According to Wikipedia, a Jacob's ladder (more formally, a high voltage traveling arc) is a device for producing a continuous train of large sparks which rise upwards. The spark gap is formed by two wires, approximately vertical but gradually diverging away from each other towards the top in a narrow "V" shape. It was named for the "ladder to heaven" described in the Bible.

   When high voltage is applied to the gap, a spark forms across the bottom of the wires where they are nearest each other, rapidly changing to an electric arc. Air breaks down at about 30 kV/cm, depending on humidity, temperature, etc. Apart from the anode and cathode voltage drops, the arc behaves almost as a short circuit, drawing as much current as the electrical power supply can deliver, and the heavy load dramatically reduces the voltage across the gap.

   The heated ionized air rises, carrying the current path with it. As the trail of ionization gets longer, it becomes more and more unstable, finally breaking. The voltage across the electrodes then rises and the spark re-forms at the bottom of the device.

   This cycle leads to an exotic-looking display of electric white, yellow, blue or purple arcs which is often seen in films about mad scientists. 

   Traveling-arc devices are dangerous. The sparks can burn through paper and plastic and start fires. Contact with the exposed high-voltage conductors can be lethal. Do Not Try This At Home!!!

What is a Tesla Coil?

   According to Wikipedia, a Tesla coil is an electrical device based on a type of resonant transformer circuit invented by Nikola Tesla around 1891. It is used to produce high voltage, low current, high frequency alternating current electricity.

   Tesla coils produce higher current than the other source of high voltage discharges, electrostatic machines. Tesla experimented with a number of different configurations and they consist of two, or sometimes three, coupled resonant electric circuits.

   Tesla used these coils to conduct innovative experiments in electrical lighting, phosphorescence, x-ray generation, high frequency alternating current phenomena, electrotherapy, and the transmission of electrical energy without wires. Tesla coil circuits were used commercially in spark gap radio transmitters for wireless telegraphy until the 1920s, and in pseudo medical equipment such as electrotherapy and violet ray devices. Today their main use is for entertainment and educational displays.

Tesla Coils are VERY Dangerous. Do Not Try This At Home!!!