We survey the close relationship between sound and light rays and
geometry. In the case where the medium is at rest, the geometry is the
classical geometry of Riemann. In the case where the medium is moving, the
more general geometry known as Finsler geometry is needed. We develop
these geometries ab initio, with examples, and in particular show how
sound rays in a stratified atmosphere with a wind can be mapped to a
problem of circles and straight lines.
