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Lightning is the enemy of electronics.  One of the earliest problems were with radio station broadcast antennas.  Tall towers that scratched the bottoms of thunderclouds.    They went looking for trouble and frequently found it.  Many towers that were not grounded, had a spark gap at the bottom levels to allow the lightning a more graceful way of exiting the system.  The alternative was to let it flow through the very expensive transmitter.  Sometimes, even with the spark gap, the transmitter still took a hit.  This photo shows the tower base insulator at the upper left and the arc gap balls.  The ball on the right is connected to a pipe that takes the impulse directly to the earth.

Telegraph and telephone pre-date radio transmitting and receiving.  Lightning following open wire lines into buildings was a cause of fires and in some cases direct lightning deaths.  

The insurance industry quickly required protectors on telegraph and telephone lines once they became available.  All of the early protectors were based on an air-gap.  The carbon block units used a thin mica spacer to make the gap small.  The gap width is proportional to the voltage at which it fires.  The carbons could be removed, separated, cleaned and put back together.  When I started my career as a telephone lineman,  cleaning carbons were a regular part of my duties following thunderstorm activity.

Friedrich Paschen discovered a relationship between electrode air gap distance and breakdown voltages and published a set of curves in 1889 that later were converted into a formula now called Paschen's Law.  

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