'The Rainbow', 1849.
© Science Museum / Science & Society Picture Library
Detail from an engraving by Josiah Wood Whymper (1813-1903) from 'Phenomena of Nature', published in London in 1849 for the Society for Promoting Christian Knowledge. 'The rainbow is one of the most beautiful appearances in nature, and is visible when the sun is shining brightly in one part of the sky, while at the same time a shower is falling in the opposite direction. In pasing through the drops of rain, the colours of the sun's rays (namely red, yellow and blue) are separated resulting in the rainbow effect.'