortly before his death he was visited by a friend of his, J. B. Pomey, and was surprised to hear that his theorem had been accepted all over the world and that many applications had been derived from it by the transmission engineers.

Thevenin is remembered as a model engineer and em-

ployee, hard-working, of scrupulous morality, strict in his principles but kind at heart. He was very much attached to his family estate at Meaux and lived there all his life, commuting daily to Paris. He remained single but shared his home with a widowed cousin of his mother's and her two children, whom he later adopted. (Much of what we know about his life we owe to Mademoiselle Chaux-Thevenin, his adopted daughter.)

He was a talented violin player and played in private. Another favoi ite pastime of his was angling, and he bought a boat for this purpose on the Marne River which accounts for his nickname, the Admiral, given to him by his students at the Institut Agronomique.

Leon Thevenin died in Paris, where he had been taken for a treatment, on September 21, 1926. In accordance with his simple tastes, he had left a formal request that no one should accompany him to the cemetery except his family, and that nothing be placed on his coffin but a rose from his garden. This is how he was buried at Meaux on September 23, 1926.

REFERENCES

1. Annales des P.T.T. (Paris, France) , December 1926, page 1090.

2. Comptes Rendus de PAcadimie des Sciences (Paris, France), December 1883, page 159.

High-Speed Target Drone

The shooting eyes of the United States Navy's antiaircraft gunners will be sharpened by the antics of a pilotless radio-controlled ram-jet-powered Martin KDM-l target drone, which will be used to simulate maneuvers of the fastest fighter planes. The KDM-l , built by the Glenn L. Martin Company, Baltimore, Md., is an improved version of the Gorgon IV (shown above). Powered by a 20-inch Marquardt ram-jet engine, the new drone will be launched in air by a twin-engine Navy model JD aircraft. The control system of the KDM-l can be preset to follow a prescribed course, but may be overridden at any time by a remote-control station. Upon exhaustion of fuel, the drone noses up, a parachute is released, and the target is recovered after dropping into the

water

844 Suchet—Leon Charles Thevenin ELECTRICAL ENGINEERING