7R OLJKWQLQJ %HQMDPLQ )UDQNOLQ URG ULQJHU...

Franklin chimes

grounded

To lightning rod

ringer

Benjamin Franklin

• Ben Franklin proposed Sentry Box experiment in 1750

• D’Alibard demonstrated Sentry Box by ‘drawing fire from clouds’ in 1752 (Franklin became famous as a result)

• At about the same time (1752) Lemmonier discovered Fair Weather Electricity

• Linss 1788: Fundamental Problem of Atmospheric Electricity: Why is there a continuous current from the air to the ground?

• (note: ions not discovered until Elster&Greitel 1899)

• Victor Hess discovered Cosmic Rays in 1911

Electric Field

ConductivityJ = σE is constant in altitude

Global Electric Circuit

First proposed by C.T. R Wilson

Two payloads see same field even though separated by over 1000 km ! So, conclusion is that this variation is planetary-scale sized.

Next time:

http://www.youtube.com/watch?v=9v-4IiqPhnU

Lightning Safety:http://www.srh.noaa.gov/jetstream/lightning/lightning_faq.htm