`Global' symmetries, such as the boost invariance of classical mechanics and
special relativity, can give rise to direct empirical counterparts such as the
Galileo-ship phenomenon. However, a widely accepted line of thought holds that
`local' symmetries, such as the diffeomorphism invariance of general relativity
and the gauge invariance of classical electromagnetism, have no such direct
empirical counterparts. We argue against this line of thought. We develop a
framework for analysing the relationship between Galileo-ship empirical
phenomena and physical theories that model such phenomena that renders the
relationship between theoretical and empirical symmetries transparent, and from
which it follows that both global and local symmetries can give rise to
Galileo-ship phenomena. In particular, we use this framework to exhibit analogs
of Galileo's ship for both the diffeomorphism invariance of general relativity
and the gauge invariance of electromagnetism.Comment: 31 pages including reference
