A cartoon to help in teaching the importance of labeling the axes of a graph. The cartoon is number 833 (December 2010) from the webcomic series at xkcd.com created by Randall Munroe. Free to use in the classroom and on course web sites under a creative commons attribution-non-commercial 2.5 license.
...experiment without mathematics will neither sufficiently discipline the mind or sufficiently extend our knowledge... is a quote by Scottish geophysicist Balfour Stewart (1828 - 1887). The quote is found in a letter from Stewart to Henry Roscoe of Owens College on June 2, 1870.
The only relevant test of the validity of a hypothesis is comparison of prediction with experience. is a quote of American economist and statistician Milton Friedman (1912 - 2006). The quote can be found in the chapter "The methodology of positive economics" written by Dr. Friedman as an original article in his 1953 book "Essays in Positive Economics" containing a collection of his earlier articles.