Willebrord Snell is best known for his discovery regarding the refraction of light rays. This discovery, known as Snell's law, demonstrates that when a ray of light passes from a thinner element such as air, into a denser element, such as water or glass, the angle of the ray bends to the vertical. Snell's law--a key revelation in the science of optics--was formulated after much experimentation in 1621. This is expressed as sin i = sin r (i=angle of incidence, r=angle of refraction and = a constant). However, he did not publish his findings, and the law did not appear in print until René Descartes discussed it (without giving Snell credit) in his Dioptrique in 1637. Snell also determined a formula to measure distances using trigonometric triangulation. His method, developed in 1615, used his home and the spires of Leiden churches as reference points. (In 1960, a plaque recognizing his work...