The velocity of high frequency sound waves has been determined in ether vapor at several pressures. The velocity is slightly less at the higher pressures.
Proceedings of the Iowa Academy of Science
©1931 Iowa Academy of Science, Inc.
Thompson, George E.
"The Velocity of Ultra Waves in Ether Vapor,"
Proceedings of the Iowa Academy of Science, 38(1), 216-216.
Available at: https://scholarworks.uni.edu/pias/vol38/iss1/61