Exploratorium
Exploratorium: Science Snacks: Convection Current
This lesson plan is a great way to show convection currents in water. Students will see what happens to water as it gets warmed.
Florida State University
Florida State University: Science, Optics & You: Willebrord Snell
Biography of Willebrord Snell (1580-1626), a Dutch mathematician known best for his work in refractive indices.
Wolfram Research
Wolfram Science World: Snell, Willebrord
This site from ScienceWorld provides a very short biographical sketch of Willebrord Snell (1591-1626 CE) and describes his most notable scientific discovery, the law of refraction. Links are provided for additional information as well.