Introduction

The nature of light has been one of physics' most intriguing mysteries. In the 17th century, two competing theories emerged: Newton's corpuscular theory and Huygens' wave theory. Both models attempted to explain light's behavior, leading to a scientific debate that would last for centuries.

Newton's Corpuscular Theory

Core Principles

Newton proposed that light consisted of tiny particles called corpuscles, which:

Successful Explanations

Newton's model effectively explained several phenomena:

$\theta_i = \theta_r$

Limitations

The corpuscular theory faced significant challenges:

$v_{water} < v_{air}$

Huygens' Wave Theory

Fundamental Concepts

Huygens proposed that light propagates as a wave through a medium called the "luminiferous ether." His principle states that:

Key Successes

The wave theory successfully explained:

$n_1 \sin(\theta_1) = n_2 \sin(\theta_2)$

Limitations

Huygens' model had its own challenges:

Historical Impact: Foucault's Experiment

Foucault's 1850 experiment measured light's speed in different media, showing that:

$v_{water} < v_{air}$

This conclusively disproved Newton's prediction that light should travel faster in denser media, dealing a significant blow to the corpuscular theory.