<http://schema.org/description>
"What are they? We&amp;#039;ll give you a hint -- or four. Earth, wind, water and fire aren&amp;#039;t among them, but our old friend and force gravity is."^^<http://www.w3.org/2001/XMLSchema#string>
<http://science.howstuffworks.com/environmental/earth/geophysics/fundamental-forces-of-nature3.htm>