wrote
...
On Jul 23, 3:48 am, "Szczepan Bialek" wrote:


The rule is simple. A mast with the polished ball on the tip attract the
direct stroke (polished ball do not dissipate).
A mast with many sharp spikes dissipate the static charge and eliminate
the
direct strike.

A mast with a ball is less likely to attract a strike. That is why
they are
used on flag poles, etc.. They don't stream near as well as a sharp
point. They can still be struck though if nothing more attractive
is around as far as streamers.
A pointed mast streams much easier and will be much more
effective as a lightning rod.
A mast with a lot of spikes is wishful thinking. You can not bleed
off the charge fast enough to eliminate strikes. It's like whizzing
in a whirlwind.

For Franklin it was obvious: "This grew into his idea for the lightning rod.
Franklin described an iron rod about 8 or 10 feet long that was sharpened to
a point at the end. He wrote, "the electrical fire would, I think, be drawn
out of a cloud silently, before it could come near enough to strike..."
From: http://www.fi.edu/pieces/hongell/

You can not eliminate a direct strike by bleeding off the charge.
You can only offer it a better and easier streaming target than
whatever you do not want struck. And the sharper and more
pointy an object, the better it streams. When is the last time
you saw a lightning rod with a polished ball on top?
They don't sell them, as they would be fairly useless.

But somebody want to catch strong lightnings:
"Blunt-tipped lightning rods are intended to intercept rather than to
prevent lightning strikes. They are intentionally located at the point of
maximum dielectric stress. (See Figure 2). " From:
http://www.nottltd.com/article.html
S*