Geometrical optics is no longer fashionable. Research workers do not expect significant new discoveries to be made in this field of classical physics. Teachers avoid the subject because its use for many generations in arid mathematical exercises has robbed it of all freshness and stimulus, with the result that it no longer seems relevant to a modern physics course. There remains - and perhaps this has grown in recent year- the technical significance of geometrical optics. It provides the basis for the design of optical instruments for use in everyday life as well as for scientific and...