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I am readying on Arago's experiment of 1810 in a book on the history of physics.

The author writes that Arago conducted the experiment assuming that light consisted of particles and that faster light should have a lower refraction angle than slower light. The book states that in that regard, Arago was a follower of Netwon's light theories.

As far as I can see (assumption of mine), up to this point in time, it had never really been proven that slower light refracts more (let alone that light consisted of particles).

If my assumption is right, why did Arago not just establish or propose a new law that states that the refraction angle of light is independant of the (incoming) light speed?

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  • $\begingroup$ Under Fermat's derivation of the refraction law the refraction coefficient does depend on the incoming light speed. $\endgroup$ – Conifold Apr 10 '17 at 20:04
  • $\begingroup$ I understand that Snell's law is a consequence of Fermat's principle that light travels along the path that takes the least time. But I believe that Fermat's principle had not been proven at the time of Arago, hence it was called a principle, not a law. $\endgroup$ – René Nyffenegger Apr 10 '17 at 21:06
  • $\begingroup$ Newton had a detailed mechanical model of light/matter interaction, which validated Snell's law with the speed ratio formula for the refraction coefficient. And by the end of 18th century the least action principle, as generalized by Maupertuis and Euler, was seen as valid for arbitrary systems of moving particles. $\endgroup$ – Conifold Apr 10 '17 at 23:34

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