Reference

Hsu, David. Chemicool. Feb. 7,2000 <http://www.chemicool.com/elements/helium.html>.

Winter, Mark.  WebElements. Feb. 7,2000 <http://www.webelements.com/webelements/elements/text/key/He.html>.

Bentor, Yinon. Chemical Element.com - Helium. Feb. 7, 2000 <http://www.chemicalelements.com/elements/he.html>.

Newton, David E. Baker, Lawrence W. Chemical Elements. Volume 2. Detroit: U*X*L, an imprint of The Gale Group.1999.

Ragge & Willow Enterprises. Corporate Thermal Airships. Feb. 7,2000. <http://sky-pro.com/rnw2/airship/corporate/>.

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