Colours of light

           In 1666 Newton made one of his greatest discoveries; he found that sunlight (white light) was made up of many different colours. Newton records that one day he noticed sunlight streaming through a hole H in a shutter, and placed a glass prism P in the path of the light to observe what would happen. To his great surprise a number of differently coloured images were obtained on a screen S placed behind the prism. 

         He immediately experimented further to find out whether the colouring was imposed on the white light by the prism, or whether the colouring was inherent in the white light itself. He led to the conclusion that white light contains a mixture of colours which are red, orange, yellow, green, blue, indigo, and violet.