Since there is no significant intrinsic dispersion, no significant distance dependence and no significant difference between the reddening curves for 0- and B- stars, all the available observational data in the Cygnus region have been used to give a weighted mean reddening curve with a mean standard error of ±0.8 per cent. Over the observed wavelength range the reddening curve can be represented by two straight lines, intersecting at about 4300A.

Objective prism spectra obtained with the 16/24/60-inch Schmidt telescope have been used for an investigation of the wavelength dependence of interstellar absorption in the spectral range from 8000A to 3450A, in a region of 30 square degrees in Cygnus centred on (20ʰ15ᵐ, 38 °). Monochromatic magnitude differences have been measured at 24 wavelengths for 28 pairs of stars down to magnitude V = 10ᵐ.0.

The mean reddening curves derived separately for 0- and early B-type stars do not differ by more than 5 per cent. The reddening law in the direction of Cygnus does not change by more than 3 per cent over distances out to 2 - 2.5 kpc. The intrinsic r.m.s. dispersion about the mean reddening curve is less than 3 per cent.