BECQUEREL HENRI (1852-1908) PHYSICIEN.

autograph manuscript, Note succincte sur la propagation des oscillations électriques, [circa 1895]; 5 1/2 pages in-fol. with 15 ink sketches. Work on radioelectricity and Hertzian waves. This note is related to Becquerel's physics courses at the École Polytechnique, where he was appointed professor in 1895. Indeed, he twice refers to the course given by Alfred CORNU (1841-1902), his colleague professor of physics at the X. "We have seen that the discharge of a capacitor, and more generally of any electrified body, through a spark, and a weak resistance, was oscillating". Becquerel translates the "time of oscillation" into an equation... "Oscillations cause self-induction phenomena in motors such that they do not propagate in them. On the contrary, they propagate in dielectrics, resin, insulating oils, wood, which, although opaque to light, behave as transparent bodies for these movements"... Then Becquerel exposes the "Hertz experiments" [Heinrich Rudolf HERTZ (1857-1894)]: "Hertz, the first to measure for electrical oscillations, a wavelength in air, mentioning also that the phenomenon is periodic in space of a speed and at a finite speed of propagation. The Hertz devices consist of two parts 1° the producer of fast oscillations, or exciter. 2° the apparatus for collecting oscillations at a distance, or the resonator. Becquerel draws in the margin an exciter and comments on this apparatus... "Hertz showed that the maximum sensitivity occurred when the period of electrical oscillation in the wire [...] was the same as for the exciter, and the receiving wire he called the resonator (by analogy with sound resonations which must have the same period of vibration as the sounds they reinforce)"... Hertz observed that on a metallic wall (a wall covered with tin foil), everything happened as if there was a reflection. If this one is normal, the incident waves are superimposed on the reflected waves, and give in space a system of nodes and bellies", whose distance he calculates. Follows a development entitled "Refraction. Various experiments", illustrated in the margin with 3 pen-and-ink sketches: "taking as exciter a rectilinear cut wire, and placing it at the focus of a cylindrical mirror (parabolic), and taking as resonator an identical system, Hertz carried out the experiment of the companion mirrors; the sparks burst between a' b' up to 20 meters away; the oscillations are parallel to the wire AB. [...] All these experiments are repeated today with waves of shorter wavelength (?=6 mm) and with apparatus quite similar to that of optics. Becquerel then studied the "Propagation of electric oscillations along wires", taking up data from Hertz's experiment, observing: "It seems that electric charges travel on the surface of wires, in the air". Follows an addition on "Electrostatic and electromagnetic iscillating fields": "with the first arrangement of the exciter of Hertz (balls), two distinct phenomena are observed in space: 1° an electrostatic effect due to the charges that accumulate periodically in the spheres A, and B. 2° an electromagnetic effect due to the currents that develop in the rectilinear conductors Aa, Bb. - The vectors corresponding to these two phenomena are rectangular... Becquerel examines these two effects, with diagrams, to conclude: "By studying the system of stationary waves due to the superposition of the incident waves and the waves reflected by a metallic wall, 1° if the resonator is vertical (pll. to the mirror), electrostatic waves. We observe a node on the mirror (or rather very close to the mirror). 2° if the resonator is horizontal (pll. to the axis AaBb), electromagnetic waves, one observes a belly on the mirror. The two systems have the same wavelength but are offset from each other "... After a note in red pencil, the manuscript ends with a crossed-out paragraph devoted to the "Reflection on a metallic wall" and the electrostatic effect produced.