Some more thoughts on lightning. Air, glass, plastics,
paper, and total vacuums are all things we consider as
insulators. Even absolutely pure water is, for all practical
purposes, an insulator. Insulators are a dividing line between
things that do conduct electricity so we get the word
"dielectric" to describe anything that is a non-conductor.

	Having said all that, one of the interesting things
about dielectrics is that there is no dielectric that can't be
breached or jumped if you get a big enough charge differential
across it and that's where big sparks happen.

	Air is generally a very good dielectric until you reach
it's dielectric breakdown. The same is true of vacuums and solid
substances like glass, vacuums and paper just to name a few.

	You have no current flow at all as you turn up the
voltage and then all Hell breaks loose. The charge splits holes
in the dielectric and makes it's way through with accompanying
pyrotechnics. There is physical damage to a solid dielectric
material and you can see the track of the arc.

	My father once went to a lecture about electricity and
they passed out blocks of Lucite which is a clear plastic used
to make plexoglass and modern sculpture. The plastic blocks had
been exposed to several million volts in a Vandigraph Generator.
A grounded probe touched one edge of the block and eventually, a
breakdown occurred which blew a tiny lightning bolt pattern
through the plastic.

	Every dielectric substance has a constant which compares
this particular material with a vacuum. A vacuum has a
dielectric constant of 1. Air is a little better with a constant
a few decimal places higher than 1.

	It reportedly takes 3 times 10 to the sixth volts to
make a spark jump 1 meter or about a yard. It takes about 3000
volts to jump a spark across a 1-millimeter gap of air so if you
can make a spark jump a quarter of an inch  on a cold dry
Winter's day, you've got about 25-thousand volts as a quarter of
an inch is near 8 millimeters.

	If you're still reading all this, I can tell you with
supreme confidence that sticking the coax in a glass jar isn't
going to do much for you if you get a direct hit but it probably
will help some if it hits near by and puts 5 or 10-thousand
volts on your antenna.

Martin

and Please be careful. You're probably better off grounding that
coax. If lightning hits directly, a lot of coax and antenna will
go poof but at least the end of the spark will be outside.
Better yet, disconnect your coax and ground it outside if you
hear thunder anywhere near you.

	I admit I don't always disconnect everything but we live
in a bit of a hole and have not had much lightning damage over
20 years.

Martin

Ed Malmgren writes:
> I think Frank is right, when lightening can jump from a cloud to earth 
> there
> is not much you can do except have things disconnected.   Also it is
> possible that the glass jar or some type of insolater may keep sparks,
> static electricity from the end of a feed line  stop a fire if in dry 
> leafs