1. N. Aujoulat: The Cave of Lascaux (Ministry of Culture and Communication, Paris August 2005), available online at http://www.culture.gouv.fr/culture/arcnat/lascaux/en/
2. J. Sterne: The Audible Past (Duke Univ. Press, Durham 2003)
3. Wikipedia: Thomas Edison, available online at
http://en.wikipedia.org/wiki/Thomas_Edison
4. J.H. Lienhard: The Telegraph, Engines of Our Ingenuity (Univ. Houston, Houston 2004), available online at
http://www.uh.edu/engines/epi15.htm
5. P. Ament: The Electric Battery (The Great Idea Finder, Mar. 2005), available online at
http://www.ideafinder.com/history/inventions/battery.htm