Strouhal numbers and the unladen swallow

An article on Slashdot (http://slashdot.org) links to an excellent article that graphically displays and explains Strouhal numbers. Animals swimming or flying at cruising speed use similar ratios of stroke frequency and amplitude to forward speed, this ratio is known as a Strouhal number. The author, Jonathan Corum, has taken a rather boring graph from Nature, and through a series of neatly drawn diagrams shows what a Strouhal number looks like.

The article can be found here (There is a at follow-up article for Monty Python fans)