664 



Professor J. A. Fleming 



[June 4, 



of Berlin. These oscillograms indicate that there are two oscillations 

 present of different frequency, producing an effect similar to beats 

 in music. Owing to the difference in frequency, the oscillations 

 alternately reinforce and extinguish each other throughout the period, 

 and as this type of oscillogram is only obtained with an inductively 

 coupled antenna, it is a proof that in such a case there are two 

 oscillations present of different frequencies. A similar result has 

 been obtained by Professor E. Taylor Jones with low-frequency 

 oscillations in coupled inductive circuits by means of an electrostatic 



Fig. 10. — Oscillogram of Secondaey Oscillation (Antenna connected) 



TAKEN WITH GeHECKE VaCUUM TdBE. 



oscillogram of his own invention. Looking at these photographs, it 

 will be seen that each represents a single train of damped oscillations 

 gradually dying away, but that in each train of oscillations there is 

 an alternate waxing and waning of the amplitude, which indicates 

 that it may be considered to be composed of two superimposed 

 oscillations of different frequency (Fig. 10a). 



Accordingly, in the case of wireless telegraph antennae inductively 

 coupled, we have in general two waves radiated of different lengths, 

 and either of these can be made to affect suitably tuned receiving 

 circuits. These waves have different damping and different maximum 

 amplitudes. 



One of the disadvantages of close inductive coupling is, therefore, 

 that we must divide the energy given to the antenna between two 

 waves of different length. As the receiving antenna is generally 

 only tuned to one of these wave lengths, we then capture and absorb 

 only the energy conveyed by the waves of that wave length. To 



