Making sound and heat waves visible. "Schlieren were first observed by Robert Hooke in 1665 using a large concave lens and two candles. One candle served as a light source. The warm air rising from the second candle provided the schliere. The conventional schlieren system is credited mostly to German physicist August Toepler, though Jean Bernard Léon Foucault invented the method in 1859 that Toepler improved upon. [wikipedia]
Jeremy Pfeiffer's first Schlieren Photos
Schlieren Photo using cell phone
In 1864, the German physicist August Toepler invented a clever optical system that let scientists “see” the invisible: tiny changes in air density.
His schlieren apparatus used a bright point light, precision lenses and a sharp knife‑edge to turn heat plumes, gas jets and even shock waves into dramatic patterns of light and dark.
Toepler was the first to visualize shock waves from electrical sparks and moving projectiles—long before high‑speed cameras existed.
More than 160 years later, schlieren systems based on his idea are still used in wind tunnels, ballistics labs and even space agencies to study supersonic aircraft and rocket exhausts.
See Also
Cymatics
Density
Differentiation
Kirlian Photography
Refraction