geometric optics

Light travels in straight lines with relatively little diffraction.

Charlottesville, Virginia New York, New York Paris, France

Pierre de Fermat (1601–1665) France, "principle of least time". Pierre Louis Maupertuis (1698–1759) "principle of least action" in 1747 or 1750? Maupertuis hoped that the principle might unify the laws of physics and support his proof of the existence of God.

The wisdom of Beekman. "We don't see things. We see light bouncing off things."


A plane mirror produces only one inversion: front-to-back. This is called a perverted image. The pair of warning signs on the right illustrates lateral inversion.

The law of reflection

θi = θr