In message 49f90619.961412546@localhost, Don Pearce
writes


But isn't that a series of splats, rather then a continuous arc? I
know how my boiler behaves when it is firing up, and it is "tick tick
tick, whoomph".

No. Unless I'm completely mistaken, it's a continuous arc - well,
probably a 50 or 100Hz arc. I think the plug's driven by the mains
(stepped up). Both sparkplug boilers were like that.
--
Ian