Page 31 - GALIET PHYSICS BLOSSOMS II+

Huyghens argued that they propagate at a different velocity, which is slower than the velocity in air. Briefly, the wave front above the interface moves horizontally at the same velocity as before, but the downward motion inside the glass is slower because light travels slower through a dense medium like glass, because aether particles recoil slower.30 This naturally changes the direction of wave front propagation. In other words, the wave fronts above the interface get ahead of the ones below. (Please see the graphic Figures on the next page, which depict how velocity behaves in both mediums more clearly).
Huyghens also posited that the primordial property of refraction is that the Sine of the angles DAE and NAF always has the same ratio whatever the inclination of ray DA, and that this ratio is the same as that of the velocity of the waves in the transparent substance towards AE and AF.31
The following figures show it more clearly:
As shown and explained above, this explains simultaneous reflection and refraction.
Weaknesses
One of the weaknesses of Huyghens’ theory was concerning the aether. For example,
• How could light interact with eaether and with matter, but matter not with aether?
30 Stamp, Phillip. Optics and the Nature of Light. 2012 Class Notes. 12. 31 Stamp, Phillip. Optics and the Nature of Light. 2012 Class Notes. 9-10.
32 http://www.walter-fendt.de/ph14e/huygenspr.htm.
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