After the interference experiment of Young in 1801, for the next 40
years or so, many experiments were carried out involving the
interference and diffraction of lightwaves; these experiments could only
be satisfactorily explained by assuming a wave model of light Thus,
around the middle of the nineteenth century, the wave theory seemed
to be very well established The only major difficulty was that since it
was thought that a wave required a medium for its propagation, how
could light waves propagate through vacuum This was explained
when Maxwell put forward his famous electromagnetic theory of light