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Prof. Townsend and Mr. Morrell on Electric 



9. In order to compare the wave-lengths calculated by 

 means oE equation (14) with those obtained experimentally, 

 a continuous-wave generator was used to induce oscillations 

 in a solenoid. The solenoid was wound with 29 turns per 

 centimetre on a wooden cylinder 5 centimetres in diameter, 

 the total length of the solenoid being 227 centimetres and 

 the specific inductive capacity of the cylinder being 3'95. 



The arrangement of the apparatus is shown in fig. 3. 

 An oscillatory circuit LC with adjustable capacity C was 

 maintained in oscillation by means of a valve, and a coil M 

 of a few turns was used to induce oscillations in the solenoid S. 



In order to reduce the effect of neighbouring bodies on the 

 capacity, the solenoid was suspended by strings at a height 

 of 120 centimetres above the table. 



In the normal oscillations having a maximum current at 

 the centre the potential is zero in the plane perpendicular to 

 the axis throughout the centre, so that when the coupling 

 coil M is in this plane it has no effect on the capacity of the 

 solenoid. 



The current in the solenoid was detected by a small in- 

 candescent lamp G connected to two loops of wire forming 

 a figure of 8. One loop passed round the solenoid, and a 

 maximum current is obtained in the lamp when the solenoid 

 is in resonance with the oscillator and the detector in a 

 position where the current in the solenoid is a maximum. 

 The electromotive forces in the two loops due to the current 

 in the coupling coil M are in opposite directions, so that the 

 current in the lamp is maintained solely by the current 

 in the solenoid. The lamp is not sufficiently sensitive to 



