A laboratory analog to the dart leader and return stroke of lightning

Luminous waves similar to the dart leader and return stroke of lightning have been produced along the ionized path left by a 10-cm spark in atmospheric air. The waves traveled more slowly along channels which had been allowed to decay for a longer time. For a wave propagating along a channel 11 μsec old, the velocity was 3.3×109 cm/sec and for 210 μsec it was 6.5×107 cm/sec. Waves propagating along older channels (greater than 50 μsec) attenuated so rapidly that they could not be seen to travel more than a few centimeters from the electrode from which they were initiated; those propagating along channels 26 to 32 μsec old traveled all the way to the opposite electrode and were then reflected back up the channel.