The Light before the quantum theory

Newton considered Light to be like a bundle of granules which propagate themselves in a line.  This theory was destroyed when Huygens (1678) offered the theory that Light was a wave.

In the 19^th century, Maxwell studied electromagnetic waves.  Maxwell generated the electromagnetic theory which explained the various behaviors of Light which were known up until then.  Maxwell and the Scientists that supported him said that electromagnetic waves couldn’t transmit themselves in a void.  Therefore there must be a substance through which Light travels as it comes to us. This substance was called ether. It was supposed that ether existed in all space, between the atoms and inclusive in the void.  Ether was invented because the science of that époch couldn’t understand the transmission of a wave in the void.  It was later demonstrated that ether doesn’t exist, and that any substance is necessary for Light propogation. 

In conclusion, it was considered that Light was like an electromagnetic wave, because it fulfilled all the properties and characteristics of a wave.