>... The discharge from the coil
> was striking a ground pole which was connected to a ground rod driven
> through the cement floor about one foot from where the water supply
> exits the ground and enters the garage. When I grounded the strike
> pole to a different ground rod on the opposite side of the garage,
> the effect was greatly diminished, so I'm guessing that current
> passing through the pipe creates a magnetic pulse which reacts to the
> earths magnetic field but I thought that I would ask the experts for
> a more definitive answer.
I would think not the Earth's field, as such, as this is
quite weak. Rather: enough current in a conductor can
change its size/shape: cf nagnetostriction