Letter: Flying in the face of logic

Sir: I suppose the thoughts that can be inspired by watching a fly buzzing around a room depend on the intellectual powers of the observer (letter, 7 June). A certain M Descartes, while musing on the movements of such a fly, realised that its position in space could be uniquely determined at any time by reference to three mutually perpendicular lines emanating from any corner of the room, and so invented cartesian co-ordinates.

DAVID MILLER

Norwich