cannot but regard the ether, which can be the seat of an electromagnetic field with its energy and its vibrations, as endowed with a certain degree of substantiality, however different it may be from all ordinary matter. (
Hendrik Lorentz, 1906)
According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time. But this ether may not be thought of as endowed with the quality characteristic of matter, as consisting of parts ('particles') which may be tracked through time.
(Albert Einstein, 1928, Leiden Lecture)