We get a lot of questions here asking what the first story of a certain type is. This is an example of a different sort of question—the last story of a certain type.
The luminiferous aether was an attempt to conceive of a medium through which electromagnetic waves could propagate. By the early 1900s, however, aether as a scientific theory was laid to rest, with special relativity and other theories offering more plausible explanations of wave propagation in vacuum.
What was the last science-fiction story to treat luminiferous aether as a legitimate scientific theory?
Things that don't count:
- Modern stories (about post WW2) that have luminiferous aether. They almost certainly are not holding forth aether as a real phenomenon. The exception would be if some advocate of aether as serious theory has written a sci-fi book.
- Fantasy stories that have something called aether, but which corresponds more to the classical element than to the 19th-century theory.