Search

On the perimeter length determination of the eight-centered oval. Several studies have shown that an eight-centered oval coincides almost perfectly with the ellipse constructed on the same axes and can be considered as a representation of the latter provided that the radii of the arcs of circles that compose it had been suitably chosen. Its perimeter's computation is then reduced to the simple sum of arc lengths of circles. However, it doesnot seem to us that this calculation, which could prove to be useful, has never been performed nor published. This note aims thus to present a geometric demonstration of the perimeter length determination of the eight-centered oval., Comment: in French

The concept of "limit cycle" was introduced by Henri Poincar\'e in his second memoir "On curves defined by a differential equation" in 1882. From the point of view of physics, a stable limit cycle (or attractive) is the representation of the periodic solution of a (mechanical or electrical) dissipative system whose oscillations are maintained by the system itself. Conversely, the existence of a stable limit cycle ensures the maintenance of the oscillations. So far, the historiography considered that the Russian mathematician Aleksandr Andronov was the first to establish such a correspondence between the periodic solution of a self-oscillating system and Poincar\'e's concept of limit cycle. The recent discovery of a series of lectures given by Henri Poincar\'e in 1908 at the School of Post and Telegraph (now Telecom Paris Tech) proves that he had already used his limit cycle concept to establish the existence of a regime of maintained waves in a wireless device of radiotechnics. This article aims on the one hand to trace the emergence of this concept since its creation by Poincar\'e and the other hand to highlight its importance and role in the history of non-linear oscillations., Comment: in French

In 1893, the "physicist-engineer" Andr\'e Blondel invents the oscilloscope for displaying voltage and current variables. With this powerful means of investigation, he first studies the phenomena of the arc then used for the coastal and urban lighting and then, the singing arc used as a transmitter of radio waves in wireless telegraphy. In 1905, he highlights a new type of non-sinusoidal oscillations in the singing arc. Twenty years later, Balthasar van der Pol will recognize that such oscillations were in fact "relaxation oscillations". To explain this phenomenon, he uses a representation in the phase plane and shows that its evolution takes the form of small cycles. During World War I the triode gradually replaces the singing arc in transmission systems. At the end of the war, using analogy, Blondel transposes to the triode most of the results he had obtained for the singing arc. In April 1919, he publishes a long memoir in which he introduces the terminology "self-sustained oscillations" and proposes to illustrate this concept starting from the example of the Tantalus cup which is then picked up by Van der Pol and Philippe Le Corbeiller. He then provides the definition of a self sustained system which is quite similar to that given later by Aleksandr Andronov and Van der Pol. To study the stability of oscillations sustained by the triode and by the singing arc he uses, this time, a representation in the complex plane and he expresses the amplitude in polar coordinates. He then justifies the maintaining of oscillations by the existence cycles which nearly present all the features of Poincar\'e's limit cycles. Finally, in November 1919, Blondel performs, a year before Van der Pol, the setting in equation of the triode oscillations. In March 1926, Blondel establishes the differential equation characterizing the oscillations of the singing arc, completely similar to that obtained concomitantly by Van der Pol for the triode. Thus, throughout his career, Blondel, has made fundamental and relatively unknown contributions to the development of the theory of nonlinear oscillations. The purpose of this article is to analyze his main work in this area and to measure their importance or influence by placing them in the perspective of the development of this theory., Comment: in French