- A SKEPTIC's GUIDE - A SKEPTIC's GUIDE 
This sort of nonsense convinced most people that MAXWELL'S EQUATIONS were wrong -- or, more charitably, incomplete. The obvious way out of this dilemma was to assume that what we perceive (in our ignorance) as vacuum is actually an extremely peculiar substance called the "luminiferous æther" through which ordinary "solid" matter passes more or less freely but in which the "field lines" of electromagnetism are actual "ripples." (Sort of.) This recovers the rationalizing influence of a medium through which light propagates, at the expense of some pretty unfamiliar properties of the medium. [You can see the severity of the dilemma in the lengths to which people were willing to go to find a way out of it.] All that remained was to find a way of measuring the observer's velocity relative to the æther.
Since "solid" objects slip more or less effortlessly through the æther, this presented some problems. What was eventually settled for was to measure the apparent speed of light propagation in different directions; since we are moving through the æther, the light should appear to propagate more slowly in the direction we are moving, since we are then catching up with it a little.23.2