Spectacular demonstration of electric arcing

DANGER, HIGH VOLTAGE! The transformer is visible in this Jacob's ladder. Mains electricity passes trough a 250/23000 turn transformer to yield a potential difference of 10000V across the two rods. The air between the rods is ionized, and as it heats up, it rises, carrying the current with it until the arc becomes unstable and breaks. (Breakdown voltage of air is approximately 30KV/cm)

The rods of the clear-based ladder can rotate, so it may take some trial and error to get the desired effect. The red-based ladder has plastic pieces that keep the rods in position.