332 Mr. C. A. Chant on the Variation of 



emitted waves o£ various lengths, extending over several 

 octaves ; but this hypothesis has been shown to be impro- 

 bable, 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* 



In Lecher's t experiments the exciter consisted of two 

 sheet-metal plates, 40 cms. square, joined by a bent wire 

 2 m. long, with a spark-gap in the middle of it. Opposite 

 each plate and parallel to it was another of the same size, 

 from which ran long straight parallel wires. On the farther 

 ends of these was laid a vacuum-tube, and across the wires 

 at different points were laid metallic bridges. When these 

 were properly placed^ namely, at the potential nodes, the 

 tube at the ends lighted up. The wave-lengths he obtained, 

 however, were not those proper to the exciter, but those of 

 that part of the wire-system on that side of the first bridge 

 next the plates which was in resonance with the rest of the 

 wire- system. 



In Cohn and Heerwagen'sJ experiments with Lecher's 

 method a condenser was added to the ends of the wires. 



Blondlot § also experimented with parallel wires, but used 

 an oscillator of quite different construction. In Lecher's 

 arrangement the capacity is large compared to the self- 

 induction ; in Blondlot's the reverse is the case. The latter 

 has the advantage that the damping is much diminished. 



These " wire-waves " have been the subject of numerous 

 investigations, a notable one being that by Drude||. He 

 found that the oscillator must be considered as composed of 

 the Blondlot semicircular primary exciter, together with that 

 portion of the secondary wire-system as far as the first 

 bridge ; and that when the bridges are properly placed there 

 is resonance between this oscillator and the rest of the system. 

 Very convenient forms of this apparatus are given by Cool- 

 idge^f and Hormell'**. 



Donleff, who used chiefly the Blondlot oscillator, joined 

 the ends of the parallel wires with a glow-lamp. His aim 



* See Poincare, Les Oscillations Electriques, Art 55 & fol. : J. J. 

 Thomson, ' Recent Researches,' p. 340. 



t E. Lecher, Wied. Ann. xli. p. 850 (1890). 



\ Cohn and Heerwag-en, Wied. Ann. xliii. p. 343 (1891). 



§ R. Blondlot, Comptes Rendus, cxiii. p. 028 (1891). 



|| P. Drude, "Eine bequerne Methode zur Demonstration des elec- 

 trischen Brechung-sexponenten von Fiussigkeiten/' Wied. Ann. lv. p. 633 

 (1895). 



«| W. D. Cooiidge, Wied. Ann. lxvii. p. 578 (1899). 



** W. G. Hormell, Am. Journ. Science, xii. p. 433 (1901). 



ft W. Donle, Wied. Ann. liii. p. 178 (1894). 



