An iron rod...

An iron rod being placed on the outside of a building from the highest part continued down into the moist earth, in any direction strait or crooked, following the form of the roof or other parts of the building, will receive the lightning at its upper end, attracting it so as to prevent it's striking any other part; and, affording it a good conveyance into the earth, will prevent its damaging any part of the building. -- Benjamin Franklin