C. A. Chant — Reception of Electric Waves. 415 



For the wire free at both ends there are two resonant lengths, 

 the resonance not being very sharp, just as we should expect it 

 to be with a radiator much damped. With the plate on the 

 outer end, however, there is only one maximum, which is very 

 clearly marked ; while with the plate on the inner end there 

 are three resonant lengths, the chief one being somewhat 

 shorter than with the plate in the former position. From theo- 

 retical considerations Wien* concluded that with both the 

 inductively- and the directly-connected radiators there should 

 be present two distinct sets of waves of different periods and 

 damping coefficients. With the Braun apparatus this is clearly 

 evident, but there is no trace of a second maximum with the 

 Slaby radiator. On the other hand, the simple Marconi radia- 

 tor gives two resonant lengths when the wire is free at both 

 ends, only one, however, with the plate on the outer end, while 

 three are shown when the plate is on the inner end. The 

 reason for this is not easy to see. 



Again, the chief resonant length with the plate on the inner 

 end is shorter than with the plate on the outer end. The only 

 reason I can suggest for this is that the presence of the large 

 metal plate alters the frequency of the radiator to some extent, 

 even though it be 2 or 3 meters away. Slabyf found that 

 wires stretched one meter above a zinc-covered floor gave a 

 wave-length ten per cent smaller than when the floor was 

 entirely of wood. He traced this to a variation of the self- 

 induction of the radiator, not of its capacity. 



S. The Effect on Resonance of Inserting a Coherer in an Open 



Circuit. 



To test for this effect the coherer was inserted in the middle 

 of the straight wire arranged as in I, II, VII, fig. 6, and this 

 then gradually shortened for resonance as before. The simple 

 Marconi radiator with antenna of 3 meters was used and the 

 receiving wire was 1 meter away. 



Three coherers were experimented with. The first was the 

 one supplied with the Braun apparatus. The second was of 

 iron turnings in a tube 20 cms long and having an internal diam- 

 eter of 8 m ™. The third had silver plugs 3 mm in diameter, l mm 

 apart, with about one-fifth of the space between filled with fine 

 powder, mostly of silver. In each case a decohering tapper 

 was arranged on an independent circuit and was kept in con- 

 tinuous action. 



*M. Wien, Wied. Ann., lxi, p. 151, 1897; Ann. der Physik, viii, p. 686, 

 1902 ; see also G. Seibt. Phys. Zeitschrift, iv, p. 485 ; Graf Arco, Elektro- 

 technische Zeitschrift, 1903, p. 1 ; A. H. Tavlor, Physical Eeview, xviii, 

 p. 230, 1904. 



f A. Slaby, Der Multiplikationsstab, ein Wellenmesser fur die Fuhkentele- 

 graphie, § 7, Elektrotechnische Zeitschrift, No. 50, 1903. 



