I think therefore I am
5
In Descartes' scheme, a light ray (here coming from upper left) hits a raindrop, penetrates it, is reflected internally one or more times, and finally exits. When a light ray moves from air to water, it changes direction. We now know - at least in some sense - that this is because the light travels in waves, and it possesses a slower speed inside water.
Descartes law of refraction
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Rene Descartes maps it out
a French philosopher, mathematician, and scientist. Dubbed the father of modern western philosophy, much of subsequent Western philosophy is a response to his writings,[10][11] which are studied closely to this day. He spent about 20 years of his life in the Dutch Republic.!