Largely (but - not necessarily "Entirely") disproven by the Michelson-Morley experiment, the Luminiferous Aether was postulated to be the medium that permeated space and allowed electromagnetic waves and light to propagate across a vacuum.
Now - while we of course reject the earlier theories that - for example - the stars and planets are candles or lights hung up in crystalline spheres - we might have been I think a little hasty getting rid of this one. Call it intuition.
Links:
- https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment
- https://en.wikipedia.org/wiki/Luminiferous_aether
While light can explain it's propagation by being both a particle and a wave - and electro-magnetic waves are explained away using "fields", it does seem that we have replaced the Aether with the term "Space", invented dark matter and a variety of other constants and equations to explain away - never satisfactorily - our relation to both space and neighboring celestial bodies. While the theory of relativity has held up for this long - the presence of an Aether, or medium - which slowed it down, or capped it's speed, would go a long ways towards overcoming it. Certainly the abundance of other planets, stars, celestial bodies in general suggests there must be some reasonable means for us to communicate - or traverse the voids - to them. Accepting the speed of light as an upper bound to the speed of our travels is not a particularly attractive option.
Anyways, the things that get me thinking far too early and never with enough coffee...