Page 25 - GALIET PHYSICS BLOSSOMS II+

moved very fast.14
Indeed, in Newton’s corpuscular theory of light, everything depends on how the aether and the light corpuscles interact, and on how aether is distributed in space. Newton assumes that
(1) when the light corpuscles are pushed from high-aether density areas towards low-aether density areas, then the light corpuscles are accelerated and
(2) the aether is densest in a vacuum (where nothing else takes up the space aether occupies), and less dense in a material body.
Based on these two assumptions, Newton concluded that if light is incident on some material body from a vacuum or from air, light will either reflect at the same speed, but in a different direction, or it will refract by entering the body, and be accelerated. Thus, Newton predicted, as Descartes did, that the light corpuscles travel faster in solid bodies where aether’s density is lowest, and slower in a vacuum, where aether’s density is densest.15 This prediction was proved incorrect in 1850. Jean Foucault showed that the speed of light in water is slower than the speed of light in air.16
Refraction, Reflection and Simultaneous Refraction and Reflection
Newton believed that his corpuscular theory could explain refraction, reflection, and simultaneous refraction and reflection. Some superficies refract or reflect rays depending on whether the medium is denser or rarer. In other words, the variation in the aether’s density between different objects explains the diverse forms of light propagation.17
To explain refraction, Newton used two level surfaces, one higher than another, with their neighboring edges connected by a slope. Then he rolled a ball along the higher surface down the slope and across the lower surface. The ball sped up due to gravity. However, when the ball was rolled on the higher surface toward the slope at a given angle, at the slope, the accelerating force pulled on the ball causing it to roll across the lower surface at a lower angle. The upper surface can be seen as air (a less dense medium), the lower surface can be seen as water (a more dense medium), and the slope can be seen as the interface of the two media, and the rolling ball can be seen as particles of light and how they behave when refracted as they pass from air to water.18
Newton imagined that matter is made of particles. When a light particle is deep within a medium as in water or glass, equal numbers of these particles surround it on all sides. If we suppose that an attractive force exists between the light and matter particles, then deep within a medium, these forces invalidate each other, and there is no force on the light particle. Therefore, a light particle deep within a medium does not experience force. If no force acts on the light corpuscles, according to Newton’s First Law, the light particle would go on travelling along in a straight line since no force acts on it. However, near an interface, let’s say, between air and water, things differ. There are
14 Stamp, Phillip. Optics and the Nature of Light. 2012 Class Notes. 24, 32.
15 Stamp, Phillip. Optics and the Nature of Light. 2012 Class Notes. 25.
16 http://ffden-2.phys.uaf.edu/211_fall2002.web.dir/Micah_Houtz/BeforeMaxwell2Single.htm 17 C Stamp, Phillip. Optics and the Nature of Light. 2012 Class Notes. 27.
18 http://library.thinkquest.org/3227/webpage/particle.html
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