Final answer:
Foucault's demonstration that light slows down in transparent materials than in air supported the wave theory of light and opposed the particle model by confirming wave-like behavior such as refraction.
Step-by-step explanation:
When Foucault demonstrated that light travels more slowly in transparent materials than in air, his work supported the wave theory of light and opposed the particle model. This is because, according to the wave theory, light traveling through materials with higher refractive indices, such as water or glass, will slow down, a phenomenon observed with waves but not with particles in the same way. Foucault's findings about the speed of light helped to refine and substantiate the wave theory's explanation of refraction.