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Harriot independently discovered what we now call Galileo’s law of fall, and also what we now call Snell’s law of refraction, but he never published.

Buffon could, if he wished, look back to the seventeenth century and identify a whole series of laws that had been discovered during the Scientific Revolution: Stevin’s law of hydrostatics, Galileo’s law of fall, Kepler’s laws of planetary motion, Snell’s law of refraction, Boyle’s law of gases, Hooke’s law of elasticity, Huygens’ law of the pendulum, Torricelli’s law of flow, Pascal’s law of fluid dynamics, Newton’s laws of motion and law of gravity.

To mention only a portion of Harriot’s work, he discovered Snell’s law of refraction two decades before mathematician Willebrord Snell; formulated laws of motion and falling bodies independently of Galileo and decades before Isaac Newton; produced the first drawing of the Moon through a telescope and made important observations of sunspots, again independently of Galileo; played with binary arithmetic nearly a century before Gottfried Wilhelm Leibniz; and was the first to develop fully symbolic algebra.

The angle can be calculated using a staple of high school physics called Snell’s law, but in the 17th century Pierre de Fermat provided a deeper explanation: the light beam acts as though it were trying to minimize its total travel time.

The angles and refractive indices of the two media are related by Snell's law.