As Luis says, the ancient Greeks postulated an ancient ether that is the medium of the supernatural that they had reason to think exists. The modern ether required for electromagnetic wave propagation has been dismissed experimentally.

My view as stated in my Dark Matter article on
www.the-atlantic-paranormal-society.com
is that dark matter contains all the properties required of the ancient Greek philosophers to be their ether.

Since this thread concerns Stafford, I should mention that he thinks that electromagnetism is responsible for the astronomical observations now attributed to dark matter,
(See www.electric-universe.org)
and that dark matter as a collection of undetected particles does not exist.