Here’s a cool DIY on making your very own Jacobs Ladder. I always goto Fry’s with my friend Eric and find that they have this giant Jacobs Ladder that’d go off as soon as you were about to touch motherboards and whatnot. But this is great that now I know how it’s made.
The basic construction and principle of a Jacobs ladder is that a metal vee is formed from two bits of wire and a high voltage is applied across them. The electricity arcs across at the bottom of the vee where the electrodes are closest together. The air that the spark is passing through is ionised making it a preffered route for the arc, so when it heats up and begins to rise it drags the arc up the metal vee pulling it wider as it goes. In a correctly set up ladder the arc will travel all the way to the top where the wires have a sharp outward bend in them to pull the arc apart to the point that it extinguishes and the whole process starts again at the bottom of the vee. Here’s a picture of the base of my own Jacobs ladder showing the mounting of the wires.