Coefficient of Coupling of Oscillation Transformers. 767 



result is obtained by making the mutual inductance between 

 the cymometer and the circuit being tested very small. We 

 have then to employ a sensitive detector for the condition of 

 resonance, viz., a Neon vacuum-tube. This condition is not 

 fulfilled if the whole inductance of the cymometer takes 

 part in creating mutual inductance. The necessary condition 

 cannot be easily satisfied if the detecting arrangement consists 

 of any form of hot-wire ammeter. In using a cymometer for 

 measuring the frequency of the oscillation in any circuit, we 

 have to be on our guard against disturbing the very quantity 

 we wish to measure, or setting up in the cymometer circuit 

 some oscillation of a different frequency. It is an obvious 

 deduction from the above investigation, that in using the 

 cymometer we should place the bar of the cymometer as far 

 away as possible from the circuit being tested. Suppose, 

 however, that we have two circuits of the same time-period 

 when separated and we couple them together inductively. 

 Then, if we investigate with the cymometer the oscillations 

 set up in the secondary circuit, w T e find it to be a complex 

 oscillation resolvable into components of different periods. 

 The cymometer therefore acts just like an electrical spectro- 

 scope. It resolves the complex vibrations in a circuit into 

 their simple components and shows us what they are. This 

 effect is very marked in the case of inductively coupled 

 aerials in wireless telegraphy. If we have a nearly closed 

 condenser circuit with spark-gap in which oscillations are 

 set up, which is inductively coupled to an aerial or antenna, 

 then, even if the two circuits are in common language "tuned" 

 to each other so that they have the same independent time- 

 period, yet when coupled, if coupled at all tightly, there are 

 two oscillations set up in the aerial of different frequencies, 

 and two waves radiated of different wave-length, which may 

 differ in length by 15 or 20 per cent. 



The cymometer in the above described form can be used to 

 measure not merely the length of the outgoing wave from a 

 sending aerial, but also the length of the wave being received. 

 To do this a coil of a few turns is wrapped around the long 

 helical inductance-coil, and this is connected between the 

 earth and the receiving aerial. The vacuum-tube is then 

 replaced by any form of electric- wave detector such as a 

 coherer or Marconi magnetic detector, and the cymometer 

 circuit adjusted by moving the handle until the maximum 

 effect is produced, or until the receiver indicates when this is 

 the case, the scale-reading of the cymometer will indicate 

 the length of the arriving waves. 



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