Short Continuous Electromagnetic Waves. 95 



pulled out to A' till A'C = \. When the first maximum 

 corresponded to 50 centimetres scale-deflexion of the thermo- 

 galvanometer, this deflexion was found to be reduced to 

 half its value if A was moved only over about 2*7 mm. 

 when the resonance wave- length was about 375 centimetres, 

 while in the whole intervening space between the two 

 successive maxima at AC = ^X and A'0 = X, the galvano- 

 meter deflexion was nowhere more than 5 millimetres. This 

 shows that though the galvanometer leads were not specially 

 protected against direct induction from the valve circuits, 

 this direct induction can be made negligibly small. The 

 very low value of the ordinates of the resonance curve over 

 the whole range between the two very sharp maxima at 

 AC = JX and A'C = X further shows that no harmonics of 

 any appreciable amplitude were present in the valve 

 circuits. 



When the free ends C of the Lecher wires pointing to the 

 valve circuits were brought too near to the generator,, it was 

 found that the resonator when tuned extracted too much 

 energy from the generator, and the valve ceased to oscillate 

 as indicated by the fall of current in A x (fig. 1). When, 

 however, the distance between the ends of the resonator and 

 the generator is kept greater than about 50 centimetres, the 

 deflexion of the milliam meter in the plate circuit will be the 

 same whether the resonator is in resonance or out of tune 

 with the valve oscillations. This indicates the absence of 

 appreciable reaction on the part of the resonator on the 

 oscillator. 



A resonance curve therefore taken under these conditions 

 will yield the natural damping-factor of the receiving 

 system. Such a curve is given in fig. 3, where the ordinates 

 represent the galvanometer deflexions (approximately pro- 

 portional to the square of the current amplitude in the 

 Lecher system), while the abscissae give the total length AG 

 of the Lecher system in millimetres. The latter was varied 

 by gradually shifting the support A, in this way pulling the 

 tubes AD more or less out of DC. 



With a careful adjustment of the valve inductances and 

 -capacity it is possible, as fig. 3 shows, to get very nearly 

 symmetrical resonance curves, though in our experiments 

 the tendency was observed for the galvanometer deflexions 

 corresponding to a wave-length longer than the resonance 

 wave-length to be somewhat bigger than those for the 

 symmetrical shorter waves. This is especially well marked 

 in fig. 4, given here as an instance of a resonance curve 

 with arbitrary adjusted valve circuits. The ordinates and 



