On Tue, 28 Dec 2004 18:56:13 -0500, "Jack Painter"
wrote:


"Ian Jackson" wrote
, Richard Clark writes
By the same logic (and experience), charge will accumulate on the
surface at the smallest radius - hence the points on lightning rods.
By extension, this is also the source of capacitor failure at either
the edges (smallest radius of a plate) or in surface burrs.


Again scraping the very bottom of the memory banks, I seem to recall
that when lightning rods were first used (in the late 1700s), the
British used sharp points. The French, in the spirit of one-upmanship,
decided that theirs should have brass balls. DOH!!!
Ian.
--

Very interesting! However the American Benjamin Franklin's pointed
lightning rods (it was not a British design) was never scientifically
challenged until a couple of years ago. Scientists have now shown that
blunt-tipped air terminals are attached by lightning with significantly
higher frequency than sharp tipped rods are. Pretty amazing that it took
over 230 years to "discover" this! So scrap the concept that a sharp edge
attracts charges, at least it does not attract lighting, the ultimate
charge.

http://www.usatoday.com/weather/reso...-rod-tests.htm
http://www.esdjournal.com/articles/f...n/franklin.htm
http://www.mikeholt.com/news/archive...tningblunt.htm
etc, etc

Jack Painter
Virginia Beach VA


Jack,

All three references are of the same article. Note the rebuttals at
the end of one of them.

I would also find it hard to believe that ANY rods on a 12000 foot
mountain were not hit in 7 years!

That study would suggest that pointed rods were excellent lightning
repellers and would protect things from being struck. Exactly what
Franklin first thought.

If not excellent repellers then it would be highly suspect of the
placement of the pointed rods on the mountain.

73
Gary K4FMX

Gary, K4FMX wrote:
"I would find it hard to believe that ANY rods on a 12,000 foot mountain
were not hit in seven years."

I saw a PBS program tonight on people scaling the highest peak in
Antarctica. It may never have been struck by lightning in modern times.
I spent two six-month hitches for my company on Tierra del Fuego. Not
quite Antarctica, but still so cold that lightnning is unknown on the
island.

Best regards, Richard Harrison, KB5WZI

"Gary Schafer" wrote
Jack,

All three references are of the same article. Note the rebuttals at
the end of one of them.

I would also find it hard to believe that ANY rods on a 12000 foot
mountain were not hit in 7 years!

That study would suggest that pointed rods were excellent lightning
repellers and would protect things from being struck. Exactly what
Franklin first thought.

If not excellent repellers then it would be highly suspect of the
placement of the pointed rods on the mountain.

73
Gary K4FMX

Hi Gary, the study is of course much more detailed than the articles
describe, I'll see if I can find you a link or post the abstract here
anyway. But no, there is absolutely no such conclusion in that study (or any
other accepted work) that any device can prevent lightning from striking a
particular point by "draining off" charges.

73,
Jack