Getting a Jacob’s ladder to work reliably can be a fussy business. You have to get the bottom wires at just the right distance to strike an arc every time, and the angle of the diverging arms so that the heat generated by the rising arc carries it upward without breaking. This depends upon the voltage and current supplied by the high voltage source (often a neon sign transformer, which has a built-in current-limiting inductor that keeps it from blowing a fuse or burning out when shorted by the arc).
The process of adjusting a Jacob’s ladder goes like:
Plug….Observe…Unplug…Adjust…Plug….Observe…Unplug…Adjust…Plug….Observe…Unplug…Adjust…Plug….Observe…Adjust—ZAP! YOW!
How did I get here across the room?