Om recorded in a schlieren field
The optical ‘Schlieren’ system (named from the German schlieren, streaks) used to record these words is a technique for recording subtle differences in refractive indices, such as would be provided by warm breath in cold air. A laser point source of light is expanded and then refocused by a mirror onto a knife-edge that blocks the direct light. Breathing in front of the mirror disturbs the light rays so that some bypass the edge and can be recorded by a camera behind it. Words were spoken in front of the mirror while I photographically recorded the patterns produced by the turbulent air.