516 Intelligence and Miscellaneous Articles. 



BY MM. E. SAKASIN AND L. DE LA KIVE. 



We have had the honour of presenting to the Academy the first 

 results which we obtained in repeating the beautiful experi- 

 ments of M. Hertz on rapid electrical oscillations (Comptes Rendus, 

 Jan. 13, 1890). We there limited ourselves to the case in which 

 the electrical oscillation is transmitted along a conducting wire. 

 We have since then repeated another of M. Hertz's experiments, 

 which consists in following the propagation of electrical induction 

 through air in the absence of any metallic conductor. The 

 primary exciter is placed in front of, and parallel to, a large plane 

 metal surface; the electrical oscillations which proceed from it, 

 travelling through air, reach the metal surface, which acts as a 

 mirror; the reflected waves form then, with the direct waves, 

 a system of stationary waves, the first node of which is at the 

 mirror. 



In order to examine the system of vibrations which are set up 

 in front of the mirror, the circular resonator is moved about in 

 two different principal positions : first, keeping it always parallel 

 to the mirror and to the primary, that is, in the plane of the wave ; 

 secondly, moving it in the plane perpendicular to the mirror 

 through the axis of the primary — the plane of vibration. In both 

 cases the results are absolutely concordant as to the position 

 of the equidistant maxima and minima of electromotive force. 

 Besides these two methods Hertz employed a third, which consists 

 in producing interferences on the same resonator between waves 

 arriving from the same exciter, either directly across the air or by 

 a conducting wire. From these experiments he concludes, by the 

 great wave-lengths from the mirror, that the velocity of propagation 

 through air in the absence of any conducting wire is almost twice 

 as great as that which is observed along a wire ; that the two 

 velocities are to each other as about 7 to 4, in opposition to the 

 theory of Maxwell, according to which these velocities should be 

 equal. 



From its theoretical importance, we have especially applied our- 

 selves to the verification of this particular point. Having observed, 

 from our previous experiments along wires, the constancy of the 

 undulating period of a given circular resonator whatever be the 

 primary exciter by which it is set to work, — the same exciter, in 

 short, permitting the observation of as many wave-lengths as there 

 are circles of different magnitudes — we have devoted ourselves to 

 comparing the wave-length given by the same circular resonator 

 along wires with those which it gives in air without wires. 



We used as a reflecting surface a large curtain of sheet lead, 2*8 

 metres in height by 3 metres in breadth, kept plaue and vertical 

 by its own weight. The primary exciters and the large Euhm- 

 korff's induction-coil were the same as those which we used in our 

 preceding researches. The exciter was placed in front of the 

 mirror, with its axis horizontal, and its break on the perpendicular 

 to the centre of the metal sheet ; its distance was between 4 and 

 10 metres. The circular resonator was fixed on a sliding chariot 

 along a large wooden optical bench. 



