Jacob's Ladders were often seen in old science fiction movies, in the laboratories of mad scientist types. They are easy to make but very dangerous.
Here's the one I made for my son Thomas:
The safety issue include:
- Severe risk of electric shock. Although the high voltage is isolated from earth, so touching one of the leads shouldn't be a problem (I haven't tried it), touching both could be fatal as the power supply is both high voltage and high power.
- Emission of ozone and nitrous oxides, which are dangerous to health even in low concentration. These really do build up fast; after a minute near this thing I have to vacate the area due to the smell.
- Danger of fire, e.g. if some paper gets in the arc.
- Total disruption of all radio communications within several tens of metres. The device might be illegal for this reason. It might also be dangerous to anyone with an implanted medical device such as a pacemaker.
It's fun though. And the sound is fantastic.