The best place to start
understanding
the theory is to start with the initial arc. The two ladder conductors
when
they are connected to the energized transformer a potential voltage
exists
between them. The dielectric separating the electrodes is air. When the
potential
is strong enough that it overcomes the dielectric strength of the
medium there
is an arc that jumps between the two electrodes. This arc ionizes the
air which
is plasma. The plasma rises because it is air that has been superheated
and
warm air rises. This propagation up the
ladder conductors continues until it reaches the top and a break in the
connection
occurs because the gap becomes large enough that the potential cannot
overcome
the dielectric strength. At this point a new arc is formed at the
bottom and
the process repeats itself.
This experiment is useful in the effect that it lets a person see an arc discharging between two electrodes and gives them an idea as to how this does effect power transmission. On a transmission line this discharging of an arc is very dangerous and is meant to be avoided at all costs.