From incident white light how will you obtain white emergent light by making use of two prisms ?

Explanation

Take a prism. Allow white light to fall on it . Obtain a spectrum. Take a second identical prism. Place it parallel to the first prism in n upside down position with the first prism [ as shown in figure]. Allow the colours of the spectrum to pass through the second prism. Obtain the beam of light emerging from the other side of the second prism.
The beam of light emerging from the other side of the second prism is a beam of white light.
Explanations : White light is made up of seven colours. The first prism produces dispersion of white light while the second prism combines light of different colours to produce white light again. The net deviation of a ray of light is zero.