Wow, check out this Jacobs Ladder too!
This is how I used a neon sign transformer to create my own classic sci-fi prop the Jacobs Ladder. A Jacobs Ladder is nothing more than two vertical wires attached to a very high voltage. The wires which form the ladder are close together at the base but diverge as they go up. When switched on an electric arc forms at the base of the wires. The arc heats the air above it and in doing so forms an easier path for the electricity to take. The arc moves upwards continually heating the air above itself and rising to take the easier path until eventually the arc reaches the end of the wires and leaps into the air. Once free of the wires it dies but a new arc starts again at the bottom of the ladder. The arc itself moves with a very distinctive buzzing noise. These devices are most usually seen in old sci-fi and horror films and the houses of strange people.