From the dictionary... Ether A hypothetical medium formerly believed to permeate all space and to be the medium through which light and other electromagnetic radiation move. The existence of ether was disproved by the American physicists Albert Michelson and Edward Morley in 1887. You think Tesla didn't know this? Tesla was not a linguist, he didn't use ether but he said the energy went through the air because to him, what else was there? Semantics.