I am learning about the history and evolution of certain physics theories, one being Newtons corpuscular theory.

I am reading that Newton predicted the corpuscles, which make up light would travel faster in a denser medium.

  1. I am a little confused as to why this would be predicted.?

I would have thought that as Newton thought that light was made of particles, when entering a denser medium, the light particles would travel slower, as they encounter/ collide with more particles in the denser medium which are inhibiting the flow of the corpuscles, therefore reducing the velocity light as a whole?

I am not quite sure why Newton would not have predicted this.

It may be that i am not understanding the textbook properly:

2.~This is what it says: 'Refraction worked if the corpuscles travel faster in a denser medium'. Before this point it also says that light was known to refract, so surely if physicists were aware of refraction of light, they where aware of the true nature of how light behaves, when entering a denser medium?

I am finding this to be a little confusing?


  • 1
    $\begingroup$ History of Mathematics and Physics would be a better forum for this question. $\endgroup$ Apr 6, 2016 at 2:19

1 Answer 1


His idea was that the corpuscles were equally attracted in all directions to particles in the medium through which they were travelling and so moved in a straight line. When they approached a boundary, say between air and water, they were more strongly attracted to the particles in one medium, say water, than they were in the air. This would cause them to bend towards the normal (unless they were already directed along the normal).

  • $\begingroup$ Understood, cheers. $\endgroup$
    – Gurjinder
    Apr 6, 2016 at 9:49

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