Posted by TheFallen on May 07, 2003
In Reply to: It depends posted by Word Camel on May 06, 2003
: : : : : One often hears ?lightning rod? in describing the attraction of vigorous or violent controversy, as in, for example, ?His comments made him a lightning rod for all sorts of vitriolic invective ? ?. This is interesting only in that the expression derives from the widely held but erroneous belief that a lightning rod is a device designed to attract lightning - ostensibly thereby to save other, more valuable objects in the vicinity.
: : : : : In fact, a more opposite function obtains: The lightning rod actually drains off static electricity from the object it protects, making it unlikely that enough charge will accumulate to initiate a strike. Think of this: If a lightning rod truly attracted lightning, why on earth would you want to put it on top of your barn? Wouldn?t it be better to place it off somewhere by itself - close but out of harm?s way, where it could ?attract? lightning without burning down the barn?
: : : : : So taken literally, the example above (?His comments ??) should mean that the individual?s comments served to ?drain away? or render less likely all sorts of invective.
: : : : Interesting. That's what I assumed -- that the rod attracted lighting and then it was discharged harmlessly down a wire to the ground.
: : : Kudos, never thought about it before.
: : Admittedly I have next to no clue about physics, but I don't understand the above. It's true that electronic engineers who handle microchips often wear earthing straps to ensure that they don't accidentally "blow" chips by zapping them with static. However, the following paste from The Columbia Encyclopedia is worth noting:
: : Lightning rod
: : A rod made of materials, especially metals, that are good conductors of electricity, which is mounted on top of a building or other structure and attached to the ground by a cable. By virtue of its position, shape, and conductivity the rod attracts lightning discharges much more readily than the building on which it is mounted. When struck, the connecting cable carries the discharge safely into the ground, preventing any damage to the building. Benjamin Franklin, in his kite experiment , proved that lightning and electricity are identical and subsequently invented the lightning rod.
: : The above affirms the belief that lightning rods are placed on top of buildings, not to dissipate any accumulated static charge, but instead to be the guaranteed harmless target point for a lightning strike. From the little I understand, lightning rods are not in the least erected to "attract" lightning, but to be a safeguard should such a strike happen. As to why one would not simply erect a lightning rod close by but out of harm's way, I think the answer's simple enough - if one has a church with a 200 foot high steeple, or even a barn with a 50 foot high apex, it'd be a lot of unnecessary work to erect a pole of similar height right next to the building that one wanted to protect - even if that was to prove protection.
: : The URL link below provides further support for the commonly held theory.
: Two points: It seems that any tall object is a target for lightening. I'm not sure why this is the case but I remember seeing a program about lightening a few years back where they determined that trees actually gave off the opposite charge to lightening and thus attract it. Perhaps this is true of houses and people too. Farmers and ranchers on the prarrie seem to fall prey to lightening strikes with relative frequency so perhaps this might help to explain why.
: Second point: I have noticed that many homes seem to have the lightening rod extending from the roof to the ground via a metal wire so that the house is earthed.
Yes, the earthing is the absolutely crucial element, so that the charge from the lightning strike is harmlessly dissipated, or earthed if you'd rather, should it hit the lightning rod. Not earthing a lightning rod would be asking for trouble.