  Coulomb effects on $\pi^\pm$ and $K^\pm$ spectra in relativistic nuclear
collisions are investigated. At collision energies around 1 GeV the ratio of
$\pi^-$ to $\pi^+$ is enhanced several times at low transverse momenta but less
at ultrarelativistic energies. We describe the ratios at SIS, AGS and SPS
energies with simple analytic models as well as more elaborate numerical models
incorporating the expansion dynamics. The Coulomb effect depends on the
properties of the source after the violent collision phase and provides
information on source sizes, freeze-out times, and expansion velocities.
Comparison with results from HBT analyses are made. Predictions for $\pi^\pm$
and $K^\pm$ at RHIC and LHC energies are given.
