In 1637 Descartes gave the corpuscular model of light and derived Snell's law. This Corpuscular model of light was further developed by Isaac Newton in his famous book entitled OPTICKS and because of the tremendous popularity of this book, the corpuscular model is very often attributed to him and is called Newton's Corpuscular theory (click here to see the video).

Corpuscular theory predicted that if the ray of light (on refraction) bends towards the normal then the speed of light would be greater in the second medium. But the experiment of Foucault proved that, on refraction if the light bent toward the normal, then the speed of light will be lesser in the second medium. Thus, Corpuscular Theory didn't satisfactorily explain refraction. But, reflection is said to be explained by this theory.

In case of reflection practically, when the light ray is incident at an angle zero with respect to the normal drawn at the interface, ray bounce back in the same direction with the angle of reflection zero. According to Corpuscular model, if corpuscle bounce back in the same direction (when angle of incidence is zero) it came from, there will be collisions with the corpuscles which are going to be incident later. Then, there will be random displacement of corpuscles. But, this is not what practically happens. So, didn't corpusuclar theory also fail to explain reflection? does wave theory explain this case?

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    $\begingroup$ Well, Newton's theory was right after all (Feynman's path integral formalism). $\endgroup$
    – jinawee
    Dec 21, 2013 at 21:13
  • $\begingroup$ @jinawee I can't find the quote from Newton but he thought about things like multiple reflexions in layers and explained it by saying the particles cast forth a field of influence that senses the surroundings (my paraphrasing, not word for word): I was naturally gobsmacked by how eerily modern that sounded - almost Bohmian mechanical. Feynman noted this quote in his QED book (the popular one) but I can't find my copy. $\endgroup$ Dec 22, 2013 at 12:28

1 Answer 1


The corpuscular model says that light is composed of tiny discrete particles.

It can explain reflection if we assume that the particles are so small that they're very unlikely to collide with each other, or that they don't interact with each other for some other reason.

For example, if the corpuscles in a beam of light take up only one trillionth of the volume of the beam, then in a light beam reflecting back on itself there will be hardly any collisions. This would also explain why two beams of light can pass through each other without interference. (If the theory had held up over time, we'd probably have experiments designed to demonstrate these rare collisions.)

Or we could consistently assume that the corpuscles interact with ordinary matter, but can freely pass through each other.

The wave model can also explain reflection. Both sound waves and waves on the surface of a body of water can reflect off hard surfaces; the reflected waves pass through the incoming waves without being disrupted.

  • $\begingroup$ Thank you for the answer Sir. According to Corpuscular theory, light we see are the consequence of the corpuscles that fall on the eye retina. If suppose there was only small volume occupied by the corpuscles in the beam, there would have been only some corpuscles falling on the eye retina, and we would have been able to see discrete holes in between the beam. And we have assumed that corpuscles hit the interface and bounce back, so they must be some what hard relatively (though of less mass), if they are, they must collide and can't pass without interacting. $\endgroup$
    – Sensebe
    Dec 21, 2013 at 22:15
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    $\begingroup$ @VINAY: As I said, the idea is that the corpuscles interact with ordinary matter but not (significantly) with each other. For example, there might be one chance in a thousand of a corpuscle colliding with an atom of ordinary matter, but only one chance in a million of two corpuscles colliding. But we know that the corpuscular theory is wrong, so you can only go go so far in making it consistent with reality. $\endgroup$ Dec 21, 2013 at 22:41

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