I don't think John Smith read the entire section on Ether...you need to
update your Physics book to the late 20th Century. Ether is considered
a non-issue in modern physics theories.



"Today, the majority of physicists hold that there is no need to
imagine that a medium for light propagation exists. They believe that
neither Einstein's general theory of relativity nor quantum mechanics
have need for it and that there is no evidence for it. As such, a
classical aether is an unnecessary addition to physics that violates
the principle of Occam's razor.

Moreover, it is hard to develop an aether theory that is consistent
with all experiments of modern physics. Any new theory of aether must
be consistent with all of the experiments testing phenomena of special
relativity, general relativity, relativistic quantum mechanics, and so
on. As outlined earlier, these conditions are often contradictory,
making such a task inherently difficult.

Nevertheless the intuitive appeal of a causal background for
"relativistic" effects cannot be denied. Some physicists hold that
there remain a number of problems in modern physics that are simplified
by an aether concept, so that Occam's razor doesn't apply."


Bruce..Radiation Physicist