Hence it is clear that after one impact, the metallic filings tube has to be brought back to its non-conductive condition, and this may be achieved in several ways.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming
The adjustment has so to be made that, whilst the dash is being recorded and a continuous tapping is kept up, yet, nevertheless the continued electromotive force in the aerial, due to the continually arriving trains of waves, is able to act against the tapping and to keep the filings in the tube in the conductive condition.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming
The coherer, or Branly filings tube, has the peculiarity that its passage from a non-conductive to a conductive condition follows immediately when the difference of potential between its ends is made sufficiently great.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming