Fermat's principle

The path between two points taken by a beam of light is the one which is traversed in the least time.

Fermat's Principle (as quoted above in its original form) can be used to describe the properties of light-rays reflected by mirrors, refracted through different media, and undergoing total internal reflection. Similar to Huygen's principle, Fermat's principle, is consistent with Snell's law.

The historical statement of the principle (above) is incomplete.

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