There is no instrument for measuring the pressure of the Ether, which is probably millions of times greater: it is altogether too uniform for direct apprehension. A deep-sea fish has probably no means of apprehending the existence of water, it is too uniformly immersed in it: and that is our condition in regard to the Ether.
Ether and Reality: A Series of Discourses on the Many Functions of the Ether of Space (1925)