There was also another controversy raging at the time, concerning the nature of light. It was known that light travelled through space with a finite speed, rather than leaping instantaneously from its source to our eyes.
But no-one knew, a century-and-a-half ago, what light was actually made of.
Most physicists agreed it travelled through space as a wave but they didn’t know what these light waves were made of, and they didn’t know how they got from one place to another. Maxwell was about to solve all these mysteries.