The reflection of light at grazing incidence from a shock wave at Mach No. 1.94 in air at atmospheric pressure is measured. It is found that the reflection coefficient is equal to that calculated when second‐order effects are included. From the variation of the reflectivity across the front it is found that the shock has a curvature of 5.4±0.4 m, a tilt of less than ±⅕, and distortion amplitude of less than 3×10−3cm.