54 Chant — Variation of Potential along 



Art. III. — The Variation of Potential along a Wire 

 Transmitting Electric Waves; by C. A. Chant. 



I. Introductory. 



Hertz* was the first to explore a wire along which electric 

 undulations were passing. His oscillator consisted of two 

 sheet-brass plates 40 cm * square, connected by a copper wire 60 cms 

 long, in the middle of which was a spark-gap. Opposite and 

 parallel to one plate was placed another of equal size, from 

 which was led off a copper wire, the first meter of which was 

 curved and the rest of it straight. As a detector he used his 

 circular resonator, 70 cms in diameter. The nodes were well 

 marked in two wires, the length of the straight portions of 

 which were 5'5 m and 8 m , respectively. The half- wave-length 

 was determined to be 2'8 m . 



These experiments were repeated and extended by Sarasin 

 and de la Rive,f who somewhat increased the effect by using 

 two wires led off from two plates placed opposite the oscil- 

 lator plates, the resonator being held between them. These 

 experimenters showed very clearly that the apparent wave- 

 length measured along the wire was dependent purely on the 

 size of the resonator, the wave-length being equal to eight 

 times the diameter of the resonator. 



Somewhat similar results were obtained by Waitz,J who 

 used a circular resonator, to which were attached two wires, 

 one joined near each terminal knob, and led off either parallel 

 to each other or in opposite directions. In the former case, 

 by sliding along a bridge laid across the wires, the sparks 

 between the resonator knobs passed through maximum and 

 minimum intensities; in the latter case, by hanging capacities 

 on the wires and sliding them along, the sparks varied similarly. 

 He worked with plate oscillators of two sizes, as well as cylin- 

 drical and spherical ones. He found that his minima depended 

 entirely on the dimensions of his circular resonator. 



The conclusion naturally drawn by Sarasin and de la Rive 

 and Waitz from their experiments was that the oscillator 

 emitted waves of various lengths, extending over several 

 octaves ; but this hypothesis has been shown to be improbable, 

 a more satisfactory explanation being based on the fact that 

 the oscillations of the oscillator are very rapidly damped, while 

 those of the resonator are very persistent.§ 



* H. Hertz, Wied. Ann., xxxiv, p. 551, 1888. Electric Waves, p. 106. 



f E. Sarasin and L. de la Rive, Archives des Sciences Physiques et Nat- 

 urelles. Geneve, xxiii, p. 113, 1890. 



XK. Waltz, Wied. Ann., xli, p. 435, 1890. 



§ See Poincare", Les Oscillations Electriques, Art. 55 and fol. J. J. Thom- 

 son, Recent Researches, p. 340. 



