The wavelength dependence of the optical rotary dispersion curve or the circular dichroism curve in the neighbourhood of an absorption band, both having characteristic shapes. If the wavelength is decreased, the rotation angle increases until it reaches a maximum and then decreases, passing through zero at the wavelength at which the maximum of absorption occurs. As the wavelength is decreased further the angle becomes negative, until it reaches a minimum after which it rises again. This pattern is called the positive Cotton effect. A mirror image of this pattern can also occur about the λ‎-axis, where λ‎ is the wavelength; this is called the negative Cotton effect. These effects occur for coloured substances and for colourless substances with bands in the ultraviolet. It is named after the French physicist Aimé Cotton (1859–1951) who discovered it in 1895.