Links

Video:

Logically equivalent (time: 2:27)
http://www.youtube.com/watch?v=2KblxQ1Ovvg

History

This is one of the best all around sites that I have found. It is titled "The MacTutor History of Mathematics Archive."
http://www-history.mcs.st-and.ac.uk/~history/

This is an award-winning site that links to all sorts of mathematics information.
http://archives.math.utk.edu/

Galilei
http://www-history.mcs.st-and.ac.uk/~history/Mathematicians/Galileo.html

Reference Topics

This site reviews propositional logic:
http://www.earlham.edu/~peters/courses/log/terms2.htm

Here is an propositional logic applet for building truth tables:
http://www.oursland.net/aima/propositionApplet.html


Argumentation and Persuasion: Logic in Argumentative Writing from the Purdue University Online Writing Lab:
http://owl.english.purdue.edu/handouts/general/gl_argpers.html