This project is a favorite of mine, and the one shown here was built for the “laboratory of the Scientists from Krypton that saved Superman from the exploding planet room thingy” of a past event.
The Jacob’s Ladder is a pair of vertical (or in extreme cases, horizontal) electrodes that are parallel to each other and connected to a source of High Voltage. The air between the bottom of the electrodes has a Dielectric Breakdown due to the high voltage potential and creates an Electrical Arc.
Due to the fact that electrical arcs are comprised of very hot plasma, the arc rises since hot air is less dense than cold air (similar to a hot air balloon). The arc reaches the top, and dissipates. However, in order to ensure the arc dissipates rather than disobey our orders to go away, a sudden increase in the angle between the electrodes is used to spread the arc out so far so fast that the High Voltage Supply cannot sustain it. Therefore, the arc destroys itself and the process repeats.