600K volts derived from 6 C cell batteries.
The final 10x up-conversion comes from the Marx generator on the right. 10 round capacitors are charged in parallel to 60K volts and then connected in series by nine spark gap switches, ideally producing a voltage multiplied by the number of capacitors stages.
At this brief moment of discharge, all nine of the metal balls in the middle tower spark simultaneously, shifting the parallel charging circuit to a series discharge (the spark across the air gap sees about 1 ohm). You can see a light source in this moment from each of the balls.