~Wire Transmitting Electric Waves. 55 



In Lecher's* 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 par- 

 allel 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 reso- 

 nance with the rest of the wire-system. 



In Cohn and Heerwagen'sf 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 arrange- 

 ment the capacity is large compared to the self-induction ; in 

 Blondlot's the reverse is the case. The latter has the advan- 

 tage 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 por- 

 tion of the secondary wire-system as far as the first bridge ; 

 and that when the bridges are properly placed there is reso- 

 nance between this oscillator and the rest of the system. Yery 

 convenient forms of this apparatus are given by Coolidge[ and 

 Hormell.l 



Donle,*"* who used chiefly the Blondlot oscillator, joined the 

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

 to diminish the wave-lengths, 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. ft From these smaller 

 plates the parallel wires went out, — in this instance to a dis- 

 tance of 5T0 cms , — and were explored by a bolometric method. 

 Rubens^ found that the oscillations along the wires were not 



*E. Lecher, Wied. Ann., xli, p. 850, 1890. 

 f Colin and Heervragen, Wied. Ann., xliii, p. 343, 1891. 

 JR. Blondlot, Comptes Rendus, cxiii, p. 628, 1891. 



§ P. Drude, Eine bequenie Methode zur Demonstration des electrisclien 

 Brechungsexponenten von Fllissigkeiten. Wied. Ann., lv, p. 633, 1895. 

 || W. D. Coolidge, Wied. Ann., lxvii, p. 578, 1899. 

 f W. G. Hormell, this Journal, xii, p. 433, 1901. 

 ** W. Donle, Wied. Ann., liii, p. 178, 1894. 

 ff Drude, Physik des Aethers, p. 446. 

 tjH. Rnbens, Wied. Ann., xlii, p. 154, 1890. 



