A Jacob's Ladder (otherwise known as a high voltage climbing arc) is an eye-catching prop for Halloween and is a necessity for all aspiring mad scientists. Jacob's ladders work by ionizing the air and drawing an electrical arc at the bottom of the ladder. Soon, the ionized air gets much too hot to stay in the same spot so it rises -- bringing the arc with it and creating that shocking effect.
So let's get started!
Step 1: Materials
The main thing you need for this instructable is a high voltage power source. Most people (including me!) use neon sign transformers to do this. Other examples of high voltage power supplies might be: a furnace ignition transformer, or a flyback transformer from an old TV. You can pretty much use anything you can get your hands on as long as it generates more than five thousand volts (5 kV). Remember that the more volts it puts out, the father you can have the electrodes from each other. If you do use a neon sign transformer, stay away from the solid-state versions.
You will also need a pair of electrodes. Thin copper tubing works superbly for this, as it is very conductive and easy to bend. I went cheap and used a coat hanger that was laying around. Be aware that most coat hangers have some type of paint or plastic coating that will have to be removed. I had to sand mine quite a bit before the coating was gone.
A non-conductive base must be used to mount the electrodes. A non flammable base is also a good thing to have if you are worried about setting something on fire. Note that at excessive voltages, wood no longer stays an insulator, and starts to conduct electricity. If this does happen, you can count on that wood to ignite.
Some high-voltage wire is also recommended. I couldn't find any, so I used some 12 gauge hook-up wire. The thicker the gauge and the insulation the better!