Evidence of the Wave Nature of Light
The two theories
Towards the end of the 17th century, Newton and Huygens had a debate.
Newton said that light was a particle, whereas Huygens said that light was a wave
The particle theory could explain relection and refraction, but not diffraction and interference, because those properties are specific to waves.
100 years later...
100 years later, Young came up with his double slit experiment to explain light interference, which had not been proven beforehand.
It showed that it could diffract through the narrow slits, and interfere to form the interference pattern on the screen at the end.