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Re: A. Einstein and science-fairs

Cliff Parker wrote:

... as far as I know there is no such thing as a definition for the speed of
light...

The definition, c, refers to a perfect vacuum. We measure v in different media,
for example, in air, partial vacuum, water, or glass. Here we can not say "by
definition". It reminds me the unit of speed "mach", the speed of sound in air
at T=?. If we want to learn how fast sound travels at T+dT, or in another
medium, then we must measure. The existence of a definition may simplify
a measurement but it can not replace it. And definitions themselves are based
on measurements and knowledge.
Ludwik Kowalski