(ii) The antenna may have oscillations excited in it inductively.
This condenser is charged electrically and then suddenly discharged and violent electrical oscillations are set up in it, that is to say, electricity rushes to and fro between the antenna and the earth.
The wheel was connected to a receiving antenna and the mercury to earth or to an equivalent balancing capacity.
To detect these currents some device has to be inserted in the antenna circuit or else inductively connected with it which is sensitive to high frequency currents.
It was then found that when electric waves fell on the antenna a sound was heard in the telephone as each wave train passed over it, so that if the wave trains endured for a longer or shorter time the sound in the telephone was of corresponding duration.