Potential along a Wire transmitting Electric Waves, 



U?> 



was to diminish the wave-length, which he reduced to 

 130 cms. Coolidge's smallest wave-length was 12 cms. 



In Rubens's experiments the exciter was of the Hertzian 

 form, with plates 40 cms. square. The two opposing parallel 

 plates were but 10 cms. square, though the smaller plates are 

 not quite as efficient as those of equal size*. From these 

 smaller plates the parallel wires went out — in this instance 

 to a distance of 570 cms. — and were explored by a bolo- 

 metric method. Rubens t found that the oscillations along 

 the wires were not the same as those of the oscillator ; in 

 other words, the oscillations were not forced along the wires, 

 but were those natural to them. 



These experiments were verified by Rutherford J, who 

 substituted a magnetic detector for the bolometer, and found 

 it equally sensitive. 



In all these experiments it will be observed that the wave- 

 lengths determined along the wires are not those proper to 

 the oscillator, but are either due to the detector used or to 

 the wires vibrating naturally. 



In Birkeland j \s§ and Jones's || researches the reverse seemed 

 to be the case. The wire-systems were both similar to that 

 of Sarasin and de la Rive, but the means of exploration were 

 different. Birkeland examined the potential at various points 

 of his wire, which was 30 m. long, by measuring the length 

 of the spark which leaped from it to an earth connexion, the 

 existence of the spark being indicated by a telephone re- 

 ceiver held to the ear. He obtained minimum points which 

 varied as the period of the oscillator was changed, thus indi- 

 cating that the measured wave-length depended on its period. 

 These minima were unequally spaced, which irregularity was 

 attributed to the damping of the waves and the loss on re- 

 flexion at the ends of the wires ; but the explanation does not 

 seem entirely satisfactory^. 



Jones used a thermal junction inserted at different points 

 of his wire which was 130 m. in length, the effect being- 

 indicated by a low-resistance galvanometer in circuit with it. 

 The oscillator was of the usual type, with plates 10 cms. 

 square, but the length of the connexion between the plates is 

 not given. Several well-defined maxima and minima were 

 ■observed, and the wave-length was determined to be approxi- 

 mately 4'3 m. It is interesting to read that " several 



* Drude, rhysik des Aethers, p. 446. 



t II. Rubens, Wied. Ann. xlii. p. 154 (1890). 



X E. Rutherford, Phil. Trans. A, 1897, vol. olxxxix. p. 1. 



§ Kr. Birkeland, Wied. Ann. xlvii. p. 583 (1892), 



i| I). E. Jones, Brit. Assoc. Report, 1891, pp. 56] _. 



If See Point-are, Les Oscillations Electriques t p. I 70. 



