Merits of Huygens’ wave theory of light:
It gives satisfactory explanation for laws of reflection, refraction and double refraction of light assuming transverse nature of the light waves. It also explains the theory of interference and diffraction. It explains the phenomenon of polarisation of light. It experimentally proved that velocity of light in rarer medium is greater than that in a denser medium.
Demerits of Huygens’ wave theory of light:
This theory could not explain rectilinear propagation of light. It could not explain Compton effect, photoelectric effect, Raman effect etc. Also it could not explain properly the propagation of light through vacuum. This is because ether has high elastic constant and zero density which gives contradictory results.
According to Huygens’ wave theory, luminiferous ether medium exists everywhere in the universe even in vacuum which is treated as material medium for propagation of light waves.
However, Michelson’s and Morley’s theory disapproved the existence of ether medium.