>In a message dated 97-12-09 11:11:30 EST, you write:
>
><< No, it's sensing the electric potential that naturally exists in the
> atmosphere, the same one responsible for lightning. With a sensitive
> instrumentation amp you can measure the voltage difference between your
> feet and your head (usually a couple hundred volts over six feet).
>  >>
>
>Is higher potential "always" up??
>
>Mark A. Corio
>Rochester MicroSystems, Inc.

If by "higher" you mean "more positive", then no. Clouds are negatively
charged with respect to the ground by as much as 1000 megavolts.
Precipitation and wind currents act like the charge transport belt of a Van
de Graaff generator (except Van de Graaf generators usually are designed to
produce a positive charge on the top electrode). The charge persists
because air is such a good insulator.

--BN



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