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Historically, the first model put forward to quantitatively try to explain these properties of light was a particle-like model of Newton in the mid 1600's. In this model, light was thought to be a beam of tiny particles. Such a model readily explained the properties of reflection and, to some extent, refraction, but failed miserably when later on the phenomena of diffraction and interference of light were discovered: it is hard to imagine even qualitatively why a beam of particles would bend around a corner when passing through an opening, or why when two particle beams meet they could interfere with each other so as to, for example, cancel each other out. For this reason, a different model was proposed, and by the mid 1800's adopted, namely the wave model of light. In this section we discuss some general properties of waves, and later we will see why this model is so successful in describing these properties of light.